摘要:

AbstractStructural changes in a two‐dimensional model membrane are studied with the aid of the molecular dynamics (MD) technique. The model parameters of the membrane forming molecules are that of a simplified phospholipid head group: each molecule consists of three spheres which represent choline, phosphate and the ester group. The head group molecule is treated as a rigid body. Their translational motion is constrained to two dimensions. The interaction of the molecules is modelled by Lennard‐Jones and Coulomb interactions. Time dependent configurations of a system with 120 molecules (with periodic boundary conditions) are analyzed by visual inspection of trajectory plots and by the study of radial distribution functions and local order parameters. The ensemble of model particles is studied as a function of the interaction parameters and the temperature.For high temperatures the system shows liquid type behaviour. For moderate and low temperatures the formation of patterns is observed. There are definitely two trends of ordering. For strong dipole‐dipole interaction (relative to the dispersion attraction) of the model particles the individual molecules form ordered chains with decreasing temperature. However, this trend is not monotonous. ForT= 400 K the local order parameter has a maximum as a function of temperature which is interpreted as an interference between dipole‐dipole ordering and an ordering principle which is related to the molecular shape.A different order phenomenon occurs when the dispersive attraction of the molecular force centers is increased while the dipole‐dipole interaction is kept constant. For relatively larger dispersion attraction the dipoles are orientally trapped by this ordering principle leading to the breakdown of dipole order.Although the present model approach cannot be overinterpreted with respect to real biomembranes, it may be very useful for the systematic studies on the interaction of bulky molecules with membranes and the study of the influence of external parameters (like pressure) on structure

ISSN:0005-9021    

DOI:10.1002/bbpc.19940980702

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1994

数据来源: WILEY

摘要:

AbstractThe static dielectric constant of a water model (extended simple point charges, SPC/E) was evaluated by molecular dynamics simulations in the (N, V, E) ensemble for temperatures ranging fromT= 324 K to 1278 K and densities from 0.257 g/cm3to 1.1108 g/cm3. The dielectric constants calculated from fluctuations of the total dipole moment of the simulation box in the absence of an external field, and those obtained from the polarization response to an applied field were demonstrated to be consistent. Simulations within the pressure‐temperature range (up to 500 MPa and 823 K) of available experimental data yield dielectric constant in very good agreement with experiment. It appears therefore that the SPC/E potential model can be used for the simulation of the dielectric properties of supercritical water and of aqueous solutions under supercritical condition

ISSN:0005-9021    

DOI:10.1002/bbpc.19940980703

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1994

数据来源: WILEY

摘要:

AbstractBoth density profiles, surface tension and the corresponding phase equilibria are governed by the same intermolecular forces. Thus an appropriate theoretical model should be able to describe both interfacial and bulk properties by the same interaction potential. The Local Density Approximation to the Density Functional Theory is applied to the modelling of surface tension and saturated liquid densities of nonpolar molecular fluids. To take into account the nonspherical molecular shape a site‐site Lennard‐Jones interaction potential is used. The reference system is described by a hard convex body equation of state whereas the attractive contributions to the free energy were obtained from a mean‐field approximation. For a series of diatomics structures (O2, N2, CO, Cl2, ethane, ethylene) and convex core geometries (n‐alkanes, benzene, CCl4) potential parameters were estimated using surface tensions and liquid densities. The geometrical parameters for the n‐alkanes could be extrapolated up to n‐octane. A functional dependence of the potential parameters on the chain length and geometry of the molecule i

ISSN:0005-9021    

DOI:10.1002/bbpc.19940980704

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1994

数据来源: WILEY

摘要:

AbstractSeveral interaction potentials of (12‐6) Lennard‐Jones type with added partial point charges were tested for fluid hydrogenchloride. The individual atom pair correlation functions were calculated with the extended RISM theory, and were compared with the weighted superposition of intermolecular atom pair correlation functions that can be determined by a neutron diffraction experiment on fluid deuteriumchloride. Since experimental results are available at the supercritical temperature of 100°C for densities ranging from 0.5 to 1.1 g·cm−3, the RISM‐calculations were performed over that range. By comparing the results of RISM‐calculations at different thermodynamic states with experimental results, we show that one can derive an interaction potential that represents the measured structure of the liquid better than potentials derived from measurements at only one thermodynamic state. Finally a new set of Lennard‐Jones parameters that leads to a fairly good agreement with the experimental results for all densities is deduced. The individual atom pair correlation functions are given and the dependence on density

ISSN:0005-9021    

DOI:10.1002/bbpc.19940980705

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1994

数据来源: WILEY

摘要:

