Self-aggregation of synthetic zinc chlorins with a chiral 1-hydroxyethyl group as a model for in vivo epimeric bacteriochlorophyll-c and d aggregates

Abstract

31-Epimerically pure zinc 3-(1-hydroxyethyl)-131-oxochlorins possessing several substituents at the 20-position were prepared. In non-polar organic solvents, the synthetic zinc complexes self-aggregated to form oligomers with >700-nm absorption and giant CD peaks, which were dependent upon the 31-absolute configuration as well as the 20-substituents. The in vitro self-aggregates of each epimeric zinc chlorin with a 20-methyl group showed similar visible and CD spectra with the in vivo bacteriochlorophyll-c (31RS=21) aggregates in extramembranous antennae of a green photosynthetic bacterium. The spontaneous in vitro self-aggregates of 31RS(=21)-epimeric mixture of the zinc 20-methylchlorins were different from the natural supramolecules, indicating that in vivo slow oligomerization of 31RS(=21)-bacteriochlorophylls-c induced the regular supramolecular structures and/or the epimerically separated assemblies.