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  • Computational Chemistry and Molecular Modeling  (787)
  • Wiley-Blackwell  (787)
  • 1980-1984  (683)
  • 1965-1969  (104)
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  • Wiley-Blackwell  (787)
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  • 1
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 3 (1969), S. 131-139 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An analytical approximation for the hypersurface E (pr-approximation) is given using the two- and three-center-functions pλμ and rμνλ, which is valid for any number N of atoms and is invariant with respect to the number of centers in its analytical structure (rule of construction). This is valid too if N is reduced either by the association of atoms or by transitions to infinity. pλμ can be fixed by two-center-systems. But rμνλ is still free except for the fulfilling of some simple requirements. The rule of construction proposed for E is an example for using so-called analytical computers.
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  • 2
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    International Journal of Quantum Chemistry 3 (1969), S. 149-167 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The general formulas which are convenient for cluster analysis of a configuration interaction wave function are presented. These formulas are then used for cluster analysis of the “complete” configuration interaction wave functions of the π-electronic models of benzene and butadiene obtained with a semiempirical method of the Pariser-Parr-Pople type using three different parameterizations. For butadiene the calculations are carried out with Hückel, Hartree-Fock, and Brueckner molecular orbitals. The results clearly indicate that Sinanoǧlu's statement [1, 2], concerning the relative unimportance of the linked parts of the tetraexcited state coefficients in the ci expansion, is justified for these delocalized systems.
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  • 3
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    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 3 (1969), S. 219-224 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Some calculations are presented on the hydrogen bond using a perturbation theory approach. Results confirm indications of earlier work that perturbation theory is capable of giving a reasonable description of hydrogen bonded systems.
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  • 4
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 5
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    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 3 (1969) 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 6
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    International Journal of Quantum Chemistry 3 (1969), S. 297-301 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The expansion of the wave function for the 23S state of the two-electron atom in the neighbourhood of the singularity at r1 = r2 = 0 is considered. The restrictions imposed on the variational functions by this expansion are discussed. For the 23S state of He, Li+, N5+ the behaviour of the variational function based on the Fock expansion in the neighbourhood of this singularity is investigated. The agreement of the variational coefficients with the theoretical coefficients is satisfactory. The calculated values of E and 〈δ(r2)〉 for He, Li+, N5+ are given.
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  • 7
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    International Journal of Quantum Chemistry 3 (1969), S. 317-325 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A method of calculating the energy of the long-range interaction between atoms and charges is presented. Simplification of the solution of the perturbation equations is achieved by a formal use of the “Double-Perturbation Method”. Numerical results for the energies of the 2pσ state of HeH+2 are obtained.
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  • 8
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    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 3 (1969) 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 9
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    International Journal of Quantum Chemistry 3 (1969), S. 445-483 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An earlier analysis of the canonical form of a pair of invertible operators obeying the exchange rule \documentclass{article}\pagestyle{empty}\begin{document}$$ AB = \omega BA $$\end{document} is extended to cover a set of operators, between each pair of which a relation of this type exists; and for which a power of each operator is the unit matrix. Such relations define a system which may be regarded as a generalization of the Dirac matrices of relativistic quantum mechanics. We concentrate upon the group theoretic aspects of such a system and its matrix representations. Applications arise from the fact that all projective representations of finite abelian groups take the form of a Dirac Group. In particular, the representations of the magnetic space groups, which are projective representations of the lattice groups, arise in this manner.
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  • 10
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    International Journal of Quantum Chemistry 3 (1969), S. 13-15 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 11
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The π-electronic properties of furan, oxazole, benzofuran, benzoxazole, anthranil, and dibenzofuran are calculated by the semiempirical self-consistent-field molecular orbital method. A single set of parameters is found which satisfactorily reproduces the π → π* electronic transition energies and other π-electronic properties.
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  • 12
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    International Journal of Quantum Chemistry 3 (1969), S. 67-71 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Alternatives to the Mulliken method of partitioning the overlap charge density in self-consistent charge molecular-orbital calculations are examined. It is found that more realistic methods may lead to significantly different self-consistent charges, and different ordering of the electronic energy levels.
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  • 13
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    International Journal of Quantum Chemistry 3 (1969), S. 621-634 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Generalizing the method of Hirschfelder, Curtiss and Bird for the calculation of the polarizability of molecules, we have calculated both the diagonal and off-diagonal polarizability tensor elements of the nucleotide bases and base pairs. In the course of calculations also the components of the permanent dipole moments have been computed for these systems.On the basis of the results obtained we have determined also the critical field strengths necessary to break off a base pair and thus to induce the unwinding of the DNA double helix. According to the data obtained, a field strength of the order 108 V/cm can induce the unwinding of DNA if its direction lies in the plane of the base pairs.
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  • 14
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The electronic spectrum of biphenylene has been studied theoretically. The investigation is based on the semi-empirical LCAO SCF MO method with various degrees of approximations. The results have been analysed with regard to the following two factors: (a) The difference in effective electronegativity between the carbon atoms in the four-membered ring and the other carbon atoms in the molecule. (b) The inclusion of doubly excited configurations in the description of the π-electronic molecular states. The theory satisfactorily interprets the excitation energies and the nature of the electronic transitions. The predictions are particularly affected by the inclusion of the doubly excited configurations. On the basis of these results, the empirical parameters used are discussed.
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  • 15
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    International Journal of Quantum Chemistry 3 (1969), S. 73-78 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An adiabetic theory of spin lattice relaxation is proposed. It is shown that if one takes account of the adiabatic adaptation of the electrons to the motion of the ionic complex the motor of the relaxation is not the crystalline potential modulation but the fluctuation of the effective magnetic field produced by the complex near the paramagnetic system.
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  • 16
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    International Journal of Quantum Chemistry 3 (1969), S. 107-113 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Using the natural orbital representation and optimizing the exponents in the Slater-type orbital basis, configuration interaction type wave functions for the helium atom are given which combine compactness and high accuracy.
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  • 17
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    International Journal of Quantum Chemistry 3 (1969), S. 141-143 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 18
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    International Journal of Quantum Chemistry 3 (1969), S. 185-194 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Polarization is shown to play a non-negligible role in two properties of the ground state of benzene-iodine type complexes: their dipole moment, and the halogen infrared spectrum. These results, compared with preceding results concerning π-π complexes, suggest that the ground-state properties of charge-transfer complexes should not be interpreted exclusively by the usual resonance mode.
