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Structure‐Dependent Demetalation Kinetics of Chlorophyll a Analogs under Acidic Conditions
Author(s) -
Saga Yoshitaka,
Hirai Yuki,
Sadaoka Kana,
Isaji Megumi,
Tamiaki Hitoshi
Publication year - 2012
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.1751-1097.2012.01213.x
Subject(s) - kinetics , chemistry , porphyrin , chlorophyll , photochemistry , photosynthesis , chlorophyll a , substituent , photosystem ii , pigment , stereochemistry , biochemistry , organic chemistry , physics , quantum mechanics
Demetalation of chlorophyll ( Chl ) a and its analogs is an important reaction in oxygenic photosynthetic organisms, which produces the primary electron acceptors in photosystem II reaction centers and is crucial in the Chl degradation. From these viewpoints, demetalation reactions of four Chl a analogs, 3,8‐divinyl‐ Chl a ( DV ‐ Chl a ), 3‐devinyl‐3‐ethyl‐ Chl a (meso Chl a ), 13 2 ‐demethoxycarbonyl‐ Chl a (pyro Chl a ) and protochlorophyll a ( PChl a ), were kinetically analyzed under weakly acidic conditions, and were compared with that of Chl a . DV ‐ Chl a exhibited slower demetalation kinetics than did Chl a , whereas demetalation of meso Chl a was faster than that of Chl a . The difference in demetalation kinetics of the three chlorophyllous pigments originates from the electron‐withdrawing ability of the vinyl group as the peripheral substituent compared with the ethyl group. Removal of the electron‐withdrawing and homoconjugating 13 2 ‐methoxycarbonyl group in Chl a ( Chl a → pyro Chl a ) accelerated demetalation kinetics by two‐fold. PC hl a possessing the porphyrin‐type skeleton exhibited slower demetalation kinetics than Chl a . The structure‐dependent demetalation properties of Chl a analogs will be useful for understanding in vivo Chl demetalation reactions in oxygenic photosynthetic organisms.