Theoretical investigation of the electronic structure of molecules involved in green-plant photosynthesis

Abstract

Some of the advances made in our theoretical understanding of the Z scheme of photosynthesis in green plants are reviewed here. The Z-scheme embodies a sequence of light-activated, and very fast, electron transfer processes. The molecules under consideration belong to the central diagonal arm of the Z-scheme. These are plastoquinone-histidine complexes Q_I and Q_II’ plastoquinones (PQ), cytochrome-<i>f</i>, and Rieske protein. The electronic structures of these species have been investigated by semiempirical quantum chemical methods — CNDO/2 and INDO. In one case, the rate of electron transfer (from Q<img src='http://www.niscair.res.in/jinfo/subscript11.gif' border=0> to Q<img src='http://www.niscair.res.in/jinfo/subscript12.gif' border=0> and from Q<img src='http://www.niscair.res.in/jinfo/subscript11.gif' border=0> to Q<img src='http://www.niscair.res.in/jinfo/subscript12.gif' border=0>) has been theoretically determined. Results of these investigations serve in two ways. On the one hand, theoretical calculations confirm the observed redox potentials, and the rate of electron transfer. On the other hand, a set of fascinating information can be obtained, which clarifies several ideas about the structure, function and placement of these biological molecules in the condensed phase of chloroplast.