scholarly journals X-ray-absorption-spectroscopic evidence for a novel iron cluster in hydrogenase II from Clostridium pasteurianum

1989 ◽  
Vol 259 (2) ◽  
pp. 597-600 ◽  
Author(s):  
G N George ◽  
R C Prince ◽  
K E Stokley ◽  
M W Adams ◽  
K E Stockley
Keyword(s):  
Structural Type ◽  
Spectroscopic Properties ◽  
The Other ◽  
Clostridium Pasteurianum ◽  
Iron Cluster ◽  
Spectroscopic Evidence ◽  
X Ray ◽  
Unknown Structure ◽  
X Ray Absorption

Hydrogenase II from Clostridium pasteurianum contains three different iron-sulphur clusters. Two are [4Fe-4S](2+.1+) clusters, whereas the other, which is thought to be the site of interaction with H2 and is known as the ‘H cluster’, is of unknown structure and possesses unusual spectroscopic properties. Analysis of the iron e.x.a.f.s. spectra shows that the H cluster contains iron co-ordinated mostly to sulphur and possesses 2.8 A (1 A = 0.1 nm) Fe--Fe separations when oxidized and 3.3 A Fe--Fe separations when reduced with H2. The data suggest that the reduced H cluster represents a new structural type of iron-sulphur cluster.

X-Ray Absorption Study of Ti and Cr Reactions with Triazine and Polyimide

1993 ◽  
Vol 323 ◽  
Author(s):  
K. Konstadinidis ◽  
R. L. Opila ◽  
M. A. Marcus ◽  
K. Short ◽  
A. E. White ◽  
...  
Keyword(s):  
Fine Structure ◽  
Polymer Matrix ◽  
Model Compound ◽  
The Other ◽  
Absorption Study ◽  
X Ray ◽  
Buried Interfaces ◽  
Metal Atoms ◽  
Π Complex ◽  
X Ray Absorption

AbstractIn this paper we present results on the use of x-ray absorption spectroscopy and in particular extended x-ray absorption fine structure (EXAFS) to study non-destructively buried interfaces between polymers and metals. In particular we study the interaction between isolated metal atoms (Ti or Cr) and the surrounding polymer matrix (polyimide or triazine). The metal atoms have been introduced into the polymer matrix using ion-implantation. We find that Cr forms a π complex with the aromatic structures of polyimide and triazine in agreement with model compound and XPS data. Ti on the other hand seems to form Ti-O-C bonds with both polymers.

Dinuclear oxofluorometallates as a new structural type of d 0 transition metal oxofluoride compound

2012 ◽  
Vol 68 (6) ◽  
pp. 602-609 ◽  
Author(s):  
Anatoly A. Udovenko ◽  
Natalia M. Laptash
Keyword(s):  
Transition Metal ◽  
Single Crystal ◽  
Structural Type ◽  
The Other ◽  
Orthorhombic Structure ◽  
X Ray Diffraction ◽  
Orthorhombic Unit Cell ◽  
Fluoride Ions ◽  
X Ray ◽  
Irradiation Process

Five isomorphous d 0 transition metal oxofluoride compounds A 3[M 2O x F11 − x ]·(AF)0.333 (A = K, Rb, NH4; M = Nb, Mo, W; x = 2, 4) have been synthesized from acid fluoride solutions, and their crystal structures have been determined by single-crystal X-ray diffraction. The basic structural building units are dinuclear M 2 X 11 (dimers) formed from NbOF5 or Mo(W)O2F4 octahedra connected by the fluorine bridging atom. In the Nb2O2F9 dimer, the O atoms occupy apical corners. In the M 2O4F7 (M = Mo, W) dimers two O atoms are also apically placed, whereas the other two O atoms are statistically disordered in equatorial planes. The arrangement of dimers is so that the hexagonal tunnels containing `free' fluoride ions are formed. During the irradiation process the orthorhombic structure of K3Nb2O2F9·(KF)0.333 transforms into a pseudo-trigonal one with a = 23.15 Å, which is the [101] diagonal of the orthorhombic unit cell. The other four trigonal crystals are merohedral twins.

scholarly journals Core-level spectra and molecular deformation in adsorption: V-shaped pentacene on Al(001)

2015 ◽  
Vol 6 ◽  
pp. 2242-2251 ◽  
Author(s):  
Anu Baby ◽  
He Lin ◽  
Gian Paolo Brivio ◽  
Luca Floreano ◽  
Guido Fratesi
Keyword(s):  
Photoelectron Spectroscopy ◽  
Spectroscopic Properties ◽  
Energy Splitting ◽  
Core Hole ◽  
Full Agreement ◽  
X Ray ◽  
Individual Contributions ◽  
X Ray Absorption ◽  
Molecular Deformation ◽  
Molecule Surface

