Redox-active metal complexes of sterically hindered phenolic ligands: Antibacterial activity and reduction of cytochrome c. Part IV. Silver(I) complexes with hydrazone and thiosemicarbazone derivatives of 4,6-di-tert-butyl-2,3-dihydroxybenzaldehyde

Abstract

Redox-active Ag(I) complexes of phenolic ligands have been synthesized using 4,6-di-tert-butyl-2,3-dihydroxybenzaldehyde isonicotinoyl hydrazone (LI) and 4,6-di-tert-butyl-2,3-dihydroxybenzaldehyde thiosemicarbazone (LII). These novel compounds have been characterized by means of chemical, physico-chemical and pharmacological screening methods. An investigation of the molecular and electronic structures of the Ag(I) complexes has been performed within the density functional theory (DFT) framework. The compounds LI and LII coordinate in their molecular forms and yield [Ag(L)2]NO3 complexes where the silver cation is coordinated by hydroxyl and ketone (or thione) moieties. The lowest MIC value (0.003μmolml−1) for the bacteria and fungi tested is characteristic of the complex [Ag(LI)2]NO3. It is comparable with or even lower than the value for some commonly used antibacterial, antifungal and silver-containing pharmaceuticals. The same complex, [Ag(LI)2]NO3, is characterized both by the highest reducing ability (determined electrochemically) and by the highest rate of reduction of bovine heart cytochrome c (determined spectrophotometrically) among the compounds under study.