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Photochemie - Neueste Forschungsartikel der Fachverlage


 
Aktuelle Fachartikel zur Photochemie und Photobiologie, sortiert nach Erscheinungsdatum.

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Photochemical & Photobiological Sciences - published by The Royal Society of Chemistry -
PPS meets the growing information needs of scientists working in the areas of photochemistry and photobiology, and indeed, encourages a synergism between these two important research areas. This international journal is published monthly on behalf of the European Photochemistry Association (EPA), the European Society for Photobiology (ESP), the Asia and Oceania Society for Photobiology (AOSP) and the Korean Society of Photoscience (KSP), and is available in both print and electronic formats.

Photochemistry and Photobiology - published by Wiley-Interscience -
... publishes original research articles and reviews on current topics in photoscience.



Aktuelle wissenschaftliche Fachartikel der genannten Journale:


On the Role of Exponential Smoothing in Circadian Dosimetry

Abstract

The effects lighting has on health through modulation of circadian rhythms are becoming increasingly well documented. Data are still needed to show how light exposures are influenced by architecture and lighting design and circadian dosimetry analyses should provide duration, phase and amplitude measures of 24-hour exposure profiles. Exponential smoothing is used to derive suitable metrics from 24-hour light measurements collected from private dwellings. A further application of these modified exposure time series as physiological models of the light drive is discussed. Unlike previous light drive models, the dose rate persists into periods of darkness following exposures. Comparisons to long duration exposure studies suggest this type of persistent light drive model could be incorporated into contemporary physiological models of the human circadian oscillator.

This article is protected by copyright. All rights reserved.

Quelle: Photochemistry and Photobiology | 18 Apr 2014 | 5:43 am CEST

Excited State Photoreaction between the Indole Side Chain of Tryptophan and Halocompounds Generates New Fluorophores and Unique Modifications

Abstract

Photoreaction of indole containing compounds with chloroform and other trichlorocompounds generates products with redshifted fluorescence. In proteins, this reaction can be used for the fluorescent detection of proteins. Little characterization of products generated through the photochemical reaction of indoles with halocompounds has been done, yet is fundamental for the development of other fluorophores, protein labeling agents, and bioactive indole derivatives. Here, we have characterized which isomers form in the photoreaction between tryptophan and chloroform using 1H-NMR of tryptophan and methylated derivatives to reveal that the two major products that are formed result from modification at the 4- and 6-carbon positions of the indole ring. Reaction at position 6 generates 6-formyl tryptophan and the reaction at position 4 generates an imine because the formyl derivative that is initially formed reacts further with the tryptophan amine group. The spectroscopic properties and product molecular weights of photoproducts formed from photoreaction of tryptophan with other trihalo and monohalocompounds are also determined. The indole ring of tryptophan can be modified with various additions from halocompounds, including the addition of labels to the indole ring via methylene groups. This opens possibilities for generating novel tryptophan based fluorophores and protein labeling strategies using this photochemistry.

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Several fluorophores were produced by photoreactions between the amino acid tryptophan and halocompounds. The reaction with trihalocompounds in aqueous solution yielded products with carbonyl groups conjugated to the aromatic system at the 4 and 6 positions of the indole fluorophore and led to emission near 500 nm. This photoreaction also proceeded with monohalocompounds, but resulted in additions to the indole fluorophore without enlarging the conjugated systems so that the fluorescence properties of the indole in tryptophan did not change significantly.

Quelle: Photochemistry and Photobiology | 17 Apr 2014 | 12:54 pm CEST

Observation of Magnetic Field Effects on Transient Fluorescence Spectra of Cryptochrome 1 From Homing Pigeons

Abstract

Cryptochromes are suggested to be involved in the bird magnetoreception based on the radical pair mechanism (RPM), a well established theory of weak magnetic field effects on chemical reactions. Two members of cryptochrome/photolyase family were found to respond to magnetic field, however, no direct responses of bird cryptochrome to magnetic field as weak as the Earth's magnetic field have been obtained so far. In this study, we used transient fluorescence spectroscopy to characterize the weak magnetic field effects of bird cryptochromes. To do this, we cloned the cryptochrome 1 gene (clCRY1) from the retina of homing pigeons (Columba livia), expressed it in insect Sf9 cells and analyzed the transient fluorescence of purified clCRY1 by application of 45–300 μT magnetic fields. The flavin adenine dinucleotide (FADox) and glucose oxidase (GOD) in PBS buffer were set as controls which could be excited by light to generate radicals, but would not be sensitive to magnetic field. We observed that the transient fluorescence spectra of clCRY1 were sensitive to the applied magnetic field at room temperature. Our result provides a new proof of the cryptochrome-based model of avian magnetoreception in vitro.

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Cryptochrome is suggested to be the most probable candidate magnetoreceptor in bird magnetoreception. Two members of cryptochrome/photolyase family have been found to be sensitive to the magnetic field and the magnetic sensitivity was proposed to be the general feature of this protein family. In this study, we constructed a magnetic field by Helmholtz coils and tested the magnetic field effects on the transient fluorescence of cryptochrome from homing pigeons at room temperature. Our results showed that, comparing to other flavin controls, the transient fluorescence of clCRY1 protein is sensitive to microtesla level magnetic field.

Quelle: Photochemistry and Photobiology | 17 Apr 2014 | 12:54 pm CEST

Chlorin e6 Derivative Radachlorin Mainly Accumulates in Mitochondria, Lysosome and Endoplasmic Reticulum and Shows High Affinity toward Tumors in Nude Mice in Photodynamic Therapy

Abstract

The efficacy of photodynamic therapy (PDT) depends upon the amount of photosensitizer accumulated in the malignant tissues. Radachlorin is a popular photosensitizer used in photodynamic therapy to treat various types of cancer. In this study, we have studied the main organelles responsible for the accumulation of radachlorin in human anaplastic thyroid cancer in vitro and in vivo. The optimal time window for uptake and clearance of radachlorin also was studied. Confocal microscopic images confirmed that the radachlorin is mainly acquired by mitochondria and partially by lysosome and endoplasmic reticulum. Studies also showed that the maximum amount of radachlorin was accumulated within 3–6 h after the treatment. Radachlorin also showed a higher affinity toward malignant tumors compared to the other organs in mice xenograft model. Uptake of radachlorin reached an optimum amount within 6 h and most of the radachlorins were also cleared from the body in next 48 h. Therefore, detailed information regarding exact accumulation sites and a time window in which maximum amount of drug is accumulated and cleared were obtained by this study. Hence, not only the efficacy of the treatment can be increased but the phototoxicity after the treatment also can be controlled.

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Cellular uptake and tumor affinity of chlorin e6 photosensitizer, radachlorin were studied in anaplastic thyroid cancer cells and xenograft nude mice model. Results showed radachlorin mainly accumulated in mitochondria and partially in lysosome and endoplasmic reticulum. It showed a higher accumulation in tumor site within 3–6 h and was further cleared from the tumor in next 24–48 h. Radachlorin also showed a higher efficacy in photodynamic therapy after 6 h of drug injection. Therefore, the knowledge of possible sites and time of photosensitizers accumulation in tumor cells may help in optimizing the efficacy of PDT.

Quelle: Photochemistry and Photobiology | 17 Apr 2014 | 12:54 pm CEST

Two Methods for Retrieving UV Index for All Cloud Conditions from Sky Imager Products or Total SW Radiation Measurements

Abstract

Cloud effects on UV Index (UVI) and total solar radiation (TR) as a function of cloud cover and sunny conditions (from sky images) as well as of solar zenith angle (SZA) are assessed. These analyses are undertaken for a southern-hemisphere mid-latitude site where a 10-years dataset is available. It is confirmed that clouds reduce TR more than UV, in particular for obscured Sun conditions, low cloud fraction (<60%) and large SZA (>60°). Similarly, local short-time enhancement effects are stronger for TR than for UV, mainly for visible Sun conditions, large cloud fraction and large SZA. Two methods to estimate UVI are developed: (1) from sky imaging cloud cover and sunny conditions, and (2) from TR measurements. Both methods may be used in practical applications, although Method 2 shows overall the best performance, as TR allows considering cloud optical properties. The mean absolute (relative) differences of Method 2 estimations with respect to measured values are 0.17 UVI units (6.7%, for 1 min data) and 0.79 Standard Erythemal Dose (SED) units (3.9%, for daily integrations). Method 1 shows less accurate results but it is still suitable to estimate UVI: mean absolute differences are 0.37 UVI units (15%) and 1.6 SED (8.0%).

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Cloud effects on UV Index (UVI) and total solar radiation (TR) are assessed. The role of cloud cover and sunny conditions (from sky images) and of solar zenith angle is investigated. The analyses are undertaken for a southern-hemisphere mid-latitude site where a 10-years dataset is available. It is confirmed that clouds affect TR more than UVI, both in reducing and enhancing the cloud-free radiation. From the analyses, two methods to estimate UVI are developed: (1) from sky imaging cloud cover and sunny conditions, and (2) from TR measurements. Methods' estimations are compared with measurements.

Quelle: Photochemistry and Photobiology | 17 Apr 2014 | 7:50 am CEST

Effects of 940 MHz EMF on Bioluminescence and Oxidative Response of Stable Luciferase Producing HEK Cells

Photochem. Photobiol. Sci., 2014, Accepted Manuscript
DOI: 10.1039/C3PP50451D, Paper
Yahya Sefidbakht, AA Moosavi-Movahedi, Saman Hosseinkhani, Fariba Khodagholi, Masoud Torkzadeh-Mahani, Forough Foolad, Reza Faraji-Dana
The effects of mobile phone frequency electromagnetic field (RF-EMF, 940 MHz) on a stable cell line (HEK293T) harbouring firefly luciferase gene were evaluated. A waveguide exposure system with 1W input...
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Quelle: RSC - Photochem. Photobiol. Sci. latest articles | 16 Apr 2014 | 1:00 am CEST

Activation of sperm EGFR by light irradiation is mediated by reactive oxygen species

Abstract

To acquire fertilization competence, spermatozoa must undergo several biochemical and motility changes in the female reproductive tract, collectively called capacitation. Actin polymerization and the development of hyper-activated motility (HAM) are part of the capacitation process. In a recent study, we showed that irradiation of human sperm with visible light stimulates HAM through a mechanism involving reactive-oxygen-species (ROS), Ca2+ influx, protein-kinases A (PKA), and sarcoma-protein-kinase (Src). Here we showed that this effect of light on HAM is mediated by ROS-dependent activation of the epidermal-growth-factor-receptor (EGFR). Interestingly, ROS mediated HAM even when the EGFR was activated by EGF, the physiological ligand of EGFR. Light irradiation stimulated ROS-dependent actin polymerization, and this effect was abrogated by PBP10, a peptide which activates the actin-severing protein, gelsolin, and causes actin-depolymerization in human sperm. Light stimulated tyrosine phosphorylation of Src-dependent gelsolin, resulting in enhanced HAM. Thus, light irradiation stimulates HAM through a mechanism involving Src-mediated actin polymerization. Light stimulated HAM and in-vitro-fertilization (IVF) rate in mouse sperm, and these effects were mediated by ROS and EGFR. In conclusion, we show here that irradiation of sperm with visible light, enhances their fertilization capacity via a mechanism requiring ROS, EGFR and HAM.

This article is protected by copyright. All rights reserved.

Quelle: Photochemistry and Photobiology | 11 Apr 2014 | 7:44 pm CEST

Photobiological characteristics of chlorophyll a derivatives as microbial PDT agents

Photochem. Photobiol. Sci., 2014, Accepted Manuscript
DOI: 10.1039/C3PP50376C, Paper
Marciana Pierina Uliana, Layla Pires, Sebastiao Pratavieira, Timothy John Brocksom, Kleber Thiago de Oliveira, Vanderlei Salvador Bagnato, Cristina Kurachi
Chlorin-e6 (chl-e6) and a hydrogenated derivative (chl-e6H) were semi-synthesized, and their photophysical properties and photodynamic activity against Escherichia coli, Staphylococcus aureus and Candida albicans evaluated. Methyl pheophorbide-a (Mepheo-a) was obtained...
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Quelle: RSC - Photochem. Photobiol. Sci. latest articles | 11 Apr 2014 | 1:00 am CEST

Quantitative cascade energy transfer in semiconductor thin films

Photochem. Photobiol. Sci., 2014, Accepted Manuscript
DOI: 10.1039/C4PP00071D, Paper
Rebecca Flamini, Assunta Marrocchi, Anna Spalletti
In this contribution we report the photophysical study of three organic blend systems comprising [60]PCBM along with different combinations of five extended semiconducting arylacetylenes, i.e. p-[(2-{[m,p- didodecyloxyphenyl]ethynyl}-7-fluorenyl)ethynyl]benzonitrile, 4,7-bis(5-{[m,p-bis(hexyloxy)phenyl]ethynyl}thien-2-yl)-2,1,3-benzothiadiazole, 9,10-bis- [(m,m-bis{[m,m-bis-(hexyloxy)phenyl]ethynyl}phenyl)ethynyl]-anthracene,...
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Quelle: RSC - Photochem. Photobiol. Sci. latest articles | 9 Apr 2014 | 1:00 am CEST

Topical Photodynamic Therapy Using Different Porphyrin Precursors Leads to Differences in Vascular Photosensitization and Vascular Damage in Normal Mouse Skin

Abstract

Different distributions of hexyl aminolevulinate (HAL), aminolevulinic acid (ALA) and methyl aminolevulinate (MAL) in the superficial vasculature are not well studied but they are hypothesized to play an important role in topical photodynamic therapy (PDT). The colocalization of fluorescent CD31 and protoporphyrin IX (PpIX) was calculated using confocal microscopy of mouse skin sections to investigate the vascular distribution after topical application. Vascular damage leads to disruption of the normal endothelial adherens junction complex, of which CD144 is an integral component. Therefore, normal CD31 combined with loss of normal fluorescent CD144 staining was visually scored to assess vascular damage. Both the vascular PpIX concentration and the vascular damage were highest for HAL, then ALA and then MAL. Vascular damage in MAL was not different from normal contralateral control skin. This pattern is consistent with literature data on vasoconstriction after PDT, and with the hypothesis that the vasculature plays a role in light fractionation that increases efficacy for HAL and ALA-PDT but not for MAL. These findings indicate that endothelial cells of superficial blood vessels synthesize biologically relevant PpIX concentrations, leading to vascular damage. Such vascular effects are expected to influence the oxygenation of tissue after PDT which can be important for treatment efficacy.

