title: Stereoselective Photoinduced Electron-Transfer Reactions of Zinc Myoglobin with Optically Active Viologens.
abstract: Photoinduced electron-transfer reactions between zinc-substituted myoglobin and optically active viologens and bisviologens, containing ((naphthyl-, ((phenyl-, and ((cyclohexyl)ethyl)carbamoyl)methyl groups, have been studied at 25 degrees C, pH 7.0 (a 0.01 M phosphate buffer), and various ionic strengths. The excited triplet state of zinc myoglobin was preferentially quenched by (S,S)-isomers of optically active viologens; both ratios of the quenching rate constants and back-electron-transfer rate constants, k((S,S))/k((R,R)), range from 1.1 to 1.5 at an ionic strength of 0.02 M with the order naphthyl > phenyl >/= cyclohexyl for the substituents. Stereoselectivity decreased with increasing ionic strengths. The steric bulk of the substituents of viologen may induce the conformational change of zinc myoglobin more effectively due to the steric repulsion between naphthyl groups and the polypeptide chain of zinc myoglobin.
authors.affiliation: Department of Chemistry, Faculty of Science, Nara Women's University, Nara 630, Japan.
authors.forename: Keiichi
authors.initials: K
authors.lastname: Tsukahara
authors.forename: Chieko
authors.initials: C
authors.lastname: Kimura
authors.forename: Junko
authors.initials: J
authors.lastname: Kaneko
authors.forename: Kaya
authors.initials: K
authors.lastname: Abe
authors.forename: Miho
authors.initials: M
authors.lastname: Matsui
authors.forename: Tomoko
authors.initials: T
authors.lastname: Hara