ABSTRACT
Let us start by reviewing the list of thermodynamic functions, that is, thermodynamic parameters, that can be directly experimentally measured and recall that the set is quite limited (Figure 14.1). Employing today’s instrumentation, one can easily measure the Gibbs energy (ΔG) and enthalpy (ΔH) of protein-ligand binding. e ΔG is measured by dosing ligand at constant protein concentration and measuring a signal that is proportional to the fraction of occupied ligand-binding sites on a protein. e ΔH is easily obtained from isothermal titration calorimetry (ITC) where the heat of binding at constant pressure can be directly measured. Other functions can only be determined through derivative and integral relations between the thermodynamic functions. For example, the temperature derivative of ΔG is negative entropy (ΔS), (∂G/∂T)P = −S; thus, plotting ΔG values determined at several temperatures as a function of temperature could yield the entropy. e temperature derivative of enthalpy is the heat capacity at constant pressure, (∂H/∂T)P = CP; thus, aer obtaining enthalpy changes at several temperatures, one can estimate the heat capacity change of a reaction.