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The ability of the vasculature to synthesize PpIX and be damaged by PDT was compared between HAL, ALA and MAL in mouse skin using confocal microscopy and fluorescent CD31 and CD144 antibodies. Colocalization of CD31 and PpIX (left images) was calculated to measure endothelial PpIX synthesis. Vascular damage was scored as loss of normal CD144 staining (right images). Both PpIX synthesis and vascular damage were highest for HAL, then ALA, then MAL. This illustrates that superficial blood vessels synthesize biologically relevant amounts of PpIX. Vascular responses can limit oxygen supply during or after PDT and are expected to influence outcome.

Quelle: Photochemistry and Photobiology | 7 Apr 2014 | 9:13 am CEST

Photoconversion changes bilin chromophore conjugation and protein secondary structure in the violet/orange cyanobacteriochrome NpF2163g3

Photochem. Photobiol. Sci., 2014, Advance Article
DOI: 10.1039/C3PP50442E, Paper
Sunghyuk Lim, Nathan C. Rockwell, Shelley S. Martin, Jerry L. Dallas, J. Clark Lagarias, James B. Ames
We report secondary structure assignments for the cyanobacteriochrome NpF2164g3 in the violet-absorbing dark-adapted state. Comparison with our previous work on the orange-absorbing photoproduct elucidates structural changes occurring upon photoconversion.
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Quelle: RSC - Photochem. Photobiol. Sci. latest articles | 7 Apr 2014 | 1:00 am CEST

Sun exposure and protection behaviour of Danish farm children Parental influence on their children

Abstract

Healthy sun habits acquired in childhood could reduce skin cancer incidence. We examined the sun exposure and protection behaviour of an expected high-exposure group of children, and the association to their parents. Open, prospective cohort study. 139 participants (40 families) kept daily sun behaviour diaries (sun exposure, sunscreen use, sunburns) over a 4-month summer period (15,985 diary days). The Pigment Protection Factor (PPF), an objective measure of sun exposure, was measured at two body sites, before and after summer. All participants presented data from the same 115 days. Risk behaviour (sun exposure of upper body) took place on 9.5 days (boys) and 15.6 days (girls). Sunburn and sunscreen use were infrequent. Boys’ sun exposure resulted in an increased photo protection over the study period of 1.7 SED (upper arm) and 0.8 SED (shoulder) to elicit erythema. Corresponding values for girls were: 0.9 SED (upper arm) and 0.5 SED (shoulder). Boys’ sunscreen use correlated to their mothers’ (r=0.523, p=0.02). Girls’ number of risk days (r=0.552, p=0.005) and sun exposure (upper arm: r=0.621, p<0.001) correlated to their mothers’. The children's sun exposure was substantial. Only mothers influenced children's sun behaviour and exposure. This may be of relevance in future sun protection campaigns.

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Quelle: Photochemistry and Photobiology | 3 Apr 2014 | 9:46 am CEST

Photo- Active Titania Float For Disinfection Of Water; Evaluation Of Cell Damage By Bioanalytical Techniques

Abstract

A photoactive float was fabricated with the modified titania to cause a feasible disinfection of water, contaminated with E.coli. The commercially available titania was doped with neodymium by pulverization technique to enhance its activity in sunlight and a multi approach technique was used to evaluate the extended efficiency of the doped sample. X-ray diffraction patterns depicted the retention of anatase phase on doping and the existence of neodymium was confirmed by the energy dispersive atomic X-ray analysis and the X-ray photoelectron spectroscopy. Transmission electron microscopy and Bruner-Emmett-Teller analysis depicted a marginal increase in the particle size and a decrease in the surface area respectively. Doping induces semiconductor behavior with lower band energy that could respond to visible light and exhibit better disinfection activity. The ‘f’ and'd’ transitions of the lanthanide in doped sample caused new electronic behavior of trapping/detrapping effect together with bandgap narrowing. The amount of malondialdehyde, protein, DNA and RNA released on destruction of E.coli was observed to be 0.915 × 10-3 μg/mL, 859.912 μg/mL, 20.173 μg/mL and 1146.073 μg/mL respectively. The above analytical methods along with standard plate count method substantiated the enhanced disinfection efficiency of the doped sample in sunlight.

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Quelle: Photochemistry and Photobiology | 1 Apr 2014 | 3:55 pm CEST

Enhanced Efficacy of Photodynamic Therapy via a Sequential Targeting Protocol

Abstract

This study was designed to examine determinants of the discovery that low-dose lysosomal photodamage (lyso-PDT) could potentiate the efficacy of subsequent low-dose mitochondrial photodamage (mito-PDT). The chlorin NPe6 and the benzoporphyrin derivative (BPD) were used to separately target lysosomes and mitochondria, respectively, in murine hepatoma cells. Lyso-PDT (LD5 conditions) followed by mito-PDT (LD15 conditions) enhanced the loss of the mitochondrial membrane potential, activation of procaspases-3/7 and photokilling. Reversing the sequence was less effective. The optimal sequence did not enhance reactive oxygen species formation above that obtained with low-dose mito-PDT. In contrast, alkalinization of lysosomes with bafilomycin also enhanced low-dose mito-PDT photokilling, but via a different pathway. This involves redistribution of iron from lysosomes to mitochondria leading to enhanced hydroxyl radical formation, effects not observed after the sequential procedure. Moreover, Ru360, an inhibitor of mitochondrial calcium and iron uptake, partially suppressed the ability of bafilomycin to enhance mito-PDT photokilling without affecting the enhanced efficacy of the sequential protocol. We conclude that sequential PDT protocol promotes PDT efficacy by a process not involving iron translocation, but via promotion of the pro-apoptotic signal that derives from mitochondrial photodamage.

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Testing for iron translocation using fluorescent probes: red = RhoNox-1 (Ferrous iron); green = LysoTracker Green (A) or MitoTracker Green (B–D). Iron is initially localized in lysosomes (A), not mitochondria (B). Treatment with Bafilomycin results in substantial translocalization to mitochondria (C), whereas a low level of lysosomal photodamage does not (D). Either effect can markedly promote the efficacy of subsequent mitochondrial photodamage but via different mechanisms.

Quelle: Photochemistry and Photobiology | 1 Apr 2014 | 12:53 pm CEST

Evaluating steady-state and time-resolved fluorescence as a tool to study the behavior of asphaltene in toluene

Photochem. Photobiol. Sci., 2014, Advance Article
DOI: 10.1039/C4PP00069B, Paper
Open Access Open Access
Hui Ting Zhang, Rui Li, Zixin Yang, Cindy-Xing Yin, Murray R. Gray, Cornelia Bohne
Fluorescence behavior of asphaltene toluene solutions at different excitation and emission wavelengths and for different asphaltene concentrations.
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Quelle: RSC - Photochem. Photobiol. Sci. latest articles | 1 Apr 2014 | 1:00 am CEST

Fluorescence from bisaryl-substituted maleimide derivatives

Photochem. Photobiol. Sci., 2014, Accepted Manuscript
DOI: 10.1039/C4PP00001C, Paper
Milena Helmer Lauer, Roberta Lopes Drekener, Carlos Roque Correia, Marcelo Gehlen
A series of bisaryl-substituted fluorescent maleimides was synthesized via Heck arylation. The compounds showed broad fluorescence emission bands in the visible region, large Stokes shift in polar solvents and emission...
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Quelle: RSC - Photochem. Photobiol. Sci. latest articles | 31 Mar 2014 | 1:00 am CEST

Preliminary Ultra-Sonication Affects the Rate of the Bacteriorhodopsin Bleaching and the Effectiveness of the Reconstitution Process in Bacterioopsin

Abstract

The formation process of polymer films based on bacteriorhodopsin (BR) analogs requests a high amount of BR samples one-time-only. The common technique for apomembrane formation

(preparation of bacterioopsin, BO) is not designed to be operated with high concentrations and high volumes of BR, so the use of this technique results in a low rate of BR bleaching.

In order to accelerate the process of BR bleaching preliminary sonication was used. It was used just as preliminary sonication before bleaching of BR samples, so also sonication was used before reconstitution of resulted BO samples. These modifications of the common technique lead to an acceleration of BR bleaching and an increase in effectiveness of reconstitution of BO in comparison with the nonmodified technique. The quantitative results of sonication's effect on the bleaching acceleration and the effectiveness of reconstitution are different depending on the BR strains.

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Quelle: Photochemistry and Photobiology | 28 Mar 2014 | 1:09 pm CET

Tyrosine 263 in Cyanobacterial Phytochrome Cph1 Optimizes Photochemistry at the prelumi-R→lumi-R Step

Abstract

We report a low-temperature fluorescence spectroscopy study of the PAS-GAF-PHY sensory module of Cph1 phytochrome, its Y263F mutant (both with known 3D structures) as well as Y263H and Y263S to connect their photochemical parameters with intramolecular interactions. None of the holoproteins showed photochemical activity at low temperature, and the activation barriers for the Pr→lumi-R photoreaction (2.5–3.1 kJ mol−1) and fluorescence quantum yields (0.29–0.42) were similar. The effect of the mutations on Pr→Pfr photoconversion efficiency (ΦPr→Pfr) was observed primarily at the prelumi-R S0 bifurcation point corresponding to the conical intersection of the energy surfaces at which the molecule relaxes to form lumi-R or Pr, lowering ΦPr→Pfr from 0.13 in the wild type to 0.05–0.07 in the mutants. We suggest that the Ea activation barrier in the Pr* S1 excited state might correspond to the D-ring (C19) carbonyl – H290 hydrogen bond or possibly to the hindrance caused by the C131/C171 methyl groups of the C and D rings. The critical role of the tyrosine hydroxyl group can be at the prelumi-R bifurcation point to optimize the yield of the photoprocess and energy storage in the form of lumi-R for subsequent rearrangement processes culminating in Pfr formation.

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Y263 in Cph1 is perfectly conserved among phytochromes, even though mutations at that site seemed to be innocuous. Here we show that, on the contrary, tyrosine is important in optimizing photochemistry toward lumi-R at the of S0/S1 conical intersection (prelumi-R). A possible structure of the prelumi-R phantom state is shown here.

Quelle: Photochemistry and Photobiology | 28 Mar 2014 | 6:13 am CET

“Pointsource” Delivery of a Photosensitizer Drug and Singlet Oxygen: Eradication of Glioma Cells in Vitro

Abstract

We describe a pointsource sensitizer-tipped micro-optic device for the eradication of glioma U87 cells. The device has a mesoporous fluorinated silica tip which emits singlet oxygen molecules and small quantities of pheophorbide sensitizer for additional production of singlet oxygen in the immediate vicinity. The results show that the device surges in sensitizer release and photokilling with higher rates about midway through the reaction. This was attributed to a self-amplified autocatalytic reaction where released sensitizer in the extracellular matrix provides positive feedback to assist in the release of additional sensitizer. The photokilling of the glioma cells was analyzed by global toxicity and live/dead assays, where a killing radius around the tip with ~0.3 mm precision was achieved. The implication of these results for a new PDT tool of hard-to-resect tumors, e.g. in the brain, is discussed.

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Quelle: Photochemistry and Photobiology | 27 Mar 2014 | 12:10 pm CET

Luminescent ionogel based on europium (III)-coordinated carboxyl -functionalized ionic liquid and gelatin

Photochem. Photobiol. Sci., 2014, Accepted Manuscript
DOI: 10.1039/C4PP00076E, Paper
Man Li, yige Wang, Yuhuan chen, Shuming Zhang
In this work, we report the preparation and luminescent properties of a novel luminescent ionogel consisting of carboxyl-functionalized ionic liquid, Eu3+ ions and gelatin. The obtained ionogel was investigated by...
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Quelle: RSC - Photochem. Photobiol. Sci. latest articles | 27 Mar 2014 | 1:00 am CET

Phosphorylation of Histone H2AX Generated by Linear Alkylbenzene Sulfonates and its Suppression by UVB Exposure

Abstract

We previously demonstrated that the nonionic surfactants, nonylphenol polyethoxylates (NPEOs) induced the phosphorylation of histone H2AX (γ-H2AX), accompanied by DNA double-strand breaks (DSBs), and that exposure to ultraviolet (UV) degraded NPEOs, which sometimes enhanced their DNA-damaging ability. In this study, we showed that linear alkylbenzene sulfonates (LAS), general anion surfactants, also generated DSBs with γ-H2AX, and this ability was attenuated by UVB exposure. In the human breast adenocarcinoma cell line, MCF-7, γ-H2AX was generated in a dose-dependent manner immediately after cells were treated with LAS, and this was attributed to the formation of DSBs and was independent of cell cycle phases. The ability to generate γ-H2AX was markedly reduced in LAS exposed to UVB. HPLC analysis revealed that LAS were a mixture of various alkyl chain lengths, the peaks of which were detected at individual retention times. UVB evenly decreased all peaks of LAS, without migration of peaks to other retention times, which indicated that UVB may degrade the benzene ring of LAS, but did not shorten the alkyl chains. UVB is an important environmental factor in the degradation of LAS exhibiting the ability to induce DSBs, the most serious type of DNA damage.

