TY  - JOUR
A1  - Kubin, Markus
A1  - Guo, Meiyuan
A1  - Kroll, Thomas
A1  - Loechel, Heike
A1  - Kallman, Erik
A1  - Baker, Michael L.
A1  - Mitzner, Rolf
A1  - Gul, Sheraz
A1  - Kern, Jan
A1  - Föhlisch, Alexander
A1  - Erko, Alexei
A1  - Bergmann, Uwe
A1  - Yachandra, Vittal
A1  - Yano, Junko
A1  - Lundberg, Marcus
A1  - Wernet, Philippe
T1  - Probing the oxidation state of transition metal complexes
BT  - a case study on how charge and spin densities determine Mn L-edge X-ray absorption energies
JF  - Chemical science
N2  - Transition metals in inorganic systems and metalloproteins can occur in different oxidation states, which makes them ideal redox-active catalysts. To gain a mechanistic understanding of the catalytic reactions, knowledge of the oxidation state of the active metals, ideally in operando, is therefore critical. L-edge X-ray absorption spectroscopy (XAS) is a powerful technique that is frequently used to infer the oxidation state via a distinct blue shift of L-edge absorption energies with increasing oxidation state. A unified description accounting for quantum-chemical notions whereupon oxidation does not occur locally on the metal but on the whole molecule and the basic understanding that L-edge XAS probes the electronic structure locally at the metal has been missing to date. Here we quantify how charge and spin densities change at the metal and throughout the molecule for both redox and core-excitation processes. We explain the origin of the L-edge XAS shift between the high-spin complexes Mn-II(acac)(2) and Mn-III(acac)(3) as representative model systems and use ab initio theory to uncouple effects of oxidation-state changes from geometric effects. The shift reflects an increased electron affinity of Mn-III in the core-excited states compared to the ground state due to a contraction of the Mn 3d shell upon core-excitation with accompanied changes in the classical Coulomb interactions. This new picture quantifies how the metal-centered core hole probes changes in formal oxidation state and encloses and substantiates earlier explanations. The approach is broadly applicable to mechanistic studies of redox-catalytic reactions in molecular systems where charge and spin localization/delocalization determine reaction pathways.
Y1  - 2018
U6  - https://doi.org/10.1039/c8sc00550h
SN  - 2041-6520
SN  - 2041-6539
VL  - 9
IS  - 33
SP  - 6813
EP  - 6829
PB  - Royal Society of Chemistry
CY  - Cambridge
ER  - 
TY  - JOUR
A1  - Vadilonga, Simone
A1  - Zizak, Ivo
A1  - Roshchupkin, Dmitry
A1  - Evgenii, Emelin
A1  - Petsiuk, Andrei
A1  - Leitenberger, Wolfram
A1  - Erko, Alexei
T1  - Observation of sagittal X-ray diffraction by surface acoustic waves in Bragg geometry
JF  - Journal of applied crystallography
N2  - X-ray Bragg diffraction in sagittal geometry on a Y-cut langasite crystal (La3Ga5SiO14) modulated by Lambda = 3 mu m Rayleigh surface acoustic waves was studied at the BESSY II synchrotron radiation facility. Owing to the crystal lattice modulation by the surface acoustic wave diffraction, satellites appear. Their intensity and angular separation depend on the amplitude and wavelength of the ultrasonic superlattice. Experimental results are compared with the corresponding theoretical model that exploits the kinematical diffraction theory. This experiment shows that the propagation of the surface acoustic waves creates a dynamical diffraction grating on the crystal surface, and this can be used for space-time modulation of an X-ray beam.
KW  - surface acoustic waves
KW  - optics
KW  - synchrotron radiation
KW  - sagittal X-ray diffraction
Y1  - 2017
U6  - https://doi.org/10.1107/S1600576717002977
SN  - 1600-5767
VL  - 50
SP  - 525
EP  - 530
PB  - International Union of Crystallography
CY  - Chester
ER  - 
TY  - JOUR
A1  - Kubin, Markus
A1  - Kern, Jan
A1  - Gul, Sheraz
A1  - Kroll, Thomas
A1  - Chatterjee, Ruchira
A1  - Loechel, Heike
A1  - Fuller, Franklin D.
A1  - Sierra, Raymond G.
A1  - Quevedo, Wilson
A1  - Weniger, Christian
A1  - Rehanek, Jens
A1  - Firsov, Anatoly
A1  - Laksmono, Hartawan
A1  - Weninger, Clemens
A1  - Alonso-Mori, Roberto
A1  - Nordlund, Dennis L.
A1  - Lassalle-Kaiser, Benedikt
A1  - Glownia, James M.
