Spectroscopic investigation of tolmetin interaction with human serum albumin

The interaction of tolmetin (TOL) with human serum albumin (HSA) in physiological buffer solution (pH 7.4) was studied by fluorescence and UV-vis absorption spectroscopy at different temperatures, combined with time-resolved fluorescence measurements. The experimental results showed that there was a strong fluorescence quenching of HSA by tolmetin. Using the continuous variation method, a single class of binding sites for TOL on HSA was put in evidence. The binding constants Ka were calculated at different temperatures, using a nonlinear fit to the experimental data, and the thermodynamic parameters ΔH(0), ΔS(0) and ΔG(0) were given. The obtained thermodynamic signature suggests that at least van der Waals and electrostatic type interactions are present. Quenching efficiency calculations, based on steady state and time-resolved spectroscopy, indicate that both static and dynamic quenching mechanisms are present.