Aggregation of synthetic zinc chlorins with several esterified alkyl chains as models of bacteriochlorophyll-c homologs

Zinc complexes of 3-hydroxymethyl-13(1)-oxochlorin possessing several branched alkyl chains as an esterified group at the 17-position were systematically prepared. In non-polar organic solvents, these compounds aggregated to form oligomers absorbing up to 800-nm light with around a 740-nm peak, which are good models for bacteriochlorophylls-c and d, extramembranous antenna pigments of photosynthetic green bacteria. All the visible spectra of the in-vitro oligomers are the same and the esterified alcohols induced no effect on the local structure of the oligomers. The circular dichroism spectra changed with elongation of esterified alkyl chains, which resulted in the similar spectra to the in-vivo oligomers. Esterified alcohols should subtly affect the supramolecular structure and/or stability of the self-aggregates. Copyright (C) 1996 Elsevier Science Ltd