title: Demetalation kinetics of natural chlorophylls purified from oxygenic photosynthetic organisms: effect of the formyl groups conjugated directly to the chlorin pi-macrocycle.
abstract: Demetalation kinetics of natural chlorophyll (Chl) d purified from Acaryochloris marina was first studied and compared with those of Chls a and b. The demetalation rate constant of Chl d, which possessed a formyl group at the 3-position, was five-fold smaller than that of Chl a possessing a vinyl group at the same position in aqueous acetone at the proton concentration of 1.2 x 10(-3) M at 25 degrees C. In contrast, the demetalation rate constant of Chl b possessing a formyl group at the 7-position was 26 times smaller than that of Chl a. The activation energy of demetalation reaction of Chl d was larger than that of Chl a, but smaller than that of Chl b. These indicate that the substitution effect of 3-formyl group on the acidic removal of central magnesium in Chls was smaller than that of 7-formyl group.
authors.affiliation: Department of Chemistry, Faculty of Science and Engineering, Kinki University, Higashi-Osaka, Osaka 577-8502, Japan.
authors.forename: Yuki
authors.initials: Y
authors.lastname: Hirai
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* / Q000302:isolation & purification; D000077194:Chlorophyll A; D000458:Cyanobacteria / Q000737:chemistry*; D007700:Kinetics; D008274:Magnesium / Q000737:chemistry*; D010788:Photosynthesis; D011166:Porphyrins / Q000737:chemistry*; D013053:Spectrophotometry
chemical_list: D011166:Porphyrins; D002734:Chlorophyll; C006969:chlorin; C037184:chlorophyll b; C107509:chlorophyll d; D008274:Magnesium; D000077194:Chlorophyll A