Abstract
The interaction between the antimicrobial drug sulfamethazine (STM) and bovine serum albumin (BSA) has been studied using steady state and synchronous fluorescence spectroscopy. Fluorescence emission data revealed that BSA (2×10−6M) fluorescence was statically quenched by STM at various concentrations, which implies that STM–BSA complex has been formed. The fluorescence emission data was analyzed via applying the Stern–Volmer analysis in combination with thermodynamic investigation, where obtained results revealed that quenching is static with quenching constants of 2.371, 1.658, and 0.916×105M−1 at 298, 304, and 310K, respectively. Binding constants and number of binding sites at different temperatures were also determined by applying the Scatchard method, which in turn were used to construct the van't Hoff plot in order to estimate the enthalpy (ΔH) and entropy changes (ΔS) for the complexation process. An average of 1.00±0.17 was estimated for the number of sites of BSA, which indicated that STM binds to BSA with stoichiometric ratio of 1:1. The values that were estimated from the van't Hoff plot for ΔH and (ΔS) were −36.8kJmol−1 and −14.9Jmol−1K−1, respectively, which indicate that the STM–BSA complex is stabilized with hydrogen bonds and van der Waals interactions. Synchronous fluorescence data was obtained at Δλ of 15 and 60nm, where obtained results confirmed that STM binds to BSA at the tryptophan residue (Trp. 213). In addition, the distance between STM and the Trp. 213 was estimated via employing the Förster's non-radiative energy-transfer theory, and was found to be 2.73nm, which in turn indicated that STM can bind to BSA with high probability.
► Fluorescence data was used to demonstrate that BSA fluorescence can be quenched by STM. ► STM can bind to BSA with stoichiometric ratio of 1:1. ► STM–BSA complex is stabilized mainly by hydrogen bonds and van der Waals interaction. ► Synchronous fluorescence data revealed that BSA undergoes conformational changes upon binding to STM. ► The distance between STM and Trp. 213 was estimated to be 2.73nm, which in turn indicates that STM can bind to BSA with high probability.