Effect of N(4)-substituent groups on transfer of 2-benzoylpyridine thiosemicarbazone derivates at the water/1,2-dichloroethane interface

Abstract

Dependent on the pH of the aqueous phase, the transfer of protonated forms of 2-benzoylpyridine N(4)-phenyl thiosemicarbazone (BPPT) (which has antimicrobial, antifungal and anticytotoxic activities) and 2-benzoylpyridine N(4)-ethyl thiosemicarbazone (BPET) across water/1,2-dichloroethane (1,2-DCE) interface has been studied by cyclic voltammetry. The protonation constants of the ligands ( p K a 1 w and p K a 2 w ) were determined by spectrophotometry. The standard partition coefficients ( log P i 0 ) and the standard Gibbs energies of ionic (cationic) species of ligands ( Δ G tr , i 0 , w → o ) were calculated from the standard transfer potentials ( Δ o w ϕ i 0 ). The standard Gibbs energies of their transfer ( Δ G tr , i 0 , w → o ) and partition coefficients of neutral species (log P N ) were determined by shake-flask method. These thermodynamic parameters were evaluated as a quantitative and qualitative measure of the lipophilicities of two compounds. The differences between the partition coefficients of cationic and neutral form of compounds [ diff ( log P I + − N ) ] were interpreted by results obtained from voltammetric data. Effect of N(4)-phenyl and ethyl groups for transfer of 2-benzoylpyridine thiosemicarbazone derivatives at macro-liquid/liquid interface was investigated. The antimicrobial activity of BPET was tested against four types of bacteria and found to be active against Staphlylococcus aureus.