Stereoselective Self-Aggregation of 3 1 -Epimerically Pure Amino Analogs of Zinc Bacteriochlorophyll-d in an Aqueous Micelle Solution.

Zinc bacteriochlorophyll-d analogs possessing an amino group instead of the original hydroxy group at the C3 ¹ position were prepared by chemical modification of naturally occurring chlorophyll-a. The synthetic 3 ¹ -epimers were successfully separated by reverse phase HPLC to give diastereomerically pure samples. The stereochemistry of the chiral C3 ¹ -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 3 ¹ -stereochemistry, indicating that each epimer produced supramolecularly different self-aggregates.
(© 2016 The American Society of Photobiology.)