title: Demetalation kinetics of chlorophyll derivatives possessing different substituents at the 7-position under acidic conditions.
abstract: Conversion of the formyl group at the 7-position in chlorophyll (Chl) b to the methyl group via the hydroxymethyl group is biologically important in Chl b degradation. To clarify the effects of the 7-substituents on demetalation properties of chlorophyllous pigments in the early process of Chl b degradation, we report demetalation kinetics of the zinc Chl derivative possessing a 7-hydroxymethyl group, which is a good model compound of the intermediate molecule in the early process of Chl b degradation, under acidic conditions, and compare its properties with those of zinc Chl derivatives possessing a methyl and a formyl group, which are model compounds of Chls a and b, respectively. Demetalation rate constants of 7-hydroxymethyl zinc chlorin were much larger than those of 7-formyl zinc chlorin, but were slightly smaller than those of 7-methyl zinc chlorin. The activation energy for demetalation reaction of 7-formyl zinc chlorin was larger than those of other derivatives. Demetalation rate constants of 7-deformyl-7-hydroxymethyl Chl b were also larger than those of Chl b, and were similar to those of Chl a. These indicate that the 7-hydroxymethyl group in the chlorin macrocycle has a smaller effect on demetalation compared with the 7-formyl group.
authors.affiliation: Department of Chemistry, Faculty of Science and Engineering, Kinki University, Higashi-Osaka, Osaka, Japan.
authors.forename: Yuki
authors.initials: Y
authors.lastname: Hirai
authors.forename: Shigenori
authors.initials: S
authors.lastname: Kashimura
authors.forename: Yoshitaka
authors.initials: Y
authors.lastname: Saga
mesh_terms: D000143:Acids / Q000737:chemistry; D002734:Chlorophyll / Q000737:chemistry* / Q000145:classification / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D015394:Molecular Structure; D011166:Porphyrins / Q000737:chemistry / Q000378:metabolism; D015032:Zinc / Q000737:chemistry*
chemical_list: D000143:Acids; D011166:Porphyrins; D002734:Chlorophyll; C006969:chlorin; D015032:Zinc