Thermodynamic analysis of binding of benzimidazole derivative with cucurbit[7]uril: A isothermal titration calorimetry study

The isothermal titration calorimetry (ITC) is a direct method to measure the heat change due to the complex formation at a constant temperature. ITC technique is the most accurate technique to directly measure binding stoichiometry, binding constant, enthalpy change, and entropy change due to complex formation. In this work, we have used ITC technique to formulate the inclusion behavior of 2-(2′-Pyridyl)benzimidazole (2-PB) with water soluble macrocyclic host cucurbit[7]uril (CB7) at three different pH's. From ITC measurement, we obtained different thermodynamic parameters associated with 2-PB-CB7 complexation. We have explained thoroughly the driving forces involved for this complexation from ITC measurement. The binding constant and other different thermodynamic parameters involve for the inclusion of 2-PB inside the cavity of CB7 at three different pH's have been estimated by using ITC technique. It was observed that the strength of supramolecular complex gradually decreases with increasing the pH value of the medium.