Calorimetric Techniques for Studying DrugDNA Interactions

Calorimetric techniques can be used to measure the heat effects accompanying a drug-DNA interaction (1 –3 ); in principle, one can calculate from these measurements both (4 ) the affinity (ΔG) and enthalpy change (ΔH) for the process. There are, however, many sites on the DNA lattice for interactions and assigning AH values for each IS dependent on the model used in the mathematical analysis. What can be obtained in most cases from careful calorimetric measurements is the AH for transferring a drug molecule from the aqueous environment to a site of high affinity on an unoccupied DNA lattice. Currently available calorimeters can be used at concentrations approaching levels used in UV-visible studies (1 –5 ). Combination of the calorimetric measurements with an analysis of the corresponding binding isotherm can provide both the enthalpy and entropy changes (ΔG = ΔH - TΔS) for attaching a drug to a DNA lattice site (1 –3 ,5 ).