Angewandte Chemie International Edition - Aktuelle Forschungsartikel
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Angewandte Chemie International Edition - Verlag: Wiley-VCH - Herausgeber: Gesellschaft Deutscher Chemiker, GDCh
Die chemische Fachzeitschrift Angewandte Chemie ist die weltweit fuehrende Chemiezeitschrift.
A complete set of 2-nitrobenzyl-modified reversible terminators have been developed, which upon exposure to UV light generate natural hydroxymethyl nucleotides (see scheme). The combination of a stereospecific (S)-tert-butyl group (R) at the benzylic carbon and a 5-OMe group (R?) on the 2-nitrobenzyl ring substantially increase the rate of photochemical cleavage. For 7-deaza-7-hydroxymethyl-2?-deoxyguanosine, these modifications led to a rate increase of more than one order of magnitude.
Proteins have been used to construct biocompatible microdevices by using maskless femtosecond laser direct writing. In their Communication on page 1558?ff., W.?F. Dong, H.?B. Sun, and co-workers report their strategy to produce microlenses from bovine serum albumin. The microlenses have controllable geometry as well as excellent imaging performance, and the focal length can be dynamically tuned by changing the pH of the surrounding solution.
Magnetic moments: The orientation of the title single-molecule magnet was investigated by magnetic single crystal and luminescence characterization, supported by ab?initio calculations, and was found to be governed by the position of the hydrogen atoms of the apical water molecules. This finding suggests that simple magneto-structural correlations can give misleading clues for research in molecular magnetism as well as in the design of MRI contrast agents.
On the right path: The mechanisms of endocytosis of cetuximab (C225) and its nanoconjugates have been elucidated in a pancreatic cancer cell line. By using gold nanoparticles as a scaffold, it is possible to switch the pathway for endocytosis from a Dyn-2-dependent caveolar mechanism to Cdc42-dependent pinocytosis/phagocytosis. Tailoring endocytotic mechanisms may enable specific intracellular pathways to be targeted.
A question of nobility: A biomimetic nickel thiolate complex (see scheme; TEA=triethylamine) exhibits unprecedented activity for the title reaction. By using a low concentration of a sacrificial donor, the system maintains significant activity for at least 60?hours. The enhanced stability of the system is ascribed to the ability to proceed through an oxidative quenching pathway.
“My favorite place on earth is where my family is. My best investment was a Colnago racing bike. …” This and more about Michael Müller can be found on page 1514.
Now we are six: Planar B6 rings embedded in one-dimensional Ti7 wheels have been found in the crystal structure of a solid-state phase (Ti7Rh4Ir2B8) for the first time. First-principles calculations indicated strong BB bonding but also significant interactions with the surrounding titanium atoms (see picture).
Jacketed supramolecular strand: Meter-long supramolecular strands were obtained by encapsulating them in polymer gels using a microfluidic channel (see picture). The nanofibers in the strands are self-assembled and aligned under the laminar flow conditions. Their mechanical strength was sufficiently high to allow their patterning onto a substrate and use them as a template for synthesizing an insoluble, conductive polymer.
Supramolecular self-assembly is used for the fabrication of nanofibers in a microfluidic channel on a macroscopic scale. In their Communication on page?1553?ff., S. Takeuchi et?al. report meter-long supramolecular strands that are encapsulated in a robust polymer gel matrix. The strands are aligned under laminar flow conditions. Their mechanical strength is sufficiently high to allow their patterning onto a substrate and use as a template for synthesizing conductive polymers.
A void in the issue: A one-step self-assembly of ?-Keggin sandwich-type silicotungstates with M2Zn2 (M=Co, Ni, Zn) tetranuclear cores and tetrabutylammonium cations gave porous ionic crystals. These porous crystals are hollow frameworks containing large voids (ca. 38×38×38?Å3, see picture, voids?yellow), between which guest molecules can be exchanged through the connecting channels.
Dissolving platinum: A noncorrosive, basic ionic liquid has been developed as a solvent system for the electrodissolution of platinum (see image). The metal was dissolved at an ultrahigh rate, and the facile recovery of pure platinum and platinum alloys from the same solution was achieved without any additional treatment of the solution or exchange of the medium.
Lewis adducts between N-heterocyclic carbenes and fullerenes have been isolated and their structures confirmed by X-ray crystallography. This work shows that simple fullerenes such as C60 or C70 can act as Lewis acids. This result not only opens new perspectives in fullerene chemistry but might also have strong implications in emerging fields such as the metal-free activation of small molecules.
Something to remember: A rotaxane could be operated as a bistable memory element under kinetic control (see picture). Data was written on the molecule by an oxidation stimulus and locked by UV light irradiation. After the writing session, the oxidized species was reduced back to the original form without losing the written data for a few hours. Light irradiation also protects nonoxidized rotaxanes from accidental writing.
It takes two: For the reduction of amides to amines iron catalysts were developed. A combination of two different iron catalysts made possible the challenging reduction of primary amides (see picture).
A shot in the arm for anticancer vaccines: Synthetic MUC1 glycopeptides bearing the STn and 2,6-ST antigens were conjugated covalently to BSA (see scheme). The obtained synthetic vaccines induced very strong immune responses in Balb/c mice. Predominant IgG isotype antibodies were induced. The antibodies exhibited strong binding to breast cancer cells of the MCF-7 cell line.
A face off: Diisobutylaluminum hydride (DIBAL-H) has been found to be an effective O-desilylating reagent at the primary face of cyclodextrins. This methodology shows high chemo- and regioselectivity and provides an effective route to orthogonally protected, multisubstituted cyclodextrin derivatives.
Who can split water? Two polymorphs of nanocrystalline cubic spinel and rhombohedral layered lithium cobalt oxides have been prepared and their application in the photocatalytic oxidation of water examined. The main factor that determines the catalytic activity of the different phases is the presence of a Co4O4 cubic core, which is present in the cubic form of the catalyst, but not in the layered structure (see scheme).
Proteins in focus: Dynamically tunable protein microdevices were built up by a simple “top-down”, maskless, femtosecond laser direct writing approach with bovine serum albumin. This technique was used to produce biocompatible microlenses that swell and shrink reversibly in response to changes in the pH of the surrounding solution. These responses to environmental stimuli can be used to focus the microlenses.
N-heterobicyclic scaffolds: Highly efficient palladium-catalyzed cyclizations of oxime esters with cyclic alkenes were used as a general entry to perhydroindole and related scaffolds. The chemistry is reliant upon the use of P(3,5-(CF3)2C6H3)3 for the key C(sp3)N bond-forming process and this facilitates cyclizations with enhanced levels of efficiency across a range of sterically and electronically distinct substrates.
Carbon in charge: A straightforward method is presented for the synthesis of carbon nanotube (CNT)/porous carbon composite electrodes with uniform distribution of the CNTs and high surface area of the carbon material. The crystallinity of the CNTs is not affected by the high-temperature activation process. Monolithic CNT/activated carbon composite electrodes that do not need binder or current collector were also developed.
A cooperative catalyst that features urea H-bonding and a cobalt center was developed for anti-selective asymmetric Henry reactions (see scheme). The H-bonds of urea play a crucial role in the improvement in yield (from 30?% to 84?%), enantioselectivity (from 78?% to 96?%), and anti diastereoselectivity (from 3:1 to 48:1). A short synthesis of (1R,2S)-methoxamine hydrochloride was also accomplished with this catalyst.
Still elusive: The reduction of dimethylimidazol-2-ylidene dichloroborane by sodium naphthalenide has been suggested to provide a borylene that cycloadds to naphthalene to make a borirane. Evidence has been provided that this borirane instead arises from coupling of a boryl radical and sodium naphthalenide. In contrast, reduction of 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene dichloroborane and the related dimesityl derivative provide novel CH insertion products that may have arisen from a borylene.
Good migrations: The highly regioselective migration of a sulfonyl group for the synthesis of functionalized pyrroles is reported (see scheme; DMF=N,N-dimethylformamide). The migration of the sulfonyl group to different positions can be controlled with high selectivity, thus allowing the formation of both ?- and ?-(arylsulfonyl)methyl pyrroles with high yields.
Let's couple together! The multicomponent reactions involving arynes offer direct access to unusual heterocyclic scaffolds and 1,2-disubstituted arenes. This transition-metal-free, one-pot construction of molecular complexity is likely to play a pivotal role in various carbon–carbon and carbon–heteroatom bond-forming reactions.
Turn off the lights! A universal nanoquencher that quenches a broad range of visible to near-infrared dyes by using a series of dark quenchers incorporated into a cell-permeable mesoporous silica nanoparticle has been developed. In combination with dye-labeled substrates, this nanoquencher boosts multiple fluorescence signals upon specific proteolysis, which allows real-time imaging of proteolytic cascades (see scheme).
Gold nanoparticles can be used as a scaffold to elucidate the mechanism of endocytosis of cetuximab and its nanoconjugates, as well as the switching of endocytic pathways (caveolar versus pinocytotic) in pancreatic cancer cells, as demonstrated by P. Mukherjee and co-workers in their Communication on page?1563?ff. Tailoring the mechanism of endocytosis may be useful for targeting specific intracellular pathways to minimize the side effects of pharmaceutical compounds.
H2-O-T! Aromatic O-heterocycles are a challenging substrates for asymmetric hydrogenation (H2). An in?situ formed chiral N-heterocyclic carbene (NHC) ruthenium complex allows the high yielding, completely regioselective, and highly asymmetric hydrogenation of substituted benzofurans at room Temperature, giving valuable 2,3-dihydrobenzofurans (see scheme).
One to two and back again: A disulfide–thiolate interconversion process in a dinuclear copper complex is induced by chloride ions (see scheme). Within this compound, the coordinating copper atoms serve either as electron source or as electron sink and thus oscillate between the oxidation states +I and +II.
Select an isoform: Linking of cosubstrate and substrate binding sites enables highly selective inhibiton of isoforms of human histone lysine demethylases. The results should provide a basis for the development of potent and selective JmjC inhibitors, possibly suitable for clinical use.
Learn about Alzheimer: The molecular conformation of a toxic ?-amyloid oligomer structure was determined by NMR spectroscopy (see picture). The measurements show a N-terminal ??strand that controls the partitioning between oligomer and protofibril formation. Targeting the N-terminus of the peptide neutralizes A?-dependent neuronal dysfunctions. The data have important implications for understanding the structural basis of Alzheimer's disease.
Highly selective CO2 sorption and inverse CO2/C2H2 sorption selectivity (4.8 at 278?K, 100?kPa) were achieved with an organic–inorganic ionic crystal. The key for the high affinity toward CO2 is the combination of structural flexibility and strong binding sites (K+) characteristic of organic–inorganic ionic crystals.
Electromagnetic vacuum fields are omnipresent in our universe, inducing many events such as spontaneous emission, Lamb shift, and Van der Waals forces. As demonstrated here, a chemical reaction can be influenced by strongly coupling the energy landscape governing the reaction pathway to vacuum fields in an optical cavity (see picture; MC=merocyanine).
One and two: The C2?compound pinBOCH2OCHO (see scheme; HBpin=pinacolborane) and several C1?compounds have been obtained from the borane-mediated reduction of CO2 under mild conditions with the catalyst precursor [RuH2(H2)2(PCy3)2]. Mechanistic investigation highlights the role of a series of new carbonyl ruthenium complexes that were characterized by multinuclear NMR spectroscopy, IR spectroscopy, and X-ray diffraction studies.
Molecular shuttlecocks: The introduction of tripodal ternary acids (red; see picture) to the cobalt/calixarene (green) systems led to the formation of four unprecedented calixarene-based nanoscale coordination cages through a [6+8] condensation. The overall periphery diameters of the nanocages ranged from 3.3 to 4.7?nm, and there were two sizes for the internal cavities (1.1 and 1.7?nm).
Good combination: Enantioselective enzymatic hydrolysis was combined with a mechanically facilitated racemization process to prepare (S)-1,1?-binapthol ((S)-binol) in high yield and enantiopurity from a racemic precursor in a single step (see scheme). The enzyme cholesterol esterase stereoselectively hydrolyzes esters of (S)-binol and ultrasound was applied to achieve mechanically facilitated racemization of the precursor material.
Calculated answer: First-principles calculations have been applied to calculate the energy barrier for the key step in CO formation on a Pt surface (see picture; Pt?blue, Pt atoms on step edge?yellow) to understand the low CO2 selectivity in the direct ethanol fuel cell. The presence of surface oxidant species such as O (brown bar) and OH (red bar) led to an increase of the energy barrier and thus an inhibition of the key step.
Rings with a twist: The highly enantioselective construction of five-membered spiroindolenines has been realized by the iridium-catalyzed intramolecular allylic dearomatization of indoles. The stereospecific migration of these spiro cyclopentane-1,3?-indole products provides enantioenriched 2,3,4,9-tetrahydro-1H-carbazoles.
The evolution of H2 and the oxygenation of hydrocarbons from photocatalytic water splitting are reported by X. Zhao et?al. in their Communication on page?1653?ff. A homogeneous system for simultaneous hydrogen production and hydrocarbon oxidation, in which water is the source of both oxygen and hydrogen, has been developed. Two photosensitizers allow the coupling of the hydrocarbon oxygenation reaction to the H2 production process. (Photo courtesy of Rachel Wang.)
Battling the flu: Zanamivir (Relenza) is widely prescribed as an anti-influenza drug. It contains a vicinal amino alcohol, which is in an anti orientation, and is readily accessed by an anti-selective catalytic asymmetric nitroaldol (Henry) reaction promoted by a heterobimetallic complex (see scheme; PMB=p-methoxybenzyl). Additional synthetic manipulation of the nitroaldol product allowed the enantioselective synthesis of zanamivir.
Ball and plane: The structure of La@C82 was clarified by single-crystal X-ray diffraction of samples co-crystallized with [NiII(OEP)] (OEP=octaethylporphyrin; see structure La?red, N?blue, Ni?yellow, H?pink). The charge-carrier mobility of the co-crystal was determined using flash-photolysis time-resolved microwave conductivity measurements. The material exhibited an anisotropic and high electron mobility of up to 0.9?cm2?V?1?s?1.
Uracil is a common form of DNA damage resulting from hydrolysis of cytosine, and cellular uracil DNA glycosylases (UDG) have evolved to remove it specifically. The use of nonnatural pyrene deoxyriboside in short DNA oligomers to directly report on UDG enzymatic activity is described. The mechanism relies on the use of uracil as a strong quencher of pyrene, and enzyme repair activity can be directly imaged with bacterial cells in real time.
