Substituent effect on the electron acceptor property of 1,4-benzoquinone towards the formation of molecular complex with sulfamethoxazole

Abstract

UV–Vis, 1H NMR, FT-IR, LC–MS and fluorescence spectral techniques were employed to investigate the mechanism of interaction of sulfamethoxazole with varying number of methoxy/chloro substituted 1,4-benzoquinones (MQ1–4) and to characterize the reaction products. The interactions of MQ1–4 with sulfamethoxazole (SULF) were found to proceed through the formation of a donor–acceptor complex, containing radical anion and its conversion to the product. Fluorescence quenching studies showed that the interaction between the donor and the acceptors are spontaneous. The results indicated that the progressive replacement of chlorine atom (−I effect) by methoxy group (+M effect) in the quinone decreased the electron acceptor property of the quinone. The results of the correlation of experimentally measured binding constants with electrochemical data and ab initio DFT calculations supported these observations.