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  • 19
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    International Journal of Quantum Chemistry 3 (1969), S. 225-230 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The zero-field splitting parameters D, E, and D* are calculated theoretically for four phenyl naphthalenes. Esr measurements show that the theoretical calculations are in good agreement with experiment. Comparison of the theoretical and experimental results gives some insight into the geometry of these molecules in their lowest triplet state.
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  • 20
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The quantum theory of the Faraday effect or magnetic rotatory power is set up for diamagnetic molecules and is based upon a variation-perturbation method which, unlike the usual Dirac perturbation theory, needs only the knowledge of the wave function ψ0(0) of the ground state of the non-perturbed molecule. The principle of this theory includes in the expression of the perturbed wave function, vectors which characterize the contribution of the different fields of perturbation. The quantities which descríbe the Faraday effect, obtained from the calculation of the electric and magnetic macroscopic dipole moments, are expressed from ψ0(0) and the vectors precedently introduced. They are determined by a variation calculus.
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  • 21
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    International Journal of Quantum Chemistry 3 (1969), S. 503-511 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The ground state wave-function of a two electrons atom may be represented to any accuracy by a 1S projected Slater determinant built on hypercomplex spin-orbitals.
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  • 22
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    International Journal of Quantum Chemistry 3 (1969), S. 535-535 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 23
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    International Journal of Quantum Chemistry 3 (1969), S. 553-568 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Single-exponential functions of the forms 1s̄ = 1s, 2s̄ = N1(2s + b1s + a3s), 2p̄ = N2(2p + c3p) are introduced as an alternative to the Slater orbitals 1s, 2s, 2p for the atoms of the first period. The orbitals are intended for molecular calculations and the parameters a and c should be chosen in order to make the basis consistent with a given preliminary description of the molecule: see Part I, G. Del Re, Intern. J. Quantum Chem. 1, 293 (1967), but, first of all, a study of their behavior in atomic systems is necessary. Therefore orbital exponents and total atomic energies are determined by optimization: the promotion coefficients a and c are zero for best-atoms and the functions become strictly hydrogen-like orbitals. Comparisons are allowed with Slater's, Roothaan's, Ransil's and SCF orbitals.Given promoted 2s̄ and 2p̄ orbitals on carbon atoms in a carbon-carbon sigma bond, we fix the coefficient a and c in order to obtain one center sp orbitals orthogonal to one another. These are discussed, mapped and compared with the two center hybrids obtained by the Löwdin orthogonalization.
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  • 24
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Procedures are presented which are expected to produce good numerical lower bounds to eigenvalues for Hamiltonians having continuous spectra. Further, it is observed how these lower bounds can be utilized in other estimation methods.
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  • 25
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A general formalism is presented for the determination of the optimum natural orbitals within the various strongly orthogonal geminals of a wavefunction describing a 2N-electron closed-shell molecule or atom. The relationship to Hartree-Fock-Roothaan theory is established; the algorithm that is developed is quadratically convergent to the desired result, and does not ignore off diagonal Lagrangian multipliers, or require an infinite series of 2 × 2 orthogonal transformations of the original basis.
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  • 26
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    International Journal of Quantum Chemistry 3 (1969), S. 711-722 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The generalized algebraic eigenvalue problem (A - λB)x = 0 arises in the use of the variation method in quantum mechanics. If, within the limitations of the computer word-length, the basis set used to expand the trial wave function is linearly dependent, the matrix B becomes singular. Three different algorithms designed to deal with this difficulty have been investigated, paying special attention to the problem of identifying which members of the basis set are effectively linearly dependent. The advantages and limitations of each method are discussed.
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  • 27
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Using the Rayleigh-Schrödinger perturbation formalism, expressions are obtained for the nth order energy and the nth order wave function. No restrictions are placed on the degeneracy of the state or the order of perturbation in which the degeneracies are resolved. By the use of suitable operators, the formulae are expressed in compact form.
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  • 28
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    International Journal of Quantum Chemistry 3 (1969), S. 823-849 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The long range intermolecular forces in terms of the interaction energies between two conjugated molecules are computed and discussed for the cases: (a) a point charge and ethylene, (b) two ethylene molecules, (c) two hexatriene molecules, (d) two benzene molecules, (e) two naphthalene molecules, and (f) two polar merocyanine molecules. The calculations are based on Buckingham's theory of long range intermolecular forces and the author's values for multipole moments and polarizabilities presented previously. The advantage of the treatment is: asymmetric molecules are correctly described and the intermolecular potential is better approximated than by the usual dipole approximation.
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  • 29
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    International Journal of Quantum Chemistry 3 (1969) 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 30
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    International Journal of Quantum Chemistry 3 (1969), S. 781-793 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Radiation damping of three atoms in a radiation field is studied for both a linear and closed-chain configuration. One atom of the system is initially excited. Use is made of the Heitler-Ma perturbation procedure up to second order. The discussion is developed in terms of the symmetry of the interactions within the system. The interactions arising from dipole transitions perpendicular to the plane of the closed chain are shown to be similar to the interactions in a two-atom system, and the results are extended to cover larger rings.
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  • 31
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    International Journal of Quantum Chemistry 3 (1969), S. 1064-1066 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 32
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    International Journal of Quantum Chemistry 19 (1981), S. 25-31 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: As an alternative to the density functional approach to estimating total molecular correlation energies, the equation Ecorr=-0.06593 ∑i=1M Ri-0.3916, where Ri=〈r2〉i½ and i runs over the localized molecular orbitals was fitted to 25 STO-3G data points with a root-mean-square error of 0.025 hartree. Other more general equations were tried but no significant improvement was observed in the fit.
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  • 33
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    International Journal of Quantum Chemistry 19 (1981), S. 105-112 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Quantum mechanical calculations have been made of vibrational transition probabilities in the collinear collision of an inert gas atom with either CO2 or OCS. The dependence of the transition probability on the relative translational energy and the reduced mass is similar to that found for atom-diatom collisions. The transition P00 → 10 (excitation of the first stretching mode) is much greater than P00 → 01 (the second stretching mode). This is largely due to the difference in frequencies but it has been shown that there is an independent mass factor responsible for this difference.
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  • 34
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: While the concept of the graph center is unambiguous (and quite old) in the case of acyclic graphs, an attempt has been made recently to extend the concept to polycyclic structures using the distance matrix of a graph as the basis. In this work we continue exploring such generalizations considering in addition to the distance matrix, self-avoiding walks or paths as graph invariants of potential interest for discriminating distinctive vertex environments in a graph of polycyclic structures. A hierachy of criteria is suggested that offers a systematic approach to the vertex discrimination and eventually establishes in most cases the graph center as a single vertex, a single bond (edge), or a single group of equivalent vertices. Some applications and the significance of the concept of the graph center are presented.
