Abstract: 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 (lgPI) and the standard Gibbs energy of transfer (⊿G0,w→otr, I ) of the protonated formof 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-DCEintherangeof pH1-5. The protonationconstants of the ligand, pKa1 andpKa2,were determinedspectrophotometrically and were found to be 12.14 and 3.24, respectively. The standard Gibbs energy of transfer (⊿G0, w→otr, N ) and the partition coefficient of neutral species (lgPN) 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 lgPI and lgPN was related to the degree of charge delocalization and was used to
evaluate qualitatively the lipophilicity of the ligand.

Key words: Lipophilicity, 2-Benzoylpyridine thiosemicarbazone, Ion transfer, Protonation constant, Liquid/liquid interface