Friday, March 13, 2009

While, On The Other Hand...

Many molecules in biology come in either left- or right-handed -- so-called "chiral" -- forms. But scientists were surprised to learn from a 1999 report in the research journal Science that electrons, in special circumstances, might move at different rates through those mirror-image structures.

Those "special circumstances" involve using circularly polarized light to get the electrons moving through chiral molecules via the photoelectric effect. Circularly polarized light can be said to rotate in space something like planets orbiting a sun. But how that made electrons behave unevenly remained "a mystery for nearly a decade," said Duke chemistry professor David Beratan. "Existing theory really wasn't up to the task of explaining this lack of symmetry."

Beratan teamed up with an international group of scholars, including two Duke colleagues, to answer that question in a December, 2008 issue of the journal Physical Review Letters. Those results were also recently reviewed in a Perspective commentary in March 13 issue of Science.

Experimentalists had found uneven results both when either polarization of light or the handedness of molecules were reversed, he noted.

Could all this theorizing lead to practical applications? Perhaps, Beratan said. "All proteins, all DNA, almost all amino acids, and many small natural products produced by biological systems, have this handedness. Maybe biology is using some of these effects as it pushes electrons around. So we may be able to use some of these effects to diagnose or to control reaction mechanisms."