| 1. |
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| 2. |
- Manzoni, A. M., et al.
(författare)
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Evolution of γ/γ' phases, their misfit and volume fractions in Al 10 Co 25 Cr 8 Fe 15 Ni 36 Ti 6 compositionally complex alloy
- 2019
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Ingår i: Materials Characterization. - : Elsevier BV. - 1044-5803. ; 154, s. 363-376
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Tidskriftsartikel (refereegranskat)abstract
- Recently introduced Al10Co25Cr8Fe15Ni36Ti6 compositionally complex alloy has been investigated in the as-cast state and after heat treatment in a thorough characterization. The combination of optical, scanning and transmission electron microscopy, three dimensional atom probe and x-ray diffraction, both at lab and synchrotron level provides precise information of the microstructural evolution. After the typical dendritic solidification the alloy reveals dendritic cores consisting of γ and γ' phases and interdendritic regions consisting of η and Heusler type phases. Homogenization removes the interdendritic regions and their phases and subsequent annealing produces a microstructure similar to Ni based superalloys consisting of γ/γ' phases. In addition, about 50 μm sized Al-Ni rich needle-shaped precipitates of Heusler type structure can be observed. The four phases and their evolution with heat treatment are investigated in detail. Special focus lies on the γ/γ' misfit determination and the determination of volume fractions by different methods.
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| 3. |
- Mori, R. Alonso, et al.
(författare)
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Sulfur-Metal Orbital Hybridization in Sulfur-Bearing Compounds Studied by X-ray Emission Spectroscopy
- 2010
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 49:14, s. 6468-6473
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Tidskriftsartikel (refereegranskat)abstract
- The electronic structure and ligand environment of sulfur was investigated in various sulfur-containing compounds with different structures and chemical states by using X-ray emission spectroscopy (XES). Calculations were performed using density functional theory (DFT) as implemented in the StoBe code. The sulfur chemical state and atomic environment is discussed in terms of the molecular orbitals and partial charges that are obtained from the calculations. The main spectral features can be modeled using our calculational approach. The sensitivity of the K beta emission to the cation and the local symmetry is discussed.
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| 4. |
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| 5. |
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| 6. |
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| 7. |
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| 8. |
- Wernet, Ph., et al.
(författare)
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The Structure of the First Coordination Shell in Liquid Water
- 2004
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 304:5673, s. 995-999
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Tidskriftsartikel (refereegranskat)abstract
- X-ray absorption spectroscopy and x-ray Raman scattering were used to probe the molecular arrangement in the first coordination shell of liquid water. The local structure is characterized by comparison with bulk and surface of ordinary hexagonal ice Ih and with calculated spectra. Most molecules in liquid water are in two hydrogen-bonded configurations with one strong donor and one strong acceptor hydrogen bond in contrast to the four hydrogen-bonded tetrahedral structure in ice. Upon heating from 25°C to 90°C, 5 to 10% of the molecules change from tetrahedral environments to two hydrogen-bonded configurations. Our findings are consistent with neutron and x-ray diffraction data, and combining the results sets a strong limit for possible local structure distributions in liquid water. Serious discrepancies with structures based on current molecular dynamics simulations are observed.
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| 9. |
- Alonso-Mori, Roberto, et al.
(författare)
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Energy-dispersive X-ray emission spectroscopy using an X-ray free-electron laser in a shot-by-shot mode
- 2012
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 109:47, s. 19103-19107
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Tidskriftsartikel (refereegranskat)abstract
- The ultrabright femtosecond X-ray pulses provided by X-ray free-electron lasers open capabilities for studying the structure and dynamics of a wide variety of systems beyond what is possible with synchrotron sources. Recently, this probe-before-destroy approach has been demonstrated for atomic structure determination by serial X-ray diffraction of microcrystals. There has been the question whether a similar approach can be extended to probe the local electronic structure by X-ray spectroscopy. To address this, we have carried out femtosecond X-ray emission spectroscopy (XES) at the Linac Coherent Light Source using redox-active Mn complexes. XES probes the charge and spin states as well as the ligand environment, critical for understanding the functional role of redox-active metal sites. K beta(1,3) XES spectra of Mn-II and Mn-2(III,IV) complexes at room temperature were collected using a wavelength dispersive spectrometer and femtosecond X-ray pulses with an individual dose of up to > 100 MGy. The spectra were found in agreement with undamaged spectra collected at low dose using synchrotron radiation. Our results demonstrate that the intact electronic structure of redox active transition metal compounds in different oxidation states can be characterized with this shot-by-shot method. This opens the door for studying the chemical dynamics of metal catalytic sites by following reactions under functional conditions. The technique can be combined with X-ray diffraction to simultaneously obtain the geometric structure of the overall protein and the local chemistry of active metal sites and is expected to prove valuable for understanding the mechanism of important metalloproteins, such as photosystem II.
