Synthesis and self-assembly of amphiphilic zinc chlorophyll derivatives possessing a crown ether at the 17-propionate residue

Abstract

Zinc 31-hydroxy-131-oxo-chlorins 1–3 possessing a 12-crown-4, 15-crown-5, and 18-crown-6 ether at the 17-propionate residue were synthesized and self-assembled in aqueous and non-polar organic media. Zn chlorins 1–3 exhibited red-shifted Qy absorption bands and large CD signals around 730 nm in an aqueous solution after standing for 2 h or 2 days, indicating the formation of their oligomeric self-aggregates as in chlorosomes of green photosynthetic bacteria. Incubation for 2 weeks decreased the absorption bands around 730 nm, accompanying an appearance of the absorption band around 675 nm. These show that Zn chlorins 1–3 finally formed thermodynamically stable anti-parallel dimers in the aqueous solution. 176-Epimerically pure 1–3 exhibited essentially the same spectral properties as the corresponding epimeric mixtures, but larger CD signals were observed around 730 nm in the spectra of epimerically pure 1 and 2 after standing for 2 h or 2 days than those of their epimeric mixtures. In a non-polar organic solvent, Zn chlorins 1–3 formed less time-dependent chlorosomal self-aggregates that exhibited Qy absorption bands around 735 nm.