• Kubin, M.; Kern, J.; Gul, S.; Kroll, T.; Chatterjee, R.; Löchel, H.; Fuller, F.; Sierra, R.; Quevedo, W.; Weniger, C.; Rehanek, J.; Firsov, A.; Laksmono, H.; Weninger, C.; Alonso-Mori, R.; Nordlund, D.; Lassalle-Kaiser, B.; Glownia, J.; Krzywinski, J.; Moeller, S.; Turner, J.; Minitti, M.; Dakovski, G.; Koroidov, S.; Kawde, A.; Kanady, J.; Tsui, E.; Suseno, S.; Han, Z.; Hill, E.; Taguchi, T.; Borovik, A.; Agapie, T.; Messinger, J.; Erko, A.; Föhlisch, A.; Bergmann, U.; Mitzner, R.; Yachandra, V.; Yano, J.; Wernet, P.: Soft x-ray absorption spectroscopy of metalloproteins and high-valent metal-complexes at room temperature using free-electron lasers. Structural Dynamics 4 (2017), p. 054307/1-16

10.1063/1.4986627
Open Access Version

Abstract:
X-ray absorption spectroscopy at the L-edge of 3d transition metals provides unique information on the local metal charge and spin states by directly probing 3d-derived molecular orbitals through 2p-3d transitions. However, this soft x-ray technique has been rarely used at synchrotron facilities for mechanistic studies of metalloenzymes due to the difficulties of x-ray-induced sample damage and strong background signals from light elements that can dominate the low metal signal. Here, we combine femtosecond soft x-ray pulses from a free-electron laser with a novel x-ray fluorescence-yield spectrometer to overcome these difficulties. We present L-edge absorption spectra of inorganic high-valent Mn complexes (Mn  6–15 mmol/l) with no visible effects of radiation damage. We also present the first L-edge absorption spectra of the oxygen evolving complex (Mn4CaO5) in Photosystem II (Mn<1 mmol/l) at room temperature, measured under similar conditions. Our approach opens new ways to study metalloenzymes under functional conditions.