It takes two: Xantphos ligands that contain amidate groups are selective for the linear versus the branched-chain products in the rhodium-catalyzed hydroformylation of 1-octene. However, the catalyst only undergoes CO2-mediated phase switching in the presence of amidine-substituted triphenylphosphine (see scheme).
Unsupported catalyst for green chemistry: The aerobic oxidation and coupling of primary alcohols (methanol, ethanol, n-butanol) to give the corresponding aldehydes and esters at temperatures below 100?°C is facilitated by unsupported nanoporous gold catalysts. The experimental conditions employed allow a close comparison to model experiments and open the door to a molecular-level understanding of the reaction.
On the sunny side: A homogeneous system for H2 production and hydrocarbon oxidation was developed in the absence of any sacrificial reagent. This system consists of [Ru(TPA)(H2O)2]2+ and [Fe3(CO)12] as catalysts and [Ru(bpy)3]2+ and [Ir(bpy)(ppy)2]+ as photosensitizers (PS). Water is the oxygen source as well as the source for H2 formation (see picture; Sub=organic substrate).
Asymmetric catalysis is predominantly associated with the use of enantiomerically pure chiral ligands and catalysts. Although racemic chiral catalysts have been employed quite extensively in polymerization, their utility in mainstream organic synthesis and catalyst development has arguably been rather overlooked. This Minireview collates various themes for the strategic application of racemic ligands and catalysts, ranging from the estimation of selectivity and determination of enantiomeric excess, through to control of regio- and stereochemical outcomes, and mechanistic studies. What emerges is a clear picture that, in isolation or in concert with enantiopure catalysts, the “even-handed” approach has much to offer.Twin set: Our obsession for (enantio)selectivity in catalysis means we tend to analyze and graphically communicate our findings in the form of single-handed cycles. However, dual-cycle racemic catalysts are of distinct utility in polymerization, prediction of stereoselectivity, and mechanistic study.
Malaria is a serious global health issue. Artemisinin combination treatments are the first-line drugs, but supplies are limited because artemisinin is obtained solely by extraction from Artemisia annua. A continuous-flow process that converts dihydroartemisinic acid into artemisinin (see scheme) was shown to be an inexpensive and scalable process that can ensure a steady, affordable supply of artemisinin.
Research into the evaporation of solutions is not only aimed at a better understanding the physics of evaporation, but increasingly at capitalizing on the extremely simple method it offers to assemble diverse nonvolatile solutes into complex ordered structures on the submicron and longer length scales. This Review highlights recent advances in evaporative assembly of confined solutions, focusing especially on recently developed approaches that provide structures with unprecedented regularity composed of polymers, nanoparticles, and biomaterials, by controlled evaporation-driven, flow-aided self-assembly. A broad range of variables that can control the deposition are explored and the future directions of this rich field are presented.Drying out: The evaporation of solutions of nonvolatile solutes is one way to generate complex ordered structures. An array of facile and robust preparative strategies based on controlled evaporative self-assembly (CESA) of confined solutions have been exploited to rationally assemble various soft and hard materials into spatially ordered structures (see picture) with engineered properties and functionality over large surface areas.
Into the fold: Intramolecular CH???O hydrogen bonding has been utilized to create new aromatic triazole foldamers. Remarkably, all the triazole units of the foldamers are guided to orientate inward to form a nitrogen ring. As a result, they can efficiently bind neutral tri- and didentate organohalogens through multiple N???X (X=Cl, Br, I) halogen bonds to form stable 1:1 complexes.
Picky cage: A dicopper(II)-paddle-wheel-based metal–organic framework (PCN-80, see picture) with a rare (3,3,4)-connected topology has been synthesized by using a unique octatopic ligand featuring 90° bridging-angle dicarboxylate moieties. PCN-80 has Brunauer-Emmett-Teller (BET) and Langmuir surface areas of 3850 and 4150?m2?g?1, respectively. It exhibits high gas-uptake capacity for H2 and large adsorption selectivity of CO2 over N2.
Highly efficient: Pinacol alkylboronates were synthesized by the reaction of tosylhydrazones with bis(pinacolato)diboron or pinacolborane under transition-metal-free conditions. This reaction represents an expeditious conversion of carbonyl functionality into a boronate group.
Exchanging BF3by CF3: The title reaction proceeds under exceedingly mild reaction conditions and provides 2-arylvinyl- and 2-heteroarylvinyl-substituted substrates with E/Z selectivities of more than 95:5. Experimental observations suggest that the reaction does not proceed through a transmetalation of the RBF3K species to the iron catalyst.
Strike! While pure ammonia is out of luck, Ni(NH2)+ gets one strike after another at the “ethylene bowling championship”. In fact, Ni(NH2)+ is so effective that no pin, not even at the neighboring lane, is safe from it.
Critical structural switch: A small initial difference in the angle within bidentate ligands (see scheme) is amplified into an incommensurable difference in the resultant structures (M12L24 or M24L48). This molecular-level emergent behavior was predicted from the empirical threshold of the ligand bend angle, determined by a ligand mixing experiment, for the critical M12L24/M24L48 switchover.
One S less: Recent crystallographic studies have revealed a new, oxygen-tolerant kind of iron–sulfide cluster [4Fe-3S], which contains only three rather than four sulfur atoms in its cage (see picture; yellow=S, red=Fe, blue=N, green=cysteine). It is proposed that the cluster’s ability to transfer multiple electrons increases the oxygen tolerance by enabling the enzyme to reduce O2 rapidly, converting the dioxygen into harmless water before it can damage the protein.
“… In the last 30 years, the chemistry prize was given 10 times for a discovery that is reasonably classified as biochemistry or molecular biology …” Read more in the Editorial by Roald Hoffmann on page ??.
High-pressure conditions afford unique all-hydrido hypervalent complexes [SiH6]2? in the crystalline hydridosilicates A2SiH6 (A=K, Rb). Compared to normal-valent silanes the SiH bond appears considerably enlarged, by about 0.15 Å. Accordingly, SiH stretching frequencies are drastically reduced, by about 400–500 cm?1, reflecting the weakness of a hypervalent SiH bond.
DMA donates: Copper(II) acetate and 8-hydroxyquinoline promote the formation of a benzofuran core through a cascade of copper-catalyzed processes wherein the key carbon atom comes from the dimethylacetamide (DMA) solvent. Strong evidence for the participation of a Wacker cyclization catalyzed solely by copper is provided, not only in the title reaction from benzophenones but also from 2-hydroxy-?-arylstyrene derivatives.
Clicking bugs: Metabolically active Gram-negative bacteria can specifically incorporate an azide-modified analogue of 3-deoxy-D-manno-octulosonic acid (1, see scheme) into the lipopolysaccharides on their membranes. This process adds a bioorthogonal chemical reporter the cell surface and allows the rapid fluorescent labeling of viable cells by click chemistry.
Dynamics and kinetics in a single stroke: The stereodynamics of the tropos-chiral diphosphine biphep and its 3,3?-dialkoxy analogues was investigated by enantioselective dynamic HPLC (DHPLC) and a novel three-column approach, in with the dynamics and kinetics of the interconversion are examined in a single experimental setup (see scheme).
Back in black: All metastable and stable phases can be identified for the solid solution arsenic/phosphorus by a combination of quantum-chemical calculations and investigations of the phase formation. Reaction paths for phase formations and transitions in situ were also evaluated. The results show that orthorhombic black arsenic (o-As) is metastable in pure form and has only been previously obtained by stabilizing impurities.
Rule of thumb: The high yielding title reaction is described with a focus on understanding the factors that govern the regioselectivity of the process (see scheme). Electronic, steric, and functional group properties all influence the selectivity, an understanding of which allows the selective formation of trisubstituted vinylsilanes, which are synthetically useful compounds for accessing stereodefined alkenes.
There and back again: Hydrogenation of esters and the reverse reaction of dehydrogenative coupling of alcohols are efficiently catalyzed by dimeric complexes of Ru and Os under neutral conditions. The Os dimer (see picture) is an outstanding catalyst for the hydrogenation of alkenoates and triglycerides, and allows production of fatty alcohols from olive oil. This complex converts ethanol into ethyl acetate and hydrogen under reflux.
Selective: The deoxygenation of simple and complex natural products employing a readily synthesized phosphoramidite and tetrazole catalysts can be executed as a two-step process, without the need to isolate intermediate deoxygenation precursors. Furthermore, a peptide-based tetrazole catalyst controls the site selectivity of deoxyerythromycin synthesis (see scheme), thus overcoming the notorious challenges with unprotected erythromycin A.
Bio-inspired crystal engineering of nanoporous zeolites is described by A. I. Lupulescu and J. D. Rimer in their Communication (DOI: 10.1002/anie.201107725). Molecular analogues of silica proteins in unicellular organisms are effective growth modifiers that exhibit molecular recognition for binding to zeolite surfaces to alter the kinetics of crystallization, tune the architecture of exterior surfaces, and selectively tailor crystal habit with precise 3D control.
Vanadium complexes catalyze CC and CO bond cleavage reactions in lignin model compounds using air as the oxidant. In their Communication (DOI: 10.1002/anie.201107020), S. K. Hanson, R. Wu, and L. A. Silks report that the selectivity for the bond cleavage is influenced by the ligand framework of the vanadium catalyst, suggesting the potential of homogeneous catalysts for controlling selectivity in the aerobic oxidation of lignin. (Picture by Josh Smith, LANL Chemistry Division.)
Dimers are a girl's best friend: The oxidative fusion reaction of ?-aminoporphyrins with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) under high-dilution conditions furnishes pyrazine-fused diporphyrins 1 in high yields. In a further application of the reaction, the oxidation of a 5,10,15,20-tetraphenylporphyrin derivative provides a singly linked diaminodiporphyrin 2 along with the pyrazine-fused diporphyrin (see scheme; only core structures are shown).
A silver key to add CF3: In presence of in situ generated AgCF3 it is possible to trifluoromethylate aromatic triazenes in high ortho selectivity and good yields by means of a CH substitution (see scheme). Owing to the further transformation possibilities offered by triazenes, a variety of CF3-substituted building blocks are then accessible.
Particles in tubes: Multiwalled carbon nanotubes containing Fe3C particles (see SEM image) are prepared by pulse-injection chemical vapor deposition. The Fe3C particles provide the nanotubes with magnetic properties. The use of the nanotubes is also investigated in in vitro drug-release studies.
Peptidesomes is the name of nanoparticles that were built by a two-step self-assembly of globular peptide dendrimers with lysine endgroups (red spheres in picture) and poly(L-leucine) carrying one glutamic acid residue (blue lines with red dot). These viral-capsid-mimicking nanoarchitectures exhibited high gene transfection efficacy and thus are promising nonviral vectors for biomedical applications.
The structure of the title aminomutase was solved. The steric bulk of Phe?455 (green CPK structure) twists the phenylpropanoate ligand (green stick) by approximately 15° about the C? axis, which precludes a stronger bidentate salt bridge with Arg?323 (magenta structure). Instead, a weaker monodentate bridge may partially explain the different configuration of the product, relative to that obtained with an isoenzyme that forms a bidentate intermediate.
Sensitive kind of dye: Co-sensitization of the TiO2 electrode using PcS15 and the dye D131 results in a dramatic enhancement of the photocurrent response for the entire visible-light region. This method provides a simple design for accessing dye-sensitized solar cells.
The enhancement of proton mobility in the two-dimensional nanochannels fabricated on fused silica substrates has been verified for the first time by fluorescence microscopy using a pH-sensitive fluorescent probe. In their Communication (DOI: 10.1002/anie.201104883), T. Kitamori and co-workers present the maximum value of the proton diffusion coefficient when the size of the extended nanochannels decreased to 180 nm, and they discuss the possible mechanism of proton transfer based on proton hopping.
Fast data collection: A general method for dual data acquisition of multidimensional magic-angle spinning solid-state NMR experiments is presented (see picture). The method uses a simultaneous Hartmann–Hahn cross-polarization from 1H to 13C and 15N nuclei and exploits the long-living 15N polarization for parallel acquisition of two multidimensional experiments.
Marine macrolides: An improved second-generation total synthesis of the anticancer macrolide spirastrellolide A methyl ester has been achieved. The synthesis features a uniformly high level of stereocontrol combined with more expedient fragment assembly, and demonstrates a critical dependence of the crucial macrolactonization step on the substitution pattern of the C22–C24 linker region.
Radical migration between aliphatic amino acid side chains can occur in solution and intramolecularly in peptides. The kinetic constant of the hydrogen transfer reaction was measured by using competition kinetics, and the half-life as well as the distance that a radical can move within a protein was calculated.
The bis(triphenylarsane) complex of the [P4]2+ dication is formed in a high-yielding one-pot synthesis. X-ray crystallography reveals a butterfly structure of the bicyclo[1.1.0]-tetraphosphane-1,4-diium core with two triphenylarsane ligands in an exo,exo configuration (see picture). Reaction of [(Ph3As)2P4]2+ with Ph3P results in quantitative formation of [(Ph3P)2P4]2+ and Ph3As.
Modus operandi: Catalytic access to the title compounds through a new asymmetric ?-arylation protocol is reported (see scheme). These products are formed in good yields and excellent enantioselectivities using a new and easily synthesized chiral N-heterocyclic carbene (NHC) ligand. Advanced DFT calculations reveal the properties of the NHC ligand and the mode of operation of the catalyst.
Tubular! The detection of a series of very large, soluble endofullerenes extending from La2C90 to La2C138 proves that endohedral metal doping is an effective strategy for stabilizing these giant molecules. The X-ray structure of the most abundant isomer, La2@D5(450)-C100 (see image), shows a tubular structure featuring a long La–La distance and maximal separation of pentagons within the cage framework.
Unexpected Smiles! An unusual and highly regioselective synthesis of dibenzoxazepinones by a domino sequence assisted by an unexpected Smiles rearrangement is reported. The process is effective on electronically differentiated phenols and shows a high tolerance to variation in the benzamide substituents. A plausible path for the reaction, supported by preliminary mechanistic data, is offered.
Nanorust: Fe2O3 nanomaterials with controllable crystal phase and morphology have been successfully fabricated. The ?-Fe2O3 nanorods that are enclosed by the reactive {110} and {100} facets are highly active and distinctively stable for selective catalytic reduction of NO with NH3. The picture shows the shape and surfaces and the surface atomic configurations of the preferentially exposed {110} and {001} planes.
Snipping tool: The rhodium(I)-catalyzed extrusion of carbon monoxide from biaryl ketones and alkyl/alkenyl aryl ketones was developed to produce biaryls and alkyl/alkenyl arenes, respectively, in high yields (see scheme). A wide range of functionalities are tolerated. Not only does this method provide an alternative pathway to construct useful scaffolds, but also offers a new strategy for CC bond activation.
