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  • Computational Chemistry and Molecular Modeling  (5)
  • Theoretical, Physical and Computational Chemistry  (5)
  • 1
    Electronic Resource
    Electronic Resource
    Binding of flexible ligands to proteins: Valproic acid and its interaction with cytochrome P450cam (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 48 (1993), S. 161-180 
    Details
    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 combined theoretical and experimental study of the binding and interaction of valproic acid (VPA) with the bacterial cytochrome P450cam enzyme and the determination of regio- and stereoselective hydroxylation product distribution was performed. From the experiments, C4—;OH VPA was found to be the predominant hydroxylation product with a small amount of C5—OH VPA formed. The experimental stereoselectivity of hydroxylation was 2R4S 〉 ∼ 2S4R 〉 2R4R 〉 ∼ 2S4S and 2S5 〉 ∼ 2R5. The overall goals of the theoretical study were twofold: (1) to characterize as completely as possible, using energy optimization and molecular dynamics simulations, the interactions of flexible ligands with their target proteins, and (2) to determine the extent to which these results could be used to develop criteria to predict or explain the experimentally observed regio- and stereoselectivity of hydroxylation of the flexible ligands. Among the useful insights into the behavior of flexible ligands upon binding to their traget proteins obtained are (1) a large change in conformation occurs for many conformers of VPA upon binding to P450cam, (2) low- energy conformers of VPA do not necessarily lead to optimum interactions with the target protein, and (3) the most favorable mode of interaction of this flexible ligand with the protein binding site has been identified and found to be a result of strong electrostatic interactions between VPA and both Tyr96 and Asp297. For the study of the hydroxylated VPA products, the challenging aspect of this problem was to determine criteria for weighing the contribution of each of the possible protein-ligand complexes. To this end, various possibilities were examined and compared with the experimental results. No single complex was found to reproduce the observed experimental regio- and stereoselectivity. This result indicates that more than one bioactive form of VPA contributes to its oxidation. Results most consistent with experiment are obtained by using the interaction energy of the protein-ligand complex as a criterion for including its contribution to product formation. Although there are remaining disparities between predicted and observed product distributions, the combined theoretical and experimental effort has led to insights into the modes of interaction of this flexible ligand that lead to its observed product specificity. © 1993 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560480718
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  • 2
    Electronic Resource
    Electronic Resource
    Molecular-orbital studies of the mechanism of xanthine oxidase-catalyzed oxidation of purines, especially 2-chloropurineSupported by the Robert A. Welch Foundation (Grant No. D-182) of Houston, Texas, and by the Texas Technological College (No. 191-4753). (1967)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 1 (1967), S. 699-719 
    Details
    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
    Description / Table of Contents: Les réactions de la 2-chloropurine et d'autre bases, catalysées par la xanthine oxidase, ont été étudiées avec des méthodes différentes basées sur l'idée des orbitales molécularies, telles que HMO, ω-SCF—HMO, et PPP. Ces études not démontré l'importance des indices de réactivité électronique pour comprendre les réactions d'enzymes. De plus il paraît possible de prédire la spécificité de l'enzyme d'une analyse systématique de la différence entre les sites de réactions prédits et observés dans des substrats avec des substituants 2- et 8-oxy.Les concepts de densité d'obritale de frontière, de superdélocalisabilité et d'énergie de localisation se sont avérés tres utiles. Les Méthodes différentes ont donné en général dees résultats consistants.
    Abstract: Ein genauses Studium der durch Xanthine-Oxidas katalysierten Reaktionen von 2-Chloropurin und anderen Basen mittels verschiedenen MO-Methoden, wie HMO, ω-SCF—HMO, PPP, zeigt dass die Enzymreaktionen in der Sprache von elektronischen Reaktivitätsindizes beschrieben werden können. Es scheint möglich das Enzymspezifizität von einer systematischen Analysis der Verschiedenheit zwischen theoretisch berechnbeten und observierten Reaktionslagen in Substraten Mit 2- und 8-oxy Substituenten vorherzusagen.De Regriffe der Grenzorbitaldichte, des Superdelokalisabilitäts und der Lokalisierungsenergie sind sich sehyr nützlich rewiesen. Verschiedence MO-Methoden gaben im allgemeinen übereinstimmende Resultate.
    Notes: A detailed study to the xanthine oxidase-catalyzed reactions of 2-chloropurine and other substrate bases with various molecular-orbital techniques such as HMO, ω-SCF—HMO, and ppp semiempirical SCF—LCAO—MO has shown that the enzyme reactions can be understood in terms of electronic reactivity indices. Furthermore, it appeared possible to suggest the enzyme specificity from a systematic analysis of discrepancy between mo theoretically predicted and observed reaction sites in substrates with 2- and 8-oxy substituents. In other words, the discrepancy does not necessarily indicate the failure of the MO melthodes for such substrates, but it is possible to utilize the result in correlating with binding specificity of the ES complex. This has been done specifically for 2-chloropurine.Among several electronic reacxtivity indices, frontier orbital density, superdelocalizability, and localization energy have been proved to be very useful. Diferent MO methods gave, in general, consistent results.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560010519
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  • 3
    Electronic Resource
    Electronic Resource
    Partial electrostatic charges for the active center of Cu, Zn superoxide dismutase (1990)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 11 (1990), S. 346-350 
    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: Atomic partial charges for three model systems that mimic the metal-ligand moiety of the active site in the enzyme Cu, Zn superoxide dismutase (SOD) have been calculated at the ab initio level. The model systems include copper and zinc complexes with imidazole, formate and ammonia ligands. The partial charges thus obtained have been incorporated into force fields for molecular simulations. Simulations carried out with these force fields justify the need for specialized charge assignments for the metals and their ligands.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540110309
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  • 4
    Electronic Resource
    Electronic Resource
    Calculation of molecular geometries, relative conformational energies, dipole moments, and molecular electrostatic potential fitted charges of small organic molecules of biochemical interest by density functional theory (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 16 (1995), S. 1483-1506 
    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: Density functional theory is tested on a large ensemble of model compounds containing a wide variety of functional groups to understand better its ability to reproduce experimental molecular geometries, relative conformational energies, and dipole moments. We find that gradient-corrected density functional methods with triple-ζ plus polarization basis sets reproduce geometries well. Most bonds tend to be approximately 0.015 Å longer than the experimental results. Bond angles are very well reproduced and most often fall within a degree of experiment. Torsions are, on average, within 4 degrees of the experimental values. For relative conformational energies, comparisons with Hartree-Fock calculations and correlated conventional ab initio methods indicate that gradient-corrected density functionals easily surpass the Hartree-Fock approximation and give results which are nearly as accurate as MP2 calculations. For the 35 comparisons of conformational energies for which experimental data was available, the root mean square (rms) deviation for gradient-corrected functionals was approximately 0.5 kcal mol-1. Without gradient corrections, the rms deviation is 0.8 kcal mol-1, which is even less accurate than the Hartree-Fock calculations. Calculations with extended basis sets and with gradient corrections incorporated into the self-consistent procedure generate dipole moments with an rms deviation of 5%. Dipole moments from local density functional calculations, with more modest basis sets, can be scaled down to achieve roughly the same accuracy. In this study, all density functional geometries were generated by local density functional self-consistent calculations with gradient corrections added in a perturbative fashion. Such an approach generates results that are almost identical to the self-consistent gradient-corrected calculations, which require significantly more computer time. Timings on scalar and vector architectures indicate that, for moderately sized systems, our density functional implementation requires only slightly less computer resources than established Hartree-Fock programs. However, our density functional calculations scale much better and are significantly faster than their MP2 counterparts, whose results they approach. © 1995 John Wiley & Sons, Inc.
    Additional Material: 8 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540161206
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  • 5
    Electronic Resource
    Electronic Resource
    Merck molecular force field. II. MMFF94 van der Waals and electrostatic parameters for intermolecular interactions (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 17 (1996), S. 520-552 
    Details
    ISSN: 0192-8651
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: This article defines the parameterization and performance of MMFF94 for intermolecular interactions. It specifies the novel “buffered” functional forms used for treating van der Waals (vdW) and electrostatic interactions, and describes the use of : (1) high quality ab initio data to parameterize vdW interactions involving aliphatic hydrogens; and (2) HF/6-31G* calculations on hydrogen-bonded complexes to parameterize nonbonded interactions in polar systems. Comparisons show that appropriate trends in the HF/6-31G* data are well reproduced by MMFF94 and that intermolecular interaction energies and geometries closely parallel those given by the highly regarded OPLS force field. A proper balance between solvent-solvent, solvent-solute, and solute-solute interactions, critically important for prospective success in aqueous simulations, thus appears to be attained. Comparison of MMFF94, OPLS, CHELPG electrostatic potential fit, QEq, Gasteiger, and Abraham charges for 20 small molecules and ions also shows the close correspondence between MMFF94 and OPLS. As do OPLS and all current, widely used force fields, MMFF94 employs “effective pair potentials” which incorporate in an averaged way the increases in polarity which occur in high dielectric media. Some limitations of this approach are discussed and suggestions for possible enhancements to MMFF94's functional form are noted. © 1996 John Wiley & Sons, Inc.
    Additional Material: 1 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    Merck molecular force field. III. Molecular geometries and vibrational frequencies for MMFF94 (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 17 (1996), S. 553-586 
    Details
    ISSN: 0192-8651
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: This article describes the parameterization and performance of MMFF94 for molecular geometries and deformations. It defines the form used for the valence-coordinate terms that represent variations in bond lengths and angles, and it describes the derivation of quadratic force constants from HF/6-31G* data and the derivation of reference bond lengths and angles from fits to MP2/6-31G*-optimized geometries. Comparisons offered show that MMFF94 accurately reproduces the computational data used in its parameterization and demonstrate that its derivation from such data simultaneously confers the ability to reproduce experiment. In particular, MMFF94 reproduces experimentally determined bond lengths and angles for 30 organic molecules with root mean square (rms) deviations of 0.014 Å and 1.2°, respectively. MM3 reproduces bond angles to the same accuracy, but reproduces experimental bond lengths more accurately, in part because it was fit directly to thermally averaged experimental bond lengths; MMFF94, in contrast, was fit to (usually shorter) energy-minimum values, as is proper for an anharmonic force field intended for use in molecular-dynamics simulations. The comparisons also show that UFF and a recent version of CHARMm (QUANTA 3.3 parameterization) are less accurate for molecular geometries than either MMFF94 or MM3. For vibrational frequencies, MMFF94 and MM3 give comparable overall rms deviations versus experiment of 61 cm-1 and 57 cm-1, respectively, for 15 small, mostly organic molecules. In a number of instances, MM3's derivation employed observed frequencies that differ substantially - by nearly 400 cm-1 in one case - from other published frequencies which had themselves been confirmed theoretically by good-quality ab initio calculations. Overall, the comparisons to experimental geometries and vibrational frequencies demonstrate that MMFF94 achieves MM3-like accuracy for organic systems for which MM3 has been parameterized. Because MMFF94 is derived mainly from computational data, however, it has been possible to parameterize MMFF94 with equal rigor for a wide variety of additional systems for which little or no useful experimental data exist. Equally good performance can be expected for such systems. © John Wiley & Sons, Inc.
    Additional Material: 6 Tab.
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  • 7
    Electronic Resource
    Electronic Resource
    Merck molecular force field. IV. conformational energies and geometries for MMFF94 (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 17 (1996), S. 587-615 
    Details
    ISSN: 0192-8651
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: This article describes the parameterization and performance of MMFF94 for conformational energies, rotational barriers, and equilibrium torsion angles. It describes the derivation of the torsion parameters from high-quality computational data and characterizes MMFF94's ability to reproduce both computational and experimental data, the latter particularly in relation to MM3. The computational data included: (i) ∼ 250 comparisons of conformational energy based on “MP4SDQ/TZP” calculations (triple-zeta plus polarization calculations at a defined approximation to the highly correlated MP4SDQ level) at MP2/6-31G* geometries; and (ii) ∼ 1200 MP2/TZP comparisons of “torsion profile” structures at geometries derived from MP2/6-31G* geometries. The torsion parameters were derived in restrained least-squares fits that used the complete set of available computational data, thereby ensuring that a fully optimal set of parameters would be obtained. The final parameters reproduce the “MP4SDQ/TZP” and MP2/TZP computational data with root mean square (rms) deviations of 0.31 and 0.50 kcal/mol, respectively. In addition, MMFF94 reproduces a set of 37 experimental gas-phase and solution conformational energies, enthalpies, and free energies with a rms deviation of 0.38 kcal/mol; for comparison, the “MP4SDQ/TZP” calculations and MM3 each gives a rms deviation of 0.37 kcal/mol. Furthermore, MMFF94 reproduces 28 experimentally determined rotational barriers with a rms deviation of 0.39 kcal/mol. Given the diverse nature of the experimental conformational energies and rotational barriers and the clear indications of experimental error in some cases, the MMFF94 results appear excellent. Nevertheless, MMFF94 encounters somewhat greater difficulty in handling multifunctional compounds that place highly polar functional groups in close proximity, probably because it, like other commonly used force fields, too greatly simplifies the description of electrostatic interactions. Some suggestions for enhancements to MMFF94's functional form are discussed. © 1996 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Merck molecular force field. I. Basis, form, scope, parameterization, and performance of MMFF94 (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 17 (1996), S. 490-519 
    Details
    ISSN: 0192-8651
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: This article introduces MMFF94, the initial published version of the Merck molecular force field (MMFF). It describes the objectives set for MMFF, the form it takes, and the range of systems to which it applies. This study also outlines the methodology employed in parameterizing MMFF94 and summarizes its performance in reproducing computational and experimental data. Though similar to MM3 in some respects, MMFF94 differs in ways intended to facilitate application to condensed-phase processes in molecular-dynamics simulations. Indeed, MMFF94 seeks to achieve MM3-like accuracy for small molecules in a combined “organic/protein” force field that is equally applicable to proteins and other systems of biological significance. A second distinguishing feature is that the core portion of MMFF94 has primarily been derived from high-quality computational data - ca. 500 molecular structures optimized at the HF/6-31G* level, 475 structures optimized at the MP2/6-31G* level, 380 MP2/6-31G* structures evaluated at a defined approximation to the MP4SDQ/TZP level, and 1450 structures partly derived from MP2/6-31G* geometries and evaluated at the MP2/TZP level. A third distinguishing feature is that MMFF94 has been parameterized for a wide variety of chemical systems of interest to organic and medicial chemists, including many that feature frequently occurring combinations of functional groups for which little, if any, useful experimental data are available. The methodology used in parameterizing MMFF94 represents a fourth distinguishing feature. Rather than using the common “functional group” approach, nearly all MMFF parameters have been determined in a mutually consistent fashion from the full set of available computational data. MMFF94 reproduces the computational data used in its parameterization very well. In addition, MMFF94 reproduces experimental bond lengths (0.014 Å root mean square [rms]), bond angles (1.2° rms), vibrational frequencies (61 cm-1 rms), conformational energies (0.38 kcal/mol/rms), and rotational barriers (0.39 kcal/mol rms) very nearly as well as does MM3 for comparable systems. MMFF94 also describes intermolecular interactions in hydrogen-bonded systems in a way that closely parallels that given by the highly regarded OPLS force field. © 1996 John Wiley & Sons, Inc.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Merck molecular force field. V. Extension of MMFF94 using experimental data, additional computational data, and empirical rules (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 17 (1996), S. 616-641 
    Details
    ISSN: 0192-8651
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: This article describes the extension of the Merck Molecular Force Field (MMFF94) to a much broader range of organic systems. It also describes a preliminary parameterization of MMFF94 for the hydronium and hydroxide ions and for various halide, alkalai, and alkalai earth ions as well as for such “protein” metals as Zn2+, Ca2+, Cu2+, Cu+, Fe2+, and Fe3+. The extension employed computational data on charge distributions, molecular geometries, and conformational energies for a series of oxysulfur (particularly sulfonamide) and oxyphosphorous compounds and for a diverse set of small molecules and ions not covered in the core parameterization. It also employed experimental data for approximately 2800 good-quality structures extracted from the Cambridge Structural Database (CSD). Some of the additional computational data were used to extend the explicit parameterization of electrostatic interactions and to more widely define a useful additive approximation for the “bond polarity” parameters (bond charge increments) used in MMFF94. Both the experimental and computational data served to define reference bond lengths and angles that the extended force field uses in conjunction with force constants obtained from carefully calibrated empirical rules. The extended torsion parameters consist partly of explicit parameters derived to reproduce MP2/6-31G* conformational energies and partly of “default parameters” provided by empirical rules patterned after those used in DREIDING and UFF but calibrated, where possible, against computationally derived MMFF94 torsion parameters. Comparisons to experimental data show that MMFF94 reproduces crystallographic bond lengths and bond angles with relatively modest root mean square (rms) deviations of approx. 0.02 Å and 2°, respectively. © John Wiley & Sons, Inc.
    Additional Material: 13 Tab.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Simulations of internal rotation potential energies for substituted ethanes (1990)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 11 (1990), S. 743-753 
    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: Two approaches to the simulation of internal rotation potential energies in substituted ethanes are formulated for general applications. Called the vicinal Fourier coefficient and vicinal pair energy methods, they differ only in form. The latter procedure has the advantage of yielding energy terms that represent pairwise interactions between vicinal substitutents. As numerical examples, the potential energies of ethane and five of its simple methyl and chloro derivatives are employed to simulate the corresponding energies of two higher derivatives of the series. The initial energy data were calculated by the molecular mechanics method (MM2) with geometry optimizations and the ab initio MO procedure (STO-3G) with standard geometries. Results indicate that simulated energies are reasonably accurate for the flexible-rotor model (MM2) and extremely accurate for the rigid-rotor model (STO-3G). Deviations appear to be systematic and may be rationalized on the basis of molecular structure.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540110607
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