By first-principle simulations we study the effects of molecular deformation on the electronic and spectroscopic properties as it occurs for pentacene adsorbed on the most stable site of Al(001). The rationale for the particular V-shaped deformed structure is discussed and understood. The molecule–surface bond is made evident by mapping the charge redistribution. Upon X-ray photoelectron spectroscopy (XPS) from the molecule, the bond with the surface is destabilized by the electron density rearrangement to screen the core hole. This destabilization depends on the ionized carbon atom, inducing a narrowing of the XPS spectrum with respect to the molecules adsorbed hypothetically undistorted, in full agreement to experiments. When looking instead at the near-edge X-ray absorption fine structure (NEXAFS) spectra, individual contributions from the non-equivalent C atoms provide evidence of the molecular orbital filling, hybridization, and interchange induced by distortion. The alteration of the C–C bond lengths due to the V-shaped bending decreases by a factor of two the azimuthal dichroism of NEXAFS spectra, i.e., the energy splitting of the sigma resonances measured along the two in-plane molecular axes.

Structure of Cu Ions in (Cu + Halogen or Chalcogen)-Ion Implanted Silica Glasses

2003 ◽  
Vol 792 ◽  
Author(s):  
Kohei Fukumi ◽  
Akiyoshi Chayahara ◽  
Hiroyuki Kageyama ◽  
Naoyuki Kitamura ◽  
Kohei Kadono ◽  
...  
Keyword(s):  
Silica Glass ◽  
The Other ◽  
Homogeneous Distribution ◽  
Local Concentration ◽  
X Ray ◽  
Silica Glasses ◽  
X Ray Absorption ◽  
Glass Heat ◽  
Cu Ions ◽  
Ion Implanted

ABSTRACTStructure of Cu ions in (Cl+Cu)-, (Br+Cu)-, (I+Cu)-, (S+Cu)- and (Se+Cu)-ion implanted silica glasses has been studied by x-ray absorption and optical absorption spectroscopies. Cu ions formed Cu-O bonds in the as-implanted glasses, due to the homogeneous distribution of Cu ions and the low local concentration of halogen and chalcogen ions in silica glass. Heat treatment at about 600°C caused the formation of bonds between Cu ions and halogen/chalcogen ions without forming Cu halide or chalcogenide crystals. It was deduced that the formation of these bonds was controlled by the diffusion of Cu ions in silica glass. On the other hands, it was inferred that the formation of Cu halide and chalcogenide crystals was controlled not only by the diffusion of halogen/chalcogen ions but also by the diffusion of matrix ions.

scholarly journals Evidence for the existence of Tc(IV) – humic substance species by X-ray absorption near-edge spectroscopy

2002 ◽  
Vol 90 (12) ◽  
Author(s):  
K. Geraedts ◽  
C. Bruggeman ◽  
A. Maes ◽  
Luc R. Van Loon ◽  
A. Rossberg ◽  
...  
Keyword(s):  
Fission Product ◽  
Humic Substances ◽  
Humic Substance ◽  
The Other ◽  
Alkaline Ph ◽  
X Ray ◽  
Other Hand ◽  
Solid Phases ◽  
The One ◽  
X Ray Absorption

SummaryThe redox–sensitive fission product technetium–99 has been investigated in systems containing different reducing solid phases (pyrite, magnetite, ironsulphide and Gorleben sand) on the one hand and Gorleben groundwater, which contains a high amount of humic substances, on the other hand. Initially, technetium–99 was added to these systems as pertechnetate (Tc(VII)), which was reduced in presence and absence of humic substances with the aid of the different reducing surfaces (neutral to alkaline pH). Both in absence and presence of humic substances, Tc concentrations were observed which exceeded the TcO

Stabilising pentavalent actinides—visible–near infrared and X-ray absorption spectroscopic studies of the utility of the [(Np3W4O15)(H2O)3(MW9O33)3]18−(M = Sb, Bi) structural type

2012 ◽  
Vol 41 (7) ◽  
pp. 2003-2010 ◽  
Author(s):  
Kevin S. Boland ◽  
Steven D. Conradson ◽  
Alison L. Costello ◽  
Andrew J. Gaunt ◽  
Stosh A. Kozimor ◽  
...  
Keyword(s):  
Near Infrared ◽  
Structural Type ◽  
Spectroscopic Studies ◽  
X Ray ◽  
X Ray Absorption
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