Authors: Jimmy Heimdal Kasper P Jensen Ajitha Devarajan Ulf Ryde
Publish Date: 2006/09/05
Volume: 12, Issue: 1, Pages: 49-
Abstract
We have studied the effect of axial ligation of chlorophyll and bacteriochlorophyll using density functional calculations Eleven different axial ligands have been considered including models of histidine aspartate/glutamate asparagine/glutamine serine tyrosine methionine water the protein backbone and phosphate The native chlorophylls as well as their cation and anion radical states and models of the reaction centres P680 and P700 have been studied and we have compared the geometries binding energies reduction potentials and absorption spectra Our results clearly show that the chlorophylls strongly prefer to be fivecoordinate in accordance with available crystal structures The axial ligands decrease the reduction potentials so they cannot explain the high potential of P680 They also redshift the Q band but not enough to explain the occurrence of red chlorophylls However there is some relation between the axial ligands and their location in the various photosynthetic proteins In particular the intrinsic reduction potential of the second molecule in the electron transfer path is always lower than that of the third one a feature that may prevent backtransfer of the electron
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