Tuesday, July 17, 2012

Details do matter in photosynthesis

In Telluride I heard David Coker give a fascinating talk about his recent work on quantum decoherence in photosynthetic proteins, reported in a recent paper with Jeremy Moix, Jianlan Wu, Pengfei Huo, and Jianshu Cao.

A 2007 Nature paper claimed to report evidence for quantum coherence of electronic excitations for a few hundred femtoseconds at liquid nitrogen temperatures in the FMO complex. This led to a flurry of theoretical activity [and various silly (at least to me) and grandiose claims about "quantum biology" and "green quantum computers"].
[Aside: it is often overlooked that the claimed coherence is just between 2 chromophores not all seven in the complex].

However, these experiments were not done on the complete photosynthetic complex, but a subset with 7 chromophores. Recent structural studies have shown that there is actually an 8th chromophore. Surely, such small details don't matter...
But, they do. Coker's group has shown that this extra chromophore changes the energy transfer pathway through the complex. Moreover, coherent oscillations between the two chromophores are no longer present. The energy transfer is incoherent in the native complex. It functions fine without quantum coherence.

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