Journal ArticleDOI
Modelling pka of carboxylic acids and chlorinated phenols
TLDR
In this paper, the AM1 hamiltonian was used to estimate aqueous pKa for 16 carboxylic acids and 15 phenols with experimental data taken from literature.Abstract:
Estimation of aqueous pKa through quantum chemical gas-phase and solution-phase calculations is investigated for 16 carboxylic acids and 15 phenols with experimental data taken from literature. Parameters based on the AM1 hamiltonian include enthalpy and free energy differences between the ground state of the ionizable compounds and their anion counterparts as well as respective transition states and intermediates along the reaction path of the aqueous proton transfer. With carboxylic acids, additional ab initio calculations are performed to evaluate the semiempirical level of theory. Aqueous solvation is modelled in three different ways: Application of continuum-solvation methods AM1-COSMO and AM1-SM2, microsolvation of the solutes through formation of clusters with three water molecules, and combination of both approaches to include both bulk water polarization and solute-solvent coupling effects. Regression equations with r values up to 0.93 for carboxylic acids and 0.96 for phenols suggest, that continuum-solvation models can be recommended to estimate aqueous pKa through electronic structure calculations.read more
Citations
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Journal ArticleDOI
Implicit Solvation Models: Equilibria, Structure, Spectra, and Dynamics.
Journal ArticleDOI
Theoretical Methods for the Description of the Solvent Effect in Biomolecular Systems.
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First Principles Calculations of Aqueous pKa Values for Organic and Inorganic Acids Using COSMO−RS Reveal an Inconsistency in the Slope of the pKa Scale
TL;DR: It is concluded that the experimental pKa scale depends differently on the free energy of dissociation than generally assumed, and a theoretical a priori prediction method for pKa, which has the regression constant and the slope as only adjusted parameters is presented.
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Experimentation with different thermodynamic cycles used for pKa calculations on carboxylic acids using complete basis set and Gaussian‐n models combined with CPCM continuum solvation methods
TL;DR: Barone and Cossi as discussed by the authors combined the complete basis set and Gaussian-n methods with the polarizable conductor model (CPCM) continuum solvation methods to calculate pKa values for six carboxylic acids.
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Prediction of the pka of carboxylic acids using the ab initio continuum-solvation model pcm-uahf
TL;DR: In this article, experimental pKa data for 16 aliphatic carboxylic acids are compared with calculated proton-transfer energies in the gas phase and in aqueous solution, at the SCF and MP2 levels with inclusion of SCF-level entropic and thermochemical corrections to yield free energies of dissociation.
References
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Development and use of quantum mechanical molecular models. 76. AM1: a new general purpose quantum mechanical molecular model
TL;DR: In this paper, a new parametric quantum mechanical molecular model, AM1 (Austin Model l), based on the NDDO approximation, is described, in which the major weaknesses of MNDO, in particular failure to reproduce hydrogen bonds, have been overcome without any increase in computing time.
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Fully optimized contracted Gaussian basis sets for atoms Li to Kr
TL;DR: In this article, various contracted Gaussian basis sets for atoms up to Kr are presented which have been determined by optimizing atomic self-consistent field ground state energies with respect to all basis set parameters, i.e., orbital exponents and contraction coefficients.
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COSMO : a new approach to dielectric screening in solvents with explicit expressions for the screening energy and its gradient
Andreas Klamt,Gerrit Schüürmann +1 more
TL;DR: In this paper, an algorithm for the accurate calculation of dielectric screening effects in solvents is presented, which leads to rather simple expressions for the screening energy and its analytic gradient with respect to the solute coordinates.
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Electronic structure calculations on workstation computers: the program system turbomole
TL;DR: TURBOMOLE as discussed by the authors is a program system for SCF that takes full advantage of all discrete point group symmetries and has only modest I/O and background storage requirements.
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Optimization of parameters for semiempirical methods I. Method
TL;DR: In this paper, a new method for obtaining optimized parameters for semi-empirical methods has been developed and applied to the modified neglect of diatomic overlap (MNDO) method.