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Linear alkylbenzene sulfonates (LAS), general anion surfactants, generated DNA double-strand breaks (DSBs) with phosphorylation of histone H2AX (γ-H2AX). The ability to generate γ-H2AX was markedly reduced in LAS exposed to UVB. HPLC analysis revealed that UVB evenly decreased all peaks of LAS, without migration of peaks to other retention times, which indicated that UVB may degrade the benzene ring of LAS, but did not shorten the alkyl chains. UVB is an important environmental factor in the degradation of LAS exhibiting the ability to induce DSBs, the most serious type of DNA damage.

Quelle: Photochemistry and Photobiology | 26 Mar 2014 | 1:14 pm CET

Membrane Damage Efficiency of Phenothiazinium Photosensitizers

Abstract

Structure–activity relationships have been widely reported for porphyrin and phthalocyanine photosensitizers, but not for phenothiazinium derivatives. Here, four phenothiazinium salts (methylene blue, toluidine blue O, 1,9-dimethyl methylene blue and the pentacyclic derivative DO15) were used to investigate how the ability to damage membranes is affected by membrane/solution partition, photophysical properties and tendency to aggregation of the photosensitizer. These two latter aspects were studied both in isotropic solutions and in membranes. Membrane damage was assessed by leakage of a fluorescent probe entrapped in liposomes and by generation of thiobarbituric acid-reactive species (TBARS), while structural changes at the lipid bilayer were detected by small-angle X-ray scattering. We observed that all compounds had similar singlet-oxygen quantum yields in ethanol, but only the photosensitizers that had higher membrane/solution partition (1,9-dimethyl methylene blue and DO15, the latter having the higher value) could permeabilize the lipid bilayer. Moreover, of these two photosensitizers, only DO15 altered membrane structure, a result that was attributed to its destabilization of higher order aggregates, generation of higher amounts of singlet oxygen within the membranes and effective electron-transfer reaction within its dimers. We concluded that membrane-based protocols can provide a better insight on the photodynamic efficiency of the photosensitizer.

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Structure–activity relationships were investigated for a series of phenothiazinium photosensitizers (methylene blue, toluidine blue O, 1,9-dimethyl methylene blue and DO15). We compared the ability of these compounds to damage membranes by quantifying the efficiency of liposome permeabilization, which was correlated with singlet-oxygen generation within the membranes, membrane/solution partition and tendency of aggregation of the photosensitizers. We concluded that membrane-based protocols can provide a better understanding on the photodynamic efficiency of the photosensitizer.

Quelle: Photochemistry and Photobiology | 26 Mar 2014 | 1:14 pm CET

The Effect of Photodynamic Action on Leakage of Ions Through Liposomal Membranes that Contain Oxidatively Modified Lipids

Abstract

Singlet oxygen, created in photosensitization, peroxidizes unsaturated fatty acids of the membrane's lipids. This generates alcoholic or aldehyde groups at double bonds' breakage points. In a previous study, we examined the leakage of a K+-induced cross-membrane electric potential of liposomes that undergo photosensitization. The question remains to what extent peroxidized lipids can compromise the stability of the membrane. In this study, we studied the effect of the oxidatively modified lipids PGPC and ALDOPC in the membrane on its stability, by monitoring the membrane electric potential with the potentiometric dye DiSC2(5). As the content of the modified lipids increases the membrane becomes less stable, and even at just 2% of the modified lipids the membrane's integrity is affected, in respect to the leakage of ions through it. When the liposomes that contain the modified lipids undergo photosensitization by hematoporphyrin, the lipid bilayer becomes even more unstable and passage of ions is accelerated. We conclude that the existence of lipids with a shortened fatty acid that is terminated by a carboxylic acid or an aldehyde and more so when photosensitized damage occurs to unsaturated fatty acids in lecithin, add up to a critical alteration of the membrane, which becomes leaky to ions.

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We measured the integrity of the liposomal membrane when it includes oxidatively modified lipids and when it is exposed to photodynamic action by photosensitization with hematoporphyrin. We demonstrate that the photodynamic process, in which unsaturated lipids of natural lecithin are damaged, is not causing the lipid bilayer to leak, but it strongly accelerates the leakage of ions if a very small fraction of the natural lipids are replaced by the modified lipids.

Quelle: Photochemistry and Photobiology | 25 Mar 2014 | 10:16 am CET

Analysis of UV-absorbing photoprotectant mycosporine-like amino acid (MAA) in the cyanobacterium Arthrospira sp. CU 2556

Photochem. Photobiol. Sci., 2014, Accepted Manuscript
DOI: 10.1039/C4PP00013G, Paper
Aran Incharoensakdi, Rajesh Prasad Rastogi
Mycosporine-like amino acids (MAAs) are ecologically important biomolecules with great photoprotective potential. The present study aimed to investigate the biosynthesis of MAA in the cyanobacterium Arthrospira sp. CU2556. High-performance liquid...
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Quelle: RSC - Photochem. Photobiol. Sci. latest articles | 25 Mar 2014 | 1:00 am CET

"Turn-On" fluorescent chemosensor for Zinc (II) dipodal ratiometric receptor: Application in live cell imaging.

Photochem. Photobiol. Sci., 2014, Accepted Manuscript
DOI: 10.1039/C4PP00034J, Paper
Kundan C Tayade, Banashree Bondhopadhyay, Hemant Sharma, Anupam Basu, Vikas V. Gite, Sanjay B. Attarde, Narinder Singh, Anil Kuwar
A dipodial ligand 2,2'-((ethane-1,2-diylbis(azanediyl))bis(ethane-1,1-diyl))diphenol was synthesized through condensation reaction and was characterized with IR, 1H NMR, 13C-NMR, and mass spectroscopy. The receptor 2 has shown marked enhancement in fluorescence intensity...
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Quelle: RSC - Photochem. Photobiol. Sci. latest articles | 25 Mar 2014 | 1:00 am CET

Treatment of oral fungal infections using antimicrobial photodynamic therapy: a systematic review of currently available evidence

Photochem. Photobiol. Sci., 2014, 13,726-734
DOI: 10.1039/C3PP50426C, Perspective
Fawad Javed, Lakshman P. Samaranayake, Georgios E. Romanos
The aim was to review the efficacy of antimicrobial photodynamic therapy (PDT) in the treatment of oral fungal infections.
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Quelle: RSC - Photochem. Photobiol. Sci. latest articles | 25 Mar 2014 | 1:00 am CET

Synthesis and characterization of novel zinc phthalocyanines as potential photosensitizers for photodynamic therapy of cancers

Photochem. Photobiol. Sci., 2014, Accepted Manuscript
DOI: 10.1039/C3PP50393C, Paper
Sharon Gail Moeno, Rui Warner Krause, Eugeny Ermilov, Weronika Kuzyniak, Michael Hoepfner
Two novel zinc phthalocyanines (Pcs): Tetramethyl Tetrakis-2,(3)-[(4-methyl-2-pyridyloxy)phthalocyaninato] zinc(II) (4) and (the negatively charged) Tetrakis-2,(3)-[(3-carboxylicacid-6-sulfanylpyridine)phthalocyaninato] zinc(II) (5), water soluble by virtue of their ionic substituent groups were synthesized. The spectroscopic properties...
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Quelle: RSC - Photochem. Photobiol. Sci. latest articles | 25 Mar 2014 | 1:00 am CET

Quantification of Ocular Biologically Effective UV Exposure for Different Rotation Angle Ranges Based on Data from a Manikin

Abstract

Human outdoor activities are randomly orientated at different angles to the sun. To quantify the ocular UV and biologically effective UV (UVBE; i.e. the ocular UV irradiance exposure for photokeratitis (UVpker), photoconjunctivitis (UVpcon), and cataract (UVcat)) exposure for different rotation angle ranges, a rotating manikin was used to monitor the ocular UV exposure at different rotation angles in clear skies during July 2010 in Sanya, China. As a result, the ocular UV and UVBE irradiance was directly influenced by the rotation angle variations, primarily for the 120° rotation angle ranges facing the morning and afternoon sun when the solar elevation was lower than 60°; during these times, the UV and UVBE spectral irradiance decreased as the rotation angle increased. When compared to the 360° rotation angle ranges (which were considered to be the average exposure situation), the cumulative ocular UVBE for 60°, 120° and 180° rotation angle ranges were maximally 91% (UVcat), 94% (UVpker) and 121% (UVpcon); 71% (UVcat), 74% (UVpker) and 95% (UVpcon); 42%(UVcat), 45%(UVpker) and 55% (UVpcon) higher respectively. Meanwhile, the cumulative ocular UVBE for the 180° rotation angle ranges facing away from the sun were 46% (UVpker), 59% (UVpcon) and 45% (UVcat) lower.

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To improve the understanding of solar UV and the biologically effective UV exposure at eye (UVBE), this study monitored the ocular UV exposure at different rotation angles using a rotating manikin in clear skies during July 2010 in Sanya, China. The rotation angle ranges were the ranges of the eye facing the sun or facing away from the sun; for example, the 60° rotation angle range facing the sun was the rotation angle of 330° to 30°, and the 180° rotation angle range facing away from the sun included the rotation angles between 90° and 270°.

Quelle: Photochemistry and Photobiology | 24 Mar 2014 | 12:07 pm CET

Measuring Exposure to Solar Ultraviolet Radiation Using a Dosimetric Technique: Understanding Participant Compliance Issues

Abstract

Personal ultraviolet dosimeters have been used in epidemiological studies to understand the risks and benefits of individuals' exposure to solar ultraviolet radiation (UVR). We investigated the types and determinants of noncompliance associated with a protocol for use of polysulphone UVR dosimeters. In the AusD Study, 1002 Australian adults (aged 18–75 years) were asked to wear a new dosimeter on their wrist each day for 10 consecutive days to quantify their daily exposure to solar UVR. Of the 10 020 dosimeters distributed, 296 (3%) were not returned or used (Type-I noncompliance) and other usage errors were reported for 763 (8%) returned dosimeters (Type-II noncompliance). Type-I errors were more common in participants with predominantly outdoor occupations. Type-II errors were reported more frequently on the first day of measurement; weekend days or rainy days; and among females; younger people; more educated participants or those with outdoor occupations. Half (50%) the participants reported a noncompliance error on at least 1 day during the 10-day period. However, 92% of participants had at least 7 days of usable data without any apparent noncompliance issues. The factors identified should be considered when designing future UVR dosimetry studies.

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Among 10 020 polysulphone UV dosimeters distributed in the AusD Study, the majority (89%) were returned with no reported issues, but 3% were not returned or used and 8% were returned with self-reported usage errors such as “missing some time,” “covered by clothing,” or “dosimeter got wet” that may potentially compromise the measurement quality. We found these noncompliance issues were more frequently reported on the first day of measurement; weekend days or rainy days; and among females; younger people; more educated participants or those with predominantly outdoor occupations. These factors should be considered when designing future UV dosimetry studies.

Quelle: Photochemistry and Photobiology | 24 Mar 2014 | 12:03 pm CET

Photobehaviour of methyl-pyridinium and quinolinium iodide derivatives, free and complexed with DNA. A case of bisintercalation

Photochem. Photobiol. Sci., 2014, Advance Article
DOI: 10.1039/C4PP00023D, Paper
Alessandra Mazzoli, Benedetta Carlotti, Giuseppe Consiglio, Cosimo G. Fortuna, Giorgia Miolo, Anna Spalletti
Interaction between azinium iodides and DNA. A bicationic dye acts as a bisintercalative agent which could increase the cytotoxicity with low dose and less collateral effects.
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Quelle: RSC - Photochem. Photobiol. Sci. latest articles | 24 Mar 2014 | 1:00 am CET

Texaphyrin sensitized near-IR-to-visible photon upconversion

Photochem. Photobiol. Sci., 2014, 13,813-819
DOI: 10.1039/C4PP00037D, Paper
Fan Deng, Wenfang Sun, Felix N. Castellano
Near-IR (NIR) absorption from a Cd(II) texaphyrin (TXP) has been successfully coupled with rubrene triplet acceptors/annihilators in vacuum degassed dichloromethane to upconvert NIR (670-800 nm) incident photons into yellow fluorescence through sensitized triplet-triplet annihilation.
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Quelle: RSC - Photochem. Photobiol. Sci. latest articles | 20 Mar 2014 | 1:00 am CET

Photochemical ligand ejection from non-sterically promoted Ru(II)bis(diimine) 4,4[prime or minute]-bi-1,2,3-triazolyl complexes

Photochem. Photobiol. Sci., 2014, 13,735-738
DOI: 10.1039/C3PP50437A, Communication
Open Access Open Access
Creative Commons Licence  This article is licensed under a Creative Commons Attribution 3.0 Unported Licence.
Christine E. Welby, Georgina K. Armitage, Harry Bartley, Alessandro Sinopoli, Baljinder S. Uppal, Paul I. P. Elliott
Complexes of the form [Ru(diimine)2(btz)]2+ (btz = 1,1[prime or minute]-dibenzyl-4,4[prime or minute]-bi-1,2,3-triazolyl) are observed to undergo photochemical ejection of the btz ligand in the absence of any promotion through steric congestion.
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Quelle: RSC - Photochem. Photobiol. Sci. latest articles | 20 Mar 2014 | 1:00 am CET

Interaction of extrinsic chemical factors affecting photodegradation of dissolved organic matter in aquatic ecosystems

Photochem. Photobiol. Sci., 2014, 13,799-812
DOI: 10.1039/C4PP00011K, Paper
Petr Porcal, Peter J. Dillon, Lewis A. Molot
Photochemical degradation of dissolved organic matter (DOM) plays an important role in the carbon cycle.
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Quelle: RSC - Photochem. Photobiol. Sci. latest articles | 20 Mar 2014 | 1:00 am CET

Photophysics of a Coumarin in Different Solvents: Use of Different Solvatochromic Models

Abstract

This study reported the photophysics of 7-(diethylamino)coumarin-3-carboxylic acid N-succinimidyl ester (7-DCCAE) in different neat solvents of varying polarity using steady-state absorption, fluorescence emission and picosecond time-resolved spectroscopy. In nonpolar solvents, the dye molecule predominantly exists in nonpolar structure and exhibits very low value of nonradiative decay rate constant (knr), demonstrating the emission takes place from S1-LE to S0 ground state. The fluorescence quantum yields, lifetime values of 7-DCCAE in different solvents are rationalized on the basis of intramolecular charge transfer (ICT) followed by twisted intramolecular charge transfer state formation (TICT) as well as specific solute–solvent interactions. Several solvatochromic models (such as Lippert, Dimroth, Kamlet–Taft, Catalán 3P and Catalán 4P models) were used to analyze the solvatochromic shift of 7-DCCAE in different solvents. The different empirical models show that the observed results are better correlate for nonchlorinated solvents and provide statistically significant best-fit result. A comparison was done between comparatively new solvatochromic model (Catalán 3P and Catalán 4P model) with Kamlet–Taft model. The ground state structure of the said molecule was optimized by using Density Functional Theory (DFT).