Meet me at the symmetry gates: A supramolecular approach using chlorides as structure-directing ligands gives high-nuclearity, mixed-valent Mn coordination clusters with {MnIIMnIII12}, {MnII3MnIII10}, and {MnII3MnIII11} core structures that have supramolecular chirality. The {MnIIMnIII12} complex (see structure: Mn blue, Cl green, O red) is the first structurally characterized Mn-based Keplerate and has one of the highest symmetries reported for a high-nuclearity Mn coordination cluster.
The germylyne complex 2 was obtained by dehydrogenation of a hydrido (hydrogermylene) complex 1 with mesityl isocyanate on heating. A reaction intermediate 3 was also isolated by a room temperature reaction, which was converted into 2 by heating with elimination of MesNHCHO. A possible mechanism for formation of 2 is elucidated by kinetic studies and DFT calculations.
F tactic: Highly fluorine-doped mesoporous metal oxides (up to 40 at?%) were synthesized by topotactic fluorination synthesis with mesoporous metal oxides starting materials and fluorine as the fluorination agent. The surface areas, pore sizes, pore volumes, and F atomic concentrations of these materials could be adjusted over a wide range by varying the fluorination time and temperature.
As you like it: The choice of solvents and substituents at the silicon atom determine what product is formed from carbon dioxide after electrophilic activation by silyl cations (see scheme). Benzoic acid as well as the C-1 building blocks formic acid and methanol are on the product tableau.
Eliminating restraints: A trigonal-bipyramidal structure has been found to be the energetically-favored geometry of the hypervalent AX5 molecule Sb(C6F5)5 in the solid state and also in fluid solution, where molecules move freely and no crystal packing effects operate (see picture).
Think before you act: A computational approach is reported for evaluating the synthetic potential of heterocyclic arynes. Routine and rapid calculations of arene dehydrogenation energies and aryne angle distortion predict the likelihood that a given hetaryne can be generated, as well as the degree of regioselectivity expected in a reaction between a given hetaryne and a nucleophilic trapping agent (see picture).
Under the surface: Ag nanoparticles are deposited onto the surface of commercially available SiO particles, and subsequent chemical etching results in the formation of nanoporous SiO (see picture) without changing the chemical and physical properties of the original SiO. Moreover, chemical-assisted thermal annealing produces a shape-preserving Si-based multicomponent system, which exhibits high-performance electrochemical properties.
New and improved: New reaction conditions for tert-Boc-based solid-phase peptide synthesis make acid-labile sialyloligosaccharyl peptide ?-thioesters accessible. To demonstrate this, a sialyloligosaccharyl-erythropoietin glycoform (see picture) with 166 amino acid residues was synthesized.
Highly selective: The title reaction is achieved with high enantiomeric and geometric control and thermodynamically unstable (Z)-enone derivatives are obtained as the major products (see scheme). The procedure tolerates a wide range of substrates to generate optically active pyrazolones with vinyl-substituted quaternary stereocenters.
Peptide profiles: The use of mesoporous materials, such as ordered mesoporous carbon, improves the efficiency and selectivity of peptide extraction for profiling complicated samples. Controling the pore size of such mesoporous materials during synthesis allows specific molecular weight cut-offs to be introduced, which can eliminate a large number of interfering entities, such as serum proteins.
This Minireview provides a critical account of the development of allene-containing advanced functional materials, starting with the design and synthesis of stable and enantiopure building blocks. A variety of systems, including shape-persistent macrocycles, foldamers, polymers, charge-transfer chromophores, dendrimers, liquid crystals, and redox-switchable chiral chromophores are discussed from the viewpoint of their syntheses, properties, and potential applications. The goal of this Minireview is to inspire new uses of enantiopure allenes for the rational design of advanced materials.Property development: A critical account of the development of allene-based molecular materials is presented in this Minireview. Shape-persistent macrocycles, foldamers, polymers, and other allene-containing functional materials are discussed, with a focus on their synthesis and chiroptical properties.
Teaming up: The important indoline scaffold is provided with enantiomeric ratios of up to 98:2 in palladium(0)-catalyzed C(sp3)–H activations of aryl triflates. The key is the combination of the electron-rich monodentate Sagephos and the bulky 9H-xanthene-9-carboxylic acid. Both participate in a highly cooperative manner in the enantiodetermining concerted-deprotonation-metalation step (see scheme, Tf=triflate).
All that glitters is gold: Highly phosphorescent gold(III) complexes (see picture) with extended ?-conjugated cyclometalating ligands exhibit rich photophysical and photochemical properties. They act as efficient photocatalysts/photosensitizers for oxidative functionalizations of secondary and tertiary benzylic amines and homogeneous hydrogen production from a water/acetonitrile mixture.
Chiral acids: A highly enantioselective iridium-catalyzed hydrogenation of ?,?-unsaturated carboxylic acids was developed for the preparation of chiral 4-alkyl-4-aryl butanoic acids.
Molybdenum-catalyzed asymmetric ring-closing metathesis has been used for the kinetic resolution of racemic planar-chiral (?6-arene)chromium complexes with excellent enantioselectivity. The products are excellent precursors for the synthesis of various planar-chiral (?6-arene)chromium derivatives and can also be applied as chiral ligands in rhodium-catalyzed asymmetric reactions.
The modulation of protein–protein interactions (PPIs) has been recognized as one of the most challenging tasks in drug discovery. While their systematic development has long been considered as intractable, this view has changed over the last years, with the first drug candidates undergoing clinical studies. To date, the vast majority of PPI modulators are interaction inhibitors. However, in many biological contexts a prolonged lifespan of a PPI might be desirable, calling for the complementary approach of PPI stabilization. In fact, nature offers impressive examples of this concept and some PPI-stabilizing natural products have already found application as important drugs. Moreover, directed small-molecule stabilization has recently been demonstrated. Therefore, it is time to take a closer look at the constructive side of modulating PPIs.Doing it the other way round: The modulation of protein–protein interactions (PPIs) by small molecules has become increasingly popular over the last few decades. However, “modulation” has mainly been perceived as “inhibition” of protein–protein interactions, omitting the complementary strategy of stabilizing such macromolecular complexes. This Minireview highlights amazing examples and the potential of this constructive side of modulating PPIs.
It happens inside: Highly active nanoreactors are prepared by encapsulating of dendritic Pt nanoparticles (NPs) grown on a polystyrene template inside hollow porous silica capsules. The catalytic activity of these Pt NPs is preserved after encapsulation and template removal. Different metals, such as Ni, can thus be reduced inside the capsules, thereby leading to the formation of composites with tunable magnetic properties.
Cracking the encryption: Parallel computing with molecular finite-state automata and fluorescently labeled DNA molecules has been used to decipher two different images encrypted onto a single DNA chip (see picture). The images were deciphered by a mixture of input molecules that were processed by biomolecular automata, a strategy that potentially offers a huge diversity of encrypted images.
With the right support: A Ir/Fe(OH)x catalyst was designed. The Fe(OH)x support stabilizes the metal catalyst used for the oxidation of carbon monoxide. The catalyst was highly active for the oxidation of carbon monoxide in the presence of excess hydrogen at room temperature and showed a wide temperature range for the total conversion of CO (see picture).
Breaking through the stoichiometry barrier: As the diameter of silver particles is decreased below a critical size of 32 nm, the molar ratio of aqueous HgII to Ag0 drastically increases beyond the conventional Hg/Ag ratio of 0.5:1, leading to hyperstoichiometry with a maximum ratio of 1.125:1 (see figure). Therein, around 99?% of the initial silver is retained to rapidly form a solid amalgam with reduced mercury.
Dendrimers crosslinked with a photochromic diarylethene (blue in picture) were labeled with the fluorescent dye Cy3 (red) for reversible fluorescence photoswitching. If the obtained nanoclusters are irradiated with UV light, the Cy3 fluorescence is quenched by the diarylethene in its ring-closed form, whereas upon irradiation with visible light, the nanoclusters show fluorescence. High-contrast fluorescence imaging was achieved inside a living zebrafish.
Rapid and direct: The carboxylation of boronic acid esters with 11CO2 provides [11C]carboxylic acids as a convenient entry into [11C]esters and [11C]amides (see scheme). This conversion of boronates is pleasingly tolerant to diverse functional groups (e.g., halo, nitro or carbonyl).
In reduced circumstances: Tetrahydroxynaphthalene reductase shows a broad substrate range including alternate phenolic compounds and cyclic ketones. Structural modeling reveals major enzyme–substrate interactions; C-terminal truncation of the enzyme causes an altered substrate preference, in accordance with stabilization of the substrate by the C-terminal carboxylate (see picture). This effect allows the identification of a homologous enzyme.
Pump it up: Insoluble polymer films that depolymerize to release soluble monomeric products when exposed to a specific analyte act as a microscale pump. Products formed as a result of depolymerization amplify the signal and create a concentration gradient that pumps fluids and insoluble particles away from the bulk polymer by a diffusiophoretic mechanism. These pumps can respond to a variety of analytes, from small molecules to enzymes.
A rapid solvothermal approach was used to synthesize aligned 1D single-crystal rutile TiO2 nanowire (NW) arrays on transparent conducting substrates as electrodes for dye-sensitized solar cells. The NW arrays showed a more than 200 times faster charge transport (see picture) and a factor four lower defect state density than conventional rutile nanoparticle films.
Quite select: A new strategy was developed for the synthesis of various oxindoles from carbamoyl chlorides. Under the optimum reaction conditions, with Ad2PBu as a ligand, tBuCONHOH as an additive, and a CO atmosphere, selective C(sp3)H activation proceeded in the presence of a C(sp2)H bond. Ad=adamantyl.
Honorary Professorship: S. Buchholz Bayer Early Excellence in Science Award: A. Thomas Burckhardt Helferich Prize: H. Kagan Honorary Doctorate: M. Antonietti
Dual capacity: A new palladium-catalyzed intermolecular sequence consisting of the CH activation and amidation of methyl groups relies on N-fluorobis(phenylsulfonyl)imide (NFSI) as both the oxidant and the nitrogen source. The reaction provides the corresponding arylamines as bissulfonimides along with HF as the only by-product. Both experimental and computational results suggest the involvement of a monomeric palladium(IV) intermediate.
Chemistry in motion: A combination of confocal microscopy (see picture) and reaction-diffusion modeling provided a powerful toolkit with which solution transport into metal–organic framework crystals was studied. Commonly used pure diffusion models are insufficient to describe this process and, instead, it is necessary to account for the interactions of the guest molecules and the MOF scaffold.
Nb2O5nanorods and nanospheres were synthesized, and their photocatalytic activity for methylene blue decomposition in water compared. Nb2O5 nanorods clearly displayed higher activity, despite their comparable surface area. With a shape-dependent surface acidity, hydrothermal stability, and high photoactivity, these Nb2O5 nanorods are a unique and exciting nanomaterial for non-classical photocatalytic mineralization of organic compounds in water.
pH values go live! A ratiometric two-photon (TP) probe (NP1, see scheme) that has a significant TP action cross-section, high photostability, negligible toxicity, and can estimate pH values in live cells and human tissues by two-photon microscopy is described. NP1 can detect the difference in pH between live cells from the gastroesophageal junction (GEJ) and the lower esophageal sphincter of patients with and without esophagitis (see image).
A bright combination: A new type of donor–acceptor dyads, carbazolylaryl-substituted ortho-carboranes, which were conveniently prepared from the corresponding acetylenes and decaborane pathways, showed unique excited-state behavior associated with electron transfer unlike the meta- and para-counterparts (see picture).
The large central cavity of the human methylamine-induced form of ?2-macroglobulin (?2M) can accommodate two medium-sized proteinases, as shown by its crystal structure. In their Communication (DOI: 10.1002/anie.201108015), F. X. Gomis-Rüth and co-workers show how the 720-KDa ?2M traps prey proteinases by a major conformational rearrangement from an open to a closed form, a process reminiscent of the action of a Venus flytrap. Photos of a meal worm in a Venus flytrap courtesy of Beatrice Murch (www.beatricemurchphotography.com).
The most mercury-rich sodium amalgam, Na11Hg52, is prepared as single crystals by the combination of electrolytic and thermochemical methods. As C. Hoch and A. Simon show in their Communication (DOI: 10.1002/anie.201108064) this amalgam has a close relationship to the chloralkali process and a surprisingly complex structure for a binary compound. Such mercury-rich amalgams serve as models of polar metals in which a transition from the classical metal–metal bonding towards ionic bonding occurs.
A nanorobot is reported that is able to perform autonomous locomotion and control the initiation, termination, and velocity by light. In their Communication (DOI: 10.1002/anie.201107733), X. Zhang, W. Tan, and co-workers design a DNA walking device by incorporating photosensitive moieties within DNA enzyme analogue structures. Based on the phenomenon of pyrene-assisted photolysis of disulfide bonds, this nanorobot shows the operational freedom and mechanical speed reminiscent of protein motors.
Two-ring and three-ring DNA catenane systems have been developed. As demonstrated by I. Willner and co-workers in their Communication (DOI: 10.1002/anie.201107591) the rings undergo programmed and reversible dynamic transitions between predesigned topologies by a strand displacement mechanism. The catenated DNA nanostructures hold great promise as nanomachines for the dynamic, programmed transport and arrangement of cargoes at the nanoscale.
Golden tendencies: The title reaction for synthesizing cyclopentenone derivatives utilizes a gold complex and 8-methylquinoline oxide as catalytic system (see scheme; IPr=1,3-bis(diisopropylphenyl)imidazol-2-ylidene). Such products are not attainable using diazocarbonyl reagents as the gold carbenoids tend towards reacting with CH bonds.
Rh COT in the act: A Ni0-catalyzed [2+2+2+2] cycloaddition provides a high-yielding, scalable synthesis of the ligand dinaphtho[a,e]cyclooctatetraene (dnCOT). dnCOT complexation with RhI gives [Rh(dnCOT)(MeCN)2]SbF6 (see scheme), an excellent catalyst for [5+2] cycloadditions of vinylcyclopropanes and ?-systems with impressive functional group compatibility.
A cell-free protein synthesis system from which the release factor RF1 has been selectively removed enables the facile incorporation of unnatural amino acids into proteins at difficult and multiple sites by optimized use of orthogonal tRNA/aminoacyl-tRNA synthetase systems. 19F NMR spectroscopy of a protein labeled combinatorially with trifluoromethyl phenylalanine (red in picture) at multiple sites establishes resonance assignments with a minimal number of samples.