AbstractViscosities of binary aqueous mixtures of Acetonitrile (AN) and 1,3‐Dimethyl‐2‐imidazolidinone (Dimethylethyleneurea, DMEU) have been measured at atmospheric pressure and temperatures of 20, 25, 30, 35 and 40°C over the entire concentration region by means of Ubbelohde capillary viscometers, type 0c. For a set of 6 viscometers kinetic energy correction functions (Hagenbach‐Couette correction) have been experimentally determined for each viscometer using tridistilled water and commercially available liquids. Further corrections accounted for buoyancy and surface tension. Viscosity measurements were carried out with at least three, usually 5 to 6 viscometers, giving viscosities with an estimated uncertainty of 0.3%. Hydrodynamic volumes were determined from relative viscosity vs. concentration curves by means of the viscosity‐B‐coefficient and compared to van der Waals volumes calculated using increments for functional groups from the literature. Our data indicate the formation of associated species of DM

ISSN:0005-9021    

DOI:10.1002/bbpc.19940980706

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1994

数据来源: WILEY

摘要:

AbstractThe viscosity of the molten system Na3AlF6–AlF3– LiF was investigated using an oscillating cylinder viscometer. The melts contained up to 27.6 mass% AlF3and 7.0 mass% LiF. The temperature ranges from 840 to 1060°C. The method is absolute and the accuracy of the viscosity data of cryolite‐based melts is better then 3%. A model is presented that reproduces reasonably well the measured data. The model assumes the presence of Na3AlF6, Li3AlF6, and NaAlF4species in the melt, and the Arrhenius behaviour of the product of viscosity and of molar volume of th

ISSN:0005-9021    

DOI:10.1002/bbpc.19940980707

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1994

数据来源: WILEY

摘要:

AbstractApparent micelle molecular weights, intrinsic viscosity, actual frictional coefficients and molal volumes have been determined for benzethonium chloride (BZCl) at 20°C in 0.01 M Tris‐HCl, containing 0.01 M NaCl. The weight average molecular weight of BZC1 was determined to 28 000 ± 1500 by static light scattering, revealing an apparent aggregation number (Napp) of 60–65. Average hydrodynamic dimensions of the BZCl micelle were obtained from measurements of sedimentation velocity, intrinsic viscosity and of the mutual diffusion coefficient above the CMC (8.4 × 10−4mol/l).By studying the autocorrelation function of light scattering of BZCl solutions above the CMC, the hydrodynamic and thermodynamic perturbations were determined. The dynamics of the micellar BZCl solutions are unperturbated by additions of polyhydric alcohols within the range of 10–40% (w/w). Above the CMC a classical hard‐sphere behavior is derived from the volume fraction dependence of the scattered intensity for BZCl. The diffusivity data are consistent with a micellar hydrodynamic radius,RHof 25.5 Å, with little or no growth of BZCl micelles upon increasing surfactant concentration evident between 0.01 M NaCl and 0.1 M NaCl at pH 7.5 (20°C).Applying the linear interaction theory we obtained theoretical fits toDappvs. BZCl concentrations over a region of low salt concentrations at

ISSN:0005-9021    

DOI:10.1002/bbpc.19940980708

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1994

数据来源: WILEY

摘要:

AbstractThe 1:2 Lewis adducts of zirconium tetrachloride (ZrCl4) and cyclopentadienylzirconium trichloride (CpZrCl3) with tetrahydrofuran (THF) have been studied in solutions by means of X‐ray absorption spectroscopy. The organometallic complex CpZrCl3(THF)2has in THF solution a structure similar to the known crystallographic solid state structure. In solution the average zirconium‐carbon distance is 0.06 Å longer, and the average Zr‐oxygen distance as well as the average Zr‐chlorine distance are 0.05 Å shorter than in the solid state. In the inorganic complex ZrCl4(THF)2the zirconium‐oxygen distance is short (2.22 Å), and the trans influence difference between chloride and tetrahydrofuran ligands gives two experimentally separable zirconium‐chlorine distances (2.39

ISSN:0005-9021    

DOI:10.1002/bbpc.19940980709

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1994

数据来源: WILEY

摘要:

AbstractThirty‐four sets of data on solid‐liquid equilibria for the entitled mixtures are examined in terms of DISQUAC. On the basis of data for systems containing n‐octane, new first dispersive interchange coefficients are given for the hydroxyl/aliphatic contacts involved. They are constant from 1‐hexadecanol. The remainder interchange coefficients are kept the same as in our previous works. The relative standard deviations for the equilibrium temperatures are less than 0.025 for all the mixtures investigated. Results depend on the difference in size of the mixture co

ISSN:0005-9021    

DOI:10.1002/bbpc.19940980710

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1994

数据来源: WILEY

摘要:

AbstractMost of useful estimation techniques for surface tension of liquids are based on empirical correlations and general methods with molecular basis are rare in the literature. In this paper we show how combining an expression derived from the hole theory of Fürth with an statistical‐mechanical based equation of state, an estimation of surface tension and its behavior with temperature is easily obtain

ISSN:0005-9021    

DOI:10.1002/bbpc.19940980711

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1994

数据来源: WILEY