We observed all the three flavonoids used in this work form 1:2 complex with CB[7]. Isothermal titration calorimetry study indicates that the complex formation process at room temperature is endothermic in nature. From our result, we observed a comparative binding feature form fluorescence and isothermal titration calorimetry measurement.

Abstract

Due to intrinsic fluorescence behavior, and the environment-dependent excited-state intramolecular proton transfer (ESIPT) process, makes special attention towards flavonoids for conducting photophysical study. The binding of fisetin, morin hydrate, and quercetin with macrocyclic molecule Cucurbit[7]urils (CB[7]) has been studied using different spectroscopic methods. The changes in the thermodynamic parameters during complex formation between the flavonoids with CB[7] are estimated by an isothermal titration calorimetry study. From the spectroscopic measurement, we have seen that in the presence of CB[7], flavonoids show the ESIPT process and the prototropic equilibrium is present between different forms of flavonoids. The isothermal titration calorimetry study shows that the complex formation between these flavonoids with CB[7] spontaneously takes place at room temperature, which is an endothermic process.