Self-aggregates of natural and modified chlorophylls as photosynthetic light-harvesting antenna systems: substituent effect on the B-ring.
Extramembranous light-harvesting antennae called 'chlorosomes' are the main sunlight-absorbing and energy-migrating systems in photosynthetic green bacteria. In a chlorosome, specific chlorophyllous pigments self-aggregate in hydrophobic environments surrounded by a lipid monolayer to form large oligomers. The self-aggregates of chlorosomal chlorophylls possessing a chlorin pi-system absorb sunlight and can emit near-infrared light, which is transferred to a bacteriochlorin pigment situated in the chlorosomal surface membrane. In vivo and in vitro self-aggregates of natural chlorosomal chlorophylls and their models have been investigated by electronic absorption analysis. Here their self-aggregation is reviewed from the viewpoint of substituent effect on the pyrrolic B-ring. Substituents at the 7- and 8-positions did not disturb the formation of their self-aggregates but affected their absorption bands.
Tamiaki
Hitoshi
H
Department of Bioscience and Biotechnology, Faculty of Science and Engineering, Ritsumeikan University, Kusatsu, Shiga 525-8577, Japan. tamiaki@se.ritsumei.ac.jp