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  • 35
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    International Journal of Quantum Chemistry 19 (1981), S. 251-257 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In this paper we define the algebraic structure of a reduced fermion density matrix. We relate the algebraic structure to certain symmetry properties of the reduced density matrix.
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  • 36
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    International Journal of Quantum Chemistry 19 (1981), S. 259-269 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A method of expansion of molecular orbital wave functions into valence bond (VB) functions is extended to molecular fragments. The wave function is projected onto a basis of mixed determinants, involving molecular orbitals as well as fragment atomic orbitals, and is further expressed as a linear combination of VB functions, characteristic of structural formulas of the fragment but whose remaining bonds are frozen. Structural weights for the fragment are deduced from this expression. Delocalized molecular orbitals are used as a startpoint, as they are after an ordinary SCF calculation. Wave functions of medium-sized molecules may be analyzed with reasonable storage requirements in a computer.
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  • 37
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    International Journal of Quantum Chemistry 19 (1981), S. 413-426 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The generalized branching diagram (GBD) spin representation is defined as the method of sequentially coupling together a number of subsystem spin eigenfunctions using the general rules of angular momentum coupling. It is shown that any GBD representation may also be obtained by Schmidt orthogonalizing a set of cannonical spin-paired (SP) functions, provided the SP basis is suitably ordered. The ordering procedure used is well suited to computer implementation. This is a generalization of results known in the literature for the Yamanouchi-Kotani and for the Serber spin representations.
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  • 38
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    International Journal of Quantum Chemistry 19 (1981), S. 383-399 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The molecule-in-molecule method of computation has been applied in a SCF study of the electronic absorption spectra of 2- and 3-phenylfurans and 2,2′- and 3,3′-bifurans. The computed values for the transition energies and band intensities differ for the different isomers and help one to assign the preferred conformer of the studied molecules. Computations were performed on planar as well as nonplanar conformers. The calculated parameters as well as the interaction energy suggest all-planar configuration for the studied molecules. A model potential for the sigma framework for the ortho-hydrogens is considered. The calculated steric repulsion energy is negligible compared to the π delocalization. The height of the rotational barrier was larger for 2-phenylfuran than for 3-phenylfuran, and larger for 2,2′-bifuran than for 3,3′-bifuran. This result is in accord with predictions based on the extent of “π” conjugation in these molecules.
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  • 39
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    International Journal of Quantum Chemistry 19 (1981), S. 451-461 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ab initio LCAO SCF MO calculations are carried out on the ground state and d-d transition states of CoF64-, CoF63-, and CoF62- complexes with a basis set of more than double-zeta quality. To obtain a better description for the excitation energy of d-d transition states, a ligand field configuration interaction calculation is performed. The calculation is improved further by taking into account the correlation energy in the central metal atom and it gives good results for the observed excitation energies. Especially, the excitation energies for the states which have the same configuration as the ground state agree with observed ones within about 1 kK. The excitation energies of several charge transfer states in the CoF62- complex are also computed at the level of SCF MO calculation and the assignments are made for the four strong bands observed in the energy region higher than the weak d-d bands.
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  • 40
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    International Journal of Quantum Chemistry 19 (1981), S. 483-484 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 41
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    International Journal of Quantum Chemistry 19 (1981), S. 505-514 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The properties of the algebraic structure of fermion density matrices are studied. The algebraic structure of a density matrix leads to a more varied and detailed classification scheme than that offered by the usual shell structure approach. Investigation of the algebraic structure of fermion density matrices by the methods of algebraic topology leads to a classification scheme based on Betti numbers.
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  • 42
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    International Journal of Quantum Chemistry 20 (1981) 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
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  • 43
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    International Journal of Quantum Chemistry 20 (1981), S. 41-48 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synchrotron radiation has been used to determine the fluorescence decay parameters of a tryptophan-containing oligopeptide, Lys-Trp-Lys, bound to nucleic acids. All fluorescence decay curves can be fitted by a sum of two exponentials. The two lifetimes very likely correspond to two conformational states of the oligopeptide. The mean fluorescence lifetime of the peptide is not markedly affected upon binding to nucleic acids even though the fluorescence quantum yield is strongly reduced. A model is presented that accounts for the existing fluorescence data: two consecutive complexes are formed both involving electrostatic interactions. In one of the complexes the tryptophyl ring is stacked with the nucleic acid bases and its fluorescence is completely quenched. The other complex emits a fluorescence having characteristics which are similar to those of the free peptide.
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  • 44
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    International Journal of Quantum Chemistry 19 (1981), S. 1099-1103 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: After emphasizing the importance of absorption spectra of metal clusters, with special reference to alkali halide IR absorption, the equilibrium configurations and the binding energies of alkali halide clusters are discussed in terms of a very simple two-body interaction.
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  • 45
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    International Journal of Quantum Chemistry 19 (1981), S. 1133-1135 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
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  • 46
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    International Journal of Quantum Chemistry 20 (1981), S. 167-178 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The paper reports comparison of electrostatic charge and energy distribution on the basis of the CNDO/2 method for six forms of prostaglandins-PGF2α, PGF1β, PGE1, PGE2, PGB1, and PGA1-having diverse physiological action. The isopotential mapping done in three dimension showed that the lower value of electrostatic potential and proximity of the two low energy regions around O9 and O11 in PGE2 and PGF2α is probably responsible for their higher abortificient activity. We also compare here the variation of the long- and short-range interaction between ring-chain and chain-chain portion of different forms and compared them with the variation in their action.
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    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We performed ab initio pseudopotential and CNDO calculations on γ-aminobutyric acid (GABA) and its Ca2+ and Mg2+ clathrates. We were particularly interested in the rotational barrier existing between two extreme conformers of GABA and its modification upon metal complexing. We found that the pseudopotential method predicts a coordination of the ions to GABA and that this coordination inverts the rotational barrier observed for the isolated molecule. We also looked into the adequacy of CNDO for the study of this type of coordination and found several shortcomings in its predictions. The biological implications of these findings are discussed and a hypothesis on the role of a GABA-Ca2+ complex is presented.
