On the influence of multiple scattering contributions to the Extended X-ray Absorption Fine Structure (EXAFS) spectra of the photosystem II manganese complex

The catalytic center of photosynthetic water oxidation is a tetra-nuclear manganese complex which presumably is covalently bound to the polypeptides of the Photosystem II (PS II) protein complex. Extended X-ray Absorption Fine Structure (EXAFS) spectra were simulated for various likely structural elements of the PS II manganese complex. The influence of multiple scattering contributions to the EXFAS spectra is assessed. It is found that for distances below 3.5 Angstrom multiple scattering contributions to the EXAFS spectrum of the PS II manganese complex are presumably negligible. However, for distances above 3.5 A multiple scattering contributions to the EXAFS spectrum of the PS II manganese complex are likely to be of relevance. We conclude that the amino acid residues (glutamate, aspartate, histidine) which are ligands of the PS II manganese complex could give rise to the EXAFS Fourier peak at about 4 Angstrom.