Influence of Explicit Hydration Waters in Calculating the Hydrolysis Constants for Geochemically Relevant Metals

Abstract

The effect of including a second, explicit solvation shell of water molecules is examined on the DFT calculation of a selection of aquo-metal ions' pK(a) values (deprotonation constants). Our goal is to gauge the accuracy of how certain cluster approximations and implicit solvation models (PCM or COSMO) affect the results. The ions in this study include: Al(3+)((aq)); Fe(3+)((aq)); Cr(3+)((aq)); Mn(3+)((aq)); Co(3+)((aq)); Ga(3+)((aq)); Fe(2+)((aq)); Mg(2+)((aq)); and Be(2+)((aq)). Overall, we find that experimental pK(a) constants can be calculated successfully to within 1-2 pH units, provided a consistent hydration structure is maintained for products and reactants.

Acidity constants and redox potentials of uranyl ions in hydrothermal solutions

“…1,5 Quantum chemistry methods combined with continuum solvent models [12][13][14] have been successfully applied to predict pK a and E 0 of many species including transition metal complexes. [15][16][17][18][19][20][21][22] For example, Steele et al calculated E 0 of UO 2 2+ /UO 2 + being 0.14 V vs. SHE (standard hydrogen electrode). 23 Hay et al predicted the 1st pK a of UO 2 2+ to be 9.6.…”

New Insights into the Configurations of Lead(II)-Benzohydroxamic Acid Coordination Compounds in Aqueous Solution: A Combined Experimental and Computational Study

“…Currently, firstprinciple calculations based on density functional theory (DFT) and some advanced experimental technologies are used to obtain more information on the molecular structure of BHA [30]. Wander et al's benchmarking calculations indicate that the DFT calculation can achieve near chemical accuracy of hydrolysis constants for metal ions in most cases [31]. Nuclear magnetic resonance and DFT calculations performed by Garcia et al show that the adopted BHA conformation of BHA aqueous solution is a closed Z (cis) configuration in aqueous solution [32].…”

Alkaline hydrolysis of ethylene phosphate: An ab initio study by supermolecule model and polarizable continuum approach

“…In the above theoretical work for the alkaline hydrolysis of EP, the authors only used implicit solvent models to investigate the solvation effects, and the observed rate constant cannot be correctly reproduced from the calculated activation free energies with PCM, except that the theoretical result with a developed model FPCM was close to the experimental estimate. Although the calculations made by Kamerlin et al indicated that the energy barrier by only implicit solvent model was closer to the experimental value than that with mixed solvation models for the hydrolysis of methyl phenyl phosphate diesters,52 some publications have demonstrated that only implicit solvent model are not sufficient for reactions involving ionic species,53–55 and many recent researches have successfully performed a combination of supermolecule (explicit solvent molecules) and continuum (implicit solvation) techniques to describe the degree of solvation for various of species 53, 55–62. So, the mixed solvation model may be adaptive for some species, here, we attempt to use this technique to study the EP hydrolysis.…”