A5053987524- X-ray Spectroscopy and Fluorescence Analysis
- Electron and X-Ray Spectroscopy Techniques
- X-ray Diffraction in Crystallography
- Catalytic Processes in Materials Science
- Photosynthetic Processes and Mechanisms
- Enzyme Structure and Function
- Metal-Catalyzed Oxygenation Mechanisms
- Electrocatalysts for Energy Conversion
- Spectroscopy and Quantum Chemical Studies
- Radioactive element chemistry and processing
- Nuclear Physics and Applications
- Advanced Chemical Physics Studies
- Advanced X-ray Imaging Techniques
- Rare-earth and actinide compounds
- Mercury impact and mitigation studies
- Iron oxide chemistry and applications
- Catalysis and Oxidation Reactions
- Electrochemical Analysis and Applications
- Luminescence Properties of Advanced Materials
- Machine Learning in Materials Science
- Advanced Photocatalysis Techniques
- Crystallography and Radiation Phenomena
- Zeolite Catalysis and Synthesis
- Magnetism in coordination complexes
- Lanthanide and Transition Metal Complexes
European Synchrotron Radiation Facility
2016-2025
European Science Foundation
2006-2021
Lawrence Berkeley National Laboratory
1998-2020
CEA Grenoble
2015-2016
Université Grenoble Alpes
2014
Seattle University
2013
University of Turin
2012
National Interuniversity Consortium of Materials Science and Technology
2012
High Energy Accelerator Research Organization
2012
University of Notre Dame
2012
X-ray absorption spectroscopy and x-ray Raman scattering were used to probe the molecular arrangement in first coordination shell of liquid water. The local structure is characterized by comparison with bulk surface ordinary hexagonal ice Ih calculated spectra. Most molecules water are two hydrogen-bonded configurations one strong donor acceptor hydrogen bond contrast four tetrahedral ice. Upon heating from 25 degrees C 90 C, 5 10% change environments configurations. Our findings consistent...
X-ray absorption spectroscopy was used to measure the damage caused by exposure x-rays Mn(4)Ca active site in single crystals of photosystem II as a function dose and energy x-rays, temperature, time. These studies reveal that conditions for structure determination x-ray crystallography cause serious specifically metal-site structure. The spectra show changes from one is characteristic high-valent Mn(4)(III(2),IV(2)) oxo-bridged cluster Mn(II) aqueous solution. This metal occurs at more than...
Intense femtosecond x-ray pulses produced at the Linac Coherent Light Source (LCLS) were used for simultaneous diffraction (XRD) and emission spectroscopy (XES) of microcrystals photosystem II (PS II) room temperature. This method probes overall protein structure electronic Mn4CaO5 cluster in oxygen-evolving complex PS II. XRD data are presented from both dark state (S1) first illuminated (S2) Our XRD-XES study shows that crystals intact during our measurements LCLS, not only with respect to...
We develop a general procedure to analyse the pre-edges in 1s x-ray absorption near edge structure (XANES) of transition metal oxides and coordination complexes. Transition complexes can be described from local model with one ion. The 3d quadrupole transitions are calculated charge-transfer multiplet program. Tetrahedral have more intense pre-edge structures due mixing 4p states, implying combination dipole transitions. Divalent similar complexes, but for trivalent tetravalent oxides,...
We report here the first direct observation of U(V) in uranium binary oxides and analyze gradual conversion U oxidation state mixed systems. Our finding clarifies previous contradicting results provides important input for geological disposal spent fuel, recycling applications, chemistry species.
The direct conversion of methane to methanol (MTM) is a reaction that has the potential disrupt great part synthesis gas-derived chemical industry. However, despite many decades research, active enough catalysts and suitable processes for industrial application are still not available. Recently, several copper-exchanged zeolites have shown considerable activity selectivity in MTM reaction. Understanding nature site these materials essential any further development field. Herein, we apply...
A key question for the understanding of photosynthetic water oxidation is whether four oxidizing equivalents necessary to oxidize dioxygen are accumulated on Mn ions oxygen-evolving complex (OEC), or some ligand-centered oxidations take place before formation and release during S(3) --> [S(4)] S(0) transition. Progress in instrumentation flash sample preparation allowed us apply Kbeta X-ray emission spectroscopy (Kbeta XES) this problem first time. The XES results, combination with...
Bacterial Mn(II) oxidization by spores of Bacillus, sp. strain SG-1 has been systematically probed over the time scale 0.22 to 77 days under in-situ conditions and at differing concentrations. Three complementary techniques, K-edge X-ray absorption near-edge spectroscopy (XANES), emission (XES), synchrotron radiation-based diffraction (SR-XRD), have utilized examine time-dependent changes in Mn oxidation state, local-, long-range structure amorphous, crystalline, cell-bound, solute species....
