Binding of tolmetin and salicylic acid to human serum albumin as a function of temperature

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Abstract
When drug-protein binding data are evaluated thermodynamically standard free energy (ΔG°), standard enthalpy (ΔH°) and standard entropy (ΔS°) are usually estimated from association constants (Ka) derived from binding data obtained at only two temperatures. Estimation of ΔH° involves the assumption of its constancy in the temperature range studied and linearity of a van't Hoff plot of In Ka versus 1/T. Sometimes the assumption of such linearity is invalid for theoretical reasons and data obtained at only two temperatures contain no information concerning linearity of this plot. We present data for the binding of both tolmetin and salicylic acid to human serum albumin as a function of temperature which make doubtful the validity of using association constants of these drugs to derive thermodynamic constants other than ΔG° values.