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Abstract. Very high affinity and very low affinity processes cannot be studied by standard protocols. Binding involving very small heat changes cannot be detected and sometimes, the large amounts of material required for accurate measurements make standard protocols impractical. Isothermal titration calorimetry (ITC) has become a gold standard in determining the binding energies and the data provided by ITC can be used as reference data by simulation and prediction methods of the thermodynamic variables. In this paper we will discuss the fundamental process of calorimetry, including a short history of isothermal titration calorimetry, a short description of the method and some applications of this technique.
Keywords: calorimetry, interactions, binding affinity, isothermal titration calorimetry
Isothermal Titration Calorimetry (ITC) is a thermodynamic technique used as an analytical tool to determine the binding affinity that occurs between two biomolecules as well as the thermodynamics of biological processes. ITC is largely considered as the gold standard assay for binding.
From historical point of view, the calorimetry has provided the first information on the characteristic of the energy transfer through heat. A large part of the empirical results obtained by calorimetry was the basis for formulating the thermodynamic principles and axioms, and other results formed the basis of calorimetric principles.
The starting point in measurement of the heat exchange was given by the experiment of James Joule who showed that the heat can be used as a form of energy, followed by chemist Joseph Black in the direction of heat exchange measurement. [WIGMANS, 2003] The credit for creating the first modern techniques of calorimetry is given to the chemist Pierre Eugène Berthelot, who invented the term of endothermic and exothermic to describe the reactions of heat exchange. [IZATT et. al 1995] One of the pioneers in developing the art of calorimetry was W. Orthmann, [HATTA 1997] who patented a differential calorimeter that could determine heat transfers of the order of HWatt.
Over the past 15 - 20 years, the sensitivity of these instruments has improved dramatically [KRAFTMAKHER, 2004]
An isothermal titration calorimeter (Figure 1) is composed of two identical cells (sample cell and reference cell) made of a highly efficient thermal conducting material such as Hastelloy, shielded by an adiabatic jacket, a syringe fitted with a stirrer, an...