Stereoselective Self‐Aggregation of 31‐Epimerically Pure Amino Analogs of Zinc Bacteriochlorophyll‐d in an Aqueous Micelle Solution |
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| Authors: | Hiroaki Watanabe Tadashi Mizoguchi Hitoshi Tamiaki |
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| Affiliation: | Graduate School of Life Sciences, Ritsumeikan University, Kusatsu, Shiga, Japan |
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| Abstract: | Zinc bacteriochlorophyll‐d analogs possessing an amino group instead of the original hydroxy group at the C31 position were prepared by chemical modification of naturally occurring chlorophyll‐a. The synthetic 31‐epimers were successfully separated by reverse phase HPLC to give diastereomerically pure samples. The stereochemistry of the chiral C31‐center in the separated amines was determined by NMR analysis of their diastereomeric amides as well as by their asymmetric synthesis from authentic stereoisomers. Both the epimers were monomeric in tetrahydrofuran to give sharp electronic absorption bands, while they self‐aggregated to form chlorosomal oligomers with the redshifted bands in an aqueous Triton X‐100 micelle solution (pH = 6.9). The resulting oligomers deaggregated by addition of p‐toluenesulfonic acid to give monomeric N‐protonated ammonium species. The aggregation and deaggregation were dependent on the 31‐stereochemistry, indicating that each epimer produced supramolecularly different self‐aggregates. |
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