Self-aggregation of synthetic zinc 3-hydroxymethyl-chlorophyll-a derivatives possessing electron-withdrawing groups at the 20-position in aqueous micelle solution

Abstract

Zinc methyl 3-hydroxymethyl-pyropheophorbides-[Formula: see text] bearing an acetyl or nitro group at the 20-position were prepared by chemically modifying natural chlorophyll-[Formula: see text]. The synthetic zinc 20-substituted bacteriochlorophyll-[Formula: see text] analogs self-aggregated in an aqueous Triton X-100 micelle solution to give red-shifted and broadened electronic absorption bands, similarly as in one of the photosynthetic light-harvesting antennas, chlorosomes. Although the sterically bulky 20-substituents of the semisynthetic zinc 31-hydroxy-131-oxo-chlorins partially disturbed the chlorosomal self-aggregates which would be produced by the [Formula: see text]–[Formula: see text] stacking of the chlorin chromophores, their electron-withdrawing abilities should enhance the specific, intermolecular interaction of Zn[Formula: see text]O32–H[Formula: see text]O=C-13 which was essential for the chlorosomal self-aggregation. Such self-assemblies using these model pigments would provide a new clue for constructing of artificial photosynthetic systems.