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This study demonstrated the photophysics of 7-(diethylamino)coumarin-3-carboxylic acid N-succinimidyl ester (7-DCCAE) in the presence of different neat solvents. Different empirical solvatochromic models were used to analyze the solvatochromic shift of 7-DCCAE in different solvents.

Quelle: Photochemistry and Photobiology | 18 Mar 2014 | 6:35 am CET

Dimerization of Resveratrol Induced by Red Light and Its Synergistic Analgesic Effects with Cobra Neurotoxin

Abstract

Resveratrol polymer has better effects than monomer in some aspects as reported, but most of synthetic methods acquire severe conditions and no analgesic effects are investigated. A novel method is found to synthesize resveratrol polymer by excitation of photosensitizer pheophorbide at red light of 630 nm. The polymer was analyzed by fluorescence spectra and HPLC, further isolated by preparative liquid chromatography and identified as a resveratrol dimer by MS and NMR. Analgesic effects were measured by acetic acid writhing and hot-plate test in mice. The resveratrol dimer has the stronger analgesic effects than monomer, and drug combination of the dimer and cobra neurotoxin enhances and prolongs analgesic effects, suggesting the synergistic action. Simulation of molecular interaction reveals that the dimer spontaneously binds to cobra neurotoxin and makes a complex substance. The dimer can interact with cyclooxygenase-2, μ receptor and nicotine receptor, the synergistic analgesic effects of the complex are attributed to its multiple targets role. The combination of resveratrol dimer and cobra neurotoxin may make up for their deficiencies in analgesic effects, and has prospects in clinical use.

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A new synthetic method is designed for resveratrol dimer, which is induced by the excitation of photosensitizer pheophorbide at red light of 630 nm, the mechanism is illustrated. The dimer interacts with cobra neurotoxin and forms a complex substance, which shows significant synergistic analgesic effects after combined administration to mice. The dimer has multiple targets, and its combination with cobra neurotoxin may make up for their deficiencies in analgesic effects suggesting good prospects in clinical use.

Quelle: Photochemistry and Photobiology | 15 Mar 2014 | 6:21 am CET

A Comparative Pilot Study of Symptom Improvement Before and After Phototherapy in Korean Patients with Perennial Allergic Rhinitis (pages 751–757)

Quelle: Photochemistry and Photobiology | 15 Mar 2014 | 4:38 am CET

One-Pot Fabrication of RGO–Ag3VO4 Nanocomposites by in situ Photoreduction using Different Sacrificial Agents: High Selectivity Toward Catechol Synthesis and Photodegradation Ability (pages 57–65)

Quelle: Photochemistry and Photobiology | 15 Mar 2014 | 4:38 am CET

Nicholas J. Turro, 1938–2012

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This volume of Photochemistry and Photobiology contains a memoriam to Nicholas J. Turro (1938–2012). It is a collection of review articles and papers, dedicated to his memory, authored by those who remember him as a teacher, mentor, colleague and friend.

Quelle: Photochemistry and Photobiology | 15 Mar 2014 | 4:38 am CET

Editorial

Quelle: Photochemistry and Photobiology | 15 Mar 2014 | 4:38 am CET

Measurement of Intracellular Oxygen Concentration During Photodynamic Therapy in vitro

Abstract

A technique is introduced that monitors the depletion of intracellular ground state oxygen concentration ([3O2]) during photodynamic therapy of Mat-LyLu cell monolayers and cell suspensions. The photosensitizer Pd(II) meso-tetra(4-carboxyphenyl)porphine (PdT790) is used to manipulate and indicate intracellular [3O2] in both of the in vitro models. The Stern–Volmer relationship for PdT790 phosphorescence was characterized in suspensions by flowing nitrogen over the suspension while short pulses of 405 nm light were used to excite the sensitizer. The bleaching of sensitizer and the oxygen consumption rate were also measured during continuous exposure of the cell suspension to the 405 nm laser. Photodynamic therapy (PDT) was conducted in both cell suspensions and in cell monolayers under different treatment conditions while the phosphorescence signal was acquired. The intracellular [3O2] during PDT was calculated by using the measured Stern–Volmer relationship and correcting for sensitizer photobleaching. In addition, the amount of oxygen that was consumed during the treatments was calculated. It was found that even at large oxygen consumption rates, cells remain well oxygenated during PDT of cell suspensions. For monolayer treatments, it was found that intracellular [3O2] is rapidly depleted over the course of PDT.

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A novel technique is described that measures the intracellular ground state oxygen concentration ([3O2]) during photodynamic therapy of cell monolayers and cell suspensions. The photosensitizer Pd(II) meso-tetra(4-carboxyphenyl)porphine (PdT790) is used to deplete the cells of 3O2 by photodynamic action while simultaneously monitoring the intracellular [3O2]. The intracellular [3O2] is calculated using the steady-state phosphorescence signal emitted by PdT790 during treatment. It was found that cells remain well oxygenated during PDT of cell suspensions, while for monolayer treatments intracellular [3O2] is rapidly reduced.

Quelle: Photochemistry and Photobiology | 14 Mar 2014 | 11:28 pm CET

Slow excited state phototautomerization in 3-hydroxyisoquinoline

Photochem. Photobiol. Sci., 2014, Advance Article
DOI: 10.1039/C3PP50356A, Paper
Neeraj Kumar Joshi, Priyanka Arora, Sanjay Pant, Hem Chandra Joshi
In the present work we report the spectral and photophysical properties of 3-hydroxyisoquinoline in various protic/aprotic solvents. We have found the signatures of tautomerization by slow excited state intramolecular proton transfer (ESIPT) in protic as well as aprotic solvents.
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Quelle: RSC - Photochem. Photobiol. Sci. latest articles | 12 Mar 2014 | 1:00 am CET

Measurements of pilots’ occupational solar UV exposure

Abstract

It is known that ultraviolet radiation (UVR) increases by 10-12% every 1,000 m altitude; UVR at the 10, 000 m of typical cruise altitude for commercial aircraft may be 2-3 times higher than at ground level. Information on the levels of solar UV exposures is essential for the assessment of the occupational risk of pilots developing sun-related eye disorders and skin cancers. The aim of the study was to investigate how UV hazard exposures can be measured during flights so that the occupational dose can be ascertained and compared with international guidance. This paper describes the development of instrumentation for automated time-stamped spectral measurements which were collected using bespoke automation software. The software enables the advanced acquisition techniques of automated dark signal capture and multiband integration control optimising the dynamic performance of the spectrometer over the full spectral range. The equipment was successfully tested in a number of aircraft and helicopter flights during 2012-13 and illustrated in this paper on an example of a Gatwick-Alicante flight.

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Quelle: Photochemistry and Photobiology | 11 Mar 2014 | 1:46 pm CET

Autonomous Portable Solar Ultraviolet Spectroradiometer (APSUS) – a New CCD Spectrometer System for Localized, Real-Time Solar Ultraviolet (280–400 nm) Radiation Measurement

Abstract

Terrestrial solar ultraviolet (UV) radiation has significant implications for human health and increasing levels are a key concern regarding the impact of climate change. Monitoring solar UV radiation at the earth's surface is therefore of increasing importance. A new prototype portable CCD (charge-coupled device) spectrometer-based system has been developed that monitors UV radiation (280–400 nm) levels at the earth's surface. It has the ability to deliver this information to the public in real time. Since the instrument can operate autonomously, it is called the Autonomous Portable Solar Ultraviolet Spectroradiometer (APSUS). This instrument incorporates an Ocean Optics QE65000 spectrometer which is contained within a robust environmental housing. The APSUS system can gather reliable solar UV spectral data from approximately April to October inclusive (depending on ambient temperature) in the UK. In this study the new APSUS unit and APSUS system are presented. Example solar UV spectra and diurnal UV Index values as measured by the APSUS system in London and Weymouth in the UK in summer 2012 are shown.

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A new prototype portable CCD (charge-coupled device) spectrometer-based instrument called APSUS (Autonomous Portable Solar Ultraviolet Spectroradiometer) has been developed which monitors spectral UV (280–400 nm) radiation levels at the earth's surface. The APSUS system enables the UV index to be calculated and disseminated to the public in real time. The APSUS unit incorporates an Ocean Optics QE65000 spectrometer contained within a robust environmental housing. It can gather reliable data from approximately April to October inclusive (depending on ambient temperature) in the UK. In this study the new APSUS unit and APSUS system are presented.

Quelle: Photochemistry and Photobiology | 10 Mar 2014 | 12:02 pm CET

Bistable Retinal Schiff Base Photodynamics of Histidine Kinase Rhodopsin HKR1 from Chlamydomonas reinhardtii

Abstract

The photodynamics of the recombinant rhodopsin fragment of the histidine kinase rhodopsin HKR1 from Chlamydomonas reinhardtii was studied by absorption and fluorescence spectroscopy. The retinal cofactor of HKR1 exists in two Schiff base forms RetA and RetB. RetA is the deprotonated 13-cis-retinal Schiff base (RSB) absorbing in the UVA spectral region. RetB is the protonated all-trans RSB absorbing in the blue spectral region. Blue light exposure converts RetB fully to RetA. UVA light exposure converts RetA to RetB and RetB to RetA giving a mixture determined by their absorption cross sections and their conversion efficiencies. The quantum efficiencies of conversion of RetA to RetB and RetB to RetA were determined to be 0.096 ± 0.005 and 0.405 ± 0.01 respectively. In the dark thermal equilibration between RetA and RetB with dominant RetA content occurred with a time constant of about 3 days at room temperature. The fluorescence emission behavior of RetA and RetB was studied, and fluorescence quantum yields of ϕF(RetA) = 0.00117 and ϕF(RetB) = 9.4 × 10−5 were determined. Reaction coordinate schemes of the photodynamics are developed.

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In HKR1 two thermally stable retinal Schiff base (RSB) forms RetA and RetB exist. RetA is deprotonated 13-cis, 15-anti RSB absorbing in the UV. RetB is protonated all-trans 15-anti and 15-syn RSB absorbing blue light. RetB is blue-light convertible to RetA with quantum efficiency of 0.4. RetA is UVA light convertible to RetB with quantum efficiency of 0.1.

Quelle: Photochemistry and Photobiology | 8 Mar 2014 | 7:55 am CET

Photoexcited States of UV Absorbers, Benzophenone Derivatives

Abstract

The UV absorption, phosphorescence and phosphorescence-excitation spectra of benzophenone (BP) derivatives used as organic UV absorbers have been observed in rigid solutions at 77 K. The triplet–triplet absorption spectra have been observed in acetonitrile at room temperature. The BP derivatives studied are 2,2′,4,4′-tetrahydroxybenzophenone (BP-2), 2-hydroxy-4-methoxybenzophenone (BP-3), 2,2′-dihydroxy-4,4′-dimethoxybenzophenone (BP-6), 5-chloro-2-hydroxybenzophenone (BP-7) and 2-hydroxy-4-n-octyloxybenzophenone (BP-12). The energy levels and lifetimes of the lowest excited triplet (T1) states of these BP derivatives were determined from the first peak of phosphorescence. The time-resolved near-IR emission spectrum of singlet oxygen generated by photosensitization with BP-7 was observed in acetonitrile at room temperature. BP-2, BP-3, BP-6 and BP-12 show photoinduced phosphorescence enhancement in ethanol at 77 K. The possible mechanism of the observed phosphorescence enhancement is discussed. The T1 states of 2-hydroxy-5-methylbenzophenone, 4-methoxybenzophenone and 2,4′-dimethoxybenzophenone have been studied for comparison.

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The energy levels and lifetimes of the lowest excited triplet states of benzophenone (BP) derivatives, BP-2, BP-3, BP-6, BP-7 and BP-12, used as organic UV absorbers in cosmetic sunscreens were determined in rigid solutions at 77 K. The time-resolved near-IR emission spectrum of singlet oxygen generated by photosensitization with BP-7 was observed in acetonitrile at room temperature. BP-2, BP-3, BP-6 and BP-12 show photoinduced phosphorescence enhancement in ethanol at 77 K.

