title: Effects of molecular structures on reduction properties of formyl groups in chlorophylls and pheophytins prepared from oxygenic photosynthetic organisms.
abstract: Reduction of the 7-formyl groups in chlorophyll (Chl) b and its demetalated compound pheophytin (Phe) b was kinetically analyzed by using tert-butylamine-borane complex (t-BuNH(2)·BH(3)), and was compared with that of the 3-formyl groups in Chl d and Phe d. Reduction kinetics of the 7-formyl group in Chl b was similar to that in Phe b in dichloromethane containing 5mM t-BuNH(2)·BH(3). Little difference of the reduction kinetics of the 7-formyl groups between Chl b and Phe b was in sharp contrast to the reduction kinetics of the 3-formyl groups in Chl d and Phe d: the 3-formyl group in Phe d was reduced 5.3-fold faster than that in Chl d. The 7-formyl groups in Chl b and Phe b were reduced more slowly than the 3-formyl groups in Chl d and Phe d, respectively. The difference of the reactivity between the 3- and 7-formyl groups was in line with (13)C NMR measurements of chlorophyllous pigments, in which the chemical shifts of carbon atoms in the 7-formyl groups of Chl b and Phe b were high-field shifted compared with those in the 3-formyl groups of Chl d and Phe d, respectively. These indicate that the 7-formyl groups in chlorophyllous pigments were less reactive for reduction to the corresponding hydroxymethyl groups than the 3-formyl groups due to the difference in electronic states of the formyl groups in the A- and B-rings of the chlorin macrocycle.
authors.affiliation: Department of Chemistry, Faculty of Science and Engineering, Kinki University, Higashi-Osaka, Osaka, Japan.
authors.forename: Kana
authors.initials: K
authors.lastname: Sadaoka
authors.forename: Shigenori
authors.initials: S
authors.lastname: Kashimura
authors.forename: Yoshitaka
authors.initials: Y
authors.lastname: Saga
mesh_terms: D001880:Boranes / Q000737:chemistry; D002082:Butylamines / Q000737:chemistry; D002734:Chlorophyll / Q000737:chemistry*; D000458:Cyanobacteria / Q000737:chemistry*; D005561:Formates / Q000737:chemistry; D007700:Kinetics; D008968:Molecular Conformation; D010084:Oxidation-Reduction; D010674:Pheophytins / Q000737:chemistry*; D018724:Spinacia oleracea / Q000737:chemistry*
chemical_list: D001880:Boranes; D002082:Butylamines; D005561:Formates; D010674:Pheophytins; C030544:formic acid; D002734:Chlorophyll; C037184:chlorophyll b; C107509:chlorophyll d; C025397:tert-butylamine