Strolling the ring: A general regioselective directed peri(C4)-metalation route to 1 through an in situ N-anionic protection of C2 is reported. The azaindoles may be elaborated by directed ortho metalation (DoM) and Suzuki coupling to more complex heterocyclic systems. An iterative ring-walk DoM sequence furnishes the exhaustively substituted 2. DMG=directed metalation group, TMEDA=N,N,N?,N?-tetramethylethylenediamine, TMS=trimethylsilyl.
In a spin: The dynamics of photoexcited ICN?(Ar)0–5 are presented. Photodetachment produces quasi-thermal electron emission that leaves ICN with up to 2.85 eV of internal energy. Photodissociation at 2.5 eV leads to one-atom caging and highly solvated anion products. Calculations indicate efficient energy transfer into CN rotation upon excitation to the 2?1/2 excited state. CN rotation is vital to explain the unique dynamics observed.
An enhancing factor: The enhancement of the electric properties of a dye molecule (IR26) by indium–tin oxide nanoparticles (ITO NPs, see picture) has been shown by measuring the near-infrared two-photon-excited transient absorption spectra. The dye molecule was excited much more efficiently in the presence of an ITO NP layer.
Regulatable nanorobots: A DNA-based walking device was designed that is capable of autonomous locomotion, with light control of initiation, termination, and velocity (see picture). This device is reminiscent of cellular protein motors in nature, especially those of green plants.
Chameleon: A new strategy for the synthesis of a wide variety of alkynyl derivatives by the reaction of substituted arylsulfonylacetylenes with organolithium species is described (see scheme). The high yields, the simplicity of the experimental procedure, the broad scope of this reaction, and the formation of CspC?sp?2 bonds without using transition metals are the main features of this methodology.
All in one: A tandem strategy has been developed wherein secondary aryl alcohols are directly coupled with aryl halides to provide stilbenoids through a dehydrative Heck sequence in the ionic liquid [hmim]Br, and with water as a by-product under microwave irradiation (see scheme). Classical methods do not permit this sequence to proceed in one pot, and some methods require multiple steps. hmim=1-n-hexyl-3-methylimidazolium.
They “know” where to go: A powerful orientation effect has been observed in complexes of mixed organocuprates [RTRNTCuLi] and substrates with CC, CN, and CS double bonds (see scheme; Th=thienyl). The preferred geometry of the intermediate complex sets up the facile addition of RT to the double bond, rather than addition of the “dummy ligand”, RNT.
A peek inside: Dynamic nuclear polarization (DNP) enhances the spectroscopic sensitivity of solid-state NMR measurements of uniformly (13C,15N)- labeled preparations of Escherichia coli cells by more than an order of magnitude (see picture; MW=microwaves, ?=enhancement factor). The major molecular components in the cells can be characterized in this way.
Unexpected: Anti-galvanic reduction (AGR), that is, metal ions are reduced by more noble metals, was found in small thiolated gold (see figure) and silver nanoparticles! These findings are not only unexpected considering the classic galvanic theory, but also provide a facile and mild method to make alloys on the nanoscale or tune the compositions, structures, and properties of nanostructures that are otherwise difficult to obtain.
A copper-catalyzed asymmetric allylic boronation (AAB) gives access to syn- and anti-1,2-diols. The method facilitates an iterative strategy for the preparation of polyols (see scheme), such as the fully differentiated L-ribo-tetrol and protected D-arabino-tetrol.
Not quasi-crystalline: Approximate five-fold symmetry appears in bronze-type Cu–Sn rods that are separated by Na atoms in Na2.8Cu5Sn5.6 (see picture). The rods are compared to the [Sn@Cu12@Sn20]12? cluster in the recently characterized A12Cu12Sn21 phases (A=Na–Cs), and a saltlike description in analogy to Zintl phases of p-block metals is introduced for these new polar intermetallic phases with a high d-block metal content.
POM-in-POM: A Wells–Dawson polyoxometalate sandwich compound with a double cubane core consisting of six vanadium atoms has been synthesized (see structure). Cluster formation was followed by mass spectrometry and the reduction of the double cubane was studied by a novel technique combining mass spectrometry and spectroelectrochemistry.
The evolution of drug resistance is one of the most fundamental problems in medicine. In HIV/AIDS, the rapid emergence of drug-resistant HIV-1 variants is a major obstacle to current treatments. HIV-1 protease inhibitors are essential components of present antiretroviral therapies. However, with these protease inhibitors, resistance occurs through viral mutations that alter inhibitor binding, resulting in a loss of efficacy. This loss of potency has raised serious questions with regard to effective long-term antiretroviral therapy for HIV/AIDS. In this context, our research has focused on designing inhibitors that form extensive hydrogen-bonding interactions with the enzyme’s backbone in the active site. In doing so, we limit the protease’s ability to acquire drug resistance as the geometry of the catalytic site must be conserved to maintain functionality. In this Review, we examine the underlying principles of enzyme structure that support our backbone-binding concept as an effective means to combat drug resistance and highlight their application in our recent work on antiviral HIV-1 protease inhibitors.Impeding the evolution of drug resistance: HIV protease inhibitors are critical to antiretroviral treatment regimens. However, the rapid onset of drug resistance limits the effectiveness of most approved inhibitors. The structure-based design of inhibitors targeting atoms in the protein backbone is an attractive strategy for maintaining drug efficacy. This approach limits the enzyme’s ability to evolve resistance without sacrificing its catalytic activity.
I’m your Venus: The crystal structure of the human methylamine-induced form of ?2-macroglobulin (?2M) shows its large central cavity can accommodate two medium-sized proteinases (see structure, front part clipped off to better show central cavity). Twelve major entrances provide access for small substrates to the cavity and the still-active trapped “prey”. The structure unveils the molecular basis of the unique “venus flytrap” mechanism of ?2M.
Well conducted: A two-dimensional porphyrin covalent organic framework is described. Owing to the eclipsed stacking alignment, the framework is conductive and allows high-rate carrier transport through the porphyrin columns (see picture). The central metal in the porphyrin rings changes the conducting nature of the material from hole to electron, and to ambipolar conduction. It also drives the high on–off ratio photoconductivity of the framework.
A red light for cancer cells: An iron(III) complex (1, see picture) that contains an anthracenyl fluorophore moiety and a catecholate ligand is a potent, metal-based PDT agent that efficiently photocleaves DNA in near-infrared light, has significant nuclear uptake, and high photocytotoxicity in red light by an apoptotic pathway in HeLa and MCF-7 cancer cells.
Sustainable Oxidations: An oxidation method to transform aryl(di)azinylmethanes into aryl(di)azinyl ketones is described. Base metals (copper and iron) as catalysts in combination with O2 as the oxidant are used, which renders this method sustainable. The utility of this method is illustrated by the synthesis of 6-(4-methylbenzoyl)pyridine-2-carbaldehyde, which is an intermediate in the preparation of the drug Acrivastine.
Dual action: A multifunctional rhodium catalyst system enables the simultaneous catalysis of two distinct transformations, hydroformylation of an alkene and reduction of an aldehyde, in a highly selective manner. This one-pot/two-step process is controlled by the cooperative action of two different supramolecular ligand systems and transforms terminal alkenes into C1-chain-elongated linear alcohols.
Six in one blow: Total syntheses of all the amathaspiramide alkaloids have been accomplished. Rapid construction of the diazaspiro[3.3]nonane core combined with regio- and diastereoselective reduction of the cyclic imide moiety with DIBAL established the route to the common structural motif. The late-stage reduction of the lactam to an imine functionality mediated by Schwartz’s reagent was the key to the streamlined syntheses.
In the nick of time: A nickel-catalyzed asymmetric intramolecular alkene insertion reaction into cyclobutanones (1) has been developed. The reaction significantly reduces the number of steps required for the synthesis of chiral benzobicyclo[2.2.2]octenones (2).
In the right light: UV light triggers bond breaking, liberates a caged carboxylic acid, and generates the central CC double bond in the photoresponsive hexatriene molecule of a dithienylethene molecular switch. Light of the same wavelength converts the colorless isomer to its colored counterpart (see picture) in a visually convenient method to report on the success of the release event.
A tale of two Michaels: The first enantioselective total synthesis of (?)-GB17 is reported. Construction of this unique naphthoquinolizinone skeleton was achieved by two stereoselective intramolecular Michael additions, one under catalyst control and the other under substrate control.
Anti-Terminator: Rise of the Molecules: Overexpression of an antiterminator gene (nusG) in Clostridium cellulolyticum induced the biosynthesis of the novel antibiotic closthioamide and related thioamides. This is the first successful genetic engineering of an anaerobe to trigger a cryptic pathway. Furthermore, synthetic probes provide valuable insights into the biogenetic relationship of the rare thioamide metabolites.
Surprising selectivity: The first enantioselective hydroformylations of simple alkenes of type RCH2CHCH2 to preferentially deliver the branched aldehyde product have been discovered using a new chiral ligand, named bobphos (see scheme). Established ligands are unselective in this reaction or show a slight preference towards the linear aldehyde.
Problem solved: An air-stable 2-pyridyl borane that can effectively couple to a wide range of aryl and heteroaryl halides and pseudohalides has evaded the synthesis community for decades. The discovery that Cu(DEA)2 powerfully enables palladium-mediated cross-couplings with air-stable boronates 1 has finally provided a general solution to this very important problem. DEA=diethanolamine, DMF=N,N?-dimethylformamide, Tf=trifluoromethanesulfonyl.
Dismembering molecules: The stable boryl(phosphino)carbene 1 can cleave small organic dioxide molecules. With CO2 and SO2, 1 gives, respectively, the phosphacumulene ylide [Mes(iPr2N)B-O-P(CCO)(NiPr2)Mes] (see scheme and structure) and boryl(phosphoryl)sulfine [Mes(iPr2N)B-C(SO)-P(O)(NiPr2)Mes] which have been structurally and spectroscopically characterized.
Fluorinated functionality: The copper-catalyzed oxidative trifluoromethylthiolation of aryl boronic acids with TMSCF3 and elemental sulfur at room temperature is described for the first time. This reaction provides a concise and efficient method for the synthesis of aryl trifluoromethyl thioethers (ArSCF3) under mild conditions.
The fundamentals: The IR spectrum of the adamantane cation, C10H16+, has been derived by resonant IR photodissociation of weakly bound C10H16+?Ln clusters (see picture). The analysis of the IR spectrum provides the first spectroscopic characterization of this fundamental cycloalkane carbocation in the gas phase and direct evidence for the Jahn–Teller distortion in the 2A1 ground electronic state.
Point the finger: Zinc-finger proteins are convenient and site-selective adaptors for targeting specific locations within DNA-origami structures. Orthogonal targeting of the specific locations in the structures was demonstrated by using two adaptors, and the application of Escherichia coli lysate that contained the adaptor-fused proteins successfully afforded the expected protein–DNA assembly.
Strained: [6]Cycloparaphenylene, a molecule with 97 kcal?mol?1 of strain energy, was synthesized. The synthetic strategy relied on two sequential oxidative dearomatization/addition sequences and a final reductive aromatization reaction (see scheme). The optoelectronic properties of [6]cycloparaphenylene were measured, and the analysis of the X-ray crystal structure revealed a linear packing geometry reminiscent of a carbon nanotube.
Double agent: The title reaction using the guanidine catalyst 1 can deliver both enantiomers of the product with excellent enantioselectivity by judicious choice of the double bond geometry of the the ?,?-unsaturated carbonyl compound. Computational studies reveal the possible origin of the inversed enantioselectivity, and the potential for enantiodivergent synthesis chiral amine-containing substrates is attractive.
The natural paragon taken seriously: A trispyrazolylborato cysteinato iron complex not only excellently mimics the active site structure of cysteine dioxygenase (see picture: both structures superimposed): a dioxygenation of cysteinate occurs on treatment with O2, and hence, the system represents the hitherto most realistic model for cysteine dioxygenase.
Saucy selection: The first catalytic, enantioselective Saucy–Marbet Claisen rearrangement has been achieved. Palladium(II) (R)-binap or tBuphox catalysts L*Pd(SbF6)2 were employed to generate allenyl oxindoles or spirolactones bearing a quaternary center with up to 98?% ee.
Linking in: Two-ring and three-ring catenane nanostructures that are made from sequences of DNA have been shown to undergo programmed and reversible reconfiguration across defined topologies by using strand displacement. The switchable nature of the configurations may enable a more flexible approach to the transport and delivery of molecular cargoes, or for the use of such structures as labels in an intracellular environment.
Vinylallenes or cross-conjugated trienes are obtained selectively in the title reaction. Two possible mechanisms are suggested to rationalize the formation of the different types of products. Control experiments indicate that p-benzoquinone (BQ) plays an important role as a ligand in addition to its role as an oxidant. E=CO2Me.
Catch me if you can: Multifunctional, polymer-based nanoparticles that are capable of temperature-responsive “catch-and-release” of a target protein have been synthesized. The process is reversible and does not denature the proteins. An optimized combination of functional monomers imparts binding selectivity toward a target protein over other proteins.
Directed, undirected! Rhodium(III)-catalyzed double CH bond activation (one directed, one undirected) provides an efficient route to biaryls (see scheme; DG=directing group). Significant kinetic isotope effects for both reaction partners and H/D scrambling between them are interesting experimental findings. While the mechanism is still unclear, a rhodium(V) species is invoked in the catalytic cycle.
Two better than one! The structural distortions in a bis(cyclopropyl) heterobimetallic lithium yttrium complex can be interpreted as two types of CC agostic interactions (see structure), one with a more covalent character with Y, the other with a more electrostatic character with Li. The CC agostic interaction with Y is reinforced by a CH agostic interaction.
Easy to hollow: A hollow porous Si nanocomposite with Ag nanoparticles (NPs) is prepared (see scheme PS=polystyrene, HP=hollow porous). The free volume in the HPSi structure effectively cushioned the volume change in Li–Si alloying and de-alloying reactions, giving an impressive performance as a high-capacity anode for lithium-ion batteries.
Microwaving plates: A facile method was developed for the fabrication of preferentially c-oriented cobalt-substituted silicoaluminophosphate-5 (CoSAPO-5) membranes on porous alumina supports. In situ microwave growth using a slip-coated TiO2 layer on the support surface resulted in an oriented CoSAPO-5 crystal layer, which was evolved into a defect-free membrane by improving crystalline intergrowth through secondary hydrothermal microwave growth.
Oxidizing noble metals: Pure N2O5 can oxidize elemental gold and palladium. The complex nitrates obtained by these reactions, (NO)[Au(NO3)4], (NO)2[Pd(NO3)4], and also the first nitrate of tetravalent platinum, (NO)2[Pt(NO3)6] (see picture for the anion: Pt gray, N green, O blue), have the potential to act as precursors owing to their high thermolability. The thermal decomposition of (NO)[Au(NO3)4] was elucidated in detail by several methods.
This Review highlights the application of high-temperature solutions for exploratory crystal growth and materials discovery of novel complex oxides. It provides an overview of the method of flux crystal growth of complex oxides and can function as a “how to” guide for those interested in oxide crystal growth. The most commonly used fluxes are discussed in terms of their applicability for dissolving specific elements and the typical reaction conditions are compiled. A large variety of recent quaternary and higher oxides that have been grown as crystals from fluxes are used to illustrate the power of the flux method to grow oxide crystals containing specific elements.The flux of the matter: The search for the “First Material”, the archetype in which a new phenomenon is first observed, has been a prime motivator for materials research. One method to discover such “First Materials” is crystal growth from high-temperature solutions using a flux as solvent (see scheme). This approach has been extremely successful in the discovery of new materials and is described using quaternary and higher oxides as examples.
Palladium-catalyzed cross-coupling reactions enable organic chemists to form CC bonds in targeted positions and under mild conditions. Although phosphine ligands have been intensively researched, in the search for even better cross-coupling catalysts attention has recently turned to the use of N-heterocyclic carbene (NHC) ligands, which form a strong bond to the palladium center. PEPPSI (pyridine-enhanced precatalyst preparation, stabilization, and initiation) palladium precatalysts with bulky NHC ligands have established themselves as successful alternatives to palladium phosphine complexes. This Review shows the success of these species in Suzuki–Miyaura, Negishi, and Stille–Migita cross-couplings as well as in amination and sulfination reactions.Adding fizz to catalysis: The Pd-PEPPSI series of catalysts (see scheme) is very active for the Suzuki–Miyaura, Negishi, Stille–Migita, aryl amination, and aryl sulfination reactions. The high reactivities of Pd-PEPPSI-IPr and Pd-PEPPSI-IPent catalysts with N-heterocyclic carbene (NHC) ligands are compared with other state-of-the-art catalysts. Pd-PEPPSI-IPent is shown to be one of the most active and general catalysts for cross-coupling reactions.
Life saver: Two unusual and toxic amino acids, 2R-amino-4S-hydroxy-5-hexynoic acid (red, see scheme) and 2R-amino-5-hexynoic acid (blue) have been isolated from the fruiting bodies of the mushroom Trogia venenata. Toxicology studies suggest that these compounds may be the cause of Sudden Unexplained Death (SUD) in Yunnan Province, China.
A molecular rectangle has been obtained from two equivalents of a dicarbene-bridged dinuclear platinum complex and two equivalents of ?,??-bis(triisopropylsiloxy)phenyl-1,4-diisocyanide. Hydrolysis of the OSi(iPr)3 bonds in this complex leads to the formation of two bridging di(NH,O)-NHC ligands and yields the molecular square (see picture) that features two types of bridging rigid ditopic di-NHC ligands.
We have contact! Material strain can have a dominating effect on contact electrification. When a deflated (relaxed) balloon is rubbed against teflon, the teflon surface charges positively, but when the same balloon is inflated (strained), the teflon surface charges negatively. This result illustrates that material strain can control contact electrification and alter the driving force of some (yet unknown) charge-transfer species.
Waterproof: cis-?-Aminocylopentanecarboxylic acid is a highly suitable building block for the synthesis of ?,?- and ?,?,?,?-peptides that have unique helical structures with high stability in methanol and aqueous media.
A good harvest: Two self-assembling strategies (micellization and electrostatic attraction) and covalent capture were employed to construct a robust, inexpensive, efficient artificial light-harvesting system (see picture). The synthesis was achieved by a one-pot reaction. A high density of the antenna chromophores was achieved without self-quenching and excimer formation, thus affording extremely efficient energy transfer.
Time to split: Supramolecular assemblies containing both photosensitizers and a ruthenium water-oxidation catalyst were prepared and characterized. The pictured assembly exhibits, for the first time, enhanced visible-light-driven water oxidation activity.
One flu over the cuckoo?s nest: The biological significance of a secondary sialic acid binding site on influenza virus neuraminidase remains elusive. On blocking the active site influenza-virus-containing virus-like particles with oseltamivir carboxylate, binding to ?(2,3)-sialyllactose is still detected. Thus the sialyllactose must bind at a secondary sialic acid binding site (see structures: docking study of ?(2,3)-sialyllactose in the secondary binding site of avian flu neuraminidase).
Be independent: Under basic conditions a furan ring entrapped in an aromatic macrocycle readily recovered the properties characteristic for a free molecule and assimilated a water molecule forming the Achmatowicz rearrangement product with a 3-pyranone subunit built in. Coordination of palladium(II) created a complex stabilizing the second tautomer with two sp3 carbon atoms (oxygen red, water green, palladium purple, and the aryl group blue).
The heteroatom helps! The introduction of an endocyclic sulfur atom enables fine-tuning of the reactivity and stability of thiacycloalkynes for copper-free click chemistry. The stabilizing effect of the endocyclic sulfur atom allows the use of highly activated seven-membered rings as reagents for bioorthogonal copper-free click chemistry.
Open vacancies: A facile one-pot synthesis of oxygen-vacancy-rich ultrathin W18O49 nanowires up to several micrometers long is described. In addition to unique optical properties, such as NIR absorption and blue-light emission, the nanowires show an unexpected ability to photochemically reduce carbon dioxide to methane (see picture) as a result of its defect structure caused by large quantities of oxygen vacancies.
Fluorine helps: A fluorinated triazolium salt pre-catalyst has been developed that efficiently promotes the asymmetric intermolecular Stetter reaction of enolizable aldehydes and nitrostyrenes (see scheme). Trans fluorination of the catalyst architecture results in unparalleled reactivity and enantioselectivity in the desired transformation. A DFT study provides evidence of an electrostatic interaction as the source of the increased enantio-induction.
Not your cup of tea? “Coffee rings” of spherical colloidal particles are left behind after water droplets resting on surfaces have dried out. This controlled evaporation of colloidal solutions can be exploited to deposit material in regular patterns (see picture). It is now shown that if spherical colloids are replaced by slightly elongated ones, the coffee ring is not formed and is replaced by an even more uniform deposition.
Bio-oil to hydrocarbon oil: An active, selective, and stable catalyst (Ni supported in zeolite HZSM-5) allows the conversion of a wide variety of CO and CO bonds in n-hexane-extracted pyrolysis oil into hydrocarbons through a cascade of hydrogenation, hydrolysis, dehydration, and dehydroaromatization reactions. Quantitative yields of C5–C9 gasoline-range hydrocarbons are obtained under mild conditions in water.
Pure crystals: Ion exchange of semiconductor nanocrystals yielded materials with poor optoelectronic properties such as low photoluminescence quantum yields. The reason for the low quantum yields of these nanocrystals are impurities at the level of a few atoms per nanocrystal. Cation-exchanged nanostructures, however, could be purified post exchange from such impurities resulting in high-quality nanocrystals (see picture).
Geminal diauration of [Ph3PAu(aryl)] complexes has been investigated to model the intermediacy of geminally diaurated gold(I)–vinyl complexes in catalysis (see scheme). The results advance our understanding of the factors influencing the stability, reactivity, and dynamics of these organometallic intermediates.
The ring and I: Hypervalent iodine compounds avoid the issues of toxicity or complicated ligands of many transition-metal-based systems. A highly enantioselective oxyamination of alkenes with N-sulfonyl ureas employing chiral, lactic acid-based hypervalent iodine reagents gives a facile synthesis of enantiomerically pure 2-arylproline derivatives (see scheme) for the first time.
Detective work: Three highly sensitive and selective fluorescent probes for the detection of H2S have been developed. Two of the probes detect H2S by the reduction of an azide moiety to an amine group, which changes the probes into their fluorescent forms and generates a fluorescent signal. In the third method, the fluorescent signal is created by using H2S as a nucleophile in a reaction that unmasks fluorescein.
Nature excels at engineering materials by using the principles of chemical synthesis and molecular self-assembly with the help of noncovalent forces. Learning from these phenomena, scientists have been able to create a variety of self-assembled artificial materials of different size, shapes, and properties for wide ranging applications. An area of great interest in this regard is solvent-assisted gel formation with functional organic molecules, thus leading to one-dimensional fibers. Such fibers have improved electronic properties and are potential soft materials for organic electronic devices, particularly in bulk heterojunction solar cells. Described herein is how molecular self-assembly, which was originally proposed as a simple laboratory curiosity, has helped the evolution of a variety of soft functional materials useful for advanced electronic devices such as organic field-effect transistors and organic solar cells. Highlights on some of the recent developments are discussed.All gelled together: Solvent-assisted gelation of functional organic molecules leading to one-dimensional fibers is an area of great interest. The recent developments in molecular self-assembly-assisted gelation of ? systems into soft functional materials and their potential application in organic electronic devices such as organic field-effect transistors and organic solar cells are reviewed (see picture).
Three not of a kind: A triphasic microfluidic route provides a flexible and promising way to fabricate colloidal photonic crystal supraparticles that are anisotropic in both geometry and function. These supraparticles are promising for applications including novel color displays (see scheme).
Channeling of mobility: A new method for the direct measurement of proton mobilities based on a pH-sensitive fluorescence probe is described. The results verify the enhancement of proton mobility in two-dimensional extended nanospace channels and contribute to a deeper understanding of ion-transport processes inside nanochannels.
Light support: Regenerated cellulose gel prepared from an aqueous alkali–urea solution serves as scaffold/template for the in situ preparation of cellulose–silica composite aerogels (see picture) by a sol–gel process from organic silicates, and drying with supercritical CO2. The resulting composite aerogels have the mechanical strength and flexibility, large surface area, semi-transparency, and low thermal conductivity of the cellulose aerogels.
A tricyclic organic host with tetrahedrally positioned amines incorporates a tetrahedron of water in the solid state. This internal water layer further solvates either an additional water molecule or a fluoride ion (see picture). The five-water cluster is an example the simple model for bulk water known as Walrafen’s pentamer.
Complex problem: The crystal structure of p38? mitogen-activated protein kinase in complex with a dibenzo[a,d]cycloheptenone inhibitor was found to be incompatible with NMR data of the same complex in solution. By using inferential structure determination with restraints from X-ray crystallography and NMR spectra, a structure that is compatible with both data sets and very close to the X-ray crystal structure was generated (see picture).
C-ing cellulose in a new light: The self-assembly of nanocrystalline cellulose (NCC) with tetraalkoxysilane produces a chiral nematic NCC–silica composite material, which upon carbonization, and then etching of the silica with dilute base solution produces a novel high surface area chiral nematic mesoporous carbon (see picture).
A simple solution: In the simple approach to silica films with perpendicular mesochannels presented herein, the substrate is immersed into a Stöber solution in which the silica precursors are hydrolyzed, cross-linked by an ammonia catalyst, and assembled with a surfactant on the substrate to form hexagonal mesostructures perpendicular to the substrate surface.
Naked-eye detection: The versatility of direct-write nanolithography was combined with the unrivaled resolution and selectivity of molecular self-assembly, to show, for the first time, the molecularly mediated placement, with nanometer accuracy, of single Au nanoparticles within a plasmonic array. In doing so, a coupled plasmonic systems was created which allowed colorimetric, naked-eye detection of protein–protein binding at extreme sensitivities.
Two arms to hold: Inspired by the structure of basic leucine-zipper proteins, high-affinity peptides, named aptides, were designed that contain a stabilizing scaffold (tryptophan zipper) and two target-binding regions (orange and blue in picture). A fluorescently labeled aptide that binds to a tumor-specific protein, was used for fluorescence imaging in vivo.
Yes, Walter, there is a polymorph of sucrose! At 4.80 GPa, (+)-sucrose, common table sugar, transforms into a new polymorph. In its structure the network of intermolecular hydrogen bonds is reformulated, with new types of H bonds being formed, and the molecular conformation changes. This structural variability is characteristic of all carbohydrates, hinders their crystallization, and is vital for organisms for which sugars are important building blocks.
Eight makes a happy Ho(l)me: The versatile octadentate TIAM ligand forms lanthanide complexes (Ln=Sm, Eu, Tb, Dy, Ho) with high quantum yields in water. This ligand is an efficient sensitizer, and also shields the metal center from solvent quenching, as shown by an X-ray diffraction study of the Ho complex.
Propylene from methane: The transformation of methane to propylene has been realized in a two-step route via CH3Cl or CH3Br. CeO2 serves as an efficient and stable catalyst for the oxidative chlorination and bromination of methane to CH3Cl and CH3Br. In the second step, a modified zeolite is highly a selective and stable catalyst for the conversion of CH3Cl or CH3Br into propylene.
It’s rapid and selective: In contrast to the dimerization of ?,?-unsaturated esters (acrylics) by carbene 3, the more nucleophilic carbene 2 selectively forms the single-addition product, and 1, the most nucleophilic carbene of the series, polymerizes acrylics. The biomass-derived methylene butyrolactones are quantitatively polymerized to produce medium- to high-molecular-weight bioplastics in less than one minute at ambient temperature. Mes=1,4,6-trimethylphenyl, TOF=turnover frequency.
Allenes are the simplest class of cumulenes, with two contiguous CC bonds, and show unique physical and chemical properties. These features make allenes particularly attractive in modern organic chemistry. In this Review, attention is paid to the advances made in catalytic asymmetric synthesis and natural product syntheses based on well-established reactions of allenes, such as propargylation, addition, cycloaddition, cycloisomerization, cyclization, etc., with or without catalysts. Their versatile reactivity, substituent-loading ability, axial to center chirality transfer, and controllable selectivity allow access to target molecules by unique and efficient approaches. The main topics in this Review are presented with selected examples from 2003 to 2011.Creative and easy syntheses of chiral compounds and natural products are possible by using allenes. These compounds display exceptional physical and chemical properties, and thus offer new possibilities in catalytic asymmetric synthesis and the total synthesis of natural products. The remarkable progress made in these two topics is summarized selectively in this Review.
Selectivity in nanoreactors: A hybrid yolk–shell nanostructure that contains gold nanoparticles in the core and thermosensitive microgel poly(N-isopropylacrylamide) (PNIPA) as shell is presented. The catalytic selectivity of Au-PNIPA nanoparticles for the reduction of hydrophilic 4-nitrophenol and more hydrophobic nitrobenzene with NaBH4 can be tuned through the volume transition of PNIPA shell (see picture).
All in a spin: A cobalt(II) coordination polymer has a highly cooperative spin-crossover (SCO) behavior with a small hysteresis loop (see picture; HS=high spin, LS=low spin). The correlation of the magnetic properties with the crystal structures was determined at different temperatures. This study reveals an unprecedented reversible symmetry breaking in a d7 SCO coordination polymer.
Skeletons in the flask: The first highly enantioselective organocatalytic version of the title reaction using an in situ substrate generation/activation catalytic mode is described (see scheme). The reaction provides an efficient enantioselective construction of functionalized azaspirocyclic skeletons. The in situ generation of the enolate provides a new way in which to use this important nucleophile in organic synthesis.
Surface chemistry: A new method for creating complex patterns on gold substrates is reported. Substrates were functionalized with nitroveratryl-protected carboxylic acid and hydroxy-terminated thiol monomers and patterned with a direct-write photolithography system to produce complex functional group gradients. In addition, two amine molecules were sequentially coupled on the substrate under spatial control (see picture).
Electrons at the crossroads in oxidation pathways stabilize radicals in five-coordinate, phenolate-rich FeIII complexes. In their Communication (DOI: 10.1002/anie.201103233), C. N. Verani and co-workers report bioinspired coordination compounds that possess low local symmetry, and show experimentally as well as by computational methods that subtle changes in the ligand and electrolyte lead to distinct sequences in which the ligand-appended phenolates are oxidized into phenoxyl species.
Zinc phthalocyanine sensitizers that contain phosphinic acid anchoring groups have an overall conversion efficiency of 3.24 % under 1 sun in a dye-sensitized solar cell (DSSC). M. K. Nazeeruddin, T. Torres, M. Grätzel, and co-workers demonstrate in their Communication (DOI: 10.1002/anie.201105950) that the phosphinic acid groups provide a stronger binding affinity relative to carboxylic acid anchoring groups, which improves the durability of DSSCs.
Well-ordered mesoporous iron silicates that have an ultralarge pore diameter and high Fe content are stable, active, and reusable catalysts for the synthesis of poly(methyleneanthracene) (PMAn) by polymerization of anthracene inside the nanopores. In their Communication (DOI: 10.1002/anie.201107145), E. Kim, A. Vinu, and co-workers report that the physical and optical properties of PMAn can be controlled by tuning the pore diameter and the iron content of the mesoporous catalysts.
Droplet attraction: Surfactants responsive to magnetic fields are reported for the first time. This new class of magnetic ionic liquid surfactants (MILSs; see picture) shows remarkable effects on surface and interfacial tension and allows access to magneto-responsive emulsions and new methods of separation, recovery, catalysis, and potential magnetophoretic applications.
Reducing hazards: A asymmetric transfer hydrogen reaction was developed to reduce prochiral allylic alcohols in high yield and excellent enantioselectivity (see example). Mechanistic studies indicate a novel enantioselective isomerization/transfer hydrogenation mechanism. This new reaction is much safer than high-pressure hydrogenation using H2 gas.
MOFs on the move: A copper-coordinated [2]pseudorotaxanate which reacts with zinc nitrate to form threefold interpenetrated networks retains most of its solution-state chemistry, including its ability to undergo electronic switching of some of the copper(I) ions under redox control.
Berylliant! Interaction of a well-defined adduct of MeBeH and an N-heterocyclic carbene (NHC) with PhSiH3 results in complete rupture of the heterocycle, and activation of the NHC through effective BeH2 insertion into a CN bond of the heterocycle (see scheme; Ar=2,6-diisopropylphenyl, IPr=1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene).
An ideal template for the production of macroporous polystyrene can be prepared from foamed oil-in-water emulsions containing styrene, water, glycerol, and sodium dodecylsulfate. After addition of a photoinitiator the mixture is polymerized with UV light and the foam structure of the precursor is transferred to the polymer. The resulting materials display densely packed cells with windows between adjacent pores (see SEM image; scale bar: 250 µm).
Creating an asymmetric environment at AuI is a challenge because of the linear coordination geometry of the ion. In their Communication (DOI: 10.1002/anie.201107789), S. Handa and L. M. Slaughter report the highly enantioselective catalysis of a tandem addition/cycloisomerization reaction of alkynylbenzaldehydes by chiral gold carbene complexes containing weak metal–? interactions. These secondary interactions help to create an asymmetric pocket around the gold atom that is analogous to a baseball glove gripping a ball. (Picture by L. M. Slaughter and S. Ball.)
Enantioselect-DeFluor: Carbon–fluorine bond cleavage by a chiral zirconium complex allows the synthesis of optically active 1,3-difluoroallene for the first time. Its absolute configuration was established by gas-phase vibrational circular dichroism spectroscopy (see picture).
A select few: An enzyme screen is used to identify two enzymes that selectively cleave porphyrin–lipid regioisomers (see picture). Either of the isomerically pure conjugates assembles into physically similar porphysome nanovesicles. Although porphysomes formed from both regioisomers are stable in serum in vivo, only one regioisomer rapidly degrades upon uptake in the liver.
A crosslinked micellar nanocarrier system for on-demand drug delivery is described by J. Luo, K. S. Lam, and co-workers in their Communication (DOI: 10.1002/anie.201107144). The reversible catechol boronate crosslink increases the stability of the nanocarriers against severe conditions in blood stream. After the ball-like nanocarriers reach the tumor target the crosslinks are cleaved by the acidic tumor environment or by exogenous cis-diols (e.g. mannitol), causing the ball to burst, releasing the drug.
16-Electron triatomic ring: Novel thiazylidynephosphane (SNP) was produced by either flash vacuum pyrolysis (ca. 1000?°C) or laser photolysis (193 nm) of SP(N3)3. Its photointerconversion to cyclic thiazaphosphirine (cyc-PSN) and thiophosphoryl nitride (SPN) was found in Ar matrix at 16 K. Cyc-PSN is the first experimentally observed 16-electron cyclic triatomic molecule.
Scratch the surface: Dehydrocondensations between carboxylates and amines by using an amphiphilic 1,3,5-triazinylammonium-based coupling agent were accelerated by the interfacial effect of micelles and emulsions of common surfactants (see figure). The reaction of carboxylates was promoted by both anionic and nonionic surfactants, and that of amines was promoted by only a nonionic surfactant. High selectivities for more lipophilic substrates were observed in micelles or emulsions.
An alloy cluster containing a 13-atom core, with a composition Ag7Au6(H2MSA)10 (H2MSA=mercaptosuccinic acid) was synthesized from silver clusters by a galvanic exchange reaction. The clusters were characterized by several spectroscopic and microscopic methods. The alloy cluster shows luminescence with a quantum yield of 3.5×10?2 at room temperature. Theoretical calculations for Ag7Au6(SCH3)10 suggest a distorted icosahedral core.
A flexible polymer for selective seawater splitting: Incorporation of a monomeric Mn-porphyrin that is normally catalytically inactive, into a flexible poly(terthiophene) film yields a remarkable light-assisted water oxidation catalyst with an apparent overpotential for water oxidation of a mere 0.09 V. The catalyst generates exclusively O2 and no Cl2 in seawater at 0.9 V versus Ag/AgCl.
The aerobic oxidation of a phenolic lignin model compound with a vanadium catalyst results in the oxidative cleavage of the CC bond between the aryl ring and the adjacent hydroxy-substituted carbon atom (see scheme). Labeling experiments indicate key mechanistic differences to a previously reported related CO bond cleavage reaction. The selectivity in CC versus CO bond cleavage depends on the choice of the vanadium catalyst.
Amphibians like water, but do they also notice volatile compounds in the air? Yes, they do. Macrolides, such as phoracantholide J (see picture; upper right structure) or the newly discovered natural product gephyromantolide A (left structure), are used for communication by mantelline frogs from Madagascar.
Pass the baton: A one-pot relay catalysis for a carbonyl ylide formation/enantioselective reduction sequence using a dirhodium(II) tetracarboxylate and chiral phosphoric acid catalyst system is described. The four-step transformation involves a rhodium carbene complex, a carbonyl ylide, and an isobenzopyrylium, the enantioselective reduction of which yields isochromanone derivatives in good yield with high selectivity.
Light to dissolve: (R)- and (S)-diamides bearing a hydrogen-bonding framework (red in picture) and a trans-azobenzene unit (blue) form an insoluble heterochiral aggregate, which can be dissolved by photoisomerization of the azobenzene unit to the cis conformation by UV irradiation (365 nm). The insoluble aggregate was formed again by subsequent irradiation with visible light (>422 nm). The precipitation and dissolution is manifestly reversible.
Aerosol processing coupled with surfactant-templated sol–gel synthesis is used to produce MoO3-SiO2-Al2O3 catalysts. By quenching the sol–gel kinetics by fast drying of the aerosol, molecular-scale dispersion of each component is achieved. The structuring agent generates an organized porosity at the nanoscale. The catalysts have a high specific surface area and outstanding olefin metathesis activity.
Being direct: A Brønsted acid catalyzed ? alkylation of ketones is described. The phosphoric acid 1 promoted this reaction to afford the desired products with high yields, high diastereoselectivities, and good to excellent enantioselectivites.
Light opens: Photocontrolled transmembrane passage of soluble dyes and delivery of small peptides into mammalian cells has been achieved using azobenzene-modified polymers (AMPs) as permeabilizing agents. Irradiation with UV and visible light triggers polarity switches upon cis–trans isomerization of the azobenzene moieties. Photoresponsive permeability and pore opening promoted by trans-AMPs, but not cis-AMPs, in supported lipid bilayers are observed.
Crystalline reagent capsules were prepared by installing CH3NCS into networked molecular capsules. While the tight encapsulation completely prevented leaching of reagent molecules into the supernatant, introduction of amines into the interstitial pores triggered reagent delivery. As a result, enhanced substrate selectivity was observed in crystalline-state thiocarbamoylation (see picture; 86:14 in favor of 2- vs. 1-naphthylamine).
An efficient and highly enantioselective copper-catalyzed allylic alkylation of disubstituted allyl halides with primary and secondary organolithium reagents using phosphoramidite ligands is reported. The use of trisubstituted allyl bromides allows, for the first time, the enantioselective synthesis of all-carbon quaternary stereogenic centers with these reactive organometallic reagents.
An Ag4diamond is encapsulated by silicotungstate ligands in TBA8[Ag4(DMSO)2(?-H2SiW10O36)2]?2?DMSO?2?H2O (Ag4; DMSO=dimethyl sulfoxide, TBA=tetra-n-butylammonium), which was obtained by reaction of TBA4H4[?-SiW10O36] with AgOAc in an organic medium. Polyoxometalate Ag4 (see picture) selectively catalyzes hydrolytic oxidation of various silanes to the corresponding silanols in high yields (72–96?%).
The genetic code of cells is near-universally triplet, and since many ribosomal mutations are lethal, changing the cellular ribosome to read nontriplet codes is challenging. Herein we review work on the incorporation of unnatural amino acids into proteins in response to quadruplet codons, and the creation of an orthogonal translation system in the cell that uses an evolved orthogonal ribosome to efficiently direct the incorporation of unnatural amino acids in response to quadruplet codons. Using this system multiple distinct unnatural amino acids have been incorporated and used to genetically program emergent properties into recombinant proteins. Extension of approaches to incorporate multiple unnatural amino acids may allow the combinatorial biosynthesis of materials and therapeutics, and drive investigations into whether life with additional genetically encoded polymers can evolve to perform functions that natural biological systems cannot.On all fours: Recent work has used quadruplet codons to encode unnatural amino acids. Multiple unnatural amino acids have been incorporated into proteins through orthogonal protein translation using a quadruplet decoding ribosome (see figure; mutations to ribosome are shown in red).
Sacrifice for the team: A one-pot method achieves remote functionalization at the ?-position of an amine moiety through the sacrificial reduction of a neighboring group. The process takes advantage of an intramolecular redox reaction, thereby avoiding the need for any external oxidants. This method was applied to a concise five-step total synthesis of indolizidine 167B.
At the end of the tether: Aryl hydrazides that have carbonyl groups tethered at the para position of the aromatic ring undergo an intramolecular Fischer indolization reaction to give the corresponding indolophanes. Strategic insertion of a double bond in the tether enables a tandem aromatic [3,3] sigmatropic rearrangement reaction to occur to give tricyclic benzo[cd]indoles.
K(l)ick it into reverse: Mechanical force (ultrasound) may be employed to promote a retrocycloaddition reaction of a 1,2,3-triazole to regenerate the parent azide and alkyne, a reaction that cannot be achieved by other means.
Push button control: A new templating motif for mechanically interlocked molecules involving benzimidazolium axles and dibenzo[24]crown-8 wheels was used to create [2]rotaxane molecular shuttles with a compact and rigid, H-shaped molecular structure for condensed-phase and solid-state applications. Four different states of the molecular shuttle were shown to exhibit different rates of motion controlled by acid–base chemistry or the presence/absence of lithium ions (see scheme).
Two key reactions in a rapid assembly of the tricyclic core of vinigrol are a stereoselective Claisen rearrangement and an intramolecular Diels–Alder reaction. The method paves the way for a total synthesis of this synthetically challenging and biologically interesting natural product.
Fluorescent probes have been synthesized on a zeptomole (10-21 mol) scale by overlaying polymer nanofibers that are doped with nonfluorescent probe precursors. In their Communication (DOI: 10.1002/anie.201105629), P. Anzenbacher, Jr. et al. show that the nanoscopic fiber junctions generate the fluorescent probes in situ, and that multiple fibers, each loaded with a different reagent, can be used to form a multiprobe sensor array that is capable of recognizing heavy-metal ions.
Sugars in space: The rotational signature of ribose, which is thus the first C5 sugar to be detected in the gas phase, is reported by E. J. Cocinero, A. Lesarri and co-workers in their Communication (DOI: 10.1002/anie.201107973). Six conformers were detected by a combination of laser vaporization and microwave spectroscopy. All adopt a pyranoside (pyr) structure, stabilized by cooperative hydrogen-bond networks, and not the furanose or linear forms usually found. The rotational spectrum opens the door to the detection of this sugar in space.
Volatile pheromones in frogs have been detected for the first time in the family Mantellidae from Madagascar. Previously only water-soluble pheromones had been found in amphibians. In their Communication (DOI: 10.1002/anie.201106592), S. Schulz and co-workers show that the femoral ducts of the male frogs contain macrolides and secondary alcohols. These compounds, including structures such as gephyromantolid A, were identified and synthesized.
Pump it: Materials that show intriguing shape changes induced by simple light exposure are emerging as candidates for artificial muscles. Recent examples are highlighted to illustrate the various molecular conformational changes induced by irradiation. Assemblies of these photo-responsive molecules are now being prepared that show functions that resemble real muscle.
Reduce to produce: Molybdenum- and vanadium-nitrogenase cofactors have been isolated and shown to reduce carbon monoxide and cyanide ions to a mixture of alkanes and alkenes in the presence of a strong reductant, europium(II) diethylenetriaminepentaacetate (see scheme). Various hydrocarbons of up to seven carbon atoms in length are detected as products in these ATP-free reactions.
