Copper-psychoactive drug complexes: a voltammetric approach to complexation by 1,4-benzodiazepines

Copper complexation by the 1,4-benzodiazepines medazepam, diazepam, flurazepam, nitrazepam, and clonazepam was investigated using differential pulse polarography and cyclic voltammetry at a mercury electrode in 0.10 M KNO3 and pH 7.0 +/- 0.1. Because the 1,4-benzodiazepines are easily reduced at a mercury electrode through the two-electron reduction of the 4,5-azomethine functional group, copper reduction, as well as that of the ligands, was analyzed under varying experimental conditions. In most situations adsorption phenomena occurred and their influence on voltammetric signals had to be carefully analyzed. The voltammetric behavior was then interpreted in terms of complex formation. The results showed that all benzodiazepines can act as ligands toward copper(II) ions, forming 1:1 and 1:2 complexes with similar stabilities. The stoichiometric acidity constants of the benzodiazepines under study were also determined by potentiometric titration in water-ethanol medium and 0.10 M KNO3 and then extrapolated to 0% concentration of ethanol.