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| 10. |
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| 11. |
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| 12. |
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| 13. |
- Kern, Jan, et al.
(författare)
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Room temperature femtosecond X-ray diffraction of photosystem II microcrystals
- 2012
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 109:25, s. 9721-9726
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Tidskriftsartikel (refereegranskat)abstract
- Most of the dioxygen on earth is generated by the oxidation of water by photosystem II (PS II) using light from the sun. This lightdriven, four-photon reaction is catalyzed by the Mn4CaO5 cluster located at the lumenal side of PS II. Various X-ray studies have been carried out at cryogenic temperatures to understand the intermediate steps involved in the water oxidation mechanism. However, the necessity for collecting data at room temperature, especially for studying the transient steps during the O-O bond formation, requires the development of new methodologies. In this paper we report room temperature X-ray diffraction data of PS II microcrystals obtained using ultrashort (<50 fs) 9 keV X-ray pulses from a hard X-ray free electron laser, namely the Linac Coherent Light Source. The results presented here demonstrate that the probe before destroy approach using an X-ray free electron laser works even for the highly-sensitive Mn4CaO5 cluster in PS II at room temperature. We show that these data are comparable to those obtained in synchrotron radiation studies as seen by the similarities in the overall structure of the helices, the protein subunits and the location of the various cofactors. This work is, therefore, an important step toward future studies for resolving the structure of the Mn4CaO5 cluster without any damage at room temperature, and of the reaction intermediates of PS II during O-O bond formation.
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| 14. |
- Kern, Jan, et al.
(författare)
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Simultaneous Femtosecond X-ray Spectroscopy and Diffraction of Photosystem II at Room Temperature
- 2013
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 340:6131, s. 491-495
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Tidskriftsartikel (refereegranskat)abstract
- Intense femtosecond x-ray pulses produced at the Linac Coherent Light Source (LCLS) were used for simultaneous x-ray diffraction (XRD) and x-ray emission spectroscopy (XES) of microcrystals of photosystem II (PS II) at room temperature. This method probes the overall protein structure and the electronic structure of the Mn4CaO5 cluster in the oxygen-evolving complex of PS II. XRD data are presented from both the dark state (S-1) and the first illuminated state (S-2) of PS II. Our simultaneous XRD-XES study shows that the PS II crystals are intact during our measurements at the LCLS, not only with respect to the structure of PS II, but also with regard to the electronic structure of the highly radiation-sensitive Mn4CaO5 cluster, opening new directions for future dynamics studies.
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| 15. |
- Kurian, R., et al.
(författare)
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Intrinsic deviations in fluorescence yield detected x-ray absorption spectroscopy : The case of the transition metal L 2,3 edges
- 2012
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Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 24:45, s. 452201-
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Tidskriftsartikel (refereegranskat)abstract
- Fluorescence yield (FY) detected x-ray absorption spectra (XAS) of 3d transition metal ions are calculated from the integrated 2p3d resonant x-ray emission spectra. The resulting FY-XAS spectra are compared with the normal XAS spectra corresponding to the absorption cross section and significant deviations between the two spectra are found. This implies that the assumption that the FY-XAS spectrum identifies with the XAS spectrum is disproved. Especially for the early transition metal systems the differences between the FY-XAS and XAS are large, due to the opening of inelastic decay channels from selected x-ray absorption final states. The theoretical calculations show that the difference between FY detection and XAS is largest for the detection in depolarized geometry. The calculations are compared with experimental spectra for oxides and coordination compounds for Fe 2+, Co 2+ and Ni 2+ systems. The implications for the sum rules in XAS and magnetic circular dichroism experiments are discussed.
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| 16. |
- Messinger, Johannes, 1963-, et al.
