The role of the iron–histidine bridge in the early steps of photosynthesis

Abstract

The role of the iron–histidine bridge in bacterial photosynthetic reaction centres has been investigated by means of ab initio computations and quantum dynamics of elementary reaction steps. Full geometry optimization and wave packet dynamics show that, upon the arrival of a photo-electron, the primary quinone takes up a proton from the H-bonded histidine in a very fast process, which occurs in a few tens of femtoseconds. The proton transfer step significantly stabilizes the charge separated state, inhibiting the backward charge recombination process. Electron transfer to the secondary quinone can then take place by switching the positions of both the H-bonded hydrogens, in a Bjerrium type mechanism involving whole hydrogen atoms rather than protons.