NMR (1H, ROESY) spectroscopic and molecular modelling investigations of supramolecular complex of β-cyclodextrin and curcumin

In this paper we have investigated the solubility enhancement of curcumin through inclusion complexation