Investigating the role of water molecules and its impact on the properties of hydrated vasodilator and anti-asthmatic theophylline agent.

[Display omitted] • Anhydrous, mono, di and trihydrate species were studied by using DFT calculations. • Mapped MEP surfaces show increase in the energies values from anhydrous to trihydrate. • Complete vibrational assignments of all the species are reported. • NBO studies reveal that the trihydrate in the gas phase is the most stable species. • The dihydrate is the most reactive species in gas phase and the anhydrous in solution. Theoretical structures of anhydrous (A), mono (M), di (D) and trihydrate (T) species of bronchodilator theophylline agent have been studied by using hybrid B3LYP/6–311++G** calculations to analyse the role of water molecules in its properties, reactivities and behaviours. The dipole moments increase with the number of water molecules (N) while the volumes (V) and solvation energies evidence behaviours lineal with N. D species shows higher V contraction, as T while A and M show slight V expansions. MEP surfaces show increase in energy from A to T. NBO studies reveal that T is most stable in the gas phase while A in solution. Gap values show that D is the most reactive species in gas phase while A in solution. Complete assignments of all the species and their scaled force constants are reported including librations of water molecules. [ABSTRACT FROM AUTHOR]