title: Substitution effects in the A- and B-rings of the chlorin macrocycle on demetalation properties of zinc chlorophyll derivatives.
abstract: Effects of peripheral substituents in the A- and B-rings of the chlorin macrocycle on demetalation of zinc chlorophyll derivatives were examined. The demetalation rate constants of zinc 8-formyl-chlorin (1) were comparable to those of zinc 3-formyl-chlorin (2). Both 1 and 2 exhibited significantly slower demetalation kinetics than the corresponding zinc chlorin 3, which had no formyl group. Comparison of demetalation kinetics between zinc 3-ethyl-chlorin (3) and zinc 3-vinyl-chlorin (4) indicated that the substitution at the 3-position of the chlorin macrocycle from a vinyl to an ethyl group accelerated removal of the central zinc. Activation energies of demetalation of zinc chlorins 1, 2, and 5 possessing a formyl group in the A- or B-ring of the chlorin macrocycle were larger than those of zinc chlorins 3 and 4 lacking a formyl group. These results indicate that the formyl groups in the A- or B-ring provide tolerance to demetalation of chlorin molecules due to their electron-withdrawing effects.
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: Shin-ichi
authors.initials: S
authors.lastname: Sasaki
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Tamiaki
authors.forename: Shigenori
authors.initials: S
authors.lastname: Kashimura
authors.forename: Yoshitaka
authors.initials: Y
authors.lastname: Saga
mesh_terms: D002734:Chlorophyll / Q000737:chemistry*; D007700:Kinetics; D009942:Organometallic Compounds / Q000737:chemistry*; D011166:Porphyrins / Q000737:chemistry*; D013057:Spectrum Analysis; D013696:Temperature; D015032:Zinc / Q000737:chemistry*
chemical_list: D009942:Organometallic Compounds; D011166:Porphyrins; D002734:Chlorophyll; C006969:chlorin; D015032:Zinc