Totally tubular: A linear M8L48+ receptor, which binds tightly and selectively to the dicyanoaurate anion, was assembled from simple organic subcomponents and copper(I) ions. The guest complex is not bound unchanged, but instead is transformed into a longer linear complex where two dicyanogold units are bridged by a central cation of copper/silver (see scheme). This complex optimally fills the cavity of the receptor but is not observed in the absence of the host.
Polypropionates made EZ: The E/Z geometry of tris(trimethylsilyl)silyl super silyl enol ethers derived from propionaldehyde controls diastereoselectivity in the aldehyde crossed-aldol reaction. These silyl enol ethers can participate in polyaldol cascade reactions, thus allowing the one-pot synthesis of four different dipropionate stereotetrads (see scheme), and polyketides bearing up to five contiguous stereocenters.
Small but powerful: TiO2(B) with the smallest particle size yet reported (2.5×4.3 nm) has been synthesized (see TEM image). Its volumetric capacity to store lithium, and hence charge, as an anode in a lithium-ion battery is greater than that of any other titanate at high rates (>1000 mA?g?1).
Unusual split: A wide variety of benzosiloles and derivatives are obtained by the Pd-catalyzed intermolecular coupling of 2-silylaryl bromides and alkynes and the accompanying selective cleavage of the C(sp3)Si bonds as a key step (see scheme). The product spectrum includes benzosiloles, benzothiophene-fused siloles, ladder-type ?-conjugated benzosiloles, and thiophene-bridged 2,5-bisbenzosiloles.
Modified point of view: A bio-inspired approach was used to tailor silicalite-1 crystallization. Growth modifiers (ZGMs) with molecular recognition for binding to specific crystal faces produced drastic changes in zeolite crystal morphology. This facile approach offers an efficient method for tuning zeolite properties.
Giving the metal the boot: The title reaction provides facile access to functionalized chiral ketones from chiral ?,??-disubstituted aldehydes in the presence of molecular oxygen (see scheme). The CC bond-cleavage approach offers an alternative or better method relative to the typical bond-forming strategies used in synthesizing chiral ketones.
A new coat: LiMn1?xFexPO4 materials with a LiFePO4 outer layer of varying thickness and a LiMn0.85Fe0.15PO4 bulk were prepared. The physical characteristics such as tap density, porosity, and spherical morphology were fine-tuned. The double-structured micron-sized LiMn0.85Fe0.15PO4/LiFePO4 material (see picture) shows properties which make this material an ideal candidate for rechargeable lithium batteries.
You may now kiss the boride: Four-coordinate boron, carbon, and nitrogen are almost always tetrahedral. The first examples of compounds with near-planar four-coordinate boron atoms have been prepared from trinuclear coordinatively unsaturated borido complexes. The two resultant tetranuclear complexes (see scheme) both feature near-planar four-coordinate boron atoms, with angle sums of 362.4° and 364.6°.
Shape-shifting: A method for reversibly transforming the shape of organic waveguides to form 2D nanosheets, 1D nanotubes, and 0D nanorings has been developed. The nanosheets can be turned into nanotubes and subsequently into nanorings by adding water to the solvent, whereas ultrasonication changes the nanotubes back into nanosheets. Both nanotubes and nanosheets act as waveguides and change the direction of incident laser light in a shape-dependent manner.
Highly functional: A copper(I)-catalyzed intramolecular carbomagnesiation under mild conditions transforms readily available alkynyl(aryl)thioethers into magnesiated benzothiophenes. Subsequent reaction with various electrophiles (acid chlorides, allyl bromides, aryl halides) provides polyfunctional benzo[b]thiophenes (see scheme). Further modification of the cyclization products affords highly diversified benzothiophene derivatives and new heterocyclic scaffolds.
Packed in like sardines: Three BF4? ions are packed into the three cavities of an interpenetrated dimer of a coordination cage (see scheme). While the inner BF4? ion is tightly bound inside the central position, the loosely bound outer anions can be replaced with halide anions by an allosteric binding mechanism and a concerted structural change. In particular, Cl? is bound with great affinity.
Into low force regime: A universal molecular force probe for measuring by AFM the strength of receptor–ligand and protein–protein complexes was developed. The protein-based force probe has the sensitivity on the order of piconewtons and provides a single-molecule fingerprint for identifying mechanical rupture events of individual complexes (see picture).
Demand and deliver: Micelles reversibly crosslinked by boronate esters (see scheme) show in vitro and in vivo stability and thus minimize premature drug release under physiological conditions. After reaching the tumor sites, drug (stars in scheme) release is activated by cleavage of the boronate esters by the acidic conditions around the tumor or in the target cells, or by the administration of mannitol.
Bioconjugation of photocaged D-luciferin with upconversion nanoparticles (UCNPs) for uncaging and bioluminescence imaging is reported by X. Liu, B. Xing, and co-workers in their Communication (DOI: 10.1002/anie.201107919). Photon upconversion of near-infrared light by the biocompatible UCNPs causes D-luciferin to be released from the surface of the UCNPs, which results in enhanced bioluminescence signals in vitro and in vivo with deep light penetration and minimum cell damage.
Thinking inside the COF: Internally functionalized, boroxine-linked three-dimensional covalent organic frameworks (COFs) can be synthesized by co-crystallizing a truncated, trifunctional monomer with the parent tetrafunctional building block. The functionalized COFs possess accessible functional groups and a distinct interior microenvironment. In the picture the orange sphere corresponds to an alkyl chain or an allyl group in the pore interior.
A new twist: The single-crystal structural analysis of BrN3 is described. In contrast to IN3, which forms chains, BrN3 forms a helical structure in the solid state (see picture). Such a structural feature has not been previously observed in covalent p-block azide chemistry.
Supramolecular coordination polymers based on stacked square-planar platinum(II) complexes such as Magnus? Salts show potential as functional materials. In their Communication (DOI: 10.1002/anie.201108197), G. H. Clever, M. Shionoya, and co-workers describe a linear array of five alternately stacked platinum(II) complexes in the form of a soluble host–guest complex. The X-ray structure of {[Pt(pyridine)4]?[PtCl4]2@cage} shows the linear, pentanuclear array within the cages and their circular packing into a hollow tubular superstructure.
The anion-templated synthesis of the first halogen bonding catenane, which recognizes chloride and bromide ions solely by halogen bonding, is described. The catenane’s ability to optically sense halide anions using fluorescence spectroscopy is demonstrated.
Director’s cut: Not only conventional alcohols but also silanols can act as directing groups in oxidative palladium(II)-catalyzed CH alkenylations. The silicon-tethered hydroxy groups are “traceless”, thereby facilitating the regioselective CH activation of toluene derivitives as well as phenols (see scheme).
Right on CueO: The O-centered structure of the trinuclear copper center in a multicopper oxidase (CueO) was shown to be an intermediate of the four-electron reduction of dioxygen (see picture). This structure was determined by in situ data collection of X-ray diffractions and copper K-edge spectra at low to high X-ray dose conditions.
Holey sheets: Nanosheet assemblies of FAU-type zeolite X with intracrystalline mesopores are prepared (see picture). This material is synthesized by soft-templating and combines micro, meso, and macropores in a hierarchically interconnected manner.
Dynamic trapping: Scanning tunneling microscopy video imaging of methyl thiolates on copper surfaces reveal the formation of defined metastable dimers with fluctuations on subsecond timescales, indicating short-term trapping of copper surface atoms (see picture). This transient stabilization of metal adatoms has important implications for applications of organosulfur species as additives and in nanoscience.
Sticks and bonds: Surface-modifying agents can be functionalized with ionic groups that enable high exhaustion from a processing bath through electrostatic self-assembly. Using cyclic oniums as the ionic functional groups, thermally induced ring-opening converts the ionic bonds to covalent bonds, thus lending permanency to the modification of the surface.
Two go in, one comes out: A series of isostructural M-MOF-74 materials (M=Co, Mn, and Mg) with high densities of open metal sites have been examined for the selective adsorption of propene over propane. Co-MOF-74 exhibits the highest thermodynamic C3H6/C3H8 selectivity (ca. 45) reported for any MOF to date.
Six for the price of one: From a single precursor, dehydroalanine, six distinct post-translational modifications can be site-selectively installed on histone proteins (see figure), including the first site-selective phosphorylation and glycosylation of histones. The first direct observation of histone deacetylase activity on a full-length modified histone as well as its interactions with both chromatin reader and writer/eraser proteins are reported.
Get smart: Organogels based on sugar ketals have been prepared with a unique combination of properties suitable for the development of flexible optical devices and potential applications as smart materials for the fabrication of microphotonic systems. Key features in the self-assembly of these gelators were conformational restrictions and interaction affinities.
The two faces of curium: The first curium borate has been prepared showing a complex structure with coordination environments for CmIII that are found in both PuIII and AmIII borates (see picture). Time-resolved laser-induced photoluminescence studies as well as X-ray diffraction experiments show two distinct CmIII sites with different coordination environments.
Identification of bacteria: A methoxyimino cephalosporin derivative containing a pair of fluorescence resonance energy transfer (FRET) fluorophores was synthesized. This probe displays selective cleavage toward different types of ?-lactamases, thereby providing a rapid assay to distinguish bacterial cells that are either sensitive or resistant to broad-spectrum ?-lactam antibiotics (see picture).
The two-step: Chroman-3-ones are important intermediates for organic synthesis and medicinal chemistry. However, their syntheses require multiple steps and are not efficient. By using gold-catalyzed alkyne oxidation, this versatile heterocycle can be prepared in only two steps from readily available phenols and with mostly high efficiencies (see scheme).
A minimal gene expression machinery has been encapsulated within large lipid vesicles that are immobilized on a microscope coverslip for fluorescence imaging (see picture). The engineered vesicle membrane acts as an exchange platform that enables the uptake of all necessary nutrients and tRNAs supplied in the outside environment, which initiates the internal synthesis of green fluorescent proteins from a DNA template. Red: membrane dye, green: synthesized GFP.
Lasting glow: Under femtosecond laser irradiation, graphene oxide nanoparticles (GONs) give strong two-photon luminescence (TPL; see picture). The presence of GONs also induces microbubbling, which causes cell death at an order of magnitude lower laser power than when cells are not labeled. The results show that GONs can be used for TPL-based imaging and photothermal cancer therapy.
How easily can ions move in DNA channels? Three-dimensional free-energy landscapes for the movement of Na+, K+, and NH4+ ions through G-quadruplex DNA channels have been obtained by molecular dynamics simulations. The computed results are in qualitative agreement with the limited experimental data: large K+ and NH4+ ions squeeze through the G-quartets with some difficulty while Na+ ions pass through with less impedance.
LiH-ghtweight: The title complex having a central (LiH)4 cube has been prepared and structurally characterized (see picture). The compound is stable towards LiH elimination at room temperature in solution, and can be employed for hydrolithiation reactivity as has been demonstrated by its reaction with benzophenone.
Diazenide surprise: The synthesis of the first alkali diazenide, Li2N2, is presented. Lithium diazenide adopts an unprecedented structure type for compounds with A2B2 composition (see picture). Spectroscopic analysis show a significant feature at 1328 cm?1 which is assigned to the stretching vibration of the [N2]2? ion. Electronic structure calculations underline the metallic character and confirm the 50?% occupation of the antibonding ? states in [N2]2?.
Neat and tidy: B(C6F5)3 efficiently converts a series of bis(alkynyl)phosphanes into highly substituted 3-borylphospholes through a twofold 1,1-carboboration reaction sequence. The boron substituted phospholes were also used as substrates in Suzuki–Miyaura type cross-coupling reactions (see scheme).
Trading up: A bioimaging system that is based on caged D-luciferin/upconversion nanoparticle conjugate has been developed. The nanoparticles upconvert near-infrared light into UV light, which triggers the photorelease of D-luciferin (see scheme) and leads to enhanced fluorescence and bioluminescence signals in vitro and in vivo. The use of near-infrared light enables deep penetration into tissue in vivo with minimum cellular damage.
Rattling the cage: The two ?-aminobutyric acid (GABA) derivatives 1 and 2 exhibit efficient and rapid (<5×10?6 s) GABA photorelease upon one-photon excitation combined with an unprecedented two-photon uncaging cross-section at ?=800 nm. Compounds 1 and 2 were successfully used for two-photon GABA release in intact brain tissue, thus offering attractive perspectives in chemical neurosciences.
Collar and tie men: The smallest trefoil knot reported to date has been prepared by an active metal template synthesis. Copper(I) ions are able to constrain the well-designed structure so that it can form the loops by complexing to the bipyridine moieties in the core of the thread and the two ends of the entangled lace on opposite faces of the loop, before acting as a catalyst to close the lace (see picture).
Neatly wrapped up: Alternately stacked square-planar platinum(II) complexes inside a dinuclear coordination cage were prepared to give a discrete and soluble Pt5-array of the Magnus’ salt type. Characterization of the complex in solution was complemented by an X-ray crystal structure of {[Pt(pyridine)4]?[PtCl4]2@Cage}; this structure showed the linear, pentanuclear array within the cages and their circular packing into a hollow tubular superstructure.
An efficient protocol has been developed for the intramolecular oxidative oxyarylation using a PdII-catalyzed tandem oxypalladation/CH functionalization strategy. This methodology allows rapid access to tetrahydro-2H-indeno-[2,1-b]furan frameworks from simple hydroxyalkenes. The reactivity of this process is orthogonal to that of Pd0-catalyzed transformations, enabling the divergent modification of a single molecule.
Self-assembly in a droplet: A supramolecular system that governs self-assembly events over hierarchies from the nano- to the micrometer range has been developed by combining a bottom-up strategy based on molecular programming with top-down droplet microscience. Discrete 1D tubular structures were created by exploiting the compartment effect of the droplet, induced during dynamic shrinking under non-equilibrium conditions (see picture).
The mercury puzzle: Using the new technique of electrocrystallization the sodium mercury alloy Na11Hg52 could be obtained in a phase pure form. This amalgam is a key component in the industrially important chlor-alkali process. The combination of different bonding situations in this phase results in it having the typical properties of a “bad” metal.
What is the channel? The thiolate ligand in the five-coordinate model complex 1 of [Fe]-hydrogenase is preferentially and reversibly protonated, even in the presence of an acyl ligand. The results suggest that the Cys176 thiolate ligand in [Fe]-hydrogenase can serve as the internal base to accept the proton after heterolytic splitting of H2.