Gold is not so inert after all! X-ray absorption spectroscopy was used to probe the activation of O2 and its reaction with CO over an Au/Al2O3 catalyst. The catalytic activity small gold particles in oxidation arises from their ability transfer charge oxygen (see picture).
The biological generation of oxygen by the oxygen-evolving complex in photosystem II (PS II) is one nature's most important reactions. recent X-ray crystal structures, while limited resolutions 3.2−3.5 Å, have located electron density associated with Mn4Ca cluster within multiprotein PS complex. Detailed structures critically depend on input from spectroscopic techniques, such as EXAFS and EPR/ENDOR, XRD resolution does not allow for accurate determination position Mn/Ca or bridging terminal...
Resonant inelastic X-ray scattering (RIXS) was used to collect Mn K pre-edge spectra and study the electronic structure in oxides, molecular coordination complexes, as well S1 S2 states of oxygen-evolving complex (OEC) photosystem II (PS II). The RIXS data yield two-dimensional plots that can be interpreted along incident (absorption) energy or transfer axis. second dimension separates (predominantly 1s 3d transitions) from main K-edge, a detailed analysis is thus possible. 1s2p final-state...
A novel concept of dosing iron ions using Fe3O4 engineered nanoparticles is used to improve biogas production in anaerobic digestion processes. Since small are unstable, they can be designed provide a controlled manner, and the highest ever reported improvement obtained. The evolution during operation followed by an array spectroscopic techniques.
An electrospun liquid microjet has been developed that delivers protein microcrystal suspensions at flow rates of 0.14–3.1 µl min −1 to perform serial femtosecond crystallography (SFX) studies with X-ray lasers. Thermolysin microcrystals flowed 0.17 and diffracted beyond 4 Å resolution, producing 14 000 indexable diffraction patterns, or four per second, from 140 µg protein. Nanoflow electrospinning extends SFX biological samples necessitate minimal sample consumption.
The catalytic performance of ceria nanoparticles is generally attributed to active sites on the particle surface. creation oxygen vacancies and thus nonstoichiometric CeO2−δ has been proposed result in Ce3+ with unpaired f electrons which can be oxidized spinless Ce4+ ions during reactions. We monitored Ce electronic structure synthesis catalase mimetic reaction colloidal under situ conditions. By means high-energy resolution hard X-ray spectroscopy, we directly probed 4f 5d orbitals....
The reduction behavior of Co/TiO2 and Co/Mn/TiO2 catalysts for Fischer−Tropsch synthesis has been investigated by soft X-ray absorption spectroscopy (XAS). In situ XAS measurements the L2,3 edges Co Mn have carried out during treatments samples in H2 at a pressure 2 mbar temperatures up to 425 °C. changes 3d valences symmetries throughout determined comparison with theoretical calculations based on charge transfer multiplet code. Furthermore, bulk Co3O4 reduced under same conditions evaluate...
The molybdenum atom in FeMoco is imperative to the high activity of enzyme and has been proposed be Mo(<sc>iv</sc>). We demonstrate that only Mo(<sc>iii</sc>) fits Mo HERFD XAS data, first example biology. Theoretical calculations further reveal an unusual spin-coupled Mo(<sc>iii</sc>).
Most of the dioxygen on earth is generated by oxidation water photosystem II (PS II) using light from sun. This light-driven, four-photon reaction catalyzed Mn 4 CaO 5 cluster located at lumenal side PS II. Various X-ray studies have been carried out cryogenic temperatures to understand intermediate steps involved in mechanism. However, necessity for collecting data room temperature, especially studying transient during O–O bond formation, requires development new methodologies. In this...
Abstract Combined high‐resolution fluorescence detection X‐ray absorption near‐edge spectroscopy, diffraction, and emission spectroscopy have been employed under operando conditions to obtain detailed new insight into the nature of Mo species on zeolite ZSM‐5 during methane dehydroaromatization. The results show that isolated Mo–oxo present after calcination are converted by CH 4 metastable MoC x O y species, which primarily responsible for C 2 H /C 3 formation. Further carburization leads...
We discuss a spectroscopic method to determine the character of chemical bonding and for identification metal ligands in coordination bioinorganic chemistry. It is based on analysis satellite lines X-ray emission spectra that arise from transitions between valence orbitals ion 1s level (valence-to-core XES). The spectra, connection with calculations density functional theory (DFT), provide information complementary other techniques, particular absorption (XANES EXAFS). spectral shape...