Energy transfer , photosynthetic reaction rate constants

A microscopic theory for describing ultrafast radiationless transitions in particular for, photo-induced ultrafast radiationless transitions is presented. For this purpose, one example system that well represents the ultrafast radiationless transaction problem is considered. More specifically, bacterial photosynthetic reaction centers (RCs) are investigated for their ultrafast electronic-excitation energy transfer (EET) processes and ultrafast electron transfer (ET) processes. Several applications of the density matrix method are presented for emphasizing that the density matrix method can not only treat the dynamics due to the radiationless transitions but also deal with the population and coherence dynamics. Several rate constants of the radiationless transitions and the analytic estimation methods of those rate... 

Most of the predictions were confirmed experimentally (apart from some anomalous cases), but one prediction, the inverted effect , (the decrease of rate constant with increasingly favorable (increasingly negative) AG°, when AG° is very large) was counterintuitive, but clearly evident in equation (1.4) and took 25 years before it was confirmed [26]. This story has been told many times and so I will not describe it here. However, the inverted effect is believed to have implications for efficiency of solar energy conversion in photosynthetic systems, as discussed elsewhere. Also, the ET theory had spin-offs for ion, atom and group transfer reactions considered in the next section. 

The primary photosynthetic process is carried out by a pigment protein complex the reaction centre (RC) embedded in a lipid bilayer membrane (Figure 6.19) and surrounded by light-harvesting complexes.1477,1481,1482 Thus energy is transferred from LH1 to a bacteriochlorophyll special pair (P) and then through a bacteriochlorophyll molecule (BC monomer) to bacteriopheophytin (BP a chlorophyll molecule lacking the central Mg2 + ion), followed by electron transfer to a quinone Qa in hundreds of ps. The neutral P is then restored by electron transfer from the nearest intermembrane space protein cytochrome c (Cyt c) in hundreds of ns. The rate constants of the... 

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