(författare)
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Absence of Mn-centered oxidation in the S2 → S3 Transition: : Implications for the mechanism of photosynthetic water oxidation
- 2001
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Ingår i: Journal of the American Chemical Society. - : AMER CHEMICAL SOC. - 0002-7863 .- 1520-5126. ; 123:32, s. 7804-7820
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Tidskriftsartikel (refereegranskat)abstract
- A key question for the understanding of photosynthetic water oxidation is whether the four oxidizing equivalents necessary to oxidize water to dioxygen are accumulated on the four Mn ions of the oxygen-evolving complex (OEC), or whether some ligand-centered oxidations take place before the formation and release of dioxygen during the S-3 --> [S-4] --> So transition. Progress in instrumentation and flash sample preparation allowed us to apply Mn K beta X-ray emission spectroscopy (K beta XES) to this problem for the first time. The K beta XES results, in combination with Mn X-ray absorption near-edge structure (XANES) and electron paramagnetic resonance (EPR) data obtained from the same set of samples, show that the S-2 --> S3 transition, in contrast to the S-0 --> S-1 and S-1 --> S-2 transitions. does not involve a Mn-centered oxidation. On the basis of new structural data from the S-3-state, manganese mu -oxo bridge radical formation is proposed for the S-2 --> S-3 transition, and three possible mechanisms for the O-O bond formation are presented.
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| 17. |
- Sierra, Raymond G., et al.
(författare)
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Nanoflow electrospinning serial femtosecond crystallography
- 2012
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Ingår i: Acta Crystallographica Section D. - : Wiley-Blackwell. - 0907-4449 .- 1399-0047. ; 68, s. 1584-1587
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Tidskriftsartikel (refereegranskat)abstract
- An electrospun liquid microjet has been developed that delivers protein microcrystal suspensions at flow rates of 0.14-3.1 mu l min(-1) to perform serial femtosecond crystallography (SFX) studies with X-ray lasers. Thermolysin microcrystals flowed at 0.17 mu l min(-1) and diffracted to beyond 4 angstrom resolution, producing 14 000 indexable diffraction patterns, or four per second, from 140 mu g of protein. Nanoflow electrospinning extends SFX to biological samples that necessitate minimal sample consumption.
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| 18. |
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| 19. |
- Aguilar-Calvo, Patricia, et al.
(författare)
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Shortening heparan sulfate chains prolongs survival and reduces parenchymal plaques in prion disease caused by mobile, ADAM10-cleaved prions
- 2020
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Ingår i: Acta Neuropathologica. - : SPRINGER. - 0001-6322 .- 1432-0533. ; 139:3, s. 527-546
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Tidskriftsartikel (refereegranskat)abstract
- Cofactors are essential for driving recombinant prion protein into pathogenic conformers. Polyanions promote prion aggregation in vitro, yet the cofactors that modulate prion assembly in vivo remain largely unknown. Here we report that the endogenous glycosaminoglycan, heparan sulfate (HS), impacts prion propagation kinetics and deposition sites in the brain. Exostosin-1 haploinsufficient (Ext1(+/-)) mice, which produce short HS chains, show a prolonged survival and a redistribution of plaques from the parenchyma to vessels when infected with fibrillar prions, and a modest delay when infected with subfibrillar prions. Notably, the fibrillar, plaque-forming prions are composed of ADAM10-cleaved prion protein lacking a glycosylphosphatidylinositol anchor, indicating that these prions are mobile and assemble extracellularly. By analyzing the prion-bound HS using liquid chromatography-mass spectrometry (LC-MS), we identified the disaccharide signature of HS differentially bound to fibrillar compared to subfibrillar prions, and found approximately 20-fold more HS bound to the fibrils. Finally, LC-MS of prion-bound HS from human patients with familial and sporadic prion disease also showed distinct HS signatures and higher HS levels associated with fibrillar prions. This study provides the first in vivo evidence of an endogenous cofactor that accelerates prion disease progression and enhances parenchymal deposition of ADAM10-cleaved, mobile prions.
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| 20. |
- Bergmann, U, et al.
(författare)
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High-resolution X-ray spectroscopy of rare events : a different look at local structure and chemistry
- 2001
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Ingår i: Journal of Synchrotron Radiation. - Univ Calif Berkeley, Lawrence Berkeley Lab, Phys Biosci Div, Berkeley, CA 94720 USA. Univ Calif Davis, Dept Appl Sci, Davis, CA 95616 USA. CALTECH, Jet Prop Lab, Pasadena, CA 91109 USA. : MUNKSGAARD INT PUBL LTD. - 0909-0495 .- 1600-5775. ; 8, s. 199-203
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Tidskriftsartikel (refereegranskat)abstract
- The combination of large-acceptance high-resolution X-ray optics with bright synchrotron sources permits quantitative analysis of rare events such as X-ray fluorescence from very dilute systems, weak fluorescence transitions or X-ray Raman scattering. Transition-metal K beta fluorescence contains information about spin and oxidation state; examples of the characterization of the Mn oxidation states in the oxygen-evolving complex of photosystem II and Mn-consuming spores from the marine bacillus SG-1 are presented. Weaker features of the K beta spectrum resulting from valence-level and 'interatomic' ligand to metal transitions contain detailed information on the ligand-atom type, distance and orientation. Applications of this spectral region to characterize the local structure of model compounds are presented. X-ray Raman scattering (XRS) is an extremely rare event, but also represents a unique technique to obtain bulk-sensitive low-energy (<600 eV) X-ray absorption fine structure (XAFS) spectra using hard ( 10 keV) X-rays. A photon is inelastically scattered, losing part of its energy to promote an electron into an unoccupied level. In many cases, the cross section is proportional to that of the corresponding absorption process yielding the same X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) features. XRS finds application for systems that defy XAFS analysis at low energies, e.g. liquids or highly concentrated complex systems, reactive compounds and samples under extreme conditions (pressure, temperature). Recent results are discussed.
