Varied Analysis of Acid Dissociation Constants by Cyclic Voltammetry and UV-Visible to Determine the Aqueous Solubility of a New Diisopropylammonium Phenylsulfonate Molecule

The determination of dissociation constant, solubility and thermodynamic parameters are very important physico-chemical parameters in substances and their knowledge is of fundamental importance for the validation of a pharmaceutical ingredient target. The determination of these parameters for an agent candidate target diisopropylammonium phenylsulfonate (besylate) (PhSO3-iPr2NH2) was determined by voltammetric and UV-visible methods.

The voltammetric method gave pKa1= 3.03±0.21 and pKa2= 10.23±0.59, while the UV-visible method determined two pKas values, pKa1= 2.21±0.04 and pKa2= 10.77±0.42 respectively. The thermodynamic parameter values calculated for the enthalpy (∆H) and entropy (∆S) of PhSO3-iPr2NH2 are of the order of ∆H= 3429.96±82.30 KJ.mol-1and ∆S = 11.85 ± 0.26 KJ.mol-1.K-1. These values suggest that the crystalline molecule is stable and the dissociation process is endothermic.

In addition, the Gibbs free energy of the molecule decreases with increasing temperature which confirmed the stability PhSO3-iPr2NH2 crystalline. The solubility shows values between 1.3 and 70 mg/mL for pH values between 2.75 and 10.5 and reaches its maximum Smax = 70mg/mL at pH equals 2.75 and 10.5.

All these physico-chemical properties of PhSO3-iPr2NH2, which are within the range of active pharmaceutical ingredients, could make it an excellent candidate of pharmaceutical ingredient. On the other hand, these results demonstrated the reliability and effectiveness of the voltammetric and UV-visible methods for the the determination of physico-chemical properties of molecules.