Chemistry

Keeping Pigments in Sync

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Science  01 Feb 2013:
Vol. 339, Issue 6119, pp. 491
DOI: 10.1126/science.339.6119.491-b

It has been clear for decades that photosynthesis involves an intricate chain of energy transfer steps, channeling the energy in light absorbed by dedicated pigments to a central complex that chemically splits water. Over the past 7 or 8 years, the advent of two-dimensional electronic spectroscopy has offered an increasingly detailed understanding of how the transfer process works. In particular, the data suggest a persistence of quantum-mechanical coherence—essentially a steady phase relationship in electronic excitation across the donors and acceptors that facilitates efficient transfer—for a much longer time than the complex molecular structure of the system would seem to allow. The underlying mechanism for sustaining coherence has remained somewhat mysterious and subject to debate. Tiwari et al. have modeled the transfer process in a framework that allows mixing of vibrational and electronic excitation, and they find that anticorrelated vibrations across the associated proteins (i.e., contraction on one side concurrent with extension on the other) could mediate electronic dynamics that give rise to the spectral signatures observed in the experiments. They further note that certain pigment vibrational frequencies match the associated electronic energy gaps, lending further plausibility to this mechanism.

Proc. Natl. Acad. Sci. U.S.A. 110, 1203 (2013).

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