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| 21. |
- Bruns, F, et al.
(författare)
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Complementary and alternative medicine experience in radiation oncology patients : first results of a multi-center approach
- 2006
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Ingår i: Trace elements and electrolytes. - 0946-2104. ; 23:4, s. 318-325
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Tidskriftsartikel (refereegranskat)abstract
- In recent years the demand and use of complementary and alternative medicine (CAM) in malignant diseases has increased noticeably. Since the general knowledge about CAM use is scant and CAM could potentially interact with standard therapies the German Working group “Trace Elements and Electrolytes in Oncology” performed a multi-centric study to comprehensively evaluate the use of CAM therapies in cancer patients treated with radiotherapy. Methods: 1,013 patients receiving consecutively radiotherapy for malignant diseases were interviewed using a standardized questionnaire including clinical and pathological tumor parameters as well as the type of CAM and reasons for CAM use. A self-assessment of patients’ personal conditions was performed in order to evaluate the subjective impact of CAM on quality of life. Results: A total of 59% of patients reported using CAM therapies. CAM use was more common in female patients, generally higher in advanced stages of disease and most common in breast cancer patients. Most frequently reported CAM therapies were vitamins (18%), mistletoe extracts (15%), selenium (10%), and other trace element preparations (7%). Multivariate logistic regression showed age, gender, tumor type and stage, and smoking behavior to be significant predictors for CAM use. A subjective improvement in quality of life due to the use of CAM was accounted for in 30% of patients. Conclusions: More than half of patients undergoing RT for cancer are using CAM therapies. Therefore, radiation oncologists should be asking for respective obtaining information about CAM use in order to avoid harmful interactions with conventional therapies. The value and potential hazards of such combined treatments have yet to be tested in further clinical studies.
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| 22. |
- Canton, Sophie, et al.
(författare)
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Toward Highlighting the Ultrafast Electron Transfer Dynamics at the Optically Dark Sites of Photocatalysts
- 2013
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Ingår i: The Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 4:11, s. 1972-1976
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Tidskriftsartikel (refereegranskat)abstract
- Building a detailed understanding of the structure function relationship is a crucial step in the optimization of molecular photocatalysts employed in water splitting schemes. The optically dark nature of their active sites usually prevents a complete mapping of the photoinduced dynamics. In this work, transient X-ray absorption spectroscopy highlights the electronic and geometric changes that affect such a center in a bimetallic model complex. Upon selective excitation of the ruthenium chromophore, the cobalt moiety is reduced through intramolecular electron transfer and undergoes a spin flip accompanied by an average bond elongation of 0.20 +/- 0.03 angstrom. The analysis is supported by simulations based on density functional theory structures (B3LYP*/TZVP) and FEFF 9.0 multiple scattering calculations. More generally, these results exemplify the large potential of the technique for tracking elusive intermediates that impart unique functionalities in photochemical devices.
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| 23. |
- Guo, Meiyuan, et al.
