scholarly journals High-resolution structure of the photosynthetic Mn 4 Ca catalyst from X-ray spectroscopy

2007 ◽  
Vol 363 (1494) ◽  
pp. 1139-1147 ◽  
Author(s):  
Junko Yano ◽  
Jan Kern ◽  
Yulia Pushkar ◽  
Kenneth Sauer ◽  
Pieter Glatzel ◽  
...  
Keyword(s):  
High Resolution ◽  
Spectroscopic Techniques ◽  
X Ray Diffraction ◽  
X Ray ◽  
High Resolution Structure ◽  
Resonant Raman ◽  
X Ray Absorption ◽  
Water Oxidizing Complex ◽  
S States ◽  
Resolution Structure

The application of high-resolution X-ray spectroscopy methods to study the photosynthetic water oxidizing complex, which contains a unique hetero-nuclear catalytic Mn 4 Ca cluster, is described. Issues of X-ray damage, especially at the metal sites in the Mn 4 Ca cluster, are discussed. The structure of the Mn 4 Ca catalyst at high resolution, which has so far eluded attempts of determination by X-ray diffraction, X-ray absorption fine structure (EXAFS) and other spectroscopic techniques, has been addressed using polarized EXAFS techniques applied to oriented photosystem II (PSII) membrane preparations and PSII single crystals. A review of how the resolution of traditional EXAFS techniques can be improved, using methods such as range-extended EXAFS, is presented, and the changes that occur in the structure of the cluster as it advances through the catalytic cycle are described. X-ray absorption and emission techniques (XANES and Kβ emission) have been used earlier to determine the oxidation states of the Mn 4 Ca cluster, and in this report we review the use of X-ray resonant Raman spectroscopy to understand the electronic structure of the Mn 4 Ca cluster as it cycles through the intermediate S-states.

Approaches to the High Resolution Structure of Periodic Membrane Proteins

1980 ◽  
Vol 38 ◽  
pp. 666-669
Author(s):  
J.W. Wiggins
Keyword(s):  
High Resolution ◽  
Membrane Proteins ◽  
Aqueous Media ◽  
Integral Membrane Proteins ◽  
X Ray Diffraction ◽  
Sequence Determination ◽  
X Ray ◽  
High Resolution Structure ◽  
Gain Access ◽  
Resolution Structure

Integral membrane proteins are particularly difficult to study at high resolution for several reasons. Amino acid sequence determination may be difficult because the fragmentation reagents cannot gain access to the required site, fragments are insoluble in aqueous media, or lipids are difficult to remove. X-ray diffraction studies cannot be undertaken without large enough crystals. Electron microscopy studies of the usual sort cannot be used because dehydration, negative staining, embedding, and other typical procedures are incompatible with the preservation and contrasting of the structure. Even determinations of molecular weight are made difficult by the presence of bound lipid and polysaccharide.

Charge density studies of 3dmetal (Ni/Cu) complexes with a non-innocent ligand

2017 ◽  
Vol 73 (4) ◽  
pp. 634-642 ◽  
Author(s):  
Yu-Chun Chuang ◽  
Chou-Fu Sheu ◽  
Gene-Hsiang Lee ◽  
Yu-Sheng Chen ◽  
Yu Wang
Keyword(s):  
High Resolution ◽  
Charge Density ◽  
Reduced Form ◽  
X Ray Diffraction ◽  
X Ray ◽  
Oxidation Reduction ◽  
Square Planar ◽  
Square Planar Complexes ◽  
X Ray Absorption ◽  
Cu Complexes

High-resolution X-ray diffraction experiments and atom-specific X-ray absorption experiments are applied to investigate a series of square planar complexes with the non-innocent ligand of maleonitriledithiolate (mnt), [S2C2(CN)2]z−, containingM—S bonds. Four complexes of (PyH)z[M(mnt)2]z−, whereM= Ni or Cu,z= 2 or 1 and PyH+= C5NH6+, were studied in order to clarify whether such one-electron oxidation–reduction, [M(mnt)2]2−/[M(mnt)2]1−, is taking place at the metal or the ligand site. Combining the techniques of metalK-,L-edge and SK-edge X-ray absorption spectroscopy with high-resolution X-ray charge density studies, it is unambiguously demonstrated that the electron redox reaction is ligand based and metal based for Ni and Cu pairs, respectively. The bonding characters in terms of topological properties associated with the bond critical points are compared between the oxidized form [ML]−and the reduced form [ML]2−. In the case of Ni complexes, the formal oxidation state of Ni remains as Ni2+and each mnt ligand carries a 2− charge in [Ni(mnt)2]2−, but only one of the ligands is formally oxidized in [Ni(mnt)2]1−. In contrast, in the case of Cu complexes, the mnt remains as 2− in both complexes, but the formal oxidation states of the metal are Cu2+and Cu3+. Bond characterizations andd-orbital populations will be presented. The complementary results of XAS, XRD and DFT calculations will be discussed. The conclusion on the redox reactions in these complexes can be firmly established.

