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H Interactions (h + interaction)

Distribution by Scientific Domains

Chemistry	60%

Selected Abstracts

Hydrogen and carbon interaction in a FeNi alloy with a vacancy

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 6 2009
Estela Gonzalez
Abstract The bonding of hydrogen and carbon to Fe and Ni in a 50:50 alloy is analysed using density functional calculations. The changes in the electronic structure of a L10 alloy upon C and H introduction at a vacancy region are addressed and a comparison with H or C in pure metals is drawn. H in bulk FeNi alloy with a vacancy locates at a tetrahedral site shifted towards the vacancy. Instead, C prefers an octahedral site (Fe based). The vacancy acts as strong traps of both C and H. Fe,Ni atoms are initially more strongly bonded to each other due to the vacancy formation. Consequently, the Fe,Fe, Fe,Ni and Ni,Ni bond strengths are diminished as new metal,C or metal,H bonds are formed. The most affected bond is the Fe,Ni, whose overlap population decreases by 72%. An analysis of the orbital interaction reveals that the Fe,H bonding involves mainly the Fe 4s, H 1s and Ni 4s orbitals. In the case of the sequential absorption, the C,H interaction is almost zero at a distance of 2.72 Å. The main interactions of these interstitials are developed with either Fe or Ni. We also consider the absorption sequence (H first or C first) and its influence on the electronic structure. Our results could be relevant to understand some steps of the carburization process during thermal cracking operations where hydrogen atoms are present. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

trans -Bis(benzylamine)dichloropalladium(II) bis(dimethyl sulfoxide) solvate

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 9 2000
Andreas Decken
The title compound, [PdCl2(C7H9N)2]·2C2H6OS, crystallizes with two molecules of dimethyl sulfoxide (DMSO) in monoclinic space group P21/n. The Pd complex is centrosymmetric and thus the phenyl rings of the benzylamine ligands are exo with respect to one another. The crystal packing reveals NH,O and CH,Cl hydrogen bonds between the organometallic molecule and the DMSO molecules, resulting in infinite chains. The distances of the ortho -H atoms on the phenyl ring to the metal center are in the range 4.71,5.34,Å, precluding any significant intramolecular Pd,H interactions. [source]

13H -Dibenzo[a,i]fluoren-13-one

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 5 2000
David G. Morris
Molecules of 13H -dibenzo[a,i]fluoren-13-one, C21H12O, straddle a crystallographic mirror plane and are essentially planar, with a dihedral angle of only 1.9,(1)° between the two naphthalene ring systems. Repulsive intramolecular C=O,H interactions therefore do not explain the larger distortions found in isomeric ketones. [source]

Van der Waals and Polar Intermolecular Contact Distances: Quantifying Supramolecular Synthons

CHEMISTRY - AN ASIAN JOURNAL, Issue 5 2008
Parthasarathy Ganguly Prof.
Abstract Crystal structures are viewed as being determined by ranges and constraints on interatomic contact distances between neighboring molecules. These distances are considered to arise from environment-dependent atomic sizes, that is, larger sizes for isotropic, van der Waals type contacts and smaller sizes for more-polar, possibly ionic contacts. Although the idea of different, or anisotropic, radii for atoms is not new, we developed a method of obtaining atomic sizes that is based on a theoretical framework. Using different atomic sizes for the same atom in different environments, we were able to rationalize some structural observations and anomalies. For example, benzene with the Pbca structure may be described in terms of two types of C,,,H interactions: a longer contact largely of the van der Waals type, and a shorter, structure-determining type (C,,,,,H,+), which we term "n-polar". Our approach is illustrated with three examples: 1),the equivalence in crystal packing of fluorobenzene, benzonitrile, pyridine N -oxide, and pyridine/HF 1:1 molecular complex, all of which take the not-so-common tetragonal P41212 space group and are practically isomorphous; 2),the similarity of the Pa3 acetylene and Pbca benzene crystal structures; and 3),the equivalence between an increase in pressure and an increase in the "n-polar" contacts in Pbca benzene; in other words, the equivalence between hydrostatic pressure and chemical pressure. In the context of crystal engineering, we describe a method whereby the topological information conveyed in a supramolecular synthon is recast in a more quantitative manner. A particular synthon, and in turn the crystal structure to which it leads, is viable within small ranges of distances of its constituent atoms, and these distances are determined by chemical factors. [source]

An interaction between opticin and heparan sulfate may provide the molecular basis for vitreoretinal adhesion

INTERNATIONAL JOURNAL OF EXPERIMENTAL PATHOLOGY, Issue 4 2004
V. John Hindson
Introduction Opticin is a member of the extracellular matrix small leucine-rich repeat (SLRP) proteoglycan/protein family, which was originally identified in the eye associated with the collagen fibrils of the vitreous humour. A putative heparin/heparan sulfate (HS) binding motif (RKERKRR) was identified at the N-terminus of human opticin, but this is absent in the bovine form. Furthermore, the strength of attachment between the vitreous and the retina was observed to be species-dependent and related to the presence or absence of this motif. We hypothesized that opticin cross-links the collagen fibrils of the vitreous to HS proteoglycans in the inner limiting lamina (a basement membrane on the inner surface of the retina), contributing towards vitreoretinal adhesion. Materials and methods Recombinant human and bovine opticin were expressed in 293-EBNA cells and purified to apparent homogeneity. Solid phase assays and surface plasmon resonance studies were used to characterize interactions between immobilized heparin/HS and opticin. Results Solid phase and BIAcore data revealed that human opticin binds heparin/HS and binds to heparin with a dissociation constant of approximately 20 nm. By contrast bovine opticin, which lacks the basic cluster, bound severalfold less tightly. Competition studies with heparin oligosaccharides indicated that the heparin/HS binding site is greater than 6 monosaccharides in length. Heparin, HS, chondroitin sulfate A (CS-A), dermatan sulfate and hyaluronan all competed with heparin for binding to human opticin but CS-C did not. Discussion Work to date suggests that the N-terminal sequence RKERKRR contributes significantly to the binding of opticin to heparin/HS. Vitreoretinal adhesion plays a key role in a number of eye diseases and inhibitors of the opticin,HS interaction could be of therapeutic value. [source]