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Portraits and habits of our birds v.2. National association of Audubon societies,1921 (by BioDivLibrary)
In this atomic force microscope image, the rings of light-harvesting complex 2 (LH2) are seen on the surface membrane of a purple bacterium. The arrangement of these complexes, as well as their shapes, help to make them extremely efficient at collecting the energy from light. Image: Jianshu Cao.
News on the solar front! Instead of energy production for human beings, have the latest information about the biological form of solar collection - photosynthesis.
Purple bacteria are among the first life forms to emerge on earth, and one of the most efficient in turning sunlight into energy via photosynthesis. It’s through research at MIT that the secret to their high efficiency is found to be its molecular structure.
A ring-shaped molecule with an unusual ninefold symmetry is critical, the researchers found. The circular symmetry accounts for its efficiency in converting sunlight, and for its mechanical durability and strength. The new analysis, carried out by professors of chemistry Jianshu Cao and the late Robert Silbey, postdoc Liam Cleary, and graduate students Hang Chen and Chern Chuang, has been published in the Proceedings of the National Academy of Sciences.
“The symmetry makes the energy transfer much more robust,” Cao says. “Most biological systems are quite soft and disordered. You would not expect a regular structure, almost a perfect structure,” as is found in this primitive microbe, he says.
In these regular round complexes, Cao says, “nature only used certain symmetry numbers: mostly ninefold, some eightfold, very few tenfold. It’s very selective.” His group’s mathematical analysis shows there are good reasons for that, he says.
These ring-shaped molecules, in turn, are arranged in a hexagonal pattern on the spherical photosynthetic membrane of purple bacteria, Cao says.
“With these symmetry numbers, the interactions between all pairs of the symmetric rings are optimized at the same time. … We believe that nature found the most robust structures in terms of energy transfer,” Cao says. Both eightfold and tenfold symmetries also work, though not as well: Only a lattice made up of ninefold symmetric complexes can tolerate an error in either direction. “You want consecutive numbers so it can tolerate such mistakes,” Cao says.
Stuart Rice, a chemistry professor at the University of Chicago says the research is a “brilliant” find, and that it “opens the door to a new way of designing efficient synthetic photosensitive devices, by coupling internal structure to packing in a fashion that is not now involved in the design process.”
Continue reading the story here.