The fifth element: An efficient new synthetic method for accessing 3,6-dihydro-2H-thiopyrans (1) in one pot has been developed. This method employs an anionic cascade, which is triggered by the addition of a vinyl nucleophile to a carbonyl group followed by S to O thiophosphate migration and an intramolecular thiolate displacement. The scope is demonstrated for a range of ketone and ester substrates.
The ?–? aromatic interactions between amino acids 6, 7, and 11 in the natural hormone somatostatin are crucial for conformational stability. In their Communication (DOI: 10.1002/anie.201106406), M. J. Macias, A. Riera, and co-workers describe that peptidic analogues obtained by replacing each phenylalanine with mesitylalanine are conformationally more rigid than the parent hormone. This strategy has yielded the first 3D structures of 14-amino-acid somatostatin analogues.
Hold me close: Highly enantioselective catalysis of tandem acetalization/cycloisomerization reactions of o-alkynylbenzaldehydes was achieved using gold complexes of chiral acyclic diaminocarbene ligands that have electron-deficient aryl substituents. X-ray crystallography and DFT calculations implicate weak gold-arene interactions—absent in the case of simple phenyl substituents—that define the chirality of the substrate binding site.
Expanding into application: Covalent organic framework (COF) films are ideally suited for vertical charge transport and serve as precursors of ordered heterojunctions. Their pores, however, were previously too small to accommodate continuous networks of complementary electron acceptors. Four phthalocyanine COFs with increased pore size well into the mesoporous regime are now described (see example).
Bio-logic-al: An autonomous, integrated “sense-act-treat” system that is based on an enzymatic biofuel cell has been developed. The system couples a biocomputing logic-detection method with a drug-release system to provide a logic-activated therapeutic intervention in response to a simulated abnormal physiological state, without the need for an external power source, control electronics, or microelectromechanical actuators.
Ultra-small fluorescent sensors and their application for fabrication of wavelength-addressable virtual sensor arrays capable of sensing metal cations are described. The fluorescent probes generated in situ within the fiber mats can be used as wearable sensors for identifying heavy metal ions in a qualitative and quantitative fashion.
Ironing it out: A FeSBA-15 catalyst with a high iron content as well as a large pore diameter has been synthesized and used for the production of soluble poly(methylene anthracene) (PMAn, see scheme). The catalyst is stable, active, reusable, and affords a high yield of high molecular weight PMAn. The properties of the PMAns obtained can be controlled by tuning the specific surface area, pore diameter, pore volume, and Fe content of the catalysts.
Attack or defend! A smart polymer surface has two reversibly switchable equilibrium states, a cationic N,N-dimethyl-2-morpholinone (CB-Ring) and a zwitterionic carboxy betaine (CB-OH). CB-Ring will kill bacteria upon contact under dry conditions, whereas CB-OH will release the previously attached and dead bacteria and further resist adhesion of bacteria under wet conditions.
Topographical cues play an important role in in vitro neuronal development. In their Communication (DOI: 10.1002/anie.201106271), Y. Nam, I. S. Choi, J. S. Lee, and co-workers show that neuritogenetic acceleration occurs on silica-bead monolayers made up of beads with a diameter of more than 200 nm, but not on monolayers of beads with smaller diameters. The biochemical study indicates neurons sense topographical differences in nanostructures and alter their behavior accordingly.
Functionalized oligoproline scaffolds that have defined lengths have been shown to control the size of silver nanoparticles that are formed in the Tollens reaction. In their Communication (DOI: 10.1002/anie.201107183), H. Wennemers and co-workers demonstrate the correlation between the molecular dimensions of the peptide scaffold and the size of the nanoparticles that are produced in an approach that opens the door to precise control of the size of metal nanoparticles.
Nucleophilic substitution belongs to the fundamental organic reaction mechanisms since the pioneering work of C. K. Ingold in the 1920s. In their Communication (DOI: 10.1002/anie.201107402), H.-P. Steinrück and co-workers monitor the alkylation of a tertiary amine attached to an imidazolium cation with a chloroalkylsulfonate anion by photoelectron spectroscopy, which can distinguish between convalently bound chlorine (Clcov) and chloride (Clion).
Feeding your face. In their Communication (10.1002/anie. 201107061), Y. Xia and co-workers show that it is possible to shape-selectively grow bimetallic palladium–silver nanocrystals. By limiting the supply of silver atoms (red) nucleation and growth occurs on only one, or a few, of the six equivalent faces of a cubic palladium seed, as represented by the presence of hungry and feeding frogs.
Sweet truth: The search for sugars in interstellar space is hampered by a lack of spectroscopic information. D-Ribose is now the first C5 sugar observed in the gas phase using microwave spectroscopy. The rotational spectrum revealed six conformations of free ribose, adopting preferentially ?-pyranose rings and higher-energy ?-pyranose forms. No evidence of ?-/?-furanoses or linear forms was found, unlike biological systems, where ?-furanoses are found in RNA.
There are strings attached: After linking the reacting groups to head groups of ionic liquids to drastically lower the vapour pressures of the reactants, ordinary liquid-phase organic reactions can be monitored by in situ X-ray photoelectron spectroscopy. This approach is demonstrated for the nucleophilic substitution of an alkyl amine and an alkyl chloride moiety, which are attached to the cation and anion of ionic liquids, respectively.
Metallized scaffolds: Oligoproline scaffolds that are functionalized with aldehyde groups have been shown to control the size of silver nanoparticles that are formed in the Tollens reaction. The size of the nanoparticles correlates linearly with the length of the scaffold and the oxidation of the aldehyde moieties during the reaction helps to stabilize the nanoparticles through coordination to the newly formed carboxylic acid groups.
Molecular insights into the roles of amine functionalization and cooperative CO2 interactions into enhancing (and diminishing) CO2 binding by metal-organic frameworks are shown both experimentally and computationally. Contrary to popular thinking, higher amination decreases CO2 binding in this system. This loss is compensated by cooperativity between CO2 triads that enhances binding by over 7 kJ?mol?1.
A totally synthetic artificial pancreas is described by Y. Miyahara et al. in their Communication (DOI: 10.1002/anie.201106252). A hydrogel bearing a phenylboronate derivative undergoes a glucose-dependent transition in its state of hydration under physiological conditions. The reversible surface-localized dehydration enables the provision of insulin to be controlled, thus offering a new basis for the treatment of diabetes with long-term stability and safety.
Oxidation of elemental palladium at elevated temperatures leads to the blue disulfate Pd(S2O7) which has an octahedral, not the usual square-planar coordination of a Pd2+ center. In their Communication (DOI: 10.1002/anie.201107197), M. S. Wickleder, R. Pöttgen, and co-workers show that this rare coordination leads to paramagnetic behavior and that ferromagnetic ordering occurs at low temperature. This is the first example for this phenomenon in an oxidic Pd2+ compound.
Give me five! Two five-coordinate complexes of iron with geometries that are based on those found in redox-versatile enzymes have been synthesized. The phenolate-rich, pentadentate N2O3 phenylene?-diamine/triphenolate ligands confer a low local symmetry on the complex so that only subtle modifications in the structure of the ligands are sufficient to completely change the sequence in which the metal and the ligands are oxidized (see scheme).
Lights off, but someone is home: Single-molecule force spectroscopy was used to investigate DNA intercalation in the presence and absence of unbound dye (see picture). Force-induced intercalation, traditionally ascribed to dye from solution binding to the DNA, occured approximately two hours after the removal of the free dye. The results show that binding/unbinding and intercalation/deintercalation are distinct processes that occur on very different time scales.
Going through the motions: Somatostatin analogues having greater conformational rigidity than somatostatin have been prepared by substituting Phe residues in the native sequence with mesityl alanine (Msa; see structure). The analogues show high affinity for SSTR receptors, thus showing that fine-tuning of noncovalent interactions between amino acid side chains can modulate peptide affinity and selectivity.
Protein free: A hydrogel containing phenylboronate was optimized so as to undergo rapid glucose-dependent changes in the state of hydration under physiological aqueous conditions. A localized dehydration of the gel surface to form a “skin layer” enabled control of the release of insulin from the gel. This dehydration is induced by fluctuations in the glucose concentration in the range between normo- and hyperglycemia.
Wheel-like assemblies are fascinating and exquisite. Anderson-type molecular wheels (structures on the periphery first proposed in 1937 and right structure) each feature six skew-edge-shared octahedra. In their Communication (DOI: 10.1002/anie.201106065), C. M. Che and co-workers report selective binding of Cu+ or Ag+ by isolated [{M(S-4-R-C6H4)2(CO)2}6] (right structure to bottom-right structure) and isolation of [{M(SPh)2(CO)2}8] (bottom left), thus demonstrating feasible expansion of Anderson-type wheels to octanuclear congeners.
Reversible biomolecular patterning in hydrogels can direct cell function in a user-defined manner. In their Communication (DOI: 10.1002/anie.201106463), K. S. Anseth and C. A DeForest report 4D spatiotemporal control over the presentation of bioligands by using a thiol–ene photoconjugation reaction, which is initiated by visible light, combined with the photocleavage of an o-nitrobenzyl ether, which is controlled by UV light. This method allows cell functions to be probed dynamically.
Lighting the way: Biochemical cues have been reversibly patterned into hydrogels with full spatiotemporal control by using two photochemical reactions. The hydrogel is conjugated with a peptide by a thiol-ene photoaddition reaction that is initiated by visible light. Subsequent, selective photocleavage of an o-nitrobenzyl ether with UV light enables dynamic presentation of the peptide to cells with control in three dimensions.
Hydrocarbon biodiesel can be quantitatively achieved on Ni/HBEA zeolite from crude algae oil in batch or continuous-flow reactors. In their Communication (DOI: 10.1002/anie.201106243), J. Lercher et al. describe the kinetics, reaction pathways, and fundamental chemistry of the elementary steps of the cascade hydrogenation reaction on algae oil. This approach opens new possibilities to produce sulfur-free high-grade green transportation fuels from microalgae on a large scale.
Intercalation of YOYO, a bisintercalating DNA dye, was studied by using single-molecule force spectroscopy. In their Communication (DOI: 10.1002/anie.201105540), D. H. Paik and T. T. Perkins show that force-enhanced intercalation, traditionally ascribed to the dye in solution binding to the DNA, can occur from a reservoir of bound dye that remained out of equilibrium with the free dye for long periods of time (>2 hours). Hence, binding/unbinding and intercalation/de-intercalation are distinct processes that can occur on very different time scales.
By stepwise catenation of bicyclo[1.1.1]pentasilane units persila[n]staffanes (n=1, 2, and 3) were synthesized as air-stable colorless crystals. A remarkable red-shift of the UV/Vis absorption bands with increasing number of bicyclo[1.1.1]pentasilane units suggests remarkable interactions between bridgehead SiSi ? orbitals and between cage SiSi ? orbitals (see picture).
It’s hip not to be square: The oxidation of elemental palladium with SO3 leads to Pd(S2O7) in which the Pd2+ is in an octahedral coordination environment of oxygen atoms (see structure Pd red, O blue, S yellow) and not the usual square-planar environment for Pd2+ species. This unexpected geometry leads to the observed paramagnetism of the compound with ferromagnetic ordering at 11.7 K.
Something to sprout about: The developmental acceleration of hippocampal neurons occurred on well-packed structures of silica beads with diameters over 200 nm (see picture; scale bar: 5 um, inset scale bar: 1 um). The neurons sensed the size differences of the nanostructures and altered their behaviors, thus implying that nanotopographical stimuli are one of the important features for guiding neurites during neural developments in vivo.
Tell the atoms where to go: By manipulating the rate at which Ag atoms were generated from a precursor, the nucleation and growth of Ag on Pd nanocubes with six equivalent {100} facets were controlled to generate three different types of bimetallic nanocrystals: Pd–Ag hybrid dimers, Pd–Ag eccentric nanobars, and Pd@Ag core–shell nanocrystals (see scheme).
Diesel oil from microalgae oil: An approach for selective conversion of crude microalgae oil to diesel-range alkanes is reported using Ni nanoclusters supported on zeolite catalysts (see picture). The cascade of catalyzed reactions for microalgae oil conversion is based on a metal-catalytic function for the integrated hydrogenolysis, hydrogenation, and decarbonylation as well as an acid-catalytic function for dehydration and isomerization.
Stopping aggregation: Carbazole-based cyanine fluorophores bind selectively to the A?(1–40) peptide and its aggregates which are responsible for causing Alzheimer’s disease. One of these fluorophores, SLOH, exerts a strong inhibitory effect on A?(1–40) fibrillogenesis (see scheme) and can pass through the blood-brain barrier making it a potential therapeutic agent for Alzheimer’s disease.
Don’t stand Stille: A direct heteroarylation polycondensation reaction was used for the synthesis of high-molecular-weight thienopyrroledione-based polymers (see scheme) in an impressive yield (up to 96?%) and in only a few synthetic steps. This new method is an alternative to the standard Stille coupling reaction and thus avoids formation of toxic tin by-products.
Anchors away! Two zinc phthalocyanine photosensitizers with different phosphinic acid anchor groups were synthesized (see scheme). Solar cells sensitized with these compounds have a short-circuit photocurrent density of 7.6±0.2 mA?cm?2, an open-circuit voltage of 559±30 mV, and a fill factor of 0.76±0.03, which corresponds to an overall conversion efficiency of 3.24?% under 1 sun.
Inventing new wheels: Reaction of [M3(CO)12] (M=Ru, Os) with 4-RC6H4SH afforded [{M(S-4-RC6H4)2(CO)2}8] (R=H; I) or [{M(S-4-RC6H4)2(CO)2}6] (R=Me, iPr; II; see scheme), all of which have been structurally characterized. The octamers I are unique metal molecular wheels featuring skew-edge-shared octahedra with a central planar M8 octagon. [{Ru(S-4-iPrC6H4)2(CO)2}6] selectively binds a Cu+ or Ag+ ion to form [M?{Ru(S(4-iPr-C6H4))2(CO)2}6]+ (III).
Intimacy promotes good chemistry: Time-resolved hard X-ray diffraction (see picture) and dispersive X-ray absorption spectroscopy coupled to time-resolved IR spectroscopy allows direct observation and quantification of the ability of materials to store and release gases under specific conditions. The nanoscale Pd/CeZrO4 interface plays a reactively deterministic role in inducing a superior performance in these catalysts.
All connected: A protein-immobilized electrode comprising hierarchical assemblies of photoactive cytochrome b562 reconstituted with zinc protoporphyrin IX exhibits remarkably enhanced photocurrent generation relative to an electrode bearing a single zinc-substituted hemoprotein layer. The protein oligomers, which bear a covalently linked protoporphyrin group, assemble by a supramolecular heme/heme pocket interaction.
Posted on 6 October 2011 | 9:41 am
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