ON THE INFLUENCE OF MULTIPLE-SCATTERING CONTRIBUTIONS TO THE EXTENDEDX-RAY-ABSORPTION FINE-STRUCTURE (EXAFS) SPECTRA OF THE PHOTOSYSTEM-IIMANGANESE COMPLEX

The catalytic center of photosynthetic water oxidation is a tetra-nucl ear manganese complex which presumably is covalently bound to the poly peptides 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 influen ce of multiple scattering contributions to the EXFAS spectra is assess ed. It is found that for distances below 3.5 Angstrom multiple scatter ing contributions to the EXAFS spectrum of the PS II manganese complex are presumably negligible. However, for distances above 3.5 A multipl e scattering contributions to the EXAFS spectrum of the PS II manganes e complex are likely to be of relevance. We conclude that the amino ac id 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.