Investigation into the nature of interactions in aspirin–water clusters including SAPT, AIM and NBO theories

Abstract

In this work, the characteristics of the O–H…O interactions in aspirin…(water) n = 1 − 3 as well as in the fluorine-substituted aspirin…(water) n = 1 − 3 complexes were studied by means of computational methods: symmetry-adapted perturbation theory, atoms in molecules (AIM) and natural bond orbital approaches. It is found that the cooperativity effect enhances significantly the O–H…O hydrogen bond; in some of the cases one can detect the covalent nature of hydrogen bonding. The magnitude of interaction energies of complexes increases with increasing the size of water cluster. In all the complexes studied herein, the electrostatic interaction between aspirin or fluorine-substituted aspirin and water is the main attractive force, and its contribution may be seven times as large as the corresponding contribution from dispersion. The AIM theory suggests for stronger O–H…O hydrogen bonds, the electronic energy density at the H…O bond critical point is negative and may be attributed to the partly covalent interaction.