Thermodynamics of organic chemical hydration: QSPR models using physicochemical HYBOT descriptors

Abstract

Stable and predictive quantitative structure-property relationship (QSPR) models of thermodynamics of chemical hydration (changes in Gibbs energy, DeltaG(air/water), enthalpy, DeltaH(air/water) and entropy DeltaS(air/water)) were obtained on the basis of physicochemical descriptors calculated by the HYBOT program. The structurally diverse training set (n = 151) and test set (n = 37) included 13 mono-functional chemical classes. The applied HYBOT descriptors comprise molecular polarizability alpha (as a volume-related term), the sum of partial negative charges on all atoms in a molecule SigmaQ(-) (as an electrostatic term) and the sum of H-bond acceptor and donor factors SigmaC(a) and SigmaC(d) (as H-bond terms). Final equations for changes in Gibbs energy and enthalpy provided good statistical criteria and standard deviations on the level of errors of experimental determinations. All four above-mentioned terms essentially contribute to hydration enthalpy and each of them increases negative values of enthalpy. Hydration Gibbs energy predominantly depends on hydrogen bonding between solute and water molecules. Steric and electrostatic terms act in opposite directions and partly compensate each other. Changes in entropy correlate with increasing H-bond acceptor ability, whereas the other three descriptors exhibit inverse correlations.

In silico Prediction of Aqueous Solubility: a Comparative Study of Local and Global Predictive Models

“…Division of QSPR models into global and local ones was rather imprecise until recently. A researcher could select chemicals of any class (acids, bases, H‐bond donor, acceptors and so on) and obtain QSPR models for each selected chemical group 17h,22e. At present the development of any local QSPR model means at least a two step process: a creation from a common data set of a collection of small subsets, and construction of local models for each such subset.…”

A step towards the a priori design of ionic liquids

“…[15][16][17] Raevsky uses similar descriptors to predict Gibbs free energies. 18 For example, the H-bond acceptor parameters for pyridine as a solvent (b) can be determined by dissolving a selection of Kamlet-Taft dyes in pyridine. Whereas the parameters for pyridine as a solute (b H 2 ) can be obtained by measuring the partition coefficient of pyridine between two phases (such as water and octanol) or by dissolving pyridine in tetrachloromethane and determining the equilibrium constant for association of pyridine with a range of acids.…”