Direct detection of oxygen ligands to the Mn4Ca complex in photosystem II by X-ray emission spectroscopy

Abstract

The Mn4CaOX cluster catalyzes the light driven oxidation of water in Photosystem II. To understand the mechanistic details of this intriguing machine it is necessary to unravel not only the geometric but also the electronic structure of this complex. X-ray emission spectroscopy can be one important tool in this endeavour due to its unique sensitivity towards light atoms ligated to a metal center. In addition X-ray emission spectroscopy provides information of the charge density distribution over the metal centers in the complex and is sensitive to protonation changes of bridging oxygens, both important questions in the light of different proposed mechanisms for water oxidation in PSII. Here we show that X-ray emission spectra of PSII can be collected with sufficient S/N from PSII samples and can yield insights into the mechanism of water oxidation.