Chemistry

Aligned for Speed

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Science  18 May 2007:
Vol. 316, Issue 5827, pp. 955
DOI: 10.1126/science.316.5827.955c

In purple photosynthetic bacteria, a ring of bacteriochlorophyll molecules assembles through noncovalent interactions to form the lightharvesting antenna complex. The ultrafast energy transfer rates of such complexes can be approached in mimic complexes with covalently linked chromophores, but complexes more efficiently synthesized through self-assembly have exhibited slower rates because of nonoptimal alignment of the molecular dipoles. Kelley et al. prepared a zinc chlorophyll derivative and established through small-angle x-ray scattering (SAXS) that it self-assembles into tetramers (shown above) in toluene solution. Transient absorption spectra reveal a much faster Förster energy transfer rate in this complex than in prior porphyrin tetramers; however, the rate was still 10 times slower than in the fastest photosynthetic proteins, suggesting that the dipole alignment could be optimized further. — PDS

J. Am. Chem. Soc. 129, 10.1021/ja071362a(2007).

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