Quelle: Photochemistry and Photobiology | 7 Mar 2014 | 6:42 am CET

Comparison of UVA-induced ROS and sunscreen nanoparticle-generated ROS in human immune cells

Photochem. Photobiol. Sci., 2014, 13,781-788
DOI: 10.1039/C3PP50428J, Paper
Cenchao Shen, Terence W. Turney, Terrence J. Piva, Bryce N. Feltis, Paul F. A. Wright
Generation of reactive oxygen species in human immune cells co-exposed to UVA and ZnO or rutile TiO2 nanoparticles is not greater than that produced in the cells by UVA alone.
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Quelle: RSC - Photochem. Photobiol. Sci. latest articles | 6 Mar 2014 | 1:00 am CET

Proposal for a modification of the UVI risk scale

Photochem. Photobiol. Sci., 2014, Advance Article
DOI: 10.1039/C4PP00006D, Perspective
Francesco Zaratti, Ruben D. Piacentini, Hector A. Guillen, Sergio H. Cabrera, J. Ben Liley, Richard L. McKenzie
Peak UVI values for the globe using a modified colour scale. With the colour scale for UVI as currently recommended by WHO, more than 78% of the globe area - representing 89% of the world's population - would be indistinguishable.
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Quelle: RSC - Photochem. Photobiol. Sci. latest articles | 6 Mar 2014 | 1:00 am CET

Bystander Effect Induced by UVC Radiation in Chinese hamster V79 cells

Abstract

In past decades, researches on radiation-induced bystander effect mainly focused on ionizing radiation such as α-particle, β-particle, X-ray and γ-ray. But few researches have been conducted on the ability of ultraviolet (UV) radiation-induced bystander effect, and knowledge of UVC-induced bystander effect is far limited. Here, we adopted medium transfer experiment to detect whether UVC could cause bystander effect in Chinese hamster V79 cells. We determined the cell viability, apoptosis rate, chromosome aberration and ultrastructure changes, respectively. Our results showed that: (1) the viability of UVC-irradiated V79 cells declined significantly with the dosage of UVC; (2) similar to the irradiated cells, the main death type of bystander cells cultured in irradiation conditioned medium (ICMs) was also apoptosis; (3) soluble factors secreted by UVC-irradiated cells could induce bystander effect in V79 cells; (4) cells treated with 4 h ICM collected from 90 mJ cm−2 UVC-irradiated cells displayed the strongest response. Our data revealed that UVC could cause bystander effect through the medium soluble factors excreted from irradiated cells and this bystander effect was a novel quantitative and kinetic response. These findings might provide a foundation to further explore the exact soluble bystander factors and detailed mechanism underlying UVC-induced bystander effect.

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This study showed that UVC radiation induced some damage in irradiated V79 cells, which might initiate apoptosis progress when damage couldn't be repaired. The UVC-irradiated apoptotic cells released gradually some soluble factors into irradiated conditioned medium (ICMs) which finally induced bystander effect in unirradiated V79 cells.

Quelle: Photochemistry and Photobiology | 5 Mar 2014 | 8:04 am CET

Efficacy of Low-Dose Ultraviolet A-1 Phototherapy for Parapsoriasis/Early-Stage Mycosis Fungoides

Abstract

Mycosis fungoides (MF) and parapsoriasis (PP) are major dermatologic conditions for which phototherapy continues to be a successful and valuable treatment option. UVA-1 phototherapy is effective in the management of cutaneous T-cell mediated diseases. The aim of the study was to evaluate the efficacy and safety of low-dose UVA-1 phototherapy for the management of PP/early-stage MF. A total of 30 patients, diagnosed with MF (n:19) or PP (n:11) were enrolled to the study. All patients were managed with low-dose UVA-1 (20 or 30 J cm−2). Response was assessed clinically and immunohistochemically. UVA-1 treatment led to clinical and histological complete remission (CR) in 11 of 19 MF patients (57.9%), partial remission (PR) in three of 19 (15.8%), after a mean cumulative dose of 1665 (range, 860–3120) J cm−2 and mean number of 73 exposure (range, 43–107) sessions. Five patients with PP (45.5%) showed CR, and PR was observed in six patients with PP (54.5%) after a mean cumulative dose of 1723 (range, 1060–3030) J cm−2 and mean number of 74 exposure (range, 53–101) sessions. We conclude that low-dose UVA-1 therapy seems to be an effective, safe, and well-tolerated treatment option for patients with PP/early-stage MF.

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Skin-directed therapies are currently available treatment options for plaque type PP/early-stage MF with some limitations, and management of the diseases is still challenging. Ultraviolet A-1 (340–400 nm) phototherapy was first described in 1978 and it has became a valuable treatment for sclerotic and T-cell mediated diseases, more deeply penetrates than UVB. This study showed that Low-dose UVA-1 therapy seems to be a safe and effective alternative to other therapeutic options in patients with PP/early-stage MF who do not tolerate or respond to PUVA and UVB therapy, without systemic effect.

Quelle: Photochemistry and Photobiology | 5 Mar 2014 | 8:04 am CET

Aggregation/disaggregation of chlorophyll a in model phospholipid-detergent vesicles and micelles

Photochem. Photobiol. Sci., 2014, Advance Article
DOI: 10.1039/C3PP50419K, Paper
Raquel F. Correia, M. Isabel Viseu, Suzana M. Andrade
A FLIM image of Chl a in pure DMPC liposomes (centre), revealing monomers in vesicle's outer monolayers (red) and H-type dimers/aggregates in inter-bilayer spaces (green).
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Quelle: RSC - Photochem. Photobiol. Sci. latest articles | 5 Mar 2014 | 1:00 am CET

Contrasting patterns of MAAs accumulation in two populations of the copepod Boeckella gracilipes

Photochem. Photobiol. Sci., 2014, Advance Article
DOI: 10.1039/C3PP50317H, Paper
Patricia E. Garcia, Marcela A. Ferraro, A. Patricia Perez, Horacio E. Zagarese, Maria C. Dieguez
Mycosporine-like amino acids from copepod Boeckella gracilipes can be controlled by local environmental conditions (UVR, temperature) and also by intrinsic factors (local adaptation).
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Quelle: RSC - Photochem. Photobiol. Sci. latest articles | 5 Mar 2014 | 1:00 am CET

Exposure of vitamins to UVB and UVA radiation generates singlet oxygen

Photochem. Photobiol. Sci., 2014, 13,820-829
DOI: 10.1039/C3PP50413A, Paper
Alena Knak, Johannes Regensburger, Tim Maisch, Wolfgang Baumler
Vitamins generate singlet oxygen when excited with UVA or UVB radiation. Vitamins are essential for cellular functions but can act as endogenous photosensitizers, leading to cell damage at the same time.
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Quelle: RSC - Photochem. Photobiol. Sci. latest articles | 4 Mar 2014 | 1:00 am CET

Extended mechanistic aspects on photoinitiated polymerization of 1,6-hexanediol diacrylate by hexaarylbisimidazoles and heterocyclic mercapto compounds

Photochem. Photobiol. Sci., 2014, 13,789-798
DOI: 10.1039/C3PP50379H, Paper
Stefan Berdzinski, Nadine Strehmel, Heike Lindauer, Veronika Strehmel, Bernd Strehmel
Chlorine substituted hexaarylbisimidazole (o-Cl-HABI) efficiently initiates radical polymerization of multifunctional acrylic esters in the presence of a heterocyclic mercapto compound if the latter can form its tautomeric thione.
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Quelle: RSC - Photochem. Photobiol. Sci. latest articles | 26 Feb 2014 | 1:00 am CET

Chemosensitization of Cancer Cells via Gold Nanoparticle-Induced Cell Cycle Regulation

Abstract

We have previously shown that plasmonic nanoparticles conjugated with nuclear-targeting and cytoplasm-targeting peptides (NLS and RGD, respectively) are capable of altering the cell cycle of human oral squamous carcinoma cells (HSC-3). In the present work, we show that this regulation of the cell cycle can be exploited to enhance the efficacy of a common chemotherapeutic agent, 5-Fluorouracil, by pretreating cells with gold nanoparticles. Utilizing flow cytometry cell cycle analysis, we were able to quantify the 5-Fluorouracil efficacy as an accumulation of cells in the S phase with a depletion of cells in the G2/M phase. Two gold nanoparticle sizes were tested in this work; 30 nm with a surface plasmon resonance at 530 nm and 15 nm with a surface plasmon resonance at 520 nm. The 30 nm nuclear-targeted gold nanoparticles (NLS-AuNPs) showed the greatest 5-Fluorouracil efficacy enhancement when 5-Fluorouracil treatment (500 μm, 48 h) is preceded by a 24-h treatment with nanoparticles. In conclusion, we show that nuclear-targeted 30 nm gold nanoparticles enhance 5-Fluorouracil drug efficacy in HSC-3 cells via regulation of the cell cycle, a chemosensitization technique that could potentially be expanded to different cell lines and different chemotherapies.

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Gold nanoparticles that target the nucleus of cancer cells have the ability to regulate the cell cycle, causing cells to accumulate in the S phase. A common chemotherapeutic agent, 5-Fluorouracil, is most effective at inducing cell death when cells are in the S phase of the cell cycle. Therefore, treatment with 5-Fluorouracil is preceded by treatment with nuclear-targeting gold nanoparticles to allow for an enhanced S phase population, resulting in enhanced drug efficacy (i.e. chemosensitization).

Quelle: Photochemistry and Photobiology | 12 Feb 2014 | 4:59 am CET

First characterisation of a CPD-class I photolyase from a UV-resistant extremophile isolated from High-Altitude Andean Lakes

Photochem. Photobiol. Sci., 2014, 13,739-750
DOI: 10.1039/C3PP50399B, Paper
Virginia Helena Albarracin, Julian Simon, Gopal P. Pathak, Lorena Valle, Thierry Douki, Jean Cadet, Claudio Dario Borsarelli, Maria Eugenia Farias, Wolfgang Gartner
This is the first report and detailed characterization of a functional CPD-photolyase in a bacterial extremophile from the Acinetobacter genus.
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Quelle: RSC - Photochem. Photobiol. Sci. latest articles | 11 Feb 2014 | 1:00 am CET

Orange fluorescent proteins constructed from cyanobacteriochromes chromophorylated with phycoerythrobilin

Photochem. Photobiol. Sci., 2014, 13,757-763
DOI: 10.1039/C3PP50411E, Paper
Ya-Fang Sun, Jin-Guo Xu, Kun Tang, Dan Miao, Wolfgang Gartner, Hugo Scheer, Kai-Hong Zhao, Ming Zhou
Novel orange fluorescent proteins are formed in E. coli, due to the capability of GAF domains to be chromophorylated with phycoerythrobilin. The strong brightness of these constructs makes them promising as biomarkers.
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Quelle: RSC - Photochem. Photobiol. Sci. latest articles | 11 Feb 2014 | 1:00 am CET

Dual-color control of nucleotide polymerization sensed by a fluorescence actuator

Photochem. Photobiol. Sci., 2014, 13,751-756
DOI: 10.1039/C3PP50438G, Paper
Madalena M. Reimao-Pinto, Ana Cordeiro, Carina Almeida, Andre V. Pinheiro, Artur Moro, Joao C. Lima, Pedro V. Baptista
Spatial and temporal control of molecular mechanisms can be achieved using photolabile bonds that connect biomolecules to protective caging groups, which can be cleaved upon irradiation of a specific wavelength, releasing the biomolecule ready-to-use.
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Quelle: RSC - Photochem. Photobiol. Sci. latest articles | 11 Feb 2014 | 1:00 am CET

Analysis of transformations of the ultrafast electron transfer photoreaction mechanism in liquid solutions by the rate distribution approach

Photochem. Photobiol. Sci., 2014, 13,770-780
DOI: 10.1039/C3PP50388G, Paper
Michael G. Kuzmin, Irina V. Soboleva
Rate distribution functions P(k), obtained directly from the experimental kinetics N(t) by an inverse Laplace transform, demonstrate transformations of the rate control factors in the course of ultrafast ET reactions.
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Quelle: RSC - Photochem. Photobiol. Sci. latest articles | 23 Jan 2014 | 1:00 am CET

Crystal thickness dependence of the photoinduced crystal bending of 1-(5-methyl-2-(4-(p-vinylbenzoyloxymethyl)phenyl)-4-thiazolyl)-2-(5-methyl-2-phenyl-4-thiazolyl)perfluorocyclopentene

Photochem. Photobiol. Sci., 2014, 13,764-769
DOI: 10.1039/C3PP50417D, Paper
Daichi Kitagawa, Seiya Kobatake
Rod-like crystals of a diarylethene derivative bent in the direction toward the incident UV light. The relationship between the initial speed and the crystal thickness can be well explained by Timoshenko's bimetal model.
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Quelle: RSC - Photochem. Photobiol. Sci. latest articles | 21 Jan 2014 | 1:00 am CET

N-Alkoxyheterocycles As Irreversible Photooxidants

Abstract

Irreversible photooxidation based on N–O bond fragmentation is demonstrated for N-methoxyheterocycles in both the singlet and triplet excited state manifolds. The energetic requirements for bond fragmentation are studied in detail. Bond fragmentation in the excited singlet manifold is possible for ππ* singlet states with energies significantly larger than the N–O bond dissociation energy of ca 55 kcal mol−1. For the * triplet states, N–O bond fragmentation does not occur in the excited state for orbital overlap and energetic reasons. Irreversible photooxidation occurs in the singlet states by bond fragmentation followed by electron transfer. Irreversible photooxidation occurs in the triplet states via bimolecular electron transfer to the donor followed by bond fragmentation. Using these two sensitization schemes, donors can be irreversibly oxidized with oxidation potentials ranging from ca 1.6–2.2 V vs SCE. The corresponding N-ethylheterocycles are characterized as conventional reversible photooxidants in their triplet states. The utility of these sensitizers is demonstrated by irreversibly generating the guanosine radical cation in buffered aqueous solution.

