title: Redox potential of chlorophyll d in vitro.
abstract: Chlorophyll (Chl) d is a major chlorophyll in a novel oxygenic prokaryote Acaryochloris marina. Here we first report the redox potential of Chl d in vitro. The oxidation potential of Chl d was +0.88 V vs. SHE in acetonitrile; the value was higher than that of Chl a (+0.81 V) and lower than that of Chl b (+0.94 V). The oxidation potential order, Chl b>Chl d>Chl a, can be explained by inductive effect of substituent groups on the conjugated pi-electron system on the macrocycle. Corresponding pheophytins showed the same order; Phe b (+1.25 V)>Phe d (+1.21 V)>Phe a (+1.14 V), but the values were significantly higher than those of Chls, which are rationalized in terms of an electron density decrease in the pi-system by the replacement of magnesium with more electronegative hydrogen. Consequently, oxidation potential of Chl a was found to be the lowest among Chls and Phes. The results will help us to broaden our views on photosystems in A. marina.
authors.affiliation: Institute of Materials Science, University of Tsukuba, Tsukuba 305-8573, Japan. masami@ims.tsukuba.ac.jp
authors.forename: Masami
authors.initials: M
authors.lastname: Kobayashi
authors.forename: Shunsuke
authors.initials: S
authors.lastname: Ohashi
authors.forename: Koji
authors.initials: K
authors.lastname: Iwamoto
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Shiraiwa
authors.forename: Yuki
authors.initials: Y
authors.lastname: Kato
authors.forename: Tadashi
authors.initials: T
authors.lastname: Watanabe
mesh_terms: D000097:Acetonitriles / Q000737:chemistry; D002734:Chlorophyll / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D000077194:Chlorophyll A; D000458:Cyanobacteria / Q000737:chemistry; D004126:Dimethylformamide / Q000737:chemistry; D004563:Electrochemistry / Q000379:methods; D066298:In Vitro Techniques; D008956:Models, Chemical; D015394:Molecular Structure; D010084:Oxidation-Reduction; D028528:Petroselinum / Q000737:chemistry; D010674:Pheophytins / Q000737:chemistry / Q000378:metabolism; D012997:Solvents / Q000737:chemistry
chemical_list: D000097:Acetonitriles; D010674:Pheophytins; D012997:Solvents; D002734:Chlorophyll; C037184:chlorophyll b; C107509:chlorophyll d; D004126:Dimethylformamide; D000077194:Chlorophyll A; C032159:acetonitrile