(författare)
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HERFD-XANES probes of electronic structures of ironII/IIIcarbene complexes
- 2020
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Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 22:16, s. 9067-9073
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Tidskriftsartikel (refereegranskat)abstract
- Iron centeredN-heterocyclic carbene (Fe-NHC) complexes have shown long-lived excited states with charge transfer character useful for light harvesting applications. Understanding the nature of the metal-ligand bond is of fundamental importance to rationally tailor the properties of transition metal complexes. The high-energy-resolution fluorescence detected X-ray absorption near edge structure (HERFD-XANES) has been used to probe the valence orbitals of three carbene complexes, [FeII(bpy)(btz)2](PF6)2(bpy = 2,2′-bipyridine, btz = 3,3′-dimethyl-1,1′-bis(p-tolyl)-4,4′-bis(1,2,3-triazol-5-ylidene)), [FeIII(btz)3](PF6)3, and [FeIII(phtmeimb)2]PF6(phtmeimb = [phenyl(tris(3-methylimidazol-2-ylidene))borate]−). The multiconfigurational restrict active space (RAS) approach has been used to simulate the metal K pre-edge X-ray absorption spectroscopy of these carbene complexes, and have reproduced the metal K pre-edge spectral features in terms of relative intensity and peak positions. The evident intensity difference between the FeIIand the other two FeIIIcomplexes has been elucidated with different intensity mechanisms in the transition. The smaller splitting between the t2gand egcharacter peak for [FeIII(btz)3](PF6)3has been observed in the experimental measurements and been reproduced in the RAS calculations. The results show how the combination of experimental HERFD-XANES measurements andab initioRAS simulations can give quantitative evaluation of the orbital interactions between metal and ligands for such large and strongly interacting systems and thus allow to understand and predict properties of novel complexes.
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| 24. |
- Hattne, Johan, et al.
(författare)
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Accurate macromolecular structures using minimal measurements from X-ray free-electron lasers
- 2014
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Ingår i: Nature Methods. - 1548-7091 .- 1548-7105. ; 11:5, s. 545-548
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Tidskriftsartikel (refereegranskat)abstract
- X-ray free-electron laser (XFEL) sources enable the use of crystallography to solve three-dimensional macromolecular structures under native conditions and without radiation damage. Results to date, however, have been limited by the challenge of deriving accurate Bragg intensities from a heterogeneous population of microcrystals, while at the same time modeling the X-ray spectrum and detector geometry. Here we present a computational approach designed to extract meaningful high-resolution signals from fewer diffraction measurements.
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| 25. |
- Hattne, Johan, et al.
(författare)
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Accurate macromolecular structures using minimal measurements from X-ray free-electron lasers
- 2014
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Ingår i: Nature Methods. - : Springer Science and Business Media LLC. - 1548-7091 .- 1548-7105. ; 11:5, s. 545-548
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Tidskriftsartikel (refereegranskat)abstract
- X-ray free-electron laser (XFEL) sources enable the use of crystallography to solve three-dimensional macromolecular structures under native conditions and without radiation damage. Results to date, however, have been limited by the challenge of deriving accurate Bragg intensities from a heterogeneous population of microcrystals, while at the same time modeling the X-ray spectrum and detector geometry. Here we present a computational approach designed to extract meaningful high-resolution signals from fewer diffraction measurements.
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| 26. |
- Kern, Jan, et al.
(författare)
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Taking snapshots of photosynthetic water oxidation using femtosecond X-ray diffraction and spectroscopy
- 2014
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 5, s. 4371-
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Tidskriftsartikel (refereegranskat)abstract
- The dioxygen we breathe is formed by light-induced oxidation of water in photosystem II. O-2 formation takes place at a catalytic manganese cluster within milliseconds after the photosystem II reaction centre is excited by three single-turnover flashes. Here we present combined X-ray emission spectra and diffraction data of 2-flash (2F) and 3-flash (3F) photosystem II samples, and of a transient 3F' state (250 mu s after the third flash), collected under functional conditions using an X-ray free electron laser. The spectra show that the initial O-O bond formation, coupled to Mn reduction, does not yet occur within 250 mu s after the third flash. Diffraction data of all states studied exhibit an anomalous scattering signal from Mn but show no significant structural changes at the present resolution of 4.5 angstrom. This study represents the initial frames in a molecular movie of the structural changes during the catalytic reaction in photosystem II.
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| 27. |
- Kotani, A., et al.
(författare)
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A new method of directly determining the core-hole effect in the Ce L-3 XAS of mixed valence Ce compounds : An application of resonant X-ray emission spectroscopy
- 2011
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Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048 .- 1873-2526. ; 184:3-6, s. 210-215
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Tidskriftsartikel (refereegranskat)abstract
- Using a simplified model, we calculate resonant X-ray emission (RXE) spectra with Ce 2p to 5d excitation and Ce nl to 2p de-excitation for mixed valence Ce compounds, where nl is 3d or valence states. If the core-hole effect is large to play an important role in the Ce L-3 XAS, the RXE spectral features for nl = 3d and valence states are significantly different, but if it is negligibly small, they are essentially the same. Therefore, these RXE spectra are useful as a new powerful method of directly determining the core-hole effect in the L-3 XAS. More detailed theoretical calculations of these RXE spectra are made for CeO2, and compared with new experimental data, indicating the importance of the core-hole effect. Similar investigations are desirable for some metallic mixed valence Ce compounds in which the core-hole effect is controversial. Finally, we point out that for nl = 5d we can observe the resonant inelastic X-ray scattering spectra corresponding to the charge-transfer excitations or Kondo resonance excitations.