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The return or reverse electron transfer that occurs in the primary charge-separated pair that is a feature of all photoinduced electron transfer reactions wastes energy and competes with useful chemistry in the charge-separated species. Here, we describe photoinduced electron transfer schemes that made irreversible by using fragmentable sensitizers. The fragmentable sensitizers are N-methoxyheterocycles that cleave a relatively weak N–O bond in either their reduced or excited forms. Sensitization mechanisms in both the singlet and the triplet manifolds are described. Irreversible oxidation of guanosine is demonstrated as an illustrative example.

Quelle: Photochemistry and Photobiology | 17 Jan 2014 | 5:48 am CET

Photochemical Generation of 9H-Fluorenyl Radicals

Abstract

A series of 9-substituted fluorenols and 9,9′-disubstituted-9,9′-bifluorenyls were irradiated to give products derived from fluorenyl radicals. Product distribution was solvent dependent. A TEMPO adduct was isolated from the photoexcitation of 9-fluorenol. An unusual unsymmetrical 3,9′-bifluorenyl was observed from the photolysis of 9-trifluoromethylfluorenol and 9,9′-di(trifluoromethyl)-9,9′-bifluorenyl in more polar or hydrogen-bonding solvents. The electronic nature of 9-substituted fluorenyl radicals was probed using theoretical calculations showing the dipolar character of species with electron-deficient groups. These constitute the first examples of “doubly destabilized” radicals.

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Substituted 9-fluorenols and 9,9′-bifluorenyls undergo photolysis to give products derived from 9-fluorenyl radicals. These intermediates decay by hydrogen abstraction giving 9H-fluorenes, or coupling to 9,9′bifluorenyls. The 9-trifluoromethyl-9-fluorenyl radical undergoes an unusual coupling to the unsymmetrical 9,3′-bifluorenyl.

Quelle: Photochemistry and Photobiology | 10 Jan 2014 | 8:55 am CET

Effect of Light on Expression of Clock Genes in Xenopus laevis Melanophores

Abstract

Light-dark cycles are considered important cues to entrain biological clocks. A feedback loop of clock gene transcription and translation is the molecular basis underlying the mechanism of both central and peripheral clocks. Xenopus laevis embryonic melanophores respond to light with melanin granule dispersion, response possibly mediated by the photopigment melanopsin. In order to test whether light modulates clock gene expression in Xenopus melanophores, we used qPCR to evaluate the relative mRNA levels of Per1, Per2, Clock and Bmal1 in cultured melanophores exposed to light-dark (LD) cycle or constant darkness (DD). LD cycles elicited temporal changes in the expression of Per1, Per2 and Bmal1. A 10-min pulse of blue light was able to increase the expression of Per1 and Per2. Red light had no effect on the expression of these clock genes. These data suggest the participation of a blue-wavelength sensitive pigment in the light-dark cycle-mediated oscillation of the endogenous clock. Our results add an important contribution to the emerging field of peripheral clocks, which in non-mammalian vertebrates have been mostly studied in Drosophila and Danio rerio. Within this context, we show that Xenopus laevis melanophores, which have already led to melanopsin discovery, represent an ideal model to understanding circadian rhythms.

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Quelle: Photochemistry and Photobiology | 26 Dec 2013 | 1:09 pm CET

One-Component Thioxanthone Acetic Acid Derivative Photoinitiator for Free Radical Polymerization

Abstract

Acetic acid–based thioxanthone (TXCH2COOH) was synthesized and characterized and used as a photoinitiator for free radical photopolymerization of methyl methacrylate (MMA) in the absence and presence of a tertiary amine (MDEA) in different solvents. Different absorption properties were observed depending on the solvent. Fluorescence and phosphorescence experiments were also carried out successfully. The fluorescence quantum yield was found to be 0.09 and the phosphorescence lifetime was calculated as 138 ms at 77 K. The photoinitiator undergoes efficient intersystem crossing into the triplet state and the lowest triplet state possesses ππ* configuration. Laser flash photolysis experiments show that transient absorption of TXCH2COOH is similar to the parent thioxanthone and the triplet lifetime was calculated as 2.3 μs at 630 nm.

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Acetic acid based thioxanthone (TXCH2COOH) phototinitiator has two absorption bands 379 and 574 nm respectively and unusual absorption of TXCH2COOH makes very valuable as a photoinitiator. Fluorescence quantum yield was found as 0.09 and triplet lifetime was calculated as 2.3 μs. Initiation mechanism of TXCH2COOH based on intermolecular hydrogen abstraction followed by decarboxylation reaction, leads to production of initiating radicals for polymerization of acrylates and methacrylates.

Quelle: Photochemistry and Photobiology | 24 Dec 2013 | 6:48 am CET

Singlet Oxygen Generation by Cyclometalated Complexes and Applications

Abstract

While cyclometalated complexes have been extensively studied for optoelectronic applications, these compounds also represent a relatively new class of photosensitizers for the production of singlet oxygen. Thus far, singlet oxygen generation from cyclometalated Ir and Pt complexes has been studied in detail. In this review, photophysical data for singlet oxygen generation from these complexes are presented, and the mechanism of 1O2 generation is discussed, including evidence for singlet oxygen generation via an electron-transfer mechanism for some of cyclometalated Ir complexes. The period from the first report of singlet oxygen generation by a cyclometalated Ir complex in 2002 through August 2013 is covered in this review. This new class of singlet oxygen photosensitizers may prove to be rather versatile due to the ease of substitution of ancillary ligands without loss of activity. Several cyclometalated complexes have been tethered to zeolites, polystyrene, or quantum dots. Applications for photooxygenation of organic molecules, including “traditional” singlet oxygen reactions (ene reaction, [4 + 2] and [2 + 2] cycloadditions) as well as oxidative coupling of amines are presented. Potential biomedical applications are also reviewed.

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Cyclometalated complexes are a relatively new class of singlet oxygen sensitizers. They generally have high singlet oxygen quantum yields, and their absorption spectra can be fine-tuned by judicious choice of ancillary ligands. One of the main advantages of these complexes is the relative ease with which they can be attached to biomolecules, polymers and nanostructures.

Quelle: Photochemistry and Photobiology | 18 Dec 2013 | 11:25 am CET

Why is Rose Bengal More Phototoxic to Fibroblasts In Vitro Than In Vivo?

Abstract

Photosensitized protein cross-linking has been recently developed to seal wounds and strengthen tissue. Although the photosensitizing dye, Rose Bengal (RB), is phototoxic to cultured cells, cytotoxicity does not accompany RB-photosensitized tissue repair in vivo. We investigated whether the environment surrounding cells in tissue or the high irradiances used for photo–cross-linking inhibited RB phototoxicity. Fibroblasts (FB) grown within collagen gels to mimic a tissue environment and monolayer cultured FB were treated with RB (0.01–1 mm) and the high 532 nm laser irradiances used in vivo for tissue repair (0.10–0.50 W cm−2). Monolayer FB were substantially more sensitive to RB photosensitization: the LD50 was >200-fold lower than that in collagen gels. Collagen gel protection was associated with increased Akt phosphorylation, a prosurvival pathway. RB phototoxicity in collagen gels was 25-fold greater at low (0.030 W cm−2) that at high (0.50 W cm−2) irradiances. Oxygen depletion at high irradiance only partially accounted for the irradiance dependence of phototoxicity as replacing air with nitrogen only increased the LD50 by four-fold in monolayers. These results indicate that the lack of RB phototoxicity during in vivo tissue repair results from upregulation of prosurvival pathways in tissue cells, oxygen depletion and irradiance-dependent RB photochemistry.

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Rose Bengal (RB) is well known to cause phototoxicity by a singlet-oxygen mechanism to cultured cells. However, when we used RB photosensitization to seal wounds or stiffen tissue by cross-linking tissue collagen, the tissue cells were not killed. Using fibroblasts in collagen gels as a tissue model, we demonstrated that the cells are protected by upregulation of prosurvival pathways, depletion of oxygen and irradiance-dependent RB photochemistry.

Quelle: Photochemistry and Photobiology | 16 Dec 2013 | 12:30 pm CET

1H NMR Study of Hydrogen Abstraction in Model Compound Mimics of Polymers

Abstract

Small molecules representing common synthetic polymers were subjected to photochemically induced hydrogen abstraction by benzophenone. Reactions were monitored using 1H NMR to query the factors that influence preferential abstraction of protons in unique chemical environments. Differences in bond dissociation energies do not fully explain the observed hydrogen abstraction preferences. To that end, we identify contributions to abstraction from prereactive complexation, radical stability, steric effects and charge transfer effects. Using representative small molecule model compounds in lieu of polymeric materials is a novel approach to understanding photochemical reaction in polymers; however, it cannot probe the contributions of macromolecular effects—e.g. polymer rigidity or side chain and backbone mobility—to preferential hydrogen abstraction.

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Small molecules representing common synthetic polymers were subjected to photochemically induced hydrogen abstraction by benzophenone. Reactions were monitored using 1H NMR to query the factors that influence preferential abstraction of protons in unique chemical environments. Differences in bond dissociation energies do not fully explain the observed hydrogen abstraction preferences. Using representative small molecule model compounds in lieu of polymeric materials is a novel approach to understanding photochemical reaction in polymers; however, it cannot probe the contributions of macromolecular effects—e.g. polymer rigidity or side chain and backbone mobility—to preferential hydrogen abstraction.

Quelle: Photochemistry and Photobiology | 13 Dec 2013 | 7:50 am CET

Fluorescence Excitation Spectrum of Bilirubin in Blood: A Model for the Action Spectrum for Phototherapy of Neonatal Jaundice

Abstract

A recent report (Lamola et al. 2013 Pediatric Research, 74, 54–60) presents a semiempirical model for facile calculation of an action spectrum for bilirubin photochemistry in vivo using the most current knowledge of the optics of neonatal skin. The calculations indicate that competition for phototherapy light by hemoglobin in the skin is the predominant factor that defines the spectrum of light absorbed by bilirubin. If the latter is correct, a valid physical analog of the calculated spectrum is the excitation spectrum of bilirubin in blood. The fluorescence excitation spectrum was recorded and, indeed, found to be very similar to the calculated spectrum. Both spectra exhibit maxima near 476 nm and widths at half height of about 50 nm. This result supports the conclusion that light between 460 and 490 nm is most effective for phototherapy of neonatal jaundice.

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Not Too Blue and Not Too Green: Current knowledge of the optical properties of skin provides a model that predicts the action spectrum for phototherapy of neonatal jaundice to be relatively narrow and peaked near 475 nm. A physical analog, the fluorescence excitation spectrum of bilirubin in blood, is in agreement with the calculated action spectrum.

Quelle: Photochemistry and Photobiology | 10 Dec 2013 | 7:55 am CET

Computational Study of the Surface-Enhanced Raman Scattering from Silica-Coated Silver Nanowires

Abstract

Surface-enhanced Raman scattering (SERS) is a popular vibrational spectroscopic technique that can have several applications in chemical and biological sensing. Within the last decade or so, our ability to chemically synthesize nanostructures has improved to the point that the rational design of a variety of SERS substrates is now viable. In this report, we describe a computational study using the finite element method (FEM) to investigate the effects of patchy silica coatings on silver nanowires. We found that varying the degree of silica coating on silver nanowires impacts the enhancement and may be explained through two processes. The first process is a consequence of changes in the dielectric environment surrounding the nanowire due to the silica. As additional layers of silica coat the nanowire, the localized surface plasmon resonance of the nanowire redshifts. The second process is a result of silica distorting the local electric field around the nanowire surface. Anisotropic silica coating can influence anticipated enhancement depending on its spatial localization with respect to excited plasmon modes in the nanowire. We propose that the design of nanostructures with patchy silica coatings can be a viable tool for increasing surface enhancement.

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The surface-enhanced Raman scattering (SERS) characteristics of patchy silica-coated silver nanowires were investigated using the finite element method. Two processes govern the predicted electromagnetic enhancement. The first process is related to changes in the dielectric environment surrounding the nanowire due to the patchy silica coating. Silica layers cause the localized surface plasmon resonance of the nanowire to redshift, subsequently altering its optical properties. The second process is related to the distortion of the plasmonic fields caused by the silica. We propose that control over the placement and structure of patchy silica can be used to rationally design nanowire-based sensors.

Quelle: Photochemistry and Photobiology | 9 Dec 2013 | 5:19 am CET

Enzyme Activity and Structural Dynamics Linked to Micelle Formation: A Fluorescence Anisotropy and ESR Study

Abstract

Activities of the enzymes, protease subtilisin and horse radish peroxidase (HRP) have been increased 50 and 40%, respectively, in the presence of the nonionic surfactant, alkyl polyglucoside, compared with the activities in buffer alone. This enzyme hyperactivity reaches a peak at 3.0 mm of surfactant. Investigation into the structure of surfactant aggregates indicates “giant” micelle superstructures at this range of surfactant concentration of 1.7 μm in diameter—dramatically decreasing to 60 and 70 nm at higher surfactant concentrations, while surface tension measurements indicate two critical micelle concentration inflection points at 0.2 and 5.0 mm, which suggests transitions in micelle structure with respect to concentration. Furthermore, electron spin resonance (ESR) indicates that the micelles in first critical micelle concentration regime are loosely packed relative to the second aggregate phase. We hypothesize that this loose packing results in diminished hydration shell repulsion between the micelles, leading to the large, micrometer-sized aggregates. We further hypothesize that it is the interaction with these loosely packed micelles that affects the flexibility of the HRP and protease enzyme structure. Time-resolved fluorescence anisotropy of subtilisin in Brij-30 indicates increasing flexibility of catalytic active site with surfactant concentration. This is correlated with an increase in enzymatic activity.

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The activities of subtilisin protease and horse radish peroxidase (HRP) in the presence of the sugar-based surfactant alkyl polyglucoside have been increased relative to that of enzyme in buffer solution alone. The mechanism of this enhancement appears to be related to micelle aggregate structure. Surface tension, dynamic light scattering and electron spin resonance were used to elucidate the specific micelle conformations that induce the observed hyperactivity. Time-resolved fluorescence spectroscopy has also been used to investigate changes in the active site flexibility and has demonstrated greater structural mobility with surfactant concentration.

