Effect of temperature on the metronidazole–BSA interaction: Multi-spectroscopic method

The interaction between metronidazole and bovine serum albumin (BSA) was investigated using fluorescence spectroscopy (FS) and resonance light scattering spectroscopy (RLS). The apparent binding constants (Ka) between metronidazole and BSA were 3.42 × 104 (20 °C), 5.78 × 104 (30 °C) and 8.23 × 104 L mol−1 (40 °C), and the binding sites values (n) were 1.48 ± 0.03. The experimental results showed that the metronidazole could be inserted into the BSA, quenching the inner fluorescence by forming the metronidazole–BSA complex. The addition of increasing metronidazole to BSA solution leads to the gradual enhancement in RLS intensity, exhibiting the formation of the aggregate in solution. It was found that both static quenching and non-radiation energy transfer were the main reasons for the fluorescence quenching. The entropy change and enthalpy change were positive, which indicated that the interaction of metronidazole and BSA was driven mainly by hydrophobic forces. The process of binding was a spontaneous process in which Gibbs free energy change was negative.