no light light pulses


(left) a photosynthetic reaction center (rc) and (right) rc + and light harvesting complexes in a membrane (image source)

Todays title of the magazine nature reported about an experiment where the electron transport in a crystall could be observed within an range in the order of 10 attoseconds (10*10^{-18}s= 10 as).

The experiment is also described in todays press release: “capturing electrons on their trip between atoms” of the Max-Planch-Institut für Quantenoptik. The researchers used two light pulses, an extreme UV pulse of 300 attoseconds (which let loose electrons which are either loosely or more strongly bound to the atoms of a Tungsten crystall) and an infrared laser puls (which interacts with the electrons when they reach the surface of the crystall). The let-loose-loosely-bound electrons were 100 attoseconds faster than the let-loose-more-strongly bound electrons.

It would be interesting to know wether such high temporal resolution could also be used for investigating electron tranfer in pigment-protein complexes such as in a photosynthetic reaction center (see image above)(correction 05.10.2012: in a FMO complex (the reaction center seems to be a part of this complex)), which was done by researchers in Berkeley e.g. in a 3 pulse two-color electronic photon echo experiment with 750 and 800 nm pulses in the femtosecond range (science 316 (5830)) or wether the high energies of the corresponding laser pulses would alter the corresponding structures, which apparently happenes if one shoots with gamma rays on a pigment.

If I understood correctly the electron transfer in the photosynthetic reaction center of Rhodobacter sphaeroides in the above experiment seems to be highly efficient due to the long coherence between the exiton states of two chromophores corresponding to the bacteriochlorophyll b (BChl-b) molecules and bacteriophaeophytin b molecules (BPh) of a photosynthetic reaction center. This coherence seems to be longer than what can explained by something which is called Foerster theory(?). On the other hand molecular dynamics simulations on the reaction center of Rhodopseudomonas viridis showed that nuclear motions of adjacent chromophores are also strongly correlated.

A fast comment – this may be a bit speculative – but the latter mechanism reminds me very much of the formation of Cooper pairs via electron phonon interaction.

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