Self ‐aggregation of zinc bacteriochlorophyll‐d analogs with an acylhydrazone moiety as the 13‐keto‐carbonyl alternative

Zinc bacteriochlorophyll-d analogs possessing an acylhydrazone moiety as the 13-keto-carbonyl alternative were prepared. Similar to self-aggregation in chlorosomes, synthetic models with R=(CH2)1~6H self-aggregated in an aqueous Triton X-100 solution to give red-shifted and broadened visible absorption bands with intense CD bands. An increase in the oligomethylene chain length moved the red-shifted Qy maxima to shorter wavelengths, and branched alkyl and benzyl substitutes have left monomeric species in the hydrophobic environment inside the micelle. The R-dependent self-aggregation was ascribable to the specific Zn…O32–H…N=C131 bond and π–π interaction of the composite chlorin chromophore along the moleculary-axis. AbstractZinc methyl 3-hydroxymethyl-pyropheophorbides-a possessing an acylhydrazinylidene group at the 131-position were prepared by chemically modifying chlorophyll-a, which were models of bacteriochlorophyll-d as one of the light-harvesting pigments in photosynthetic green bacteria. Similar to the self-aggregation of natural bacteriochlorophyll-d in the antenna systems called chlorosomes, some of the synthetic models self-aggregated in an aqueous Triton X-100 solution to give red-shifted and broadened visible absorption bands. The newly appeared oligomeric bands were ascribable to the exciton coupling of the chlorin π-systems along the moleculary-axis, leading to intense circular dichroism bands in the red-shifted Qy and Soret regions. The self-aggreg...
Source: Photochemistry and Photobiology - Category: Science Authors: Tags: RESEARCH ARTICLE Source Type: research