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| 28. |
- Kotani, A., et al.
(författare)
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Spectator and participator processes in the resonant photon-in and photon-out spectra at the Ce L-3 edge of CeO2
- 2012
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Ingår i: European Physical Journal B. - : Springer Science and Business Media LLC. - 1434-6028 .- 1434-6036. ; 85:8, s. 257-
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Tidskriftsartikel (refereegranskat)abstract
- We study both theoretically and experimentally the photon-in and photon-out spectra of CeO2, which are caused by the Ce 2p to Ce 5d excitation followed by the three different de-excitation channels: (i) Ce 3d to Ce 2p (denoted by 3d-RXES), (ii) O 2p to Ce 2p (v-RXES), and (iii) Ce 5d to Ce 2p (RIXS). In 3d- and v-RXES, the 5d electron plays a role of a spectator, but in RIXS it is a participator. By extending our single impurity Anderson model (SIAM), which was used recently for our calculations of v-and 3d-RXES spectra of CeO2, we study the polarization dependence in the spectator and participator spectra, and we perform more detailed calculations for 3d- and v-RXES spectral features, as well as new calculations for the RIXS spectrum with charge transfer excitations. The polarization dependence is different for the spectator and participator spectra; we have no polarization correlation between the incident and emitted photons for the spectator spectra but a strong polarization correlation for the participator spectrum. The theoretical calculations predict that the charge transfer excitations in RIXS occur in the transfer-energy range overlapped with v-RXES, but the RIXS and v-RXES spectra can be discriminated by taking advantage of the different polarization dependence. The overlapped RIXS and v-RXES spectra are observed successfully by our experiments and well reproduced by our SIAM calculations.
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| 29. |
- Kvashnina, K., et al.
(författare)
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Electron transfer during selenium reduction by iron surfaces in aqueous solution: high resolution X-ray absorption study
- 2009
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Ingår i: Journal of Physics, Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 190:012191, s. 1-4
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Tidskriftsartikel (refereegranskat)abstract
- In several designs proposed by different countries, high-level radioactive waste will be disposed in a canister with a copper outer container and a cast iron or carbon steel insert. If the iron insert comes into contact with anoxic geological water, anaerobic corrosion could take place and release fission products such as 79Se to the biosphere. This paper present studies of the long-term kinetics of selenate (SeO42-) in the presence of iron surface under anaerobic conditions by Near Edge X-ray Absorption Spectroscopy (XANES). Substantial changes in the selenium oxidation state is found and discussed in details. We assume that such behaviour corresponds to the electron transfer from iron to selenium, which couldn't take place on oxidized iron surface. When selenate was in contact with polish steel foil in groundwater solution, reduction of Se and formation of Se(II-)was found. These findings suggest that depending of corroded or oxidised iron surface, the selenium mobility in nuclear waste disposal systems will be different.
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| 30. |
- Kvashnina, K. O., et al.
(författare)
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Chemical State of Complex Uranium Oxides
- 2013
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 111:25, s. 253002-
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Tidskriftsartikel (refereegranskat)abstract
- We report here the first direct observation of U(V) in uranium binary oxides and analyze the gradual conversion of the U oxidation state in the mixed uranium systems. Our finding clarifies previous contradicting results and provides important input for the geological disposal of spent fuel, recycling applications, and chemistry of uranium species.
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| 31. |
- Kvashnina, Kristina O., et al.
(författare)
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Direct study of the f-electron configuration in lanthanide systems
- 2011
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Ingår i: Journal of Analytical Atomic Spectrometry. - : Royal Society of Chemistry (RSC). - 0267-9477 .- 1364-5544. ; 26:6, s. 1265-1272
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Tidskriftsartikel (refereegranskat)abstract
- The valence shell electron configurations within a few electron volts above the Fermi level in cerium, ytterbium, europium and samarium compounds were probed by resonant X-ray emission spectroscopy (RXES) at the L-3 absorption pre-edge. The rare earth systems show distinct spectral signatures depending on the f-electron configuration. The high energy resolution experimental results reported here are well reproduced by atomic multiplet calculations confirming the localized character of the 4f electrons. The magnitude of the electron-electron interactions within the 4f shell and between 3d and 4f electrons is analyzed. The present technique is a powerful tool for the study of the 4f valence electron configuration that, unlike L-3 absorption spectroscopy at the main edge, is little influenced by valence electron relaxation following core hole creation.
