Molecular Insight into Inclusion Complex Formation of Curcumin and Calix[4]arene

The effect of the complex formation with calix[4]arene on the tautomerism of curcumin was studied in water by means of theoretical calculations at M062X/6-31G(d,p) level of theory. The results show that both tautomeric forms can enter and leave the host cavity without sterical problems. The binding of the diketo tautomeric form was found to be more favorable (by 2.1kcal mol(-1) in the gas phase and 1.7kcal mol(-1) in water) than the binding to the same host system of the preferred keto-enol tautomeric form. This results in attenuation of the energy difference between the tautomers in the complex, but does not shift dramatically the position of the tautomeric equilibrium in the guest molecule. The predicted spectral characteristics of the individual tautomers and their complexes reproduce well the experimental observations.