Isothermal titration calorimetry

In chemical thermodynamics, isothermal titration calorimetry (ITC) is a physical technique used to determine the thermodynamic parameters of interactions in solution. ITC is the only technique capable comprehensively characterizing thermodynamic and even kinetic profile of the interaction by simultaneously determining binding constants (${\displaystyle K_{a}}$), reaction stoichiometry (${\displaystyle n}$), enthalpy (${\displaystyle \Delta H}$), Gibbs free energy (${\displaystyle \Delta G}$) and entropy (${\displaystyle \Delta S}$) within a single experiment. It consists of two cells which are enclosed in an adiabatic jacket.

The compounds to be studied are placed in the sample cell, while the other cell, the reference cell, is used as a control and contains the buffer in which the sample is dissolved. The technique quantifies the heat released or absorbed during the binding process by incrementally adding one reactant (via a syringe) to another (in the sample cell) while maintaining constant temperature and pressure. Heat-sensing devices within the ITC detect temperature variations between two cells, transmitting this information to heaters that adjust accordingly to restore thermal equilibrium between the cells. This energy is converted into binding enthalpy using the information about concentrations of the reactants and the cell volume. Compared to other calorimeters, ITC does not require any correctors since there is no heat exchange between the system and the environment. ITC is also highly sensitive with a fast response time and benefits from modest sample requirements. While differential scanning calorimetry (DSC) can also provide direct information about the thermodynamic of binding interactions, ITC offers the added capability of quantifying the thermodynamics of metal ion binding to proteins.