Density functional theory calculations of hydrogen bonding energies of drug molecules

Hydrogen bonding energies of several drug molecules have been calculated using hybrid density functional theory with inclusion of basis set superposition error corrections. The calculated total hydrogen bonding energy of each drug molecule has been compared with the result of a conceptually simple additive model, from which the summation of hydrogen bonding energies of individual polar groups present in the drug molecule are considered. It is shown that the validity of the additive model is strongly conditional, and to some extent predictable: In cases where the hydrogen bonding group is isolated the addition model can be of relevance, while in cases where the hydrogen bonding groups are interconnected through π-conjugation rings or chains of the drug molecules it introduces substantial errors. It is suggested that such strong cooperative effects of hydrogen bonds should always be taken into account for evaluation of the hydrogen bonding energies of drug molecules.