title: Isolation and structure determination of a complete set of bacteriochlorophyll-d homologs and epimers from a green sulfur bacterium Chlorobium vibrioforme and their aggregation properties in hydrophobic solvents.
abstract: Eight bacteriochlorophyll (BChl)-d homologs and epimers were isolated from a strain of the green sulfur bacterium Chlorobium vibrioforme. By a combination of mass spectrometry and 1H-NMR spectroscopy using the chemical shifts of meso- and 3(1)-protons and 1H-1H NOE correlations, the molecular structures were determined as (3(1)R)-8-ethyl-12-methyl, (3'R)-8-ethyl-12-ethyl, (3(1)R)-8-propyl-12-methyl, (3(1)S)-8-propyl-12-methyl, (3(1)R)-8-propyl-12-ethyl, (3(1)S)-8-propyl-12-ethyl, (3(1)S)-8-isobutyl-12-methyl and (3(1)S)-8-isobutyl-12-ethyl. The aggregation behavior of the epimerically pure BChls-d in hydrophobic organic solvents was examined to investigate the absolute configuration of the 3-(1-hydroxyethyl) group as well as the bulkiness of the C8 and C12 side-chains by using electronic-absorption and fluorescence-emission spectroscopies At high concentration of the BChls-d in CH2Cl2, the absolute configuration of the 3-(1-hydroxyethyl) group governed the formation of a subunit as a building block for the subsequent higher assembly. Upon dilution of the resulting subunit with hexane, the bulkiness of the C8 and C12 side-chains were found to affect the association of the subunits differently: the bulkiness of the C8 side-chain acted as a promoter for the association due to a stabilized hydrophobic interaction among the relevant larger side-chain, whereas the bulkiness of the C12 side-chain acted as an inhibitor for that association due to introduction of a particular steric-hindrance around the side-chain in the aggregates.
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: Yoshitaka
authors.initials: Y
authors.lastname: Saga
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Tamiaki
mesh_terms: D019414:Chlorobi / Q000737:chemistry*; D002734:Chlorophyll / Q000031:analogs & derivatives* / Q000737:chemistry / Q000302:isolation & purification; D019281:Dimerization; D013058:Mass Spectrometry; D015394:Molecular Structure; D019906:Nuclear Magnetic Resonance, Biomolecular; D013237:Stereoisomerism
chemical_list: D002734:Chlorophyll