An algorithm for first-principles calculation of vibrational spectroscopy of polyatomic molecules is proposed, which combines electronic ab initio codes with the vibrational self-consistent field (VSCF) method, and with a perturbation-theoretic extension of VSCF. The integrated method directly uses points on the potential energy surface, computed from the electronic ab initio code, in the VSCF part. No fitting of an analytic potential function is involved. A key element in the approach is the approximation that only interactions between pairs of normal modes are important, while interactions of triples or more can be neglected. This assumption was found to hold well in applications. The new algorithm was applied to the fundamental vibrational excitations of H(2)O, Cl(-)(H(2)O), and (H(2)O)(2), using the Moller-Plesset method for the electronic structure. The vibrational frequencies found are in very good accord with experiments. Estimates suggest that this electronic ab initio/VSCF approach should be feasible, with reasonable computational resources, for all-mode calculations of vibrational energies and wave functions for systems of up to 10-15 atoms. The new method can be also very useful for testing the accuracy of electronic structure codes by comparing with experimental vibrational spectroscopy. (C) 1999 American Institute of Physics. [S0021-9606(99)01928-5].
Covalent modification of human IgG and gelatin (type A) by fatty acid esters (C8, C12 and C16) of N-hydroxysuccinimide was carried out. Prepns. of hydrophobized IgG contg. 9 and 25 attached caprylic and 25 palmitic chains and prepns. of gelatin with low and high degree of modification were obtained. The adsorption of unmodified and modified proteins at a hydrophobic surface obtained by coating silica with a phosphatidyl choline monolayer was studied. It was found that an increase in the proteins' hydrophobicity leads to an increase in their adsorption detg. by hydrophobic binding which overcomes the electrostatic repulsion between the neg. charged surface and the neg. charged protein mols. An increase in the IgG hydrophobicity also resulted in the formation of a more compact monolayer. An increase in gelatin adsorption after its hydrophobization led to either the formation of a more compact monolayer or the formation of a more condensed mol. configuration after attachment of alkyl chains. For both proteins the adsorption can be accompanied by penetration of these chains into the phospholipid monolayer. [on SciFinder(R)]
An Amber-type of force field, based on experimental vibrational frequencies which is suitable for monosaccharides. is presented. In the present force field, the atomic partial charges and some torsional parameters are derived from a fit of calculated vibrational energy levels to known experimental spectra for alpha-D-glucose. The vibrational spectra were calculated using the vibrational self-consistent field (VSCF) method, which includes contributions from both anharmonic and mode-coupled terms. We find that with a reparametrization of the force field the agreement between the experimental and calculated vibrational spectra is +/-3.3 cm(-1) for alpha-glucose and +/-5.1 cm(-1) for beta-glucose. Using the VSCF method, we an also able to lend support to the idea that the COH bending motion is strongly coupled to the methylene and methine modes, as well as the other internal modes. We then test our spectroscopically derived force field by calculating the anomeric effect for alpha –> beta glucose. Molecular dynamics simulations are performed separately for both anomers (alpha and beta) in order to evaluate configurational entropy, and hence free energy. We find that out of six simulations. half correctly predict the anomeric free energy Delta G(alpha–>beta) = -0.3 kcal/mol, while two simulations yield a Delta G(alpha–>beta) = +0.2 kcal/mol, and in one simulation Delta G(alpha–>beta) similar to 0.0 kcal/mol. We also calculate the atomic pair distribution function, g(r), and show that in most simulations, the beta-conformer is slightly more adept at structuring the surrounding water molecules, resulting in better hydrogen bonding fur this anomer. However, we believe that our force field, which is static, is unable to represent adequately the dynamic interactions between the pyranose sugar and the surrounding water molecules. This resulted in a large fluctuation about the average calculated anomeric free energy of Delta G(alpha–>beta) similar to -0.1 kcal/mol. Thus, while the current all atom force field is well suited for spectroscopic studies of monosaccharides, it is not yet well suited for dynamical studies.
G Markovich, CP Collier, SE Henrichs, F Remacle, RD LEVINE, and JR Heath. 1999. “Architectonic quantum dot solids.” ACCOUNTS OF CHEMICAL RESEARCH, 32, Pp. 415-423.
Ariel Shisha-Halevy. 1999. “Bohairic Narrative Grammar.” In Ägypten und Nubien in spätantiker und christlicher Zeit, II: Schrifttum, Sprache und Gedankenwelt, Acts of the 6th International Congress of Coptic Studies, edited by S Emmel, Pp. 375–389. Wiesbaden: Reichert.