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| 32. |
- Rasmussen, Jay, et al.
(författare)
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Amyloid polymorphisms constitute distinct clouds of conformational variants in different etiological subtypes of Alzheimers disease
- 2017
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : NATL ACAD SCIENCES. - 0027-8424 .- 1091-6490. ; 114:49, s. 13018-13023
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Tidskriftsartikel (refereegranskat)abstract
- The molecular architecture of amyloids formed in vivo can be interrogated using luminescent conjugated oligothiophenes (LCOs), a unique class of amyloid dyes. When bound to amyloid, LCOs yield fluorescence emission spectra that reflect the 3D structure of the protein aggregates. Given that synthetic amyloid-beta peptide (A beta) has been shown to adopt distinct structural conformations with different biological activities, we asked whether A beta can assume structurally and functionally distinct conformations within the brain. To this end, we analyzed the LCO-stained cores of beta-amyloid plaques in postmortem tissue sections from frontal, temporal, and occipital neocortices in 40 cases of familial Alzheimers disease (AD) or sporadic (idiopathic) AD (sAD). The spectral attributes of LCO-bound plaques varied markedly in the brain, but the mean spectral properties of the amyloid cores were generally similar in all three cortical regions of individual patients. Remarkably, the LCO amyloid spectra differed significantly among some of the familial and sAD subtypes, and between typical patients with sAD and those with posterior cortical atrophy AD. Neither the amount of A beta nor its protease resistance correlated with LCO spectral properties. LCO spectral amyloid phenotypes could be partially conveyed to A beta plaques induced by experimental transmission in a mouse model. These findings indicate that polymorphic A beta-amyloid deposits within the brain cluster as clouds of conformational variants in different AD cases. Heterogeneity in the molecular architecture of pathogenic A beta among individuals and in etiologically distinct subtypes of AD justifies further studies to assess putative links between A beta conformation and clinical phenotype.
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| 33. |
- Sevillano, Alejandro M., et al.
(författare)
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Prion protein glycans reduce intracerebral fibril formation and spongiosis in prion disease
- 2020
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Ingår i: Journal of Clinical Investigation. - : AMER SOC CLINICAL INVESTIGATION INC. - 0021-9738 .- 1558-8238. ; 130:3, s. 1350-1362
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Tidskriftsartikel (refereegranskat)abstract
- Posttranslational modifications (PTMs) are common among proteins that aggregate in neurodegenerative disease, yet how PTMs impact the aggregate conformation and disease progression remains unclear. By engineering knockin mice expressing prion protein (PrP) lacking 2 N-linked glycans (Prnp(1)(80Q)(/196Q)), we provide evidence that glycans reduce spongiform degeneration and hinder plaque formation in prion disease.Prnp(1)(80Q)(/196Q )mice challenged with 2 subfibrillar, non-plaque-forming prion strains instead developed plaques highly enriched in ADAM10-cleaved PrP and heparan sulfate (HS). Intriguingly, a third strain composed of intact, glycophosphatidylinositol-anchored (GPI-anchored) PrP was relatively unchanged, forming diffuse, HS-deficient deposits in both the Prnp(1)(80Q/196Q) and WT mice, underscoring the pivotal role of the GPI-anchor in driving the aggregate conformation and disease phenotype. Finally, knockin mice expressing triglycosylated PrP (Prnp(187N)) challenged with a plaque-forming prion strain showed a phenotype reversal, with a striking disease acceleration and switch from plaques to predominantly diffuse, subfibrillar deposits. Our findings suggest that the dominance of subfibrillar aggregates in prion disease is due to the replication of GPI-anchored prions, with fibrillar plaques forming from poorly glycosylated, GPI-anchorless prions that interact with extracellular HS. These studies provide insight into how PTMs impact PrP interactions with polyanionic cofactors, and highlight PTMs as a major force driving the prion disease phenotype.
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| 34. |
- Skirecki, T, et al.