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  • 48
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    International Journal of Quantum Chemistry 19 (1981) 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
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  • 49
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    International Journal of Quantum Chemistry 19 (1981), S. 493-500 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In the frame of direct minimization of MC-SCF energy by an orthogonal transformation of the basis, a new procedure for iteratively solving the orbital equations is presented, in which the orthogonal matrix is calculated by the singular value and vector decomposition of a nonsymmetric matrix. The procedure is applied to the self-consistent electron pair theory and tested on LiH molecule. Convergence rate and numerical stability are found to be satisfactory.
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A method for basis set generation for SCF calculations is proposed. Using SCF orbitals and orbital energies obtained in the extended basis set the Fock operator can be expressed as its spectral resolution. The sum of differences between occupied orbital energies and corresponding eigenvalues obtained by the diagonalization of this operator in the new smaller basis set is a criterion of the quality of this new set. The present method consists of the minimization of this sum by changing the parameters that determine the new basis functions. An example of the optimization of the different Gaussian basis sets for the LiH molecule is described.
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    International Journal of Quantum Chemistry 19 (1981), S. 637-648 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An SCF LCAO MO calculation on the methane-methane-methane system is presented, in order to analyze the deviation from pairwise additivity of the interaction energy. Three-body terms are shown to be remarkably similar to those of noble gas trimers both in magnitude and in their dependence on the geometrical arrangements of the three molecules.
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    International Journal of Quantum Chemistry 19 (1981), S. 673-679 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Making use of different information measures, the Pauli exclusion principle and the first Hund rule were found to be related to a trend toward acquiring a maximum information content of the atoms and molecules, and more generally, for any fermion system. The bosons conversely always have a minimum (zero) information content with respect to the permutation symmetry of their wave functions. Some new interpretations of the Pauli principle are presented.
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    International Journal of Quantum Chemistry 19 (1981), S. 681-691 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A first principles method based on an APW-k · p band structure calculation is derived in order to obtain the self-consistent eigenenergies, crystal potential, and electronic density. The simplicity and extensions of the method are discussed, including comparison with the results obtained by the use of the Chadi and Cohen special points technique.
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    International Journal of Quantum Chemistry 19 (1981), S. 719-720 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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    International Journal of Quantum Chemistry 19 (1981), S. 729-734 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An analytic atomic active electron model potential adjusted to experimental single-particle energy levels is used to generate wave functions for the valence and excited states of O1+, F2+, Ne3+, Na4+, and Mg5+. Using these wave functions in conjunction with the Born approximation and the LS-coupling scheme, we calculate optical oscillator strengths for excitations from the 1s22s22p3(4S3/2) ground state. The results are compared to experimental data and other calculations. Systematic trends along the isoelectronic sequence are discussed.
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    International Journal of Quantum Chemistry 19 (1981), S. 763-769 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A coupled perturbation theory for the antisymmetrized product of separated geminals (APSG) approximation is derived. The variational principle for the APSG wave function in an external oscillating field is employed and a set of equations of the form analogous to the normal RPA is obtained. At this level the reduced resolvent in the form of a spectral expansion is written and it is used for the evaluation of the second-order properties.
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    International Journal of Quantum Chemistry 19 (1981), S. 805-819 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A charge density distribution study, based on ab initio SCF-6-31G wave functions, on the optimized geometry of 1,2-dioxethane indicates its high instability which results from (i) the high ring strain, (ii) the large amount of charge contained on the nonbonded sides of the oxygen nuclei, and (iii) the weak binding character of the charge density in the O—O bond region. The redistribution of the charge density when 1,2-dioxethane undergoes change in its nuclear configuration has been discussed. This redistribution of charge along the reaction path (the dissociation of 1,2-dioxethane to formaldehyde products) shows clearly the preceding nature of the electron cloud. The characteristic features of the charge density distribution of the two Hartree-Fock solutions to which the SCF procedure converges have been analyzed and discussed.
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    International Journal of Quantum Chemistry 19 (1981), S. 859-871 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: By applying the projection operator method it is shown that the complicated Hamiltonian of a E ⊗ ∊ JT system with nonlinear coupling coefficients can be written in terms of two Hamiltonians which are simple to handle and transform according to irreducible representations E, A1, and A2 of C3v point group. A variational approach is then used to calculate the ground state energy, using the Hamiltonian that transforms according to E, as an explicit function of the linear and nonlinear coupling parameters. The energies calculated in the strong coupling limit are finally compared with the corresponding previously calculated energies.
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    International Journal of Quantum Chemistry 19 (1981), S. 901-906 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A coupled channel formulation for the static Stark effect on the hydrogen atom is used to obtain directly the complex resonance energies through an iterative matching procedure. The formulation makes use of a complex coordinate. This solves the initialization problem in a very simple way, since the boundary conditions can be those used for bound states. A comparison is made with the results of Reinhardt and collaborators who expand the complex rotated resonance wave function in a basis of integrable functions.
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    International Journal of Quantum Chemistry 20 (1981), S. 347-356 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Single chain and packing energy calculations have been made on polyglycine (threefold and fourfold helical structures) with interchain NH…O hydrogen bonds. In conformation A of polyglycine, in which the NH groups point away from the helix axis and the CO groups are nearer to the helix axis, the conformational energy is nearly the same for threefold and fourfold structures. However, the minimum energy conformation corresponds to a threefold structure of polyglycine with peptide configurations in conformation B in which the CO groups point away from the helix axis and NH groups are nearer to the helix axis. This structure is consistent with the polyglycine II x-ray diffraction data.
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    International Journal of Quantum Chemistry 20 (1981), S. 393-406 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The ab initio MO and semiempirical multireference (MR) CI calculations were carried out to elucidate the energy differences between peroxy 1,4-diradical (DR) and 1,4-zwitterionic (ZWI) intermediates, which play crucial roles in photo-oxygenation reactions of nitrogen-activated C—C double bonds of enamines, indoles, and tryptamines. It is found that ZWI is more stable than DR in the case of electron-rich enamines. Protic solvents such as methanol are highly effective for the stabilization of ZWI by hydrogen bondings. From the present theoretical results, it is concluded that tryptophane undergoes the photooxidative cleavage reaction to give formylkynurenine under a specific condition, where polar solvents or catalysts sufficiently stabilize the ZWI state for the species.
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    International Journal of Quantum Chemistry 20 (1981), S. 461-478 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The present state in the chemistry of peptides and proteins capable of transporting ions across biological and model membranes have been reviewed. The mechanisms of action of peptide ionophores valinomycin and enniatin and also the channel-forming peptide gramicidin-A have been discussed on the basis of spatial structure and dynamic conformational properties of the compounds. Recent progress in the studies of bacteriorhodopsin, cholinergic receptor from postsynaptic membrane, and sodium channel from the excitable nerve membrane, the integral membrane proteins acting as proton or metal ion channel formers is also discussed.