EFFECT OF HEAT TREATMENT ON MICROSTRUCTURE AND MAGNETOSTRICTIVE PROPERTY OF MELT-SPUN Fe85Ga15 RIBBONS

2013 ◽  
Vol 27 (30) ◽  
pp. 1350174 ◽  
Author(s):  
HAO LIU ◽  
HAIOU WANG ◽  
MENGXIONG CAO ◽  
WEISHI TAN ◽  
YANGGUANG SHI ◽  
...  
Keyword(s):  
Heat Treatment ◽  
Fine Structure ◽  
High Resolution ◽  
Nearest Neighbor ◽  
Annealed Sample ◽  
X Ray Diffraction ◽  
X Ray ◽  
Absorption Fine ◽  
Melt Spun ◽  
X Ray Absorption

In order to study the microstructure of Fe – Ga alloy, Fe 85 Ga 15 ribbons prepared with different wheel velocity were studied by high resolution X-ray diffraction (HRXRD) and extend X-ray absorption fine structure (EXAFS). HRXRD patterns showed that only disordered A 2 phase was observed in as-cast Fe 85 Ga 15 alloy. A modified- DO 3 phase was detected in all of the melt spun samples. The HRXRD associated with EXAFS results indicated that Ga atoms were located as second-nearest neighbor along [100] orientation. A little DO 3 phase was found in ribbons annealed at 1000°C under 0.06 MPa Ar atmosphere. The result of magnetostriction measurement revealed that in the ribbon prepared with higher wheel velocity, more modified- DO 3 phase will enhance the magnetostriction. DO 3 phase in the annealed sample will deteriorate the magnetostrictive properties of Fe – Ga ribbons.

scholarly journals Experimental Investigations of the Interaction of SO2 with MgO

1999 ◽  
Vol 590 ◽  
Author(s):  
Andrea Freitag ◽  
J. A. Rodriguez ◽  
J. Z. Larese
Keyword(s):  
High Resolution ◽  
Film Thickness ◽  
Room Temperature ◽  
Temperature Programmed Desorption ◽  
Experimental Investigations ◽  
X Ray Diffraction ◽  
High Quality ◽  
X Ray ◽  
Temperature Programmed ◽  
X Ray Absorption

ABSTRACTHigh resolution adsorption isotherms, temperature programmed desorption (TPD), x-ray diffraction (XRD) and x-ray absorption near edge spectroscopy (XANES) methods were used to investigate the interaction of SO2 with high quality MgO powders. The results of these investigations indicate that when SO2 is deposited on MgO in monolayer quantities at temperatures near 100K both SO3 and SO4 species form that are not removed by simply pumping on the pre-dosed samples at room temperature. TPD and XANES studies indicate that heating of pre-dosed MgO samples to temperatures above 350 °C is required for full removal of the SO3/SO4 species. XANES measurements made as a function of film thickness indicate for coverages near monolayer completion that the SO4 species form first.

Study of Diffuse Scattering by Means of High Resolution Structure Images

1976 ◽  
Vol 34 ◽  
pp. 476-477
Author(s):  
Sumio Iijima ◽  
G. R. Anstis
Keyword(s):  
High Resolution ◽  
Neutron Diffraction ◽  
Diffuse Scattering ◽  
Reciprocal Space ◽  
The Other ◽  
X Ray ◽  
Actual Model ◽  
High Resolution Structure ◽  
Made In ◽  
Resolution Structure

Disorders in crystals with relatively simple structures which gave diffuse scattering have been extensively studied by X-ray or neutron diffraction methods. All these investigations were based on traditional diffraction methods and observations were made in reciprocal space (note observable diffraction intensities can be considered only in terms of interatomic vectors) and therefore the results obtained there leaves considerable ambiguity, particularly when we try to derive an actual model of the disordered crystals. A solution of this problem will be given only by knowing all atom positions in an assembly of atoms and for this case the observable diffracted intensity is given bywhere (xi,yi) and (xj,yj) represent position vectors of the i th and j th atoms with scattering factors fi and fj from an arbitrary origin. On the other hand, a crystal containing imperfections can be defined by

Electronic structure of (MePh3P)2[NiII(bdtCl2)2]·2(CH3)2SO and (MePh3P)[NiIII(bdtCl2)2] (bdtCl2 = 3,6-dichlorobenzene-1,2-dithiolate)

2021 ◽  
Vol 77 (6) ◽  
Author(s):  
Julia Adamko Koziskova ◽  
Yu-Sheng Chen ◽  
Su-Yin Grass ◽  
Yu-Chun Chuang ◽  
I-Jui Hsu ◽  
...  
Keyword(s):  
Electronic Structure ◽  
High Resolution ◽  
Theoretical Calculations ◽  
Nickel Complexes ◽  
Oxidation States ◽  
X Ray Diffraction ◽  
X Ray ◽  
X Ray Absorption ◽  
Bond Character ◽  
Density Modeling

High-resolution X-ray diffraction experiments, theoretical calculations and atom-specific X-ray absorption experiments were used to investigate two nickel complexes, (MePh3P)2[NiII(bdtCl2)2]·2(CH3)2SO [complex (1)] and (MePh3P)[NiIII(bdtCl2)2] [complex (2)]. Combining the techniques of nickel K- and sulfur K-edge X-ray absorption spectroscopy with high-resolution X-ray charge density modeling, together with theoretical calculations, the actual oxidation states of the central Ni atoms in these two complexes are investigated. Ni ions in two complexes are clearly in different oxidation states: the Ni ion of complex (1) is formally NiII; that of complex (2) should be formally NiIII, yet it is best described as a combination of Ni2+ and Ni3+, due to the involvement of the non-innocent ligand in the Ni—L bond. A detailed description of Ni—S bond character (σ,π) is presented.

Sign in / Sign up

Export Citation Format

Share Document