(författare)
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Compartment-Specific Differences in the Activation of Monocyte Subpopulations Are Not Affected by Nitric Oxide and Glucocorticoid Treatment in a Model of Resuscitated Porcine Endotoxemic Shock
- 2022
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Ingår i: Journal of clinical medicine. - : MDPI AG. - 2077-0383. ; 11:9
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Tidskriftsartikel (refereegranskat)abstract
- Inhaled nitric oxide (iNO) remains one of the treatment modalities in shock, and in addition to its vasoactive properties, iNO exerts immunomodulatory effects. We used a porcine model of endotoxemia with shock resuscitation (control) and additional treatment with iNO and a steroid (treatment group). After 20 h, bone marrow (BM), peripheral blood (PB), and bronchoalveolar lavage fluid (BALF) were collected to analyze the immunophenotype and mitochondrial membrane potential (Δφ) in three subsets of monocytes. In both groups, SLA-DR expression decreased twofold on the circulating CD14+CD163+ and CD14−CD163+ monocytes, while it did not change on the CD14+CD163+. Δφ increased only in the CD14−CD163+ subpopulation (0.8 vs. 2.0, p < 0.001). The analysis of compartment-specific alterations showed that nearly 100% of BALF CD14+CD163+ and CD14−CD163+ monocytes expressed SLA-DR, and it was higher compared to PB (32% and 20%, p < 0.0001) and BM (93% and 67%, p < 0.001, respectively) counterparts. BALF CD14+CD163+ had a threefold higher Δφ than PB and BM monocytes, while the Δφ of the other subsets was highest in PB monocytes. We confirmed the compartmentalization of the monocyte response during endotoxemic shock, which highlights the importance of studying tissue-resident cells in addition to their circulating counterparts. The iNO/steroid treatment did not further impair monocyte fitness.
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| 35. |
- Vanko, Gyoergy, et al.
(författare)
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Spin-state studies with XES and RIXS: From static to ultrafast
- 2013
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Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048. ; 188, s. 166-171
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Tidskriftsartikel (refereegranskat)abstract
- We report on extending hard X-ray emission spectroscopy (XES) along with resonant inelastic X-ray scattering (RIXS) to study ultrafast phenomena in a pump-probe scheme at MHz repetition rates. The investigated systems include low-spin (LS) Fe-II complex compounds, where optical pulses induce a spin-state transition to their (sub)nanosecond-lived high-spin (HS) state. Time-resolved XES clearly reflects the spin-state variations with very high signal-to-noise ratio, in agreement with HS-LS difference spectra measured at thermal spin crossover, and reference HS-LS systems in static experiments, next to multiplet calculations. The 1s2p RIXS, measured at the Fe Is pre-edge region, shows variations after laser excitation, which are consistent with the formation of the HS state. Our results demonstrate that X-ray spectroscopy experiments with overall rather weak signals, such as RIXS, can now be reliably exploited to study chemical and physical transformations on ultrafast time scales. (C) 2012 Elsevier B.V. All rights reserved.
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| 36. |
- Yano, J, et al.
(författare)
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X-ray damage to the Mn4Ca complex in single crystals of photosystem II: : A case study for metalloprotein crystallography
- 2005
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - , Phys Biosci Div, Melvin Calvin Lab, Berkeley, CA 94720 USA. Univ Calif Berkeley, Dept Chem, Berkeley, CA 94720 USA. Tech Univ Berlin, Max Volmer Lab Biophys Chem, D-10623 Berlin, Germany. Stanford Synchrotron Radiat Lab, Stanford, CA 94305 USA. European Synchrotron Radiat Facil, F-38043 Grenoble, France. Free Univ Berlin, Inst Kristallog, D-14195 Berlin, Germany. Max Planck Inst Bioanorgan Chem, D-45470 Mulheim, Germany. : NATL ACAD SCIENCES. - 0027-8424 .- 1091-6490. ; 102:34, s. 12047-12052
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Tidskriftsartikel (refereegranskat)abstract
- X-ray absorption spectroscopy was used to measure the damage caused by exposure to x-rays to the Mn4Ca active site in single crystals of photosystem II as a function of dose and energy of x-rays, temperature, and time. These studies reveal that the conditions used for structure determination by x-ray crystallography cause serious damage specifically to the metal-site structure. The x-ray absorption spectra show that the structure changes from one that is characteristic of a high-valent Mn-4(III2,IV2), oxo-bridged Mn4Ca cluster to that of Mn(II) in aqueous solution. This damage to the metal site occurs at a dose that is more than one order of magnitude lower than the dose that results in loss of diffractivity and is commonly considered safe for protein crystallography. These results establish quantitative x-ray dose parameters that are applicable to redox-active metalloproteins. This case study shows that a careful evaluation of the structural intactness of the active site(s) by spectroscopic techniques can validate structures derived from crystallography and that it can be a valuable complementary method before structure-function correlations of metalloproteins can be made on the basis of high-resolution x-ray crystal structures.
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