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    International Journal of Quantum Chemistry 20 (1981), S. 495-504 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The role of water structure around model membrane systems (e.g., liposomes) on phase transition of the lipid dipalmitoyl phosphatidylcholine was investigated. Water structure was altered by changing pH and by addition of solutes which are known breakers and makers of water structure. The structure makers broadened the zone of transition and changed the overall phase transition profile, while the main effect of structure breakers was to cause a shift in the transition temperature. The observed variation of Chapman transition temperature and broadening of zone of transition with varying pH is discussed in terms of altered water structure around the membrane-aqueous interface. Binding studies with the dye 1-anilino-8-napthalene sulfonate showed that structure makers or breakers did not bind to the liposome surface directly. Thus the structure makers and breakers act on the membranes perhaps by altering the water structure differentially. Possible associated mechanisms of action are discussed.
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    International Journal of Quantum Chemistry 20 (1981), S. 543-554 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Infrared spectroscopy has been employed to study possible base pair interactions, in nonpolar media, between O6-methylguanine and uracil, cytosine and adenine; and between derivatives of N4-hydroxycytosine and adenine. The association constants of O6-methylguanine with uracil, cytosine, and adenine are well below 1M-1, whereas those for interaction of 1-methyl-N4-methoxycytosine and its 5-methyl derivative with adenine are identical, K = 14M-1. The significance of the latter finding is discussed in relation to the conformation of the exocyclic N4-methoxy group. Quantum chemical calculations, with the aid of the perturbation method, were carried out for the interaction of O6-methylguanine with uracil, cytosine, and adenine, to establish the most energetically favoured configurations for interactions of the free bases, and of the same base pairs in the B form of DNA. The role of the conformation of the exocyclic  - OCH3 group in O6-methylguanine is discussed. The relevance of both the experimental and theoretical results to mutagenesis by O6-methylguanine and N4-hydroxycytosine is examined.
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    International Journal of Quantum Chemistry 20 (1981) 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
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    International Journal of Quantum Chemistry 20 (1981), S. 843-859 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An ab initio LCAO SCF MO calculation was performed on planar Fe-porphine with a double zeta basis set consisting of 300 CGTO's. SCF wave functions of several states of Fe-porphine and its cation were obtained. The net charge of Fe is in the range of 1.39 to 1.53. The highest occupied orbital is ascertained to be a pure porphine π-MO, 1a1u. The calculated ionization potentials of the two highest occupied orbitals, 1a1u and 5a2u are 5.98 and 6.43 eV, respectively. They are in good agreement with experiments. The role of the porphine macrocycle on the oxidation of Fe is discussed in terms of gross atomic populations and with contour maps of the density difference.
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    International Journal of Quantum Chemistry 20 (1981), S. 887-889 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The limiting of the 〈r12-1〈/〈r1-1〈 ratio in the He sequence is critically examined at different levels of approximations leading to some interesting results.
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    International Journal of Quantum Chemistry 20 (1981), S. 921-926 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Along the lines of previous work [S. Romano and E. Clementi, Gazz. Chim. Ital. 108, 319 (1978); Int. J. Quantum Chem. 14, 839 (1978); 17, 1007 (1980)], we carried out Monte Carlo simulation on serine-water clusters (the neutral molecule and two conformers of the zwitterion) surrounded by an appropriate dielectric continuum simulating the bulk solvent. Results for clusters in vacuo and in the dielectric continuum were compared; similarities and differences could be qualitatively interpreted as produced by competition among different factors.
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    International Journal of Quantum Chemistry 20 (1981), S. 933-949 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The self-consistent APW-k · p method is utilized to obtain the band structure of NaCl in the “muffin-tin” approximation. Qe have investigated the convergence of many intermediate results, e.g., crystalline potential, matrix elements of the momentum operator, and energy eigenvalues at the Γ point. The summation in reciprocal space, included in the definition of the matrix D of the theory, is performed by direct sum and also by a special points technique. For the convergence criteria used, the results converged after five iterations.
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    International Journal of Quantum Chemistry 20 (1981), S. 1073-1076 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Generalized oscillator strengths and integrated cross sections from threshold to 1 keV are calculated in the Born approximation for the electron impact excitation of O II.
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    International Journal of Quantum Chemistry 20 (1981), S. 1067-1071 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: One-electron properties may be evaluated by configuration interaction methods using analytical differentiation of the total energy with respect to an external perturbation parameter. Dipole moments are reported using such a method for CO and H2CO. Inclusion of single substitutions does not change calculated dipole moments appreciably with this method. The differences between this method and the direct evaluation of an expectation value are discussed.
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    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We are engaged in research directed toward the development of compact and accurate correlation functions for many-electron systems. Our computational tool is the variational method in which the many-electron integrals are calculated by Monte Carlo using the fermion Metropolis sampling algorithm. That is, a many-fermion system is simulated by sampling the square of a correlated antisymmetric wave function. The principal advantage of the method is that interelectronic distance rij may be included directly in the wave function without adding significant computational complexity. In addition, other quantities of physical and theoretical interest such as electron correlation functions and representations of Coulomb and Fermi “holes” are very easily obtained. Preliminary results are reported for He, H2, and Li2.
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    International Journal of Quantum Chemistry 20 (1981), S. 1165-1177 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A recently proposed orthonormality constrained orbital optimization technique is operationally modified further by coupling it to a gradient biased method, namely the steepest descent procedure of McWeeny. The hybrid technique developed in this way is shown to have better convergence properties in closed and unrestricted open-shell calculations. The technique can be adapted to MCSCF procedures as well. The important role played by "orbital symmetries" in the operation of the method is analysed. Similarities and differences of the present method with the orthogonal gradient method are pointed out. Possible avenues of circumventing convergence difficulty that one may encounter in pathological cases, particularly in ab initio calculations involving extended basis set, are suggested.
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  • 74
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    International Journal of Quantum Chemistry 20 (1981), S. 1225-1231 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Interactions of catecholamines with acidic sites in the biophase are likely to be involved in the control of the receptors activity as well as in storage and transport mechanisms. In view of the importance of the phenomena a model study of ethanolamine-phosphate complexes was made. The electrostatic interaction energy surface was calculated in the charge density multipole expansion approximation with terms up to quadrupole. The consecutive minimal energy conformation shows the importance for the interaction with the biophase of the catechol ring steric and electronic relation to the side chain.
