Investigation of the lipophilicity of 2-benzoylpyridine-thiosemicarbazone based on the ion transfer across the liquid/liquid interface

The ion transfer reaction of 2-benzoylpyridine-thiosemicarbazone (HL), which has antimicrobial and antifungal properties and anticancer activity, has been studied to determine its lipophilicity by cyclic voltammetry at the water/1,2-dichloroethane (1,2-DCE) interface. The physicochemical parameters such as standard partition coefficient (IgP(I)) and the standard Gibbs energy of transfer of the protonated form of the ligand were measured as a function of pH in aqueous phase. The protonated form of the ligand exhibited reversible or quasi-reversible voltammograms at the 1,2-DCE in the range of pH 1-5. ne protonation constants of the ligand, pK(a1) and pK(a2), were determined spectrophotometrically and were found to be 12.14 and 3.24, respectively. The standard Gibbs energy of transfer and the partition coefficient of neutral species (lgP(N)) were also determined by the shake-flask method. The standard Gibbs energy of transfer of this compound across the water/1,2-DCE interface was evaluated as the quantitative measure of its lipophilicity. The difference between IgP(I) and lgP(N) was related to the degree of charge delocalization and was used to evaluate qualitatively the lipophilicity of the ligand.