title: Stereochemical determination of chlorophyll-d molecule from Acaryochloris marina and its modification to a self-aggregative chlorophyll as a model of green photosynthetic bacterial antennae.
abstract: Acaryochloris marina is a unique photosynthetic prokaryote containing chlorophyll(Chl)-d as a major photoactive pigment (over 95%). The molecular structure of Chl-d is proposed as the 3-formyl analog of Chl-a. However, the stereochemistry of Chl-d at the 13(2)-, 17- and 18-positions has not yet been established unambiguously. In the first part of this paper, we describe the determination of their stereochemistries to be 13(2)-(R)-, 17-(S)- and 18-(S)-configurations by using 1H-1H NOE correlations in 1H-NMR and circular dichroism spectra as well as chemical modification of Chl-a to produce stereochemically defined Chl derivatives. In the second part of the paper, we report a facile synthesis of a self-aggregative Chl by modifying isolated Chl-d. Since Chl-d was characterized by its reactive 3-formyl group, the formyl group was reduced with t-BuNH2BH3 to afford the desirable Chl, 3-deformyl-3-hydroxymethyl-pyrochlorophyll-d (3(1)-OH-pyroChl-d). The synthetic 3(1)-OH-pyroChl-d molecules spontaneously self-organized to form well-ordered aggregates in a non-polar organic solvent. The self-aggregates are a good model of major light-harvesting antenna systems of green photosynthetic bacteria, chlorosomes, in terms of the following three findings. (1) Both the red-shifted electronic absorption band above 750 nm and its induced reverse S-shape CD signal around 750 nm were observed in 0.5% (v/v) THF-cyclohexane. (2) The stretching mode of the 13-carbonyl group was downshifted by about 35 cm(-1) from the wavenumber of its free carbonyl. (3) The self-aggregates were quite stable on titration of pyridine to the suspension, in comparison with those of natural chlorosomal bacteriochlorophyll-d possessing the 3-(1-hydroxyethyl) group.
authors.affiliation: Department of Bioscience and Biotechnology, Faculty of Science and Engineering, Ritsumeikan University, Kusatsu, Shiga 525-8577, Japan.
authors.forename: Tadashi
authors.initials: T
authors.lastname: Mizoguchi
authors.forename: Ayumi
authors.initials: A
authors.lastname: Shoji
authors.forename: Michio
authors.initials: M
authors.lastname: Kunieda
authors.forename: Hideaki
authors.initials: H
authors.lastname: Miyashita
authors.forename: Tohru
authors.initials: T
authors.lastname: Tsuchiya
authors.forename: Mamoru
authors.initials: M
authors.lastname: Mimuro
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Tamiaki
mesh_terms: D001429:Bacteriochlorophylls / Q000138:chemical synthesis / Q000737:chemistry*; D019414:Chlorobi / Q000737:chemistry*; D002734:Chlorophyll / Q000737:chemistry*; D002851:Chromatography, High Pressure Liquid; D000458:Cyanobacteria / Q000737:chemistry*; D008968:Molecular Conformation; D011725:Pyridines / Q000737:chemistry; D012680:Sensitivity and Specificity; D013057:Spectrum Analysis; D013237:Stereoisomerism; D017186:Titrimetry
chemical_list: D001429:Bacteriochlorophylls; D011725:Pyridines; D002734:Chlorophyll; C459779:bacteriochlorophyll d; C023666:pyridine