X-Ray Absorption Linear Dichroism Spectroscopy (XALDS) on the Photosystem II Manganese Complex: Radiation Damage and S1-State K-edge Spectra

X-ray absorption spectroscopy (XAS) at the Mn K-edge is used to unravel the structure of the oxygen-evolving manganese complex which is embedded in the Photosystem II (PS II) protein complex; measurements on multilayers of PS II-containing membrane sheets provide angular information (XALDS). (1) By XAS and electron spin resonance (ESR) we investigated origin and characteristics of the radiation damage which is caused by prolonged exposure to intense synchrotron radiation. (2) By a derivative analysis of XALD-edge spectra, eight distinct transitions are resolvable (a to h). In contrast to the transitions c to e of the edge rise, f (6562 eV) and g (6565 eV) on top of the Mn K-edge exhibit characteristics of a formally-allowed electric dipole transition with an angle between transition dipole and membrane normal greater (f) and smaller (g) than the magic angle (= 54.7°), respectively