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  • 75
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    International Journal of Quantum Chemistry 20 (1981), S. 1273-1284 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Several useful “redefined zero-order Hamiltonian” variants of the Rayleigh-Schrödinger perturbation theory are derived by exploiting the freedom of choice for the orthogonality integral between zero- and first-order wavefunctions. It is found that the more common Hamiltonian repartitioning schemes follow quite naturally, as a consequence of certain consistency requirements. The strategy adopted may as well be employed to derive various newer and profitable zero-order Hamiltonians depending on the nature of the problems. This implication is strengthened by demonstrating the calculational success of one such derived scheme. Feenberg's “scale-changed” Hamiltonian approach is also reinterpreted in the present context.
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  • 76
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  • 77
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    International Journal of Quantum Chemistry 20 (1981), S. 1333-1334 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
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  • 78
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    International Journal of Quantum Chemistry 20 (1981), S. 1334-1335 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
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  • 79
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    International Journal of Quantum Chemistry 20 (1981), S. 63-71 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A simple method is presented for the construction of contracted Gaussian basis sets with little or no energy-optimization. The contraction coefficients are fitted by a least-squares procedure to the orbital expansion coefficients of the completely decontracted basis. The method is applied to the construction of minimum basis sets of first-row atoms from (6s, 3p) uncontracted atomic basis sets, and of [6s, 4p] contracted bases from (12s, 8p) uncontracted bases of second-row atoms. The results are better than using the expansion coefficients directly and are usually comparable to fully energy-optimized bases.The method can also be used to generate balanced atomic contraction coefficients from molecular calculations. This is shown with a (7s, 3p) and a (6s, 3p) basis, both contracted to a minimum basis. The contracted basis sets are employed in several small molecules, and the results are compared with calculations done with the decontracted bases and with contracted bases where the contraction coefficients were energy optimized in the molecules.
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  • 80
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    International Journal of Quantum Chemistry 20 (1981), S. 129-138 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Conformational properties of pyrazofurins, which were previously designated as pyrazomycins in both β- and α-anomeric forms, have been investigated by the PCILO method. The results indicate that the most preferred conformation for β anomer is anti-gg, while that for α anomer is syn-gg when intramolecular hydrogen bonding between sugar and the base is allowed. However, in the absence such hydrogen bonding, which mimicks the situation in aqueous solution, both β and α pyrazofurins show exactly similar preference for anti-gg conformation. The biological significance of this result has been discussed. Further the β anomer is energetically more favorable than the α anomer. This result is in agreement with the experimental observations, which indicate that β pyrazofurin is more populated than a pyrazofurin in aqueous solution at room temperature.
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  • 81
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    International Journal of Quantum Chemistry 20 (1981), S. 171-183 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An investigation is carried out of the influence of counterions bound to yeast tRNAPhe on the electrostatic potential and steric accessibility of this macromolecule. Two types of cations are considered, the Mg2+ ions located in the crystal of tRNAPhe, with their waters of hydration, and Na+ ions, which are positioned by theoretical estimation. Possible effects of the counterions on the chemical reactivity of tRNAPhe are pointed out.
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    International Journal of Quantum Chemistry 20 (1981), S. 231-239 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The hydrogen-bond geometry observed by neutron diffraction of 24 carbohydrate and 32 amino acid crystal structures is analyzed and compared. Of the 100 O—H———O bonds in the carbohydrate structures, 25 were three-centered (bifurcated). This bigamous behavior is rationalized in terms of the 25% greater number of acceptor oxygens than donor hydroxyls and the need to preserve the “cooperative effect.” The predominant hydrogen bonds in the amino acids are the zwitterion type , 64 out of a total of 145. Of these, 51 are three-centered. Again the rationale appears to be an equilization of donor and acceptor functions, since each carboxylate group generally accepts between four and six hydrogen bonds.
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    International Journal of Quantum Chemistry 20 (1981), S. 265-270 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The dicarbonyl methylglyoxal reacts with the lysine residues of proteins to give brown colored products with a small oxygen-dependent free radical content. Electron spin resonance (ESR) experiments employing ethylene diamine as a model for protein lysine residues are reported. The prevention of imine formation between methylglyoxal and the amine models either by pretreatment of methylglyoxal with glutathione or by methylation of the amine led to brightly colored reaction products and a much higher radical content. From an analysis of the ESR spectra it is clear that the reactions between methylglyoxal and the simple model amines developed far beyond those in the protein-methylglyoxal systems. It is proposed that this difference is accounted for by the enormous steric effects of the proteins. The relevance of the observations to the “browning” reaction in foods is briefly discussed.
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    International Journal of Quantum Chemistry 20 (1981), S. 307-316 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Steady-state conductivity and dielectric measurements in the range of 10-5 Hz to 33 GHz are reported for bovine serum albumin and lysozyme as a function of hydration and NaCl content. The electrical properties are understandable in terms of the existence of charge carriers whose hopping-type transport process is directly influenced by the nature of the protein-water interaction. These mobile charges are considered to be protons originating from ionizable carboxylic groups.
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    International Journal of Quantum Chemistry 20 (1981), S. 347-357 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: It is outlined how the authors arrived at the existence problem of the intermediate states (IS) possibly appearing in bounded crystals with perfect bulk structure and of certain zig-zag states (ZZS) in almost periodic (even disordered) biopolymers. Earlier results are summarized and commented. An example is given for how to enhance the appearance probability of ISS. It is shown that within a narrow critical interval, the width of which is about the eighth of the average separation of the bulk states in the k space of the finite linear chains, any state becomes an his (almost IS), which is very similar to the IS and approaches it continuously. Estimating the effects of in-plane and in-terplane vibrations of stacked aromatic planar compounds on the delocalized π-electron structures, it is concluded that the valence modes have a strong effect on the in-plane π-electronic systems, but a very small one on the interplane π-electronic interactions. The longitudinal acoustical modes of finite polynucleotide DNA models and their root mean square amplitudes are estimated by the method of Peticolas. According to the results obtained, DNA-like and layered graphitelike systems seem to be the probable host systems of 1%. if they exist at all. The appropriateness of the recursion method is discussed to search for unusual electronic states and structures. Such studies are the first unsteady but exciting steps toward the construction of the molecular computers.
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    International Journal of Quantum Chemistry 20 (1981), S. 117-127 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ab-initio molecular orbital (MO) calculations on the model peptide, N-methylacetamide (NMA), protonated N-methylacetamide (p-NMA), and two natural dipeptides, glyclyglycine (Gly-Gly) and alanylalanine (Ala-Ala), are reported. Calculations at the STO-3G. 3-21G. and 4-31 G levels account for the predominance of the trans conformation in globular proteins. By use of p-NMA as a model precursor, the formation of the peptide bond is studied by the methods of molecular quantum mechanics. These calculations lead to the conclusion that the trans conformation should predominate, in agreement with the crystal structural data on globular proteins. In order to reduce the amount of computer time required for what are evidently the first ab-initio MO calculations on natural dipeptides, force-field calculations have been employed to obtain the conformational potential energy maps.
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  • 87
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    Topics: Chemistry and Pharmacology
    Notes: Ab-initio MODPOT/VRDDO/MERGE SCF calculations were carried out on 2,6-dimethyl-N-nitroso morpholine and on four isomers of α-hydroxy substituted derivatives. The NNO bond angle is found to be 1135°, in agreement with that observed in dimethyl nitrosamine. The two methyl groups are found to be most stable in the equatorial position. The axial position is found to be the most stable orientation for the α-hydroxy group in both the syn and the anti isomers. This is in agreement with the observed axial orientation of straight chain alkyl substituents at the α position in N-nitroso piperidine. An investigation was made on the effects of internal rotation in the parent compound. A 90° rotation about the N—N bond raises the energy ∼.0526 a.u. or ∼33 kcal/mol. In the 90° orientation, population analysis shows a decrease of ∼0.1 e in the gross atomic population (GAP) of the nitroso oxygen and in the total overlap population for the N—N bond. There is a corresponding increase of ∼0.05 e in the GAP on the amino nitrogen. The GAP on other heavy atoms and overlap in other bonds show little effect from internal rotation of the nitroso group. Electrostatic molecular potential energy contour maps indicate differences as a function of conformation.
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    International Journal of Quantum Chemistry 20 (1981), S. 201-219 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The FSGO molecular fragment technique has been employed to perform ab-initio SCF-MO calculations on morphine and naloxone in the free-base and N-protonated forms. Particular features of electronic structure which have been investigated are molecular-orbital (MO) density distributions, energies and ordering, as well as the correlation of specific orbitals between different molecular species. It has been found that high-energy occupied and low-energy unoccupied MOS are centered on the aromatic moiety of both drugs, enabling the ring to act either as an electron donor or as an acceptor in a charge-transfer interaction. Comparison of corresponding MOs in the free base and the acid cation of both morphine and naloxone demonstrates that the field of the cationic head causes a dramatic downward shift in orbital energies. Thus in the N-protonated drugs the acceptor capability of the benzene ring is greatly enhanced at the expense of its suitability as a donor. Furthermore, the allyl group of naloxone becomes highly activated as an electron acceptor through N-protonation. Investigation of the molecular electrostatic potential of the free-base species has revealed preferred avenues of approach for electrophilic and nucleophilic entities. However, the N-protonated species shows no regions of attraction for electrophiles. In both the free base and the acid cation, the vicinities of the nitrogen atom and the 3-hydroxy group are found to be favorably disposed for electrostatic interactions with receptor entities possessing the proper charge or polarity. Based on the findings with regard to electronic structure, a simple model has been suggested to explain the binding of morphine and naloxone at the opioid receptor.
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    International Journal of Quantum Chemistry 20 (1981), S. 257-264 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Hemoglobin-catalyzed hydroxylation of aniline may be taken as a model for similar reactions catalyzed by cytochrome P-450. Using ultraviolet-difference spectroscopy and 1H nuclear relaxation techniques, the binding of aniline to hemoglobin was examined. From the magnitude of paramagnetic effects of ferric iron on aniline protons, using the correlation time determined from the magnetic field dependence of water proton relaxation rates, aniline was found to bind to methemoglobins such that the aromatic protons are 8.5 ± 0.7 Å, away from the high-spin Fe3+. A mode of binding is proposed where the aniline molecule is hydrogen bonded to the distal histidine of hemoglobin.
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    International Journal of Quantum Chemistry 20 (1981), S. 277-285 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The solution conformations of two DNA octanucleotides, (GGAATTCC)·(GGAATTCC) and (AAAGCTTT)·(AAAGCTTT), have been investigated by theoretical calculations of NMR shifts. The calculations of proton chemical shifts have been made, taking into consideration the ring current effects and the atomic magnetic anisotropies of the bases. The computed shielding constants for B-DNA, alternating B-DNA, the Levitt propeller-twisted model and the Dickerson propeller-twist model (based on crystallographic data) have been compared with experimentally available shifts. For the (AAAGCTTT)·(AAAGCTTT) double helix the experimental data are available only for the exchangeable protons HN1 and HN3; thus a complete and detailed evaluation is impossible for this system. For (GGAATTCC)·(GGAATTCC) the results indicate that the A·T pairs are propeller twisted à la Levitt and Dickerson.
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    International Journal of Quantum Chemistry 20 (1981), S. 1285-1300 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The exponential transformation of the molecular orbitals, that has been previously used to achieve a process with a convergence of quadratic quality in SCF closed-shell calculations [J. Chem. Phys. 72, 1452 (1980)] has been extended to UHF determinantal wave functions built from different orbitals for different spins. Explicit formulas are given for the first and second derivatives of the energy to be varied. The method is illustrated by UHF calculations for systems described as standard singlets (Li2 and F2) or triplets (NH) at the RHF approximation level, as well as for CH, CH2, CH3 molecular fragments in their valence states.
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    International Journal of Quantum Chemistry 20 (1981), S. 1331-1332 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
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  • 93
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
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    International Journal of Quantum Chemistry 20 (1981), S. 1-47 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The development of a flexible intra- and intermolecular empirical potential function is described, which is designed for investigating the geometric structure of large molecular systems. The intramolecular components in the potential consist of harmonic bond stretching and angle bending terms, out-of-plane deformation terms, and torsional terms; intermolecular components include nonbonding, hydrogen bonding, and electrostatic terms. Bond lengths, angles, and torsional angles are predicted to within 2% of experiment, with most cases being within 1%. The suitability of the intermolecular potential was tested by crystal packing calculations; in all cases the results obtained were in excellent agreement with experiment.
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    International Journal of Quantum Chemistry 20 (1981), S. 109-116 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In an attempt to account for the selectivity displayed by valinomycin with respect to the binding of alkali metal cations, theoretical computations were performed of the interaction energies of this macrocyclic carrier with Na+, K+, Rb+, and Cs+. Subtracting from these interaction energies the corresponding dehydration energies of the cations yields a set of values of the energy balance, the ordering of which follows the ordering of the binding constants measured experimentally in polar solvents. The possibility of extending the procedure to the alkaline-earth cations Mg2+ and Ca2+ is examined.
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    International Journal of Quantum Chemistry 20 (1981), S. 81-93 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ascorbic acid enhances the free radical electron spin resonance signal obtained when methylamine interacts with methylglyoxal. Previous ab-initio calculations have shown that methylglyoxal and other ketoaldehydes may act as possible electron acceptors in Szent-Györgyi's theory of cancer. Ascorbic acid is also known to be involved in cancer.The ab-initio SCF method has been used to study the electronic structure of ascorbic acid and its metabolites. The bulk of the calculations involved the use of α-hydroxytetronic acid as a model for ascorbic acid, and related compounds as models for the ascorbyl radical and dehydroascorbic acid. Complete geometry optimizations by the force method were carried out for the model compounds, using an STO-3G basis set.To obtain an estimate of possible charge transfer involving these molecules, ab-initio “supermolecule” calculations were carried out using formamide and glyoxal. A large number of planar and stacked orientations were considered The anion acts as a substantial donor in many of the stacked conformations, but the charge transfer is rather small in all these systems.
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    International Journal of Quantum Chemistry 20 (1981), S. 139-148 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Aminoacyladenylates play a central part in both protein enzymatic and polypeptide prebiotic synthesis. Previous general studies on aminoacyladenylate conformations were extended to some aspects related to polypeptide prebiotic synthesis. Major conclusions drawn from these quantum mechanical PCILO calculations are: (1) In the presence of an ammonium group the glycylphosphate system forms a double seven-membered ring. This folded conformation possesses an important rigidity. This occurs in neutral or acidic solutions. It agrees with experimental observations showing that there is no polymerization in this case, in the absence of catalyst. Thus the catalytic part of montmorillonite clays, which can break the ring by compensation of the anionic and cationic charges, can be understood. (2) When the amine group remains in its neutral form (in basic solutions), numerous stereo structures are allowed for the glycylphosphate stem, among which a ring of weak stability. This is still in good agreement with the observation of polycondensation at high pH without catalyst. (3) The phosphate linking system is flexible enough to allow the extension of the polypeptide chain between the clay layers. This is in accordance with the mechanism proposed by Paecht-Horowitz in which the phosphate is locked on the edge of the montmorillonite sheet.
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    International Journal of Quantum Chemistry 20 (1981), S. 185-196 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Local coordinate systems are introduced into open sets of topological spaces, defined for the nuclear configuration space R of polyatomic nuclear systems. The open sets are directly related to common chemical concepts, such as chemical structure, reaction mechanism, and stability of reaction paths. A topological model of molecules and chemical reactions is a generalization of the geometrical model, and is particularly suitable to account for the nonrigid nature of chemical structures. The coordinate neighborhoods defined on R and on its submanifolds represent the extent and natural limits for partial analyses of multidimensional potential surfaces.
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    International Journal of Quantum Chemistry 20 (1981), S. 221-229 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The transfer of the central proton between the two NH3 units of (H3NHNH3)+ is studied using the 4-31 G basis set within the ab-initio Hartree-Fock formalism. Electron density difference maps are constructed which clearly indicate electronic redistributions which accompany the half-transfer of the proton from its equilibrium position (NH—N) to the midpoint of the hydrogen bond (N—H—N). The overall loss of electronic charge from the proton-accepting molecule originates in three distinct regions of space, while a density buildup of smaller magnitude is observed in a characteristic region centered about the N nucleus. Similar regions are noted for the proton-donating molecule, although the changes are reversed in sign. A partitioning of the total density changes into contributions from the various molecular orbitals demonstrates that the a1 orbitals are associated with density shifts along the H-bond axis. Changes in the N lone pairs are attributed chiefly to the (5a1,6a1) pair and are somewhat attenuated by opposite shifts involving the (3a1. 4a1) pair. Orbitals of e symmetry lead to polarizations of the NH bonds and density shifts perpendicular to the H-bond axis.
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    International Journal of Quantum Chemistry 20 (1981), S. 247-256 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: To study the arrangement of substrates at the active site of creatine kinase, we have measured the paramagnetic effects of CrADP, an exchange-incrt paramagnetic analog of MgADP, on the nuclear spin lattice relaxation rates 1 /T1 of the protons of water and the protons and phosphorus nucleus of P-creatine in the presence and absence of rabbit muscle creatine kinase. Relaxivity titrations measuring the paramagnetic effect of CrADP on 1/T1 of water protons at several concentrations of the enzyme in the presence of P-creatine were used to study the binding of CrADP to the enzyme·P-creatine complex. The existence of a ternary enzyme·CrADP-P-creatine complex was confirmed by observing the paramagnetic effects of enzyme-bound CrADP on the 1 /T1 of the 31P nucleus and protons of P-creatine. From the magnitude of paramagnetic effects arising within the enzyme·CrADP·P-creatine complex, using the electron spin relaxation time estimated from the magnetic field dependence of 1 /T1 of fast exchanging water protons, a Cr3+-phosphorus distance of 6.0 Å, and Cr3+-proton distances of 11 and 12 Å, were obtained. These results imply the absence of a direct coordination of the phosphoryl group of P-creatine by the nucleotide-bound metal on creatine kinase but indicate proximity of enzyme-bound substrates and are consistent with van der Waals contact between a phosphoryl oxygen of P-creatine and the hydration sphere of the nucleotide-bound metal. Since the metal ion is coordinated to the γ-phosphoryl group of ATP on the enzyme, the overall migration of the phosphoryl group during phosphoryl transfer is ∼3 Å, toward the nucleotide-bound metal.Creatine kinase failed to catalyze phosphoryl transfer from P-creatine to CrADP as monitored by the disappearance of the 31P NMR signal of P-creatine in a solution containing CrADP, P-creatine and creatine kinase. The ability of an isomer of β,γ-bidentate CrATP to act as a partial substrate and our observation of the absence of phosphoryl transfer from P-creatine to CrADP indicate that metal ion coordination of the transferable phosphoryl group precedes phosphoryl transfer and is a requirement of the creatine kinase reaction.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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