Search results for "Hydrogen"
showing 10 items of 4254 documents
Structure and Dynamics of the Instantaneous Water/Vapor Interface Revisited by Path-Integral and Ab Initio Molecular Dynamics Simulations
2015
The structure and dynamics of the water/vapor interface is revisited by means of path-integral and second-generation Car-Parrinello ab-initio molecular dynamics simulations in conjunction with an instantaneous surface definition [A. P. Willard and D. Chandler, J. Phys. Chem. B 114, 1954 (2010)]. In agreement with previous studies, we find that one of the OH bonds of the water molecules in the topmost layer is pointing out of the water into the vapor phase, while the orientation of the underlying layer is reversed. Therebetween, an additional water layer is detected, where the molecules are aligned parallel to the instantaneous water surface.
Crystal structure and Hirshfeld surface analysis of 1-(4-chlorophenyl)-2-{[5-(4-chlorophenyl)-1,3,4-oxadiazol-2-yl]sulfanyl}ethanone
2017
The title heterocyclic compound is contains an oxadizole and two chloro-substituted phenyl rings. In the crystal, C—H⋯N hydrogen bonding links the molecules into undulating ribbons parallel to the b axis. Hirshfeld surface analysis indicates that the most important contributions for the crystal packing are the H⋯C (18%), H⋯H (17%), H⋯Cl (16.6%), H⋯O (10.4%), H⋯N (8.9%) and H⋯S (5.9%) interactions.
Crystal structure and Hirshfeld surface analysis of 3-oxours-12-ene-27a,28-dioic acid (quafrinoic acid)
2017
The title compound, known as quafrinoic acid, is a pentacyclic triterpene isolated from Nauclea Pobeguinii. The compound is composed of five fused six-membered rings and the molecular conformation is stabilized by intramolecular C—H⋯O interaction, forming S6 and S8 rings.
Quantifying the limits of transition state theory in enzymatic catalysis
2017
Significance Transition state theory (TST) is the most popular theory to calculate the rates of enzymatic reactions. However, in some cases TST could fail due to the violation of the nonrecrossing hypothesis at the transition state. In the present work we show that even for one of the most controversial enzymatic reactions—the hydride transfer catalyzed by dihydrofolate reductase—the error associated to TST represents only a minor correction to the reaction rate. Moreover, this error is actually larger for the reaction in solution than in the enzymatic active site. Based on this finding and on previous studies we propose an “enzymatic shielding” hypothesis which encompasses various aspects …
Effect of H Adsorption on the Magnetic Properties of an Fe Island on a W(110) Surface
2019
<p>Low-dimensional materials, such as ultrathin films, nanoislands and wires, are actively being researched due to their interesting magnetic properties and possible technological applications for example in high density data storage. Results of calculations of an Fe nanoisland on a W(110) support are presented here with particular focus on the effect of hydrogen adsorption on its magnetic properties. This is an important consideration since hydrogen is present even under ultra-high vacuum conditions. The calculations are based on density functional theory within the generalized gradient approximation. The adsorption of H atoms is found to strongly decrease the magnetic moment of the …
Protein-lipid interactions at the air-water interface.
2010
International audience; Protein−lipid interactions play an important role in a variety of fields, for example in pharmaceutical research, biosensing, or food science. However, the underlying fundamental processes that govern the interplay of lipids and proteins are often very complex and are therefore studied using model systems. Here, Langmuir monolayers were used to probe the interaction of a model protein with lipid films at the air−water interface. The protein β-lactoglobulin (βlg) is the major component in bovine milk serum, where it coexists with the milk fat globular membrane. During homogenization of milk, βlg adsorbs to the interface of lipid fat globules and stabilizes the oil-in-…
Different Dissolution Media Lead to Different Crystal Structures of Talinolol with Impact on Its Dissolution and Solubility
2003
During the performance of dissolution tests with immediate and controlled-release talinolol tablets it was detected that the type of the buffer used as dissolution medium had a strong influence on the solubility and the dissolution behavior of the drug. It was proven that talinolol appeared in different crystal structures with strongly differing solubilities when pure water, acetate, or phosphate buffers were employed as dissolution media. The resulting crystal structures were characterized by means of light microscopy, differential scanning calorimetry, and X-ray powder diffraction. All methods were adjuvant to detect changes in talinolol crystal structures. The different solubility and di…
On dewetting dynamics of solid films of hydrogen isotopes and its influence on tritium [Beta] spectroscopy
2000
The dewetting dynamics of solid films of hydrogen isotopes, quench-condensed on a graphite substrate, was measured at various temperatures below desorption by observing the stray light from the film. A schematic model describing the dewetting process by surface diffusion is presented, which agrees qualitatively with our data. The activation energies of different hydrogen isotopes for surface diffusion were determined. The time constant for dewetting of a quench-condensed T2 film at the working temperature of 1.86 K of the mainz neutrino mass experiment was extrapolated.
AES and CEMS analysis of the formation of layers on Si steel under thermal treatment in a flux of H2/water vapour
1991
The near surface diffusion and reaction processes in iron-silicon steel (3.1 wt.%Si) during 10 min decarburization in water vapour/hydrogen have been studied. The decarburization temperature has been varied between 506 and 714°C for the fixed partial pressure ratio pH2O/pH2=0.017. An outer layer of SiO2 forms on the surface with its thickness increasing with temperature. From 600°C upwards, the decarburization process is hindered and a cementite layer is formed below the SiO2 layer. The formation of fayalite at the surface has been studied at a fixed decarburization temperature with pH2O/pH2 ranging from 0.017 to 0.49. The scale thickness reduces abruptly just before the ratio pH2O/pH2 nece…