Experimental evidence of the bulk photovoltaic effect in photorefractive K1-xLixTa1-xNbyO3 (KLTN) crystals is shown. The dependence of the bulk photovoltaic effect on the pbotorefractive impurities type is presented. The current voltage characteristic is presented for different temperatures. It was found that, in Fe-doped KLTN crystals at low temperature, the bulk photovoltaic effect is the dominant transport mechanism contributing to the photorefractive process.
Over the past decade, casino gambling has become increasingly popular as a local economic development strategy. This article makes the case that using gambling as an economic development tool presupposes a rather different economicdevelopment “game” from that traditionally played. While the introduction of gambling into a community might induce the same short-run effects (local jobs and incomes) as the introduction of any other economic development project, the economic development processes at work are very different. This article compares the way the economic development game is traditionally played to the way it is played “in reverse” when casino gambling is used as the tool. The main differences are in the areas of community-corporate relations, fiscal versus economic impacts, market development, the role of government, and the provision of public goods. In light of these differences, distinctions in strategic behavior are drawn. Empirical evidence from Indiana is used to analyze the economic development game as played in the traditional setting of corporate recruitment and in the context of casino gambling. The conclusions point to some of the factors that constrain a community from fully maximizing its negotiating advantage as a resource holder.
A many-electron description of charge migration along a molecular backbone is discussed. Reference is made to site selective reactivity and the recent experiments of Weinkauf and Schlag on the dissociation of peptide ions following a localized ionization. The use of many-electron states allows a classification of the charge migration pathways through either covalent or ionic states. Electron correlation is introduced via Coulomb repulsion of electrons of opposite spins a-la Hubbard. Complete configuration interaction is implemented using the unitary group basis of Paldus. The primary factor determining charge migration is found to be the local ionization potential. It is shown that, at lower levels of excitation, the majority of possible initial states which describe localized ionization at one end of the chain lead to a preferential dissociation at the other end of the chain. (C) 1999 American Institute of Physics. [S0021-9606(99)30111-2].
Covalent modification of glucose oxidase from Aspergillus niger by the palmitic acid ester of N-hydroxysuccinimide at a molar ratio ester:protein of 56:1 results in the formation of the enzyme deriv. with 11 attached palmitic chains. Surface hydrophobicity measurements by a fluorescent probe, 8-anilino-1-naphthalenesulfonate, indicate a drastic increase in the hydrophobicity index of glucose oxidase after such a modification. The modified glucose oxidase displays a much higher adsorption affinity for hydrophilic (silica) as well as for hydrophobic (silica coated by phosphatidyl choline and cholesterol monolayers and polystyrene latex beads) surfaces, and forms more compact surface layers compared to the native glucose oxidase. Such a difference results from a spontaneous formation of micelle-like aggregates (clusters) of the hydrophobized enzyme mols. (av. size 500 nm), which come into contact with a surface. A possible structure of the glucose oxidase surface layers and the nature of the forces detg. the adsorption of the enzyme on various adsorbents are discussed. (c) 1999 Academic Press. [on SciFinder(R)]
Covalent modification of human IgG by fatty acid esters (C8 and C16) of N-hydroxysuccinimide was carried out. Surface hydrophobicity measurements, using the fluorescent probe 8-anilino-1-naphthalenesulfonate, indicate an increase in the surface protein hydrophobicity with an increase in the no. and in the length of the attached alkyl chains. The modified IgGs decrease surface tension at the air/soln. interface more effectively than the native protein. The values of the mol. cross-sectional areas (ΔA) estd. from the kinetic data are at 100-300 Å2 and reflect the size of protein segments at the interface during the adsorption process. About 40-50% increase in the ΔA was obsd. upon attachment of the C8 groups to the native IgG. The lengthening of the bound alkyl chain from C8 to C16 results in a further increase in this value. The influence of the overall IgG hydrophobicity and the length of the attached alkyl chain on the dimensions of the mobile protein segment at the surface are discussed. (c) 1999 Academic Press. [on SciFinder(R)]
Diffusion quantum Monte Carlo (DQMC) is a powerful method for calculating the vibrational ground state of large systems but is inapplicable in general for excited states. We propose a general method for excited states, based on combining DQMC with the approximate vibrational self-consistent field (VSCF) approach; the latter is used to obtain the nodes of the excited state wavefunctions. The combined DQMC-VSCF is approximate but found high accuracy in test calculations of Ar-3. DQMC-VSCF is also applied to collective mode excitations of Ar-13. The method provides full spectroscopic assignment for the computed excited states through VSCF. (C) 1999 Elsevier Science B.V. All rights reserved.
