Electrochemical and Spectroscopic Studies on the Interaction Modes of Calf Thymus DNA with Antibacterial Schiff Bases obtained from Substituted Salicylaldehydes and Sulfamethizole

In this study, two Schiff bases have been prepared from the condensation of sulfamethizole (SMTZ) with 3-methoxy and 5-nitro derivatives of salicylaldehyde. These compounds have been characterized by elemental analysis, FT-IR, UV-Vis, 1H-NMR, melting point and X-ray measurements. The in vitro anti-bacterial properties of these Schiff bases against various microorganisms (E. coli ATCC 25922, S. aureus ATCC 25923 and trimethoprim sulfamethoxazole resistant clinical isolate E. coli (SXT-R E. coli)) have been also investigated. The Schiff base with -NO2 (Schiff base B, MIC: 0.5 μg mL−1) shows stronger antibacterial activity than SMTZ, other reactive compounds and the Schiff base with -OCH3 (Schiff base A) against S. aureus ATCC 25923. The interaction of the Schiff bases with calf thymus DNA (CT-DNA) in the physiological pH (7.4) was studied by electrochemical and spectroscopic methods. The electrochemical and spectroscopic data revealed that Schiff bases bind to CT-DNA in 1:1 stoichiometry. The binding affinity followed the order Schiff base A > Schiff base B. It has been found that the binding affinity orders determined from different methods are in good agreement with each other. The obtained results indicate that Schiff base A binds to CT-DNA by means of electrostatic forces; however, Schiff base B could interact with CT-DNA molecule by intercalative mode.