Ab Initio Study on the Stability of NgnBe2N2, NgnBe3N2 and NgBeSiN2 Clusters

The global minima of Be₂N₂, Be₃N₂ and BeSiN₂ clusters are identified using a modified stochastic kick methodology. The structure, stability and bonding nature of these clusters bound to noble gas (Ng) atoms are studied at the MP2/def2‐QZVPPD level of theory. Positive Be?Ng bond dissociation energy, which gradually increases down Group 18 from He to Rn, indicates the bound nature of Ng atoms. All of the Ng‐binding processes are exothermic in nature. The Xe and Rn binding to Be₂N₂ and Be₃N₂ clusters and Ar?Rn binding to BeSiN₂ are exergonic processes at room temperature; however, for the lighter Ng atoms, lower temperatures are needed. Natural population analysis, Wiberg bond index computations, electron density analysis, and energy decomposition analysis are performed to better understand the nature of Be?Ng bonds.     

Field distribution and flux-line depinning in MgB (2)

We report the first observation of the field distribution and flux-line lattice (FLL) depinning in the vortex-state (VS) of a type-II superconductor probed by conduction electron spin resonance (CESR). CESR was performed in MgB (2) (T(c) approximately 39 K) at 4.1 GHz (1455 Oe) and 9.5 GHz (3390 Oe). The field distribution, n(H), and a standard deviation of sigma approximately 14 Oe (at 28 K/4.1 GHz and at 7 K/9.5 GHz) were inferred, respectively, from the distortion and broadening of the CESR in the VS. For both frequencies, the FLL depinning temperature was determined.     

The fluorescent probe prodan characterizes the warfarin binding site on human serum albumin

Abstract— The fluorescent probe Prodan (6-propionyl-2-dimethyl-aminonaphthalene) binds with high affinity to human serum albumin (HSA). The spectral characteristics of the Prodan bound to the protein are very different from the free Prodan in solution. These differences allowed the spectra to be deconvoluted into log-normal bands in order to quantify the bound and unbound ligand and to calculate the binding constant at different temperatures. From such temperature dependence, we found the binding to be exothermic with a van't Hoff enthalpy of -22.8 kJ mol^-1. Thermodynamic analysis suggests that the in teraction may be mainly caused by hydrophobic forces and electrostatic interactions. The above analysis of the spectra and the measures of the fluorescence polarization during the successive presence of six specific drugs suggest that the Prodan binding site corresponds with the warfarin binding site on HSA, whereas under the present experimental conditions the other characteristic binding sites of HSA were not affected. Thus, this fluorescent probe provides a rapid and simple means for the characterization of a specific binding site on HSA and also for detecting potential or nonspecific drug-protein interactions.     

Soft-x-ray laser interferometry of a plasma with a tabletop laser and a Lloyd's mirror

We report what is believed to be the first demonstration of soft-x-ray interferometry of a plasma with a tabletop soft-x-ray laser. A Lloyd's mirror interferometer was used in combination with a very compact lambda = 46.9 nm capillary-discharge-pumped laser to map the electron density in the cathode region of a pinch plasma.     

Scattering from particles on surfaces: visibility factor and polydispersity

We have developed an experimental method based on the visibility factor of light-scattering minima to obtain size-polydispersity information from contaminants upon a flat substrate. We verify the method by using double-interaction-model calculations and use this technique to examine experimentally the radial variation of a micrometer-sized fiber and the size polydispersity of spherical particles upon a substrate.     

The Reactivity Of singlet carbenes. An ab initio study

The energy barriers for the addition to ethylene of a series of carbenes have been calculated at an ab initio level. using the STO-3G and 3-21G basis sets. It is shown that the usual extrapolation of experiment results, which predicts that the reactivity of carbenes decreases when increasing its nucleophilic character, is not valid.     

The degree of hybridization in paramagnetic complexes

It is argued that in a series of complexes formed by ions of the same type and having the same geometry and ligand the degree of hybridization $\text{?}{}_{\mathrm{s}}\text{?}{}_{\mathrm{\sigma }}$ tends to decrease when covalency increases. This rule which discards any sp² explanation for the ligand hybridization has been well verified through series of d⁹ and s¹ complexes. The validity of such a rule, also useful for understanding the behaviour of $\text{?}{}_{\mathrm{s}}\text{?}{}_{\mathrm{gs}}$ in some D_2h systems, outlines that ligand core polarization effects are negligible in these cases.     

Electronic and steric effects in fragmentation reactions of Os3(CO)9(mu-C4Ph4)

P-Donor nucleophiles of cone angle >or=145 degrees are known to react with Os3(CO)9(mu-C4Ph4) quite differently from those with cone angles 相似文献