Determination of 31-stereochemistry in synthetic bacteriochlorophyll-d homologues and self-aggregation of their zinc complexes Original Research Article

Zinc complex of methyl 31-octadecyl-bacteriopheophorbide-d was prepared from modification of naturally occurring chlorophyll-a. The 31-epimerically pure samples were obtained by HPLC separation and their stereochemistry including the absolute configuration at the secondary alcoholic 31-position was determined by combination of esterification to methoxy(trifluoromethyl)phenylacetate and NMR spectroscopy (Mosherʹs method). Both the epimers were monomeric in a polar organic solvent and self-aggregated in a non-polar solvent to give oligomers as well as dimers possessing red-shifted visible absorption bands. Visible spectra of the non-polar organic solutions were dependent upon the 31-chirality and such a diastereoselective control on the self-aggregation led to the formation of self-aggregates with different supramolecular structures.