Acidity constants and its dependence on solvent selection from first-principles calculations using cluster-continuum models

Abstract

Dissociation constants of selected carboxylic acids in aqueous and organic solvents were calculated at quantum chemical level. We considered cases in which trace quantities of water may be present, as well as cases in which water was entirely absent. In the latter cases, alternative proton acceptors need to be considered. For aqueous solvent, short-range solvation effects are considered by adding explicit water molecules as the first solvent shell. In the absence of water, corresponding organic solvents are used directly as the proton acceptors and the resulted pK a are quite comparable to those obtained from previous case of aqueous solvent.

Prediction of pKa Using DFT: the Nicotianamine Polyacid Example

“…The overestimation of pK a in the basic pH domain and the underestimation of pK a in the acidic domain would be reduced using additional water molecules or positioning the water molecules in different orientations and positions, such as to optimize the net charge on carboxylic and amine functional groups for example. 42 Because in our approach we cannot guarantee the location of the global minimum energy structure, advanced strategies based on the exploration of the multidimensional potential energy surface would provide the minimum energy structure and improve pK a values (basin hopping/metadynamics/...). Such investigation of the geometries for NA would improve the calculated pK a values.…”

Design and Prediction of Corrosion Inhibitors from Quantum Chemistry

“…The pKa's are shown for the two imidazoles in Table III. Note: the pKa is only considered to be relevant for the aqueous phase in this work, although there is the potential for acid dissociation chemistry in non-aqueous phases (but much less so, see the work by Pham et al 11 ). The pKa is within 1.0 units for the imidazoles for which literature data is available.…”