Synthesis of 3 2-substituted bacteriochlorophyll- d analogs and their self-aggregation in a nonpolar organic solvent

Abstract

Zinc complexes of 3 1-epimerically pure 3 2,3 2,3 2-trifluoro-bacteriopheophorbide- d methyl ester were prepared and their self-aggregation was examined in 1% (v/v) dichloromethane and hexane by visible and circular dichroism spectroscopies. Both the synthetic 3 1-trifluoromethylated diastereomers gave amorphous self-aggregates in the nonpolar organic solvent, while the corresponding nonfluorinated compounds possessing the 3 1-methyl group formed well-ordered and large oligomers similar to in vivo aggregates of bacteriochlorophyll- d in a chlorosome, a main light-harvesting antenna of green photosynthetic bacteria. The difference is ascribed to steric factor of the 3-CF 3 group, which was supported by optical properties of other synthetic zinc 3 1-hydroxy-13 1-oxo-chlorins possessing trifluoromethyl or secondary/tertiary substituents at the 3 1-position in the nonpolar organic solvent.