Simulation of Thermophysical Properties of Phenylpropanolamine Drug in Water by Ab Initio and DFT Methods

Abstract

In this study, the pKa value of the phenylpropanolamine, dissolved in water, was theoretically calculated at T = 298.15, 303.15, 308.15, 313.15, 318.15, and 323.15 K using ab initio and DFT methods with B3LYP/6-31+G(d) level of theory basis set. Tomasi’s method was used to study on the hydrogen bonds (IHB,s) between various species of phenylpropanolamine and water molecule. Some structural properties such as total atomic charge, au, the bond lengths between the indicated atoms, d, the angles between the indicated atoms, A, and the dihedral angle between the indicated atoms, D, were calculated for phenylpropanolamine in water at constant temperature. In addition, the changes in entropy (ΔS) and enthalpy (ΔH) were obtained for deprotonation process of phenylpropanolamine in water. In this research work, we showed that there is a good agreement between the experimentally determined and theoretically calculated pKa of the phenylpropanolamine, in water, at T = 298.15 K.