- Kubin, Markus;
- Kern, Jan;
- Gul, Sheraz;
- Kroll, Thomas;
- Chatterjee, Ruchira;
- Löchel, Heike;
- Fuller, Franklin D;
- Sierra, Raymond G;
- Quevedo, Wilson;
- Weniger, Christian;
- Rehanek, Jens;
- Firsov, Anatoly;
- Laksmono, Hartawan;
- Weninger, Clemens;
- Alonso-Mori, Roberto;
- Nordlund, Dennis L;
- Lassalle-Kaiser, Benedikt;
- Glownia, James M;
- Krzywinski, Jacek;
- Moeller, Stefan;
- Turner, Joshua J;
- Minitti, Michael P;
- Dakovski, Georgi L;
- Koroidov, Sergey;
- Kawde, Anurag;
- Kanady, Jacob S;
- Tsui, Emily Y;
- Suseno, Sandy;
- Han, Zhiji;
- Hill, Ethan;
- Taguchi, Taketo;
- Borovik, Andrew S;
- Agapie, Theodor;
- Messinger, Johannes;
- Erko, Alexei;
- Föhlisch, Alexander;
- Bergmann, Uwe;
- Mitzner, Rolf;
- Yachandra, Vittal K;
- Yano, Junko;
- Wernet, Philippe
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.