Isothermal Titration Calorimetry (ITC)

 

Abstract

Calorimetry is a technique for thermodynamic measurement of heat changes DQ. The investigation of thermal effects that are the result of chemical and biomolecular reactions with ITC is a fundamental analytical method. Here, ITC provides information about thermodynamics, kinetics and physical processes. Unlike other characterization methods, ITC requires no modification and/or a immobilization of the starting reactants [1]. Calorimeters are classified by measuring principle, mode of operation, and design. With regard to design, a distinction is made between single and twin calorimetry. In a single calorimeter, the temperature of the calorimeter is measured against the environment temperature. A twin calorimeter, on the other hand, requires a reference cell with the same effective heat capacity against which the temperature is measured. In this way, thermic interference can be offset and the selectivity of the calorimeter can be increased. The group of Prof. Gauglitz uses a "Thermal Activity Monitor" (TAM) 2277 from Thermometric. This calorimeter with a twin measuring system operates in isothermal mode and is suitable for investigating exo and endothermic processes.

Measuring Principle

Temperature difference (DT) caused by heat effects due to chemical or biochemical reactions can be measured directly or through compensation. The heat exchanged (DQ) is determined by the integral of the voltage-time-signal.


Application

Characterisation of the interaction behavior of the PDMS-R4A polymer

Isothermal titration calorimetry is suitable for investigating the interaction between polymers of optical sensoric layers and analytes. We therefore used the isothermal titration calorimeter TAM to characterise a polydimethylsiloxansystem (PDMS) with an added R4A selector as well as the propylamin and propanol analytes.

All measurements were performed in aqueous solutions using both the PDMS-R4A polymer and the pure PDMS as reference system. From the time-resolved power signal, three different signals were obtained for the calorimetry measurement, which let access to the interaction of analytes to (a) the R4A (selector) (b) the PDMS and (c) the water phase. On the basis of heat exchanges we demonstrated that there are interactions of different intensities between the analytes and the polymer with their different functional groups.

Literature:
  • [1] A.Weber, M. Dettling, H. Brunner, G. E. M. Tovar, Macromolecular Rapid Communication, 2002, 23, 824-828.