Self-aggregates of a synthetic cadmium chlorin in solid film as a photosynthetic antenna model.

Self-aggregates of a synthetic cadmium chlorin possessing 3(1)-hydroxyl and 13-carbonyl groups were prepared in dried thin film. The solid film was characterized by visible and infrared absorption spectroscopies at both transmission and reflection modes. The spectra given by the two different modes were essentially the same and resembled those in the extramembranous antennas of green photosynthetic bacteria. The circular dichroism and resonance Raman spectra also supported the similarity between the artificial self-aggregates and the natural systems. Electron diffraction of the aggregated film by transmission electron microscopy indicated the presence of an orderly structure with a 6.4-A interval, which was estimated for the close Cd-Cd distance of the stacking in the self-aggregates. The in vitro self-assembly in the solid state is a good structural model for the in vivo antenna.