Quelle: Photochemistry and Photobiology | 5 Dec 2013 | 11:49 am CET

A Spectroscopic and Theoretical Investigation of a Free-Base meso-Trithienylcorrole

Abstract

The unique optical properties of free-base meso-tris(5-methylthien-2-yl)corrole were compared to those of the widely investigated meso-triphenyl-substituted analogue. A combination of spectroscopic and computational experiments was undertaken to elucidate the relationship between structural features of the neutral, mono-anionic and mono-cationic forms of the corroles and their corresponding optical properties. A general bathochromic shift was measured for the thienyl-substituted corrole. The experimental spectra are supported by excited state calculations. A systematic series of ground state minimizations were performed to determine energy minima for the flexible and solvent-sensitive molecules. Trithienylcorrole was found to have a more nonplanar macrocycle in conjunction with a high degree of π-overlap with the meso-substituents. Both structural features contribute to their bathochromically shifted optical spectra. The configurational character of the thienyl-substituted corrole is shown to have a larger degree of molecular orbital mixing and doubly excited character, which suggest a more complex electronic structure that does not fully adhere to the Gouterman four-orbital model. The reactivity of the thienyl groups, particularly with respect to their ability to be (electro)-polymerized, combined with the tight coupling of the meso-thienyl groups with the corrole chromophore elucidated in this work, recommends the meso-thienylcorroles as building blocks in, for instance, organic semiconductor devices.

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The unique optical properties of free-base meso-trithienylcorrole in its neutral, mono-anionic and mono-cationic forms were compared to those of the widely investigated meso-triphenyl-substituted analogue using a combination of spectroscopic and computational experiments. The generally bathochromically shifted spectra measured for the thienyl-substituted corrole were found to be due to a more nonplanar macrocycle conformation in conjunction with a high degree of π-overlap with the meso-substituents.

Quelle: Photochemistry and Photobiology | 5 Dec 2013 | 11:49 am CET

Effects of Light Energy and Reducing Agents on C60-Mediated Photosensitizing Reactions

Abstract

Many biomolecules contain photoactive reducing agents, such as reduced nicotinamide adenine dinucleotide (NADH) and 6-thioguanine (6-TG) incorporated into DNA through drug metabolism. These reducing agents may produce reactive oxygen species under UVA irradiation or act as electron donors in various media. The interactions of C60 fullerenes with biological reductants and light energy, especially via the Type-I electron-transfer mechanism, are not fully understood although these factors are often involved in toxicity assessments. The two reductants employed in this work were NADH for aqueous solutions and 6-TG for organic solvents. Using steady-state photolysis and electrochemical techniques, we showed that under visible light irradiation, the presence of reducing agents enhanced C60-mediated Type-I reactions that generate superoxide anion (O2.−) at the expense of singlet oxygen (1O2) production. The quantum yield of O2.− production upon visible light irradiation of C60 is estimated below 0.2 in dipolar aprotic media, indicating that the majority of triplet C60 deactivate via Type-II pathway. Upon UVA irradiation, however, both C60 and NADH undergo photochemical reactions to produce O2.−, which could lead to a possible synergistic toxicity effects. C60 photosensitization via Type-I pathway is not observed in the absence of reducing agents.

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The photosensitization pathways of C60 vary with the irradiation energy and reducing agents. C60/visible light-initiated Type-I reactions take place only in the presence of electron donors with the formation yield of superoxide anions below 0.2 in dipolar aprotic solvents. Under UVA irradiation, both C60 and UVA-active reducing agents may produce reactive oxygen species, leading to a synergistic toxicity.

Quelle: Photochemistry and Photobiology | 2 Dec 2013 | 1:29 pm CET

The Contribution of Reactive Oxygen Species to the Photobleaching of Organic Fluorophores

Abstract

Photoexcitation of fluorophores commonly used for biological imaging applications generates reactive oxygen species (ROS) which can cause bleaching of the fluorophore and damage to the biological system under investigation. In this study, we show that singlet oxygen contributes relatively little to Cy5 and ATTO 647N photobleaching at low concentrations in aqueous solution. We also show that Cy5 generates significantly less ROS when covalently linked to the protective agents, cyclooctatetraene (COT), nitrobenzyl alcohol (NBA) or Trolox. Such fluorophores exhibit enhanced photostability both in bulk solutions and in single-molecule fluorescence measurements. While the fluorophores ATTO 647N and ATTO 655 showed greater photostability than Cy5 and the protective–agent-linked Cy5 derivatives investigated here, both of ATTO 647N and ATTO 655 generated singlet oxygen and hydroxyl radicals at relatively rapid rates, suggesting that they may be substantially more phototoxic than Cy5 and its derivatives.

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Photoexcitation of fluorophores generates reactive oxygen species (ROS) which can cause bleaching of the fluorophore and damage to the biological system. We show that singlet oxygen contributes relatively little to Cy5 and ATTO 647N photobleaching at low concentrations in aqueous solution. We also show that Cy5 generates significantly less ROS when covalently linked to the protective agents, cyclooctatetraene (COT), nitrobenzyl alcohol (NBA) or Trolox. Such fluorophores exhibit enhanced photostability and generated less ROS than fluorophores that are commonly used, suggesting that they may be substantially less phototoxic than the common fluorophores.

Quelle: Photochemistry and Photobiology | 2 Dec 2013 | 1:29 pm CET

Theoretical Study of the Reaction Formalhydrazone with Singlet Oxygen. Fragmentation of the C=N Bond, Ene Reaction and Other Processes

Abstract

Photobiologic and synthetic versatility of hydrazones has not yet been established with 1O2 as a route to commonly encountered nitrosamines. Thus, to determine whether the “parent” reaction of formalhydrazone and 1O2 leads to facile C=N bond cleavage and resulting nitrosamine formation, we have carried out CCSD(T)//DFT calculations and analyzed the energetics of the oxidation pathways. A [2 + 2] pathway occurs via diradicals and formation of 3-amino-1,2,3-dioxazetidine in a 16 kcal/mol−1 process. Reversible addition or physical quenching of 1O2 occurs either on the formalhydrazone carbon for triplet diradicals at 2–3 kcal mol−1, or on the nitrogen (N(3)) atom forming zwitterions at ~15 kcal/mol−1, although the quenching channel by charge-transfer interaction was not computed. The computations also predict a facile conversion of formalhydrazone and 1O2 to hydroperoxymethyl diazene in a low-barrier ‘ene’ process, but no 2-amino-oxaziridine-O-oxide (perepoxide-like) intermediate was found. A Benson-like analysis (group increment calculations) on the closed-shell species are in accord with the quantum chemical results.

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Coupled cluster and density functional theory calculations were carried out for the formalhydrazone and 1O2 reaction to investigate C=N bond cleavage and N-nitrosamine formation. A 3-amino-1,2,3-dioxazetidine intermediate is found to arise from a [2 + 2] reaction that should rapidly collapse to N-nitrosamine and formaldehyde, but a lower activation energy is calculated for an ‘ene’ process to a hydroperoxymethyl diazene species. A minimum energy structure for the 2-amino-oxaziridine-O-oxide (perepoxide-like) intermediate was not located.

Quelle: Photochemistry and Photobiology | 2 Dec 2013 | 1:29 pm CET

Photophysics of Glycosylated Derivatives of a Chlorin, Isobacteriochlorin and Bacteriochlorin for Photodynamic Theragnostics: Discovery of a Two-photon-absorbing Photosensitizer

Abstract

The photophysical properties of a chlorin, isobacteriochlorin and bacteriochlorin built on a core tetrapentafluorophenylporphyrin (TPPF20) and the nonhydrolyzable para thioglycosylated conjugates of these chromophores are presented. The photophysical characterization of these compounds was done in three different solvents to correlate with different environments in cells and tissues. Compared with TPPF20 other dyes have greater absorption in the red region of the visible spectrum and greater fluorescence quantum yields. The excited state lifetimes are from 3 to 11 ns. The radiative and nonradiative rate constants for deactivation of the excited state were estimated from the fluorescence quantum yield and excited state lifetime. The data indicate that the bacteriochlorin has strong absorption bands near 730 nm and efficiently enters the triplet manifold. The isobacteriochlorin has a 40–70% fluorescence quantum yield depending on solvent, so it may be a good fluorescent tag. The isobacteriochlorins also display enhanced two-photon absorption, thereby allowing the use of 860 nm light to excite the compound. While the two-photon cross section of 25 GM units is not large, excitation of low chromophore concentrations can induce apoptosis. The glycosylated compounds accumulate in cancer cells and a head and neck squamous carcinoma xenograft tumor model in mice. These compounds are robust to photobleaching.

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Click-type chemistry allows tetraglycosylation of the perfluorophenyl derivatives of a chlorin, bacteriochlorin, and an isobacteriochlorin in high yields. The four non-hydrolysable sugars target the chromophores to mouse models of head and neck squamous cell carcinoma. Here the glycosylated chlorin allows fluorescence imaging of these tumors.

Quelle: Photochemistry and Photobiology | 28 Nov 2013 | 11:30 am CET

Interaction of H2@C60 and Nitroxide through Conformationally Constrained Peptide Bridges

Abstract

We synthesized two molecular systems, in which an endofullerene C60, incarcerating one hydrogen molecule (H2@C60) and a nitroxide radical are connected by a folded 310-helical peptide. The difference between the two molecules is the direction of the peptide orientation. The nuclear spin relaxation rates and the para → ortho conversion rate of the incarcerated hydrogen molecule were determined by 1H NMR spectroscopy. The experimental results were analyzed using DFT-optimized molecular models. The relaxation rates and the conversion rates of the two peptides fall in the expected distance range. One of the two peptides is particularly rigid and thus ideal to keep the H2@C60/nitroxide separation, r, as large and controlled as possible, which results in particularly low relaxation and conversion rates. Despite the very similar optimized distance, however, the rates measured with the other peptide are considerably higher and thus are compatible with a shorter effective distance. The results strengthen the outcome of previous investigations that while the para → ortho conversion rates satisfactorily obey the Wigner's theory, the nuclear spin relaxation rates are in excellent agreement with the Solomon–Bloembergen equation predicting a 1/r6 dependence.

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We synthesized two molecular systems, in which a nitroxide and an endofullerene C60, incarcerating one hydrogen molecule (H2@C60), are connected by a folded 310-helical peptide. Despite the similar apparent distance r, reversing the orientation of the peptide bridge significantly affects the nuclear spin relaxation rate and the para → ortho conversion rate of the incarcerated hydrogen molecule. Overall, the results strengthen the outcome of previous investigations that while the conversion rates satisfactorily obey the Wigner's theory, the relaxation rates are in excellent agreement with the Solomon–Bloembergen equation.

Quelle: Photochemistry and Photobiology | 28 Nov 2013 | 8:17 am CET

Oxidation of Plasmalogen, Low-Density Lipoprotein and RAW 264.7 Cells by Photoactivatable Atomic Oxygen Precursors

Abstract

The oxidation of lipids by endogenous or environmental reactive oxygen species (ROS) generates a myriad of different lipid oxidation products that have important roles in disease pathology. The lipid oxidation products obtained in these reactions are dependent upon the identity of the reacting ROS. The photoinduced deoxygenation of various aromatic heterocyclic oxides has been suggested to generate ground state atomic oxygen (O[3P]) as an oxidant; however, very little is known about reactions between lipids and O(3P). To identify lipid oxidation products arising from the reaction of lipids with O(3P), photoactivatable precursors of O(3P) were irradiated in the presence of lysoplasmenylcholine, low-density lipoprotein and RAW 264.7 cells under aerobic and anaerobic conditions. Four different aldehyde products consistent with the oxidation of plasmalogens were observed. The four aldehydes were: tetradecanal, pentadecanal, 2-hexadecenal and hexadecanal. Depending upon the conditions, either pentadecanal or 2-hexadecenal was the major product. Increased amounts of the aldehyde products were observed in aerobic conditions.

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The photodeoxygenation of dibenzothiophene S-oxide has been suggested to generate ground state atomic oxygen (O[3P]). The reactivity of the putative O(3P) is distinct from other reactive oxygen species (ROS) and little is known about its reactivity with lipids and other biomolecules. In this work, exposure of low-density lipoprotein (LDL) to O(3P) yielded four aldehyde products. The same aldehydes were observed after the oxidation of an isolated plasmalogen by O(3P).

Quelle: Photochemistry and Photobiology | 28 Nov 2013 | 8:16 am CET

A2E-Mediated Photochemical Modification to Fibronectin and its Implications to Age-Related Changes in Bruch's Membrane

Abstract

Lipofuscin accumulates normally with age and is more pronounced in retinal dystrophies such as age-related macular degeneration. The major bis-retinoid component of lipofuscin is A2E. In addition to cell damage effects by A2E, we have previously demonstrated that blue-light–mediated A2E leads to modifications in the basement membrane protein laminin. Therefore, the purpose of this study was to advance the understanding of A2E photooxidation effects on fibronectin, the major glycoprotein of Bruch's membrane. In this study, A2E was irradiated with blue light in the presence of a fibronectin peptide consisting of amino acids from the integrin binding region. The modification sites were identified via LC/MS. Our research indicated that blue light irradiation caused cleavage throughout the A2E molecule closest to the pyridinium ring, and attached to the fibronectin peptide preferentially at lysine and arginine residues. All of these reactions are similar to the Maillard reaction. Altogether this study suggests that blue-light–irradiated A2E modifies peptides and forms advance glycation endproducts. Furthermore, these results can be used to identify modifications that occur in Bruch's membrane in vivo.

