Solvation Energies of the Proton in Methanol

Abstract

pKa's, proton affinities, and proton dissociation free energies characterize numerous properties of drugs and the antioxidant activity of some chemical compounds. Even with a higher computational level of theory, the uncertainty in the proton solvation free energy limits the accuracy of these parameters. We investigated the thermochemistry of the solvation of the proton in methanol within the cluster-continuum model. The scheme used involves up to nine explicit methanol molecules, using the IEF-PCM and the strategy based on thermodynamic cycles. All computations were performed at B3LYP/6-31++G(dp) and M062X/6-31++G(dp) levels of theory. It comes out from our calculations that the functional M062X is better than B3LYP, on the evaluation of gas phase clustering energies of protonated methanol clusters, per methanol stabilization of neutral methanol clusters and solvation energies of the proton in methanol. The solvation free energy and enthalpy of the proton in methanol were obtained after converging the partial solvation free energy of the proton in methanol and the clustering free energy of protonated methanol clusters, as the cluster size increases. Finally, the recommended values for the solvation free energy and enthalpy of the proton in methanol are -257 and -252 kcal/mol, respectively.

Solvation enthalpies of the proton in polar and non-polar solvents: Theoretical study

“…Another theoretical study investigated the thermochemistry of the proton solvation in methanol within the cluster-continuum model. Used calculation scheme involves up to nine explicit methanol molecules using the IEF-PCM at B3LYP/6-31++G** (Δ solv H(H + ) = -1084 kJ mol -1 ) and M062X/6-31- ) levels of theory (Fifen et al 2013). For the majority of studied solvents, differences in proton solvation enthalpies related to B3LYP and BHLYP functionals are within 5 kJ mol , with exception of CHCl 3 and DMSO.…”

Hydrogen-bonded ring closing and opening of protonated methanol clusters H+(CH3OH)n (n = 4–8) with the inert gas tagging

“…[16][17][18][19]25 Temperature or vibrational energy dependence of structures has been reported particularly for charged clusters including water molecules. 7,[37][38][39][40][41][42][43][44][45] One of the important features of the H-bond networks of H + (MeOH) n is their simplicity. 4,[30][31][32][33][34][35][36] Methanol is also a typical protic solvent, and hydrogen-bond (H-bond) network structures of protonated methanol clusters, H + (MeOH) n , have been studied by infrared (IR) spectroscopy and density functional theory (DFT) calculations.…”

“…44,45 These previous studies suggest that protonated methanol clusters are a very suitable model system to examine temperature dependence of microscopic H-bonded network structures, though their experimental confirmation has not yet been systematically performed. 44,45 These previous studies suggest that protonated methanol clusters are a very suitable model system to examine temperature dependence of microscopic H-bonded network structures, though their experimental confirmation has not yet been systematically performed.…”

“…[46][47][48] All structurally distinct isomers we identified using empirical models were first re-optimized by using B3LYP/6-31+G(d). 44 As for relative energies among structural isomers, however, the reasosonable accuracy of the B3LYP/6-31+G(d) level evaluation has been confirmed by the comaprison with the dispersion-corrected DFT method. The latter has extensively been demonstrated by Chang and co-workers in protonated H-bonded clusters by comparing with their experimental IR spectral data.…”

Solvation enthalpies and Gibbs energies of the proton and electron: Influence of solvation models

“…On the other hand, the results for solvation enthalpies and Gibbs energies of the proton and electron in other solvents are still limited (Fifen et al 2011;Fifen et al 2013;Rottmannová et al 2013;Marković et al 2013;Škorňa et al 2014). In a recent paper, a comprehensive examination of the solvation enthalpies and Gibbs energies of the proton and electron in twenty solvents of different polarities was carried out (Marković et al 2016).…”