PARENT SESSION
Posters P3A Bacteriochlorophyll based antenna systems. Abstracts (219-238)

Self-aggregation of synthetic zinc 17,18-cis-bacteriochlorophyll-d derivative. Hitoshi Tamiaki^*,1, Takuya Watanabe¹, Michio Kunieda¹, ¹ Department of Bioscience and Biotechnology, Kusatsu, Shiga, Japan

ABSTRACT- Bacteriochlorophyll(BChl)-d self-aggregates without any assistance of peptides to form the core part of main light-harvesting antennas (= chlorosomes) in some green sulfur photosynthetic bacteria. Isolated BChls-d also self-aggregated in nonpolar organic solvents to give oligomers possessing similar supramolecular structures with natural systems. As model compounds, zinc 3¹-hydroxy-13¹-oxo-chlorins were prepared by modifying naturally occurring chlorophylls and their self-aggregation in nonpolar organic solvents was investigated by visible absorption spectroscopy; the self-aggregates had red-shifted and broadened peaks compared with the monomeric. All the natural and artificial chlorophylls examined so far have had a 17S,18R-trans-chlorin moiety in the molecular structure. Here we report synthesis of zinc 17,18-cis-chlorin possessing 3¹-hydroxy and 13-keto carbonyl groups and its self-aggregation in a nonpolar organic solvent. Zinc methyl 3¹-demethyl-17,18-cis-bacteriopheophorbide-d was prepared by photo-reduction of the corresponding porphyrin possessing the 17-18 double bond. From the absorption spectral analysis, the synthetic cis-chlorin self-aggregated in 1%(v/v) tetrahydrofuran(THF)-hexane to give an oligomer possessing red-shifted and broadened peaks, compared to the monomeric in THF. The red-shifted values by self-aggregation were smaller than those observed in the corresponding trans-isomer, indicating that self-aggregates of the present cis-isomer took more disordered supramolecular structures than those of the natural-type trans-isomer.

KEY WORDS: Chlorosome, Self-assembly, Bacteriochlorophyll, Dihydroporphyrin