Stevens researchers provide new information about mass spectrometry
Report from Attygalle and colleagues in Center for
Mass Spectrometry.
HOBOKEN, N.J. - Fresh data on mass spectrometry
are presented in the report �Low-energy collision-induced fragmentation
of negative ions derived from ortho-, meta-, and para-hydroxyphenyl
carbaldehydes, ketones, and related compounds,� produced by Professor
Athula Attygalle and his colleagues in the Center for Mass Spectrometry
at Stevens Institute of Technology.
According to a study, �Collision-induced dissociation (CID) mass
spectra of anions derived from several hydroxyphenyl carbaldehydes and
ketones were recorded and mechanistically rationalized. For example,
the spectrum of m/z 121 ion of deprotonated ortho-hydroxybenzaldehyde
shows an intense peak at m/z 93 for a loss of carbon monoxide
attributable to an ortho-effect mediated by a charge-directed
heterolytic fragmentation mechanism.�
�In contrast, the m/z 121 ion derived from meta and para isomers
undergoes a charge-remote homolytic cleavage to eliminate an *H and
form a distonic anion radical, which eventually loses CO to produce a
peak at m/z 92. In fact, for the para isomer, this two-step homolytic
mechanism is the most dominant fragmentation pathway. The spectrum of
the meta isomer on the other hand, shows two predominant peaks at m/z
92 and 93 representing both homolytic and heterolytic fragmentations,
respectively. (18)O-isotope-labeling studies confirmed that the oxygen
in the CO molecule that is eliminated from the anion of
meta-hydroxybenzaldehyde originates from either the aldehydic or the
phenolic group. In contrast, anions of ortho-hydroxybenzaldehyde and
2-hydroxy-1-naphthaldehyde, both of which show two consecutive CO
eliminations, specifically lose the carbonyl oxygen first, followed by
that of the phenolic group. Anions from 2-hydroxyphenyl alkyl ketones
lose a ketene by a hydrogen transfer predominantly from the alpha
position. Interestingly, a very significant charge-remote
1,4-elimination of a H(2) molecule was observed from the anion derived
from 2,4-dihydroxybenzaldehyde,� wrote Attygalle and his colleagues
from Stevens.
The researchers concluded: �For this mechanism to operate, a labile
hydrogen atom should be available on the hydroxyl group adjacent to
the carbaldehyde functionality.�
Further Information and Source:
-
Athula B. Attygalle, Josef Ruzicka, Deepu Varughese, Jason B.
Bialecki, Sayed Jafri: Low-energy collision-induced fragmentation of negative ions
derived from ortho-, meta-, and para-hydroxyphenyl carbaldehydes,
ketones, and related compounds.
In: Journal of Mass Spectrometry;
Volume 42, Issue 9, Date: September 2007, Pages: 1207-1217; doi;
10.1002/jms.1252