Prediction of hydrogen-bonding interaction energies with new COSMO-based molecular descriptors

Abstract

Quantum chemical (QC) calculations and the Linear Solvation Energy Relationship (LSER) approach have been combined for the development of a simple method for the prediction of hydrogen-bonding interaction energies. Each hydrogen-bonded molecule is characterized by an acidity or proton donor capacity, α, and/or a basicity or proton acceptor capacity, β. When two molecules, 1 and 2, interact, their overall hydrogen-bonding interaction energy is c(α1β2 + α2β1), where c is a universal constant equal to 2.303RT = 5.71 kJ/mol at 25 0C. When the two molecules are identical, the self-association energy is 2cαβ and this is particularly useful for the development of the method. Molecular descriptors α and β are reported for several common hydrogen-bonded molecules but they may be obtained in a straightforward manner for any hydrogen-bonded molecule, even for those not synthesized yet. A high number of hydrogen-bonding interaction energies may be predicted already out of the reported descriptors. The descriptors α and β are heavily based on the molecular surface charge distributions already available or easily obtained via relatively cheap DFT / basis-set QC calculations. The new predictive scheme is particularly useful for solvation studies and equation-of-state developments in molecular thermodynamics. The capacity of the method to address the role of conformational changes on hydrogen bonding is discussed. The limitations of the method, especially its application to systems of complex solvent molecules with many distant hydrogen-bonding sites, are also discussed.

keywords:COSMO-RS, Hydrogen-bonding, Intramolecular association, Sigma-profiles, Solvation thermodynamics