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PHOTOSENSITIZATION BY PHENYLALANINE OF CARBOXYLIC ACIDS, AMIDES, AND PEPTIDES IN FROZEN AQUEOUS SOLUTION *
Author(s) -
MEYBECK A.,
MEYBECK J.
Publication year - 1972
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1972.tb06305.x
Subject(s) - chemistry , radical , amide , phenylalanine , aqueous solution , electron paramagnetic resonance , photochemistry , amino acid , hydrogen atom abstraction , alkyl , carboxylic acid , organic chemistry , aromatic amino acids , biochemistry , physics , nuclear magnetic resonance
— In order to elucidate the mechanism of the photosensitization of proteins and peptides by aromatic amino acids, the behaviour of aliphatic carboxylic acids and amides upon irradiation in frozen aqueous solution in the presence of phenylalanine (l‐Phe) has been studied by EPR spectroscopy. EPR signals are much stronger when acids or amides are irradiated in the presence of l‐Phe, showing that they are photosensitized by the aromatic amino acid. The species observed are either alkyl radicals, or radicals formed by abstraction of a hydrogen atom from a molecule of acid or arnide. A mechanism is proposed which involves the capture by carboxyl or amide carbonyl groups of hydrated electrons released by the photo‐excited l‐Phe, followed by the splitting of the resulting anion free radical with the formation of alkyl radicals, and transfer reactions leading to more stable free radicals. In peptides, which are also photosensitized by l‐Phe, electrons are captured preferably by the carboxylic carbonyl groups.