A computational study of the interactions of the phloroglucinol molecule with water

Phloroglucinol (C6H6O3, 1,3,5-trihydroxybenzene) is the parent structure of a broad class of molecules, many of which exhibit biological activities (antibacterial, antifungal, antiviral, antidepressant). The interactions of its two conformers with water molecules are studied both in vacuo and in water solution. The preferred association complexes in vacuo involve one, two or three water molecules H-bonded to each OH group of phloroglucinol. The resulting adducts comprise 3, 6, 9 or 15 water molecules (two water molecules being bridged by a third one in the adducts with 9 or 15 water molecules). The two conformers show interesting differences for the complexes with three water molecules, in relation to their different geometry and symmetry. Calculations on all complexes were performed at HF level with the 6-31G(d,p) basis set. For the smaller adducts, B3LYP and MP2 calculations with the same basis set, and calculations with the addition of diffuse orbitals, were also performed. The PCM model was utilised for calculations in solution.