Electric potential distributions around discrete charges in a dielectric membrane—electrolyte solution system

Within the framework of the linearized Debye-Hückel theory an exact solution of the problem of calculating the electric potential caused by discrete fixed charges located at arbitrary positions with respect to a dielectric membrane-solution interface is presented. It takes into account the existence of an electrolyte solution on both sides of the membrane. Asymmetric ionic conditions are allowed for. For some interesting typical cases of fixed charge locations and electrolyte ionic strengths electric potential distributions were calculated and discussed. It is shown that, if the fixed charges were at or in front of the membrane surface, the characteristic distance of the electric potential decay was comparable to the Debye-Hückel length. At the opposite membrane surface only very small electric potentials can be observed. If, however, the fixed charge was placed below the membrane surface the electric potential in lateral direction and towards the other membrane surface largely increased. This effect was very sensitive to the position of the fixed charge with respect to the membrane surface.     

Ab initio calculation of the interaction energy in the P2 binding pocket of HIV‐1 protease

Interactions at the P2 binding pocket of human immunodeficiency virus type 1 (HIV‐1) protease have been studied using calculated interaction energies for model systems that mimic this binding pocket. Models were built for the P2 pocket of HIV‐1 protease in complex with TMC114, nelfinavir, and amprenavir. A two‐step procedure was applied. In the first step, the size of the model system was confined to ～40 atoms, and the interaction energy was calculated at different computational levels. In the second step, the size of the system was increased to 138 atoms, and the calculations were only performed at the HF/6‐31G** level. The interaction energy of the HIV‐1 protease/TMC114 complex was found to be more favorable than the interaction energies of the other complexes because of the additional hydrogen bond interaction this inhibitor is able to make with the HIV‐1 protease backbone. The results of the calculations are supported by stockholder charges and electrostatic potential maps. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Atomic charges,dipole moments,and Fukui functions using the Hirshfeld partitioning of the electron density

In the Hirshfeld partitioning of the electron density, the molecular electron density is decomposed in atomic contributions, proportional to the weight of the isolated atom density in the promolecule density, constructed by superimposing the isolated atom electron densities placed on the positions the atoms have in the molecule. A maximal conservation of the information of the isolated atoms in the atoms-in-molecules is thereby secured. Atomic charges, atomic dipole moments, and Fukui functions resulting from the Hirshfeld partitioning of the electron density are computed for a large series of molecules. In a representative set of organic and hypervalent molecules, they are compared with other commonly used population analysis methods. The expected bond polarities are recovered, but the charges are much smaller compared to other methods. Condensed Fukui functions for a large number of molecules, undergoing an electrophilic or a nucleophilic attack, are computed and compared with the HOMO and LUMO densities, integrated over the Hirshfeld atoms in molecules.     

The rotational barrier of an enaminonitrile. Charge and energy redistribution during rotation about the C-N bond

Ab initio quantum mechanical techniques were used together with PROAIM electron density partitioning and CHELPG electrostatic potential analysis to examine the charge density distribution of model enaminonitrile1 in its planar ground state and in its two rotational transition states. The barrier to rotation about the C-N bond was calculated to be 15.4 and 15.6 kcal/mole for the two rotational transition states at the HF/6-31G^** level of theory, and was found to originate from a redistribution of electronic kinetic energy between the amino group and the rest of the molecule in a manner similar to that found for formamide and sulfonamide. Similarly, the C-N bond length and amino group electron population were found to depend upon the C-N torsional angle. Electrostatically derived atomic point charges were also examined at each stationary point using the CHELPG program. CHELPG electrostatic potential results were found to represent the traditional external viewpoint of the charge density consistent with a resonance model, while the results from PROAIM calculations were found to describe the underlying charge density and kinetic energy density redistribution responsible for the rotational barrier.     

多孔和铸装高能推进剂的燃烧转爆轰

为研究多孔和铸装高能推进剂的危险性能 ,设计加工了燃烧转爆轰的实验装置 ,并建立了以光电管为主的测试系统。经实验发现 ,多孔装药在燃烧向爆轰的转变过程中有冲击波 /爆轰波的回传现象 ,而铸装药则没有。     

Interaction of the atoms in molecules of pyridine and its derivatives according to the results of ab initio calculations

Nonempirical quantum-chemical calculations of pyridine and its 2-, 3-, and 4-X-substituted derivatives (X = F, Cl, Br, Me, and Et) by RHF/6-311G(d) and MP2/6-311G(d) methods indicate an alternation of charges on the atoms of the pyridine ring and of the occupancy of their valence p_y-orbitals. This is caused by the polarization of bonds under the action of the charges of the atoms geminal to C(n). Bonding molecular orbitals in these molecules, formed as a result of the p_y-orbitals, occurring in the plane of the pyridine ring, are not an indication (characteristic) of p, π-conjugation between the unshared electron pair of the heteroatom of a substituent X and the π-electron system of the ring. The results of the calculations by these methods did not differ in principle. Dedicated to Academician of the Russian Academy of Sciences M. G. Voronkov in honor of his 85^th birthday. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1671–1681, November, 2006.     

Investigation of dipolar reorientation dynamics of pure bulk polymers using second harmonic generation

Second harmonic generation (SHG) in three corona-poled, pure, bulk polymers is studied as a function of temperature. It is found that this technique readily yields dynamical information that is complementary to that obtained from the technique of dielectric relaxation (DR). The SHG results are compared to those from DR in the same temperature ranges above T_g. It is found that in the temperature ranges examined, the relaxation times obtained from SHG are several orders fo magnitude longer than those measured by dielectric relaxation. This is explained as being due to the strong correlation between oriented dipoles and to trapped charges injected by the poling process. Fitting measured data to the Williams-Landau-Ferry (WLF) equation indicates that more free volume is needed in SHG for dipolar reorientation than is needed in DR. An SHG relaxation elongation phenomenon at constant temperature is found to occur in the pure bulk polymers and is similar to that found in chromophore-doped polymers previously studied. The SHG technique is developed as a new tool to directly study the reorientational dynamics of polar polymer segments. © 1994 John Wiley & Sons, Inc.     

Energy Mechanism of Charges Analyzed in Real Current Environment

We analyze in this work the energy transfer process of accelerated charges, the mass fluctuations accompanying this process, and their inertial properties. Based on a previous work, we use here the dipole antenna, which is a very convenient framework for such analysis, for analyzing those characteristics. We show that the radiation process can be viewed by two energy transfer processes: one from the energy source to the charges and the second from the charges into the surrounding space. Those processes, not being in phase, result in mass fluctuations. The same principle is true during absorption. We show that in a transient period between absorption and radiation the dipole antenna gains mass according to the amount of absorbed energy and loses this mass as radiated energy. We rigorously prove that the gain of mass, resulting from electrical interaction has inertial properties in the sense of Newton's third low. We arrive to this result by modeling the reacting spacetime region by an electric dipole.     

Guided elastic waves and perfectly matched layers

Elastic waveguides support propagating modes that have two possible features, negative group velocities and long wavelengths that, for some frequencies, degrade the accuracy or otherwise poison existing numerical schemes that utilise perfectly matched layers (PMLs) to mimic infinite domains. We illustrate why negative group velocities and long waves are potentially an issue and describe how these problems are overcome. Detailed numerical simulations confirm the accuracy of the modified scheme and provide both theoretical and pragmatic estimates for the parameters within the PML model, in particular for the damping function. We also contrast and compare different implementations of the PML model using spectral and finite difference methods.