Man-made mimics of light harvesting bacteria antennae are bringing Japanese researchers closer to making photoactive nanodevices.

Green photosynthetic bacteria have unique light harvesting systems called chlorosomes. Each chlorosome is made of a large number of bacteriochlorophyll molecules, which self organise to form rod-like aggregates that are attached to the bacterial cytoplasmic membrane. Chlorosomes play a key role in absorbing light energy and transferring it to the reaction centre of bacteria.

Chlorophyll-d  (Chl-d), a magnesium containing cyclic structure, is a major photoactive molecule found in Acaryochloris marina. Hitoshi Tamiaka and co-workers from Ritsumeikan University and Kyoto University have established the complete stereochemistry of Chl-d. Modification of the 3-formyl group of Chl-d with a hydroxyl group allows the compound to self aggregate in a non-polar solvent.These model compounds are also stable in suspension compared to their natural counterparts. 

Tamiaka's method can be used for studying the components of bacterial chlorosomes such as Chl-d, since stereochemically pure chl-d is difficult to isolate from natural sources in sufficient amounts. 'The present artificial aggregates could be useful for the construction of novel photoactive nanodevices based on spontaneous self-aggregation of Chl molecules,' said Tamiaka.

Katherine Vickers