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  • 1
    Electronic Resource
    Electronic Resource
    Ab initio study of the HCO-3/H2O exchange in the (NH3)3ZnII(HCO-3) complex (1995)
    Springer
    Theoretica chimica acta 91 (1995), S. 333-351 
    Details
    ISSN: 0040-5744
    Keywords: Key words: Carbonic anhydrase (CA) ; HCO-3/H2O exchange ; Continuum model ; Environmental effects
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary.  The displacement of bicarbonate anion in the (NH3)3ZnII(HCO- 3) complex with water has been studied through ab initio calculations. It has been found that H2O binds to the (NH3)3ZnII(HCO- 3) species yielding a stable pentacoordinate (NH3)3ZnII(HCO- 3)(H2O) complex. The results also indicate that deprotonation of water in the pentacoordinate species facilitates the release of HCO- 3, although, the presence of HCO- 3 in the coordination sphere of ZnII makes such deprotonation more difficult. Environmental effects have been considered in the study of HCO- 3/H2O exchange.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01133079
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  • 2
    Electronic Resource
    Electronic Resource
    Analysis of the gas-phase addition of water to formaldehyde: A semiempirical and ab initio study of bifunctional catalysis by H2O (1992)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 13 (1992), S. 1037-1046 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Semiempirical AM1, MNDO-PM3, and MNDO/M, as well as ab initio Hartree-Fock and Möller-Plesset calculations using the 4-31G, 6-31G(d,p), and 6-31 +G(d,p) basis sets have been done on the water-assisted addition of water to formaldehyde. ab initio methods predict a reduction of 30% of the bimolecular ΔG0,
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540130902
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  • 3
    Electronic Resource
    Electronic Resource
    Theoretical study of the addition of hydrogen halides to olefins: A comparison between (HCl)2 and (HF)2 additions to ethylene (1987)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 8 (1987), S. 481-488 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The addition of HCl and (HCl)2 to ethylene is theoretically studied by means of ab initio SCF techniques using the 3-21G basis set. A statistical thermodynamics analysis is also carried out. When a comparison is made with the HF and (HF)2 additions to ethylene, the general fact of the catalytic action of the second HX molecule in the (HX)2 complex is revealed. The behavior of HF, however, is very different from that of HCl, since in the former case the driving force in the termolecular transition state is the bonding between fluorine and carbon, while in the latter case the driving force is the bonding between carbon and hydrogen, as generally accepted for electrophilic reactions. The use of density plots of the transition states on the plane of the cycle allows us to conclude that, while both HF and HCl termolecular transition states are hexacyclic, the bimolecular transition state of the HCl addition is bicentric and not tetracentric as previously reported.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540080428
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  • 4
    Electronic Resource
    Electronic Resource
    Monte Carlo simulation of the diabatic free energy curves for a dissociative electron transfer reaction in a polar solvent (1992)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 13 (1992), S. 1057-1065 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: In the present work we have carried out a Monte Carlo simulation of a dissociative electron transfer reaction in a polar solvent. In particular, we have chosen as a very simple model the electrochemical reduction of hydrogen fluoride to give a hydrogen atom and a fluoride anion in a dipolar solvent. From a classical point of view, the electron transfer occurs at the intersection region S* of the diabatic potential hypersurfaces Hpp and Hss, corresponding to the precursor and successor complexes, respectively. We have evaluated both diabatic surfaces using potential functions that have been built up with ab initio methods by us. For each of the obtained configurations the parameter ΔE = Hss - Hpp has been calculated. This parameter is then used as the reaction coordinate for obtaining the diabatic free energy curves of the reaction. Because the activation energy is high, a suitable mapping potential along with the statistical perturbation theory is employed to force the system to evolve toward the intersection region S*. A total of 68,340,000 configurations have been generated. The main conclusion of this article is that Marcus' relationship seems to fail for this kind of inner-sphere processes. © 1992 by John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540130904
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  • 5
    Electronic Resource
    Electronic Resource
    Ab initio study of substituent effect on the addition of hydrogen fluoride to fluoroethylenes (1990)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 11 (1990), S. 170-180 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: An ab initio 3-21G study of the direct addition of HF to C2HnF(4-n), with n = 0 to 4, has been performed to investigate the effect of the substituent on the reaction. Geometry optimization of all charge-transfer complexes and transition states has been done. Standard analysis of activation energies of addition reactions, vibrational and thermodynamical analysis, as well as Morokuma energy decomposition, BSSE correction, PMO analysis, and Pauling bond orders were used to explain the results. A subset of the reactions, including that of C2H4 as reference one and the two most favorable cases, was also studied at the MP2/6-31G(d,p)//HF/6-31G(d,p) level. The barriers so obtained are in agreement with the indirectly found from experimental data. It was found that the effect of the substituent is not monotonic for the additions. Decomposition of the interaction energy is shown to be adequate to explain this nonmonotonic behavior. The implications for laser chemistry of the addition of hydrogen halides to fluorosubstituted olefins is briefly discussed.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540110203
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  • 6
    Electronic Resource
    Electronic Resource
    A Monte Carlo simulation of free energy relationships for the electron transfer reaction between Fe+ and Fe2+ in water (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 12 (1991), S. 1165-1171 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: A free energy barrier ΔF≠ = 174.2 kJ/mol for the self-exchange electron transfer reaction model Fe+/Fe2+ in water has been calculated by combining Monte Carlo simulations and the statistical perturbation theory. We have shown that, even for those electron transfer reactions that present a very high free energy barrier of activation, the free energy curve behaves parabolically versus the reaction coordinate, which justifies the quadratic expression for the activation free energy done by Marcus.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540121002
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  • 7
    Electronic Resource
    Electronic Resource
    Vibrational Stark effect: Theoretical determination through the semiempirical AM1 methodA contribution from the “Grup de Química Quántica de l'institut d'Estudis Catalans” (1992)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 13 (1992), S. 821-829 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The vibrational Stark effect of a series of small molecules has been calculated by means of the semiempirical AM1 method through addition of the electron-field interaction term in the one-electron Hamiltonian. Optimized geometrical parameters along with harmonic frequencies and line intensities are determined for different strengths of the applied uniform electric field. The perturbed spectra are compared with theoretical studies carried out at the ab initio level and with experimental results. The vibrational Stark effect of the retinal molecule is also computed, showing that this kind of study is feasible in systems of biochemical interest. © 1992 by John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540130705
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