Synthesis, spectroscopic, biological and DFT studies of new t-butyl substituted salicylaldimines having disulfide moiety

Abstract

In this study, two new t-butyl substituted salicyladimines, N,N′-bis(5-t-butylsalicylidene) diphenyl disulphide-2,2′-diamine and N,N′-bis(3-t-butylsalicylidene) diphenyl disulphide-2,2′-diamine were synthesized and characterized by spectroscopy and X-ray diffractometry. The effect of the t-butyl group on the keto-enol tautomerism in solution and solid state was investigated. According to X-ray and spectroscopic data (UV–Vis), both salicyladimines were found to be mainly in the enol-tautomeric form. Density functional theory (DFT) method was used to complement this research work. The theoretical results are in good agreement with those obtained experimentally. The anti-oxidant and anti-bacterial activities of the substituted salicyladimines were compared to the parent Schiff base, N,N′-bis(salicylidene) diphenyl disulphide-2,2′-diamine. The t-butyl derivatives show enhanced activity which can be related to the enol form of the Schiff bases and possibly due to the increase in dipole and quadrupole moments in addition to increase in hydrophobicity and decrease solubility in water.