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The bis-retinoid A2E is the major fluorophore in lipofuscin. Blue-light–irradiated A2E generates a variety of reactive aldehydes that alter the structure of fibronectin. The additions of A2E derived aldehydes resemble the Maillard reaction. These results can be used to identify similar modifications that occur in Bruch's membrane in vivo.

Quelle: Photochemistry and Photobiology | 28 Nov 2013 | 8:16 am CET

Transient Spectroscopy of 5,7-diiodo-3-butoxy-6-fluorone (DIBF)

Abstract

DIBF (5,7-diiodo-3-butoxy-6-fluorone) is a visible light photosensitizer for diaryliodonium salts, the latter being used in cationic photopolymerizations. Although photopolymerization of cycloaliphatic epoxide resins can be initiated by direct excitation of UV-absorbing diaryliodonium salts, such as (p-octyloxy)phenyliodonium hexafluoroantimonate (OPPI), the short wavelengths required cause some practical problems. Sensitizers, of which DIBF is among the best, obviate the deep UV problem by allowing visible-wavelength activation of the photoinitiator. Addition of 9,10-diethoxyanthracene (AN 910 E) dramatically accelerates photopolymerization under visible irradiation of the DIBF/OPPI system. We report herein the transient spectroscopy of the photosensitizer DIBF and discuss likely mechanisms for sensitization of OPPI.

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Transient absorption spectroscopy examines the role of DIBF as a visible light photosensitizer in cationic polymerization. Rapid intersystem crossing produces a reactive triplet state of DIBF, which subsequently activates an ultraviolet absorbing photoinitiator (OPPI). Addition of 9,10-diethoxyanthracene (AN 910 E) dramatically accelerates polymerization by facilitating the activation of OPPI from the triplet state of DIBF, although electron or energy transfer is too slow to observe within the 1 ns window of the experiment.

Quelle: Photochemistry and Photobiology | 25 Nov 2013 | 11:22 am CET

Brush-first and Click: Efficient Synthesis of Nanoparticles that Degrade and Release Doxorubicin in Response to Light

Abstract

New strategies for the synthesis of multifunctional particles that respond to external stimuli and release biologically relevant agents will enable the discovery of new formulations for drug delivery. In this article, we combine two powerful methods: brush-first ring-opening metathesis polymerization and copper-catalyzed azide–alkyne cycloaddition click chemistry, for the synthesis of a novel class of brush-arm star polymers (BASPs) that simultaneously degrade and release the anticancer drug doxorubicin (DOX) in response to 365 nm light. In vitro cell viability studies were performed to study the toxicity of azide- and DOX-loaded BASPs. The former were completely nontoxic. The latter showed minimal toxicity in the absence of light; UV-triggered DOX release led to IC50 values that were similar to that of free DOX.

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Brush-first ring-opening metathesis copolymerization of a poly(ethylene glycol) (PEG)-branch-alkyl chloride macromonomer with a photocleavable bis norbornene crosslinker leads to the formation of brush-arm star polymer (BASP) nanostructures with PEG coronas, photocleavable cores and alkyl chloride functionalities. Conversion of these chlorides to azides, followed by copper-catalyzed azide–alkyne ‘click’ conjugation of a caged doxorubicin (DOX)-alkyne derivative, yielded BASPs that simultaneously degrade and release DOX upon exposure to 365 nm light. These materials displayed low toxicity against MCF-7 human cancer cells in the absence of light; irradiation led to IC50 values similar to that of free DOX.

Quelle: Photochemistry and Photobiology | 25 Nov 2013 | 11:22 am CET

Coordination Chemistry-Assembled Multicomponent Systems Built from a Gable-Like Bis-Porphyrin: Synthesis and Photophysical Properties

Abstract

Multiporphyrinic assemblies were quantitatively formed, in one step, from a gable-like zinc(II) bis-porphyrin ZnP2 and free-base porphyrins bearing pyridyl groups. The different fragments are held together by axial 4′-N(pyridyl)–Zn interactions. Formation of a macrocycle ZnP2•(4′-cisDPyP) and a bis-macrocycle (ZnP2)2•(TPyP) is discussed. The macrocycle and the bis-macrocycle were crystallized and studied by X-ray diffraction, which confirmed the excellent complementarity between the various components. Spectrophotometric and spectrofluorimetric titrations and studies reveal high association constants for both multiporphyrinic assemblies due to the almost perfect geometrical match between the interacting units. As expected, energy transfer from the zinc porphyrin component to the free-base porphyrin quenches the fluorescence of the zinc porphyrin components in both compounds. But while in ZnP2•(4′-cis DPyP) sensitization of the emission of the free-base porphyrin was observed, in (ZnP2)2•(TPyP) excitation of the peripheral Zn porphyrin units does not lead to quantitative sensitization of the luminescence of the free-base porphyrin acceptor. An unusual HOMO–HOMO electron transfer reaction from ZnP2 to the excited TPyP unit was detected and studied.

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Various noncovalent multiporphyrinic assemblies could be built from a gable-like bis-Zn porphyrin. Both energy and electron transfer processes have been characterized in these assemblies. In the three-component system, unusual electron transfer from a Zn porphyrin to a free-base porphyrin was evidenced.

Quelle: Photochemistry and Photobiology | 30 Oct 2013 | 12:11 pm CET

Synthesis, Characterization, Photophysics and Photochemistry of Pyrylogen Electron Transfer Sensitizers

Abstract

A series of new dicationic sensitizers that are hybrids of pyrylium salts and viologens has been synthesized. The electrochemical and photophysical properties of these “pyrylogen” sensitizers are reported in sufficient detail to allow rationale design of new photoinduced electron transfer reactions. The range of their reduction potentials (+0.37–+0.05 V vs SCE) coupled with their range of singlet (48–63 kcal mol−1) and triplet (48–57 kcal mol−1) energies demonstrate that they are potent oxidizing agents in both their singlet and triplet excited states, thermodynamically capable of oxidizing substrates with oxidation potentials as high as 3.1 eV. The pyrylogens are synthesized in three steps from readily available starting materials in modest overall 11.4–22.3% yields. These sensitizers have the added advantages that: (1) their radical cations do not react on the CV timescale with oxygen bypassing the need to run reactions under nitrogen or argon and (2) have long wavelength absorptions between 413 and 523 nm well out of the range where competitive absorbance by most substrates would cause a problem. These new sensitizers do react with water requiring special precautions to operate in a dry reaction environment.

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Hybrids of pyrylium salts and viologens photochemically generate radical-cation/radical-cation pairs with substantial intra-ion repulsion that increases the rate constant of separation, kSEP, and competitively inhibits energy wasting return electron transfer. These first representatives of dicationic charge-shift sensitizers generate radical cations that do not react with oxygen on the CV timescale and absorb between 413 and 523 nm well outside the range where competitive absorbance by most substrates would cause a problem.

Quelle: Photochemistry and Photobiology | 30 Oct 2013 | 12:11 pm CET

Immobilized Organic Photosensitizers with Versatile Reactivity for Various Visible-Light Applications

Abstract

Various photosensitizers were grafted by conventional peptide coupling methods to functionalized silica with several macroscopic shapes (powders, films) or embedded in highly transparent and microporous silica xerogel monoliths. Owing to the transparency and free-standing shape of the monoliths, the transient species arising from irradiation of the PSs could be analyzed and were not strikingly different from those observed in solutions. The observed reactivity for either liquid–solid (α-terpinene oxygenation vs dehydrogenation) or gas–solid (dimethylsulfide, DMS, solvent-free oxidation) reactions was consistent with the properties of the excited states of the PSs under consideration. Immobilized anthraquinone-derived materials preferentially react in both cases by electron transfer from the substrate to the triplet state of the sensitizer, in spite of an efficient singlet oxygen production. The recently developed 9,14-dicyanobenzo[b]triphenylene-3-carboxylic acid, DBTP-COOH, efficiently reacts via energy transfer to yield singlet oxygen from its triplet state. It was shown to perform better than 9,10-dicyanoanthracene and rose bengal for DMS oxidation and α-terpinene photooxygenation to ascaridole, respectively. Thus, by a proper choice of the organic immobilized photocatalyst, it is possible to develop efficient and reusable materials, activated under visible light, for various applications and to tune the reaction pathway, opening the way to green oxidation processes.

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The properties and applications of several silica materials, containing anthraquinone and cyanoanthracene derivatives as photosensitizers, have been investigated. Besides the photochemistry results, either for liquid α-terpinene or gaseous dimethylsulfide oxidation, the direct detection of the transient species and the determination of singlet oxygen lifetimes and quantum yields in highly transparent and porous silica monoliths were carried out. This overview allows a critical comparison of the properties of the sensitizers, and of various silica macrostructurations. The visible-light activity of these easily prepared materials opens the route to tunable green photochemistry.

Quelle: Photochemistry and Photobiology | 25 Oct 2013 | 2:17 pm CEST

Aliphatic β-Nitroalcohols for Therapeutic Corneoscleral Cross-Linking: Chemical Stability Studies Using 1H-NMR Spectroscopy

Abstract

Recent studies suggest that aliphatic β-nitro alcohols may represent a useful class of compounds for use as in vivo therapeutic corneoscleral cross-linking agents with higher order nitroalcohols (HONAs) showing enhanced efficacy over the mono-nitroalcohols. The current study was undertaken in order to evaluate the chemical stability of these compounds during storage conditions. Two mono-nitroalcohols (2-nitroethanol=2ne and 2-nitro-1-propanol=2nprop) and two HONAs, a nitrodiol (2-methyl-2-nitro-1,3-propanediol=MNPD), and a nitrotriol (2-hydroxymethyl-2-nitro-1,3-propanediol=HNPD) were monitored for chemical stability by 1H-NMR for up to 7 months. Each compound was studied at two concentrations (1% and 10%) either in unbuffered H2O or 0.2 m NaH2PO4/Na2HPO4 (pH=5), and at 0°C and room temperature (RT) for a total of eight conditions for each compound. The 1H-NMR spectra for the starting material were compared to subsequent spectra. Under all four of the conditions studied, both the nitrodiol (MNPD) and nitrotriol (HNPD) were stable for the duration of 7 months. 2nprop became unstable under all conditions at 3 months. 2ne was the most unstable of all the compounds tested. HONAs exhibit excellent chemical stability under long-term storage conditions. In contrast, the nitromonols tested are significantly less stable. These findings are relevant to the translation of this technology into clinical use.

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Certain β-nitroalcohols undergo a base-catalyzed thermally driven retronitroalcohol reaction to give formaldehyde under physiologic conditions. Because they also exhibit a favorable safety profile (unlike free formaldehyde), they represent a potentially useful class of agents for clinical therapeutic corneoscleral tissue cross-linking. In this brief report, compound stability under long-term storage conditions was studied in anticipation of clinical translation of this potential treatment modality. Higher order nitroalcohols (a nitrodiol and nitrotriol) were found to be significantly more stable than their mononitroalcohol counterparts.

Quelle: Photochemistry and Photobiology | 21 Oct 2013 | 7:52 am CEST

Decay Kinetics of Benzophenone Triplets and Corresponding Free Radicals in Soft and Rigid Polymers Studied by Laser Flash Photolysis

Abstract

The kinetics of transients formed under photoexcitation of benzophenone (B) dissolved in three different polymers was studied by ns laser flash photolysis. These polymers were the soft rubbers poly (ethylene-co-butylene) (EB), polystyrene block-poly(ethylene-ran-butylene)-block-polystyrene (SEBS) and hard polystyrene (PS). We monitored the decay kinetics of triplet state 3B*and of ketyl radicals BH. We observed exponential decay of 3B* and two-stage decay kinetics of BHin EB. The first stage is a fast cage recombination of a radical pair (BH, radical of polymer R). The second slow stage of BH decay follows the second-order law with a relatively high rate constant, which corresponds to recombination of BH in a homogeneous liquid with a viscosity of only ~0.1 P (about five times of 2-propanol viscosity). Application of a magnetic field (MF) of 0.2 T leads to deceleration of both stages of BH decay in EB by approximately 20%. Decay kinetics of both transients were observed in SEBS. There was no MF effect on BH decay in SEBS. We only observed 3B* in PS. Decay kinetics of 3B* in this case were described as polychromatic dispersive first-order kinetics. We discuss the effects of polymer structure on transient kinetics and the MF effect.

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The kinetics of transients formed under photoexcitation of benzophenone (B) dissolved in two soft rubbery polymers and hard polystyrene was studied by ns laser flash photolysis. We observed exponential decay of 3B* and two-stage decay kinetics of BHin poly(ethylene-co-butylene) (EB). The first stage is a fast cage recombination of a radical pair (BH, radical of polymer R). Application of a magnetic field (MF) of 0.2 T leads to deceleration of both stages of BH decay in EB by approximately 20%. We discuss the effects of polymer structure on transients kinetics and the MF effect.

Quelle: Photochemistry and Photobiology | 19 Oct 2013 | 8:55 am CEST

Visualizing Carbene Equilibria

Abstract

Reviewed herein are equilibria between halocarbenes and halocarbanions, carbenes and carbene complexes and carbenes and O-ylides. The transient species were visualized by laser flash photolysis coupled with UV–Visible spectroscopy. This methodology enabled the determination of equilibrium constants and the extraction of associated thermodynamic parameters. Parallel computational studies provided anticipated structures and energies for the transient species, as well as electronic absorption wavelengths and oscillator strengths.

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Laser flash photolysis UV–Vis spectrum of phenylchlorocarbene (PhCCl) in 0.75 mm trimethoxybenzene/pentane solution 50 ns after the laser flash. PhCCl absorptions are at 324 and 596 nm. The absorption of the PhCCl-trimethoxybenzene π complex is at 484 nm.

Quelle: Photochemistry and Photobiology | 30 Jul 2013 | 12:17 pm CEST




 


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