Pheophytinization kinetics of chlorophyll c under weakly acidic conditions: Effects of acrylic acid residue at the 17-position

Pheophytinization of chlorophyll (Chl) c1, which was isolated from the diatom Chaetoceros gracilis, was kinetically analyzed under weakly acidic conditions, and was compared with that of protochlorophyllide (PChlide) a and chlorophyllide (Chlide) a. Chl c1 possessing a trans-acrylic acid residue at the 17-position exhibited slower pheophytinization kinetics than PChlide a and Chlide a, both of which possessed a propionic acid residue at the same position. The difference in pheophytinization properties between Chl c1 and (P)Chlide a was ascribable to the electronegativity of the 17-substituent in Chl c1 larger than that of (P)Chlide a due to the C171-C172 double bond with the conjugated 172-carboxy group in Chl c1. Demetalation kinetics of PChlide a was slower than that of Chlide a, which originated from the effect of the π-macrocyclic structures.