Spectroscopic investigation on the mechanism of formation of molecular complexes of albendazole and trimethoprim with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone

UV–vis, 1H NMR, FT-IR, mass and fluorescence spectral techniques were employed to investigate the mechanism of interaction of albendazole and trimethoprim with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) and to characterize the reaction products. The interaction of DDQ with trimethoprim (TMP) and albenadazole (ALB) were found to proceed through the formation of donor–acceptor complex, containing DDQ radical anion and its conversion to the product. Fluorescence quenching studies indicated that the interaction between the donors and the acceptor are spontaneous and the interaction of TMP–DDQ (binding constant = 2.9 × 105) is found to be stronger than that the ALB–DDQ (binding constant = 3 × 103) system. Also, the binding constant increased with an increase in polarity of the medium indicating the involvement of radical anion as intermediate.

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► Structural characterization of molecular complexes of two drugs has been studied.
► The point of attachment of these drugs with the acceptor has been spectroscopically established.
► Trimethoprim was found to form relatively stronger complex with DDQ than albenadazole.
► Spectrofluorimetric and thermodynamic studies corroborate the observations.