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  • 1
    ISSN: 0948-5023
    Keywords: Keywords: Amides ; Hydrolysis ; Reaction mechanism ; Peptides ; Theoretical calculations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The hydrolysis of amides is a model reaction to study peptide hydrolysis. This process has been previously considered in the literature at the ab initio level. In this work, we revisit different reaction mechanisms (water-assisted, non-assisted, neutral and acid-catalyzed) with various theoretical methods : semiempirical, ab initio and Density Functional. The ab initio calculations are carried out at a computational level which is substantially higher than in previous studies. We describe the structure of the transition states and discuss the influence of the catalyst. We also compute the activation free energies for these processes at the Density Functional Theory level. Comparison of the methods allows to outline the main trends of these theoretical approaches which may be useful to design new computational strategies for investigating biological reaction mechanisms through the use of combined Quantum Mechanics/Molecular Mechanics methods.
    Type of Medium: Electronic Resource
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  • 2
    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
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