Thermal Analysis

Abstract

This review deals with the application of various thermal analytical methods to supramolecular compounds, with particular reference to host–guest systems. Examples include the use of dilatometry in the measurement of single crystal unit cell parameters over a range of temperatures in order to study structural phase transformations. Thermal gravimetry (TG) is employed to determine the stoichiometry of inclusion compounds and is particularly useful in studying decompositions that occur in multiple steps. The kinetics of decomposition yields activation energies of solid-state reactions while differential thermal analysis allows the estimation of enthalpy changes in reactions. Thermal methods applied to active pharmaceutical ingredients deal with such problems as the identification of polymorphs, the characterization of cocrystals and hydrated multicomponent gels. The question of increase in the bioavailability of insoluble drugs is discussed using examples of including the drug molecules into various cyclodextrins. Differential scanning calorimetry (DSC) is employed to obtain precise melting endotherms of pharmaceuticals and hence determining their purity. The topic of guest exchange in organic clathrates and in metal organic frameworks is discussed in terms of TG, DSC, and hot-stage microscopy. Temperature-modulated DSC is useful in determining thermal stability, glass transitions, and polymorphic transformations of different analytes and is particularly important in the analysis of the properties of polymers.