A1  - Krzywinski, Jacek
A1  - Moeller, Stefan
A1  - Turner, Joshua J.
A1  - Minitti, Michael P.
A1  - Dakovski, Georgi L.
A1  - Koroidov, Sergey
A1  - Kawde, Anurag
A1  - Kanady, Jacob S.
A1  - Tsui, Emily Y.
A1  - Suseno, Sandy
A1  - Han, Zhiji
A1  - Hill, Ethan
A1  - Taguchi, Taketo
A1  - Borovik, Andrew S.
A1  - Agapie, Theodor
A1  - Messinger, Johannes
A1  - Erko, Alexei
A1  - Föhlisch, Alexander
A1  - Bergmann, Uwe
A1  - Mitzner, Rolf
A1  - Yachandra, Vittal K.
A1  - Yano, Junko
A1  - Wernet, Philippe
T1  - Soft x-ray absorption spectroscopy of metalloproteins and high-valent metal-complexes at room temperature using free-electron lasers
JF  - Structural dynamics
N2  - 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 similar to 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. (C) 2017 Author(s).
Y1  - 2017
U6  - https://doi.org/10.1063/1.4986627
SN  - 2329-7778
VL  - 4
PB  - American Institute of Physics
CY  - Melville
ER  - 
TY  - JOUR
A1  - Roshchupkin, Dmitry
A1  - Ortega, Luc
A1  - Plotitcyna, Olga
A1  - Erko, Alexei
A1  - Zizak, Ivo
A1  - Vadilonga, Simone
A1  - Irzhak, Dmitry
A1  - Emelin, Evgenii
A1  - Buzanov, Oleg
A1  - Leitenberger, Wolfram
T1  - Piezoelectric Ca3NbGa3Si2O14 crystal: crystal growth, piezoelectric and acoustic properties
JF  - Journal of geophysical research : Space physics
N2  - Ca3NbGa3Si2O14 (CNGS), a five-component crystal of lanthanum-gallium silicate group, was grown by the Czochralski method. The parameters of the elementary unit cell of the crystal were measured by powder diffraction. The independent piezoelectric strain coefficients d(11) and d(14) were determined by the triple-axis X-ray diffraction in the Bragg and Laue geometries. Excitation and propagation of surface acoustic waves (SAW) were studied by high-resolution X-ray diffraction at BESSY II synchrotron radiation source. The velocity of SAW propagation and power flow angles in the Y-, X-and yxl/+36 degrees-cuts of the CNGS crystal were determined from the analysis of the diffraction spectra. The CNGS crystal was found practically isotropic by its acoustic properties.
Y1  - 2016
U6  - https://doi.org/10.1007/s00339-016-0279-1
SN  - 0947-8396
SN  - 1432-0630
VL  - 122
SP  - 2803
EP  - 2812
PB  - Springer
CY  - New York
ER  - 
TY  - JOUR
A1  - Kroll, Thomas
A1  - Kern, Jan
A1  - Kubin, Markus
A1  - Ratner, Daniel
A1  - Gul, Sheraz
A1  - Fuller, Franklin D.
A1  - Löchel, Heike
A1  - Krzywinski, Jacek
A1  - Lutman, Alberto
A1  - Ding, Yuantao
A1  - Dakovski, Georgi L.
A1  - Moeller, Stefan
A1  - Turner, Joshua J.
A1  - Alonso-Mori, Roberto
A1  - Nordlund, Dennis L.
A1  - Rehanek, Jens
A1  - Weniger, Christian
A1  - Firsov, Alexander
A1  - Brzhezinskaya, Maria
A1  - Chatterjee, Ruchira
A1  - Lassalle-Kaiser, Benedikt
A1  - Sierra, Raymond G.
A1  - Laksmono, Hartawan
A1  - Hill, Ethan
A1  - Borovik, Andrew S.
A1  - Erko, Alexei
A1  - Föhlisch, Alexander
A1  - Mitzner, Rolf
A1  - Yachandra, Vittal K.
