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

Abstract Pheophytinization of chlorophyll (Chl) c 1 , 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 c 1 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 c 1 and (P)Chlide a was ascribable to the electronegativity of the 17-substituent in Chl c 1 larger than that of (P)Chlide a due to the C17 1 –C17 2 double bond with the conjugated 17 2 -carboxy group in Chl c 1 . Demetalation kinetics of PChlide a was slower than that of Chlide a , which originated from the effect of the π-macrocyclic structures.