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PHOTOREDUCTION OF ZINC PORPHIN BY ASCORBIC ACID*
Author(s) -
Seely G.R.,
Talmadge K.
Publication year - 1964
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.1751-1097.1964.tb08775.x
Subject(s) - porphin , chlorin , chemistry , zinc , photochemistry , tetrapyrrole , ascorbic acid , autocatalysis , pyrrole , amine gas treating , redox , inorganic chemistry , organic chemistry , photosensitizer , porphyrin , catalysis , food science , enzyme
— Zinc porphin is photoreduced to zinc chlorin through an intermediate dihydroporphin (PH 2 ) by ascorbic acid in ethanol containing 1% to 10% (v/v) piperidine. Under the same conditions zinc chlorin is more slowly photoreduced to zinc tetrahydroporphin. The reactions leading to chlorin are photosensitized by the product chlorin and so are autocatalytic in red light. Quantum yields for these reactions range up to 0.05.Other aliphatic amines catalyze these reactions, but at rates peculiar to the amine. The immediate product of reduction of zinc porphin, PH 2 , is distinguished by an intense band at 437 nm; it reverts to porphin in the dark in the presence of oxygen or dehydroascorbic acid. Its conversion to chlorin is effected by light absorbed by porphin or chlorin, but not by light absorbed by PH 2 itself. A suggested structure for PH 2 , compatible with the observed reactions, has added hydrogens on one bridge carbon and one β‐pyrrole carbon. The possibility of an analogy between these reactions and the biochemical conversion of protochlorophyll to chlorophyll is discussed.