A1  - Yano, Junko
A1  - Wernet, Philippe
A1  - Bergmann, Uwe
T1  - X-ray absorption spectroscopy using a self-seeded soft X-ray free-electron laser
JF  - Optics express : the international electronic journal of optics
N2  - X-ray free electron lasers (XFELs) enable unprecedented new ways to study the electronic structure and dynamics of transition metal systems. L-edge absorption spectroscopy is a powerful technique for such studies and the feasibility of this method at XFELs for solutions and solids has been demonstrated. However, the required x-ray bandwidth is an order of magnitude narrower than that of self-amplified spontaneous emission (SASE), and additional monochromatization is needed. Here we compare L-edge x-ray absorption spectroscopy (XAS) of a prototypical transition metal system based on monochromatizing the SASE radiation of the linac coherent light source (LCLS) with a new technique based on self-seeding of LCLS. We demonstrate how L-edge XAS can be performed using the self-seeding scheme without the need of an additional beam line monochromator. We show how the spectral shape and pulse energy depend on the undulator setup and how this affects the x-ray spectroscopy measurements. (C) 2016 Optical Society of America
Y1  - 2016
U6  - https://doi.org/10.1364/OE.24.022469
SN  - 1094-4087
VL  - 24
SP  - 22469
EP  - 22480
PB  - Optical Society of America
CY  - Washington
ER  - 
TY  - JOUR
A1  - Mitzner, Rolf
A1  - Rehanek, Jens
A1  - Kern, Jan
A1  - Gul, Sheraz
A1  - Hattne, Johan
A1  - Taguchi, Taketo
A1  - Alonso-Mori, Roberto
A1  - Tran, Rosalie
A1  - Weniger, Christian
A1  - Schröder, Henning
A1  - Quevedo, Wilson
A1  - Laksmono, Hartawan
A1  - Sierra, Raymond G.
A1  - Han, Guangye
A1  - Lassalle-Kaiser, Benedikt
A1  - Koroidov, Sergey
A1  - Kubicek, Katharina
A1  - Schreck, Simon
A1  - Kunnus, Kristjan
A1  - Brzhezinskaya, Maria
A1  - Firsov, Alexander
A1  - Minitti, Michael P.
A1  - Turner, Joshua J.
A1  - Möller, Stefan
A1  - Sauter, Nicholas K.
A1  - Bogan, Michael J.
A1  - Nordlund, Dennis
A1  - Schlotter, William F.
A1  - Messinger, Johannes
A1  - Borovik, Andrew S.
A1  - Techert, Simone
A1  - de Groot, Frank M. F.
A1  - Föhlisch, Alexander
A1  - Erko, Alexei
A1  - Bergmann, Uwe
A1  - Yachandra, Vittal K.
A1  - Wernet, Philippe
A1  - Yano, Junko
T1  - L-edge x-ray absorption spectroscopy of dilute systems relevant to metalloproteins using an X-ray free-electron laser
JF  - The journal of physical chemistry letters
N2  - L-edge spectroscopy of 3d transition metals provides important electronic structure information and has been used in many fields. However, the use of this method for studying dilute aqueous systems, such as metalloenzymes, has not been prevalent because of severe radiation damage and the lack of suitable detection systems. Here we present spectra from a dilute Mn aqueous solution using a high-transmission zone-plate spectrometer at the Linac Coherent Light Source (LCLS). The spectrometer has been optimized for discriminating the Mn L-edge signal from the overwhelming 0 K-edge background that arises from water and protein itself, and the ultrashort LCLS X-ray pulses can outrun X-ray induced damage. We show that the deviations of the partial-fluorescence yield-detected spectra from the true absorption can be well modeled using the state-dependence of the fluorescence yield, and discuss implications for the application of our concept to biological samples.
Y1  - 2013
U6  - https://doi.org/10.1021/jz401837f
SN  - 1948-7185
VL  - 4
IS  - 21
SP  - 3641
EP  - 3647
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Veldkamp, Markus
A1  - Erko, Alexei
A1  - Gudat, Wolfgang
A1  - Abrosimov, Nikolai V.
A1  - Alex, Volker
A1  - Khasanov, Salavat
A1  - Neissendorfer, Frank
A1  - Pietsch, Ullrich
A1  - Shekhtman, Veniamin
T1  - Si(1-x)Ge(x) laterally graded crystals as monochromators for X-Ray absorption spectroscopy studies
Y1  - 1999
ER  - 
TY  - JOUR
A1  - Kanngiesser, Birgit
A1  - Hahn, O.
A1  - Wilke, Max
A1  - Nekat, B.
A1  - Malzer, Wolfgang
A1  - Erko, Alexei
T1  - Investigation of oxidation and migration processes of inorganic compounds in ink-corroded manuscripts
N2  - We studied the oxidation and migration processes of inorganic compounds in iron gall inks with a combination of micro X-ray fluorescence analysis (micro-XRF) and micro X-ray absorption near edge structure spectroscopy (micro-XANES). With elemental mapping by micro-XRF, the correlation of the minor elements in the ink to the major element Fe was investigated. Along concentration profiles of Fe, micro-XANES measurements were carried out in order to determine the oxidation state and the local environment. With the help of model inks, we could show that Cu is a further important element in the paper degradation process due to iron gall ink corrosion. (C) 2004 Elsevier B.V. All rights reserved
Y1  - 2004
SN  - 0584-8547
ER  -