Lab-Made Complexes Are 'Sun Sponges'

A ring of protein and pigments, half synthetic and half natural, can be used to quickly prototype light-harvesting antennas that absorb more sunlight than fully natural ones.

In diagrams it looks like a confection of self-curling ribbon with bits of bling hung off the ribbon here and there. In fact it is a carefully designed ring of proteins with attached pigments that self-assembles into a structure that soaks up sunlight.

The scientists who made it call it a testbed, or platform for rapid prototyping of light-harvesting antennas-structures found in plants and photosynthesizing bacteria-that take the first step in converting sunlight into usable energy. The antennas consist of protein scaffolding that holds pigment molecules in ideal positions to capture and transfer the sun's energy. The number and variety of the pigment molecules determines how much of the sun's energy the antennas can grab and dump into an energy trap.

In the August 6, 2013 online edition of Chemical Science, a new publication of the Royal Society of Chemistry, the scientists describe two prototype antennas they've built on their testbed. One incorporated synthetic dyes called Oregon Green and Rhodamine Red and the other combined Oregon Green and a synthetic version of the bacterial pigment bacteriochlorophyll that absorbs light in the near-infrared region of the spectrum.

Both designs soak up more of the sun's spectrum than native antennas in purple bacteria that provided the inspiration and some components for the testbed. The prototypes were also far easier to assemble than synthetic antennas made entirely from scratch. In this sense they offer the best of both worlds, combining human synthetic ingenuity with the repertoire of robust chemical machinery selected by evolution.