title: Dependence of pKa on solute cavity for diprotic and triprotic acids.
abstract: A systematic study of ΔG(aq)/pK(a) for monoprotic, diprotic, and triprotic acids has been carried out based on DFT/aug-cc-pVTZ combined with CPCM and SMD solvation modeling. All DFT/cavity set combinations considered showed similar accuracy for ΔG(aq)(1)/pK(a1) (70% within ±2.5 kcal mol(-1) of experiment) while only the M05-2X/Pauling cavity combination gave reasonable results for ΔG(aq)(2)/pK(a2) when both pK(a) values are separated by more than three units (70% within ±5.0 kcal mol(-1) of experiment). The choice of experimental data is critical to the interpretation of the calculated accuracy especially for several inorganic acids. For the calculation of ΔG(aq)(3)/pK(a3), the larger experimental uncertainty and an unrealistic orbital population of diffuse function for trianions in the gas phase hinders an evaluation of the predictive performance. We find the M05-2X functional with the Pauling cavity set is the best choice for ΔG(aq)(2)/pK(a2) prediction in aqueous media while all DFT/cavity sets considered were competitive for ΔG(aq)(1)/pK(a1).
authors.affiliation: Department of Chemistry and Biochemistry, Auburn University, Auburn, Alabama 36849, USA.
authors.forename: Tae Bum
authors.initials: TB
authors.lastname: Lee
authors.forename: Michael L
authors.initials: ML
authors.lastname: McKee
mesh_terms: D000143:Acids / Q000737:chemistry*; D008956:Models, Chemical; D011789:Quantum Theory; D012995:Solubility; D013816:Thermodynamics
chemical_list: D000143:Acids