摘要:

The issue of membrane capacitance (C) is re-examined. The influence of fluctuations is studied using the non-local electroelastic model developed previously. The effect of undulations is compared with that due to voltage-induced thinning of the bilayer. It is shown that the undulatory contribution to the voltage dependence ofCis significant at small surface tensions, but at higher tensions the role of compression becomes dominant. At all tensions, the effect of non-locality does not exceed 15–20% of the total undulatory contribution. The same results hold if ionic screening by the electrolyte (in a Poisson-Boltzmann approximation) is taken into consideration.

ISSN:0026-8976    

DOI:10.1080/00268970009483282

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

When nuclear Overhauser enhancement spectroscopy (NOESY) experiments are performed around the critical point ωτc= 1.12, internuclear cross-relaxation rates are dependent on the resonance frequency ω, where τcis the reorientation time of the distance vector between two magnetic dipoles. Therefore, the correlation times and, consequently, the internuclear distances can be determined precisely by measuring the cross-relaxation rates under two magnetic fields. An application with a cyclic pentapeptide is given as an example, demonstrating the use of the two-field NOESY method in molecular structure studies. NOESY experiments with mixing times beyond 500 ms are discussed.

ISSN:0026-8976    

DOI:10.1080/00268970009483283

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Atomistic molecular dynamics simulations have been used to elucidate the conformational properties of cyclooctane in the gas and bulk liquid phases. Accurate reproduction of the gas phase structure, and of the liquid phase densities and solubility parameters have been used as prerequisites to the prediction of conformational properties. The gas phase results clearly indicate the presence of a conformational mixture consisting of the crown, boat-chair, twist-boat-chair and boat-boat conformers at all temperatures (161, 313 and 400 K) studied. The fraction of the crown family of conformers was found to be relatively insensitive to temperature. However, the relative concentrations of the twist-boat-chair and boat-chair conformations was found to be highly temperature dependent with the boat-chair being favoured at low temperatures. Bulk packing was found to have a profound effect on the conformational properties in the liquid phase. At the temperatures studied (313 and 400 K) the boat-chair family was predominant, with the crown and boat families being essentially absent. The twist-boat-chair conformation was detected in the liquid phase at both temperatures. The pseudorotation pathway for the twist-boat-chair to boat-chair interconversion was prevalent in both gas and liquid phases establishing the conformational flexibility and the relative importance of the twist-boat-chair conformer in comparison to the crown family. The study successfully explains the separate experimental findings in both the gas and liquid phases of cyclooctane.

ISSN:0026-8976    

DOI:10.1080/00268970009483284

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

High levelab initiocalculations carried out for the2A′ and2A″ states of ArNO(X2Π) predict a crossing near the T-shape configuration, with the2A′ minimum being slightly deeper. Spin-orbit coupling is included through a model treatment and results in two potential energy surfaces with similar topologies, nearly parallel to each other and close to the averaged non-relativistic surface. These results are used to construct a DIM-like model for ArnNO clusters. The lowest energy cluster structures are found to resemble those for Arn+1with NO lying in the surface. The set of major magic numbers (structures of pronounced stability) is also the same as for the Arn+1clusters, and is emphasized further by the detachment of NO, which requires a larger energy than for detachment of a single Ar atom. The relations of the difference between the two dissociation energies and of the ArnNO(1/2 → 3/2) excitation energy to the magic numbers are discussed.

ISSN:0026-8976    

DOI:10.1080/00268970009483285

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A new united-atom force field is proposed for branched and linear alkanes. The proposed force field is used to study vapour-liquid equilibria for pure components and binary mixtures. Results of phase equilibria simulations are found to be in good agreement with available experimental data.

ISSN:0026-8976    

DOI:10.1080/00268970009483286

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

By means of the Direct Simulation Monte Carlo (DSMC) method, the Boltzmann equation is numerically solved for a gas of hard spheres enclosed between two parallel plates kept at different temperatures and subject to the action of a gravity field normal to the plates. The profiles of pressure, density, temperature and heat flux are seen to be quite sensitive to the value of the gravity accelerationg.If the gravity field and the heat flux are parallel (g> 0), the magnitudes of both the temperature gradient and the heat flux are smaller than in the opposite case (g< 0). When considering the actual heat flux relative to the value predicted by the Fourier law, it is seen that, ifg> 0, the ratio increases as the reduced local field strength increases, while the opposite happens ifg< 0. The simulation results are compared with theoretical predictions for Maxwell molecules.

ISSN:0026-8976    

DOI:10.1080/00268970009483287

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The low lying quartet spectrum of the molecular helium cation is investigated by configuration interaction calculations. Using large Gaussian basis sets, potential energy curves forn4Σ+u,gandn4Πu,gare computed for the statesn= 1,…, 5. Several of these states lead to equilibrium configurations having rather extended bond lengths and some of them also a relatively large dissociation energy. The spectroscopic properties of these equilibrium configurations are studied. Quartet He+2is most strongly bound in its lowest state 14ΣuwithRe= 3.424 Å andDe= 1.348 eV.

ISSN:0026-8976    

DOI:10.1080/00268970009483288

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Simulations of thick films of liquid alkanes supported on a wax-like substrate were carried out at a number of temperatures in order to investigate the structure and dynamics of molecules near the solid-liquid and the liquid-vapour interfaces. Films of butane, octane and a mixture were investigated. Near the solid surface the liquids were found to be structured and molecular diffusion slowed. However, there was no evidence of a frozen layer at this interface even near the bulk freezing temperature. The mixed liquid showed considerable segregation at both interfaces with preferential absorption of butane at the liquid-vapour interface and octane at the liquid-solid interface.

ISSN:0026-8976    

DOI:10.1080/00268970009483289

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor