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  • Articles: DFG German National Licenses  (5)
  • Solvent effects  (2)
  • Theoretical, Physical and Computational Chemistry  (2)
  • Conformational analysis  (1)
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  • Articles: DFG German National Licenses  (5)
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  • 1
    Electronic Resource
    Electronic Resource
    Effect of Solvation on Ozonolysis Reaction Intermediates and Transition States (2000)
    Springer
    Journal of molecular modeling 6 (2000), S. 608-617 
    Details
    ISSN: 0948-5023
    Keywords: Ozonolysis ; Ozone ; Reaction mechanisms ; Solvent effects ; Theoretical calculations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Electrostatic solvent effects on the ozonolysis of ethylene have been investigated using correlated ab initio and density functional approaches. We use a simple polarizable continuum model for the solvent. It allows us to evaluate the medium effect on both the electronic and nuclear structure of the chemical species involved in the reaction. The computations confirm that basically the reaction proceeds through the Criegee mechanism. However, formation of the van der Waals complexes ethyl-ene/ozone and carbonyl oxide/formaldehyde also appears to play a role. All the calculated species are stabilized with respect to the reactants except the transition state corresponding to the primary ozonide formation. In general, electrostatic solvent effects are relatively small for activation barriers of single reaction steps and more substantial for the corresponding reaction energies. Moreover, the medium significantly modifies the structure of some species for which polarization effects are crucial.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s0089400060608
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Molecular dynamics simulation in aqueous solution of N-methylazetidinone as a model of β-lactam antibiotics (1999)
    Springer
    Theoretical chemistry accounts 101 (1999), S. 336-342 
    Details
    ISSN: 1432-2234
    Keywords: Key words:N-Methylazetidinone ; Molecular dynamics ; β-Lactam hydrolysis ; Solvent effects
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract. In this article, we analyze the results of a molecular dynamics simulation in aqueous solution of the N-methylazetidinone molecule, often used to model β-lactam antibiotics. The radial distribution functions (RDFs) corresponding to the most interesting atoms, in terms of reactivity, are presented. We focus our study on the effect of a polar environment on the molecule. The solvent structure around the system is compared to the structure of β-lactam-water complexes, as obtained in a previous study of reaction mechanisms for the neutral and alkaline hydrolyses of N-methylazetidinone. Two types of complexes have been considered which are related to different hydrolysis mechanisms having similar energy barriers at the rate-limiting step of the reaction path. In the first type, the β-lactam-water interaction takes place through the oxygen carbonyl atom and there is agreement between the maxima of the RDFs obtained here and the ab initio structure of the complexes previously reported. In the second type, the interaction takes place through the nitrogen atom and we do not predict a coordination layer around the β-lactam nitrogen atom. The results suggest that in aqueous solution hydrolysis of the carbonyl group is the most probable starting point for the overall hydrolysis reaction. Some discussion on the use of cluster models to represent the solvent effect is included.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002140050450
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    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    QSAR and conformational analysis of the antiinflammatory agent amfenac and analogues (1993)
    Springer
    Journal of computer aided molecular design 7 (1993), S. 183-198 
    Details
    ISSN: 1573-4951
    Keywords: QSAR ; Conformational analysis ; Prostaglandin synthase ; Antiinflammatory ; Amfenac
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The new nonsteroidal antiinflammatory drug (NSAID) arylacetic amfenac (2-amino-3-benzoylphenylacetic acid) and 19 substituted derivatives were studied in order to correlate the biological activities with the structure-related parameters. The geometry of amfenac in neutral and anionic form was totally optimized, starting from standard geometries and crystallographic data, using semiempirical AM1 and MNDO quantum-mechanical methods. Conformational analysis shows the existence of a rigid structure for rotations of the acetic acid chain (α°) and the central carbonyl group (γ°) around the bonds with the phenylamine ring, whereas the carboxyl group (β°) and the phenyl ring of the benzoyl group (δ°) can rotate almost freely. Electrostatic potential maps were analyzed and showed that the electrostatic orientation effect seems to make an important contribution to the binding of the active compounds to prostaglandin synthase. An electrostatic orientation model of the binding site is proposed. The frontier orbital charge distribution was also described for each compound. On the other hand, steric, electronic and hydrophobic (log P) parameters were calculated and QSAR analysis showed that the most significant parameter for the antiinflammatory activity was the π-electron density of the HOMO orbital in the second aromatic ring. These results suggest a possible electronic charge transfer between the aromatic fragments and the receptor.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00126444
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Conformational analysis of 2-cyano-1,1-dihydroxyethane in solution (1996)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 9 (1996), S. 119-127 
    Details
    ISSN: 0894-3230
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The conformational space of the 2-cyano-1,1-dihydroxyethane molecule was studied at the semi-empirical PM3 level and ab initio MP2/6-31G**//6-31G level in the gas phase and in a low-polarity medium. This system has been chosen as a model compound for 2-cyanocyclohexanone propylene and ethylene acetals. This has allowed the study of the role of polar groups on the relative conformation of two adjacent OH groups, which is of interest also in relation to the anomeric effect in carbohydrate chemistry. Solvent effects are taken into account using a continuum model with general cavity shapes.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
  • 5
    Electronic Resource
    Electronic Resource
    Computation of hydration free energies using a parameterized continuum model: Study of equilibrium geometries and reactive processes in water solution (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 17 (1996), S. 148-155 
    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: A parameterized self-consistent reaction field model allowing computation of the total free energy of hydration of organic molecules at the ab initio level is presented. The approach uses electrostatic plus polarization energies calculated with the help of a continuum model. The remaining solvation free energy terms are obtained by a simple formula based on atomic parameters and atomic accessible surface areas (ASAs), which are determined with the ASA analytical algorithm. Analytical derivatives of the atomic surfaces areas have been implemented. The atomic parameters have been obtained by a linear regression fit of the calculated and experimental free energies of solution in water for a set of 35 molecules, leading to a standard deviation of 0.75 kcal/mol. Effects of nonelectrostatic terms on solute geometries, association energies, and activation barriers are illustrated. © 1996 by John Wiley & Sons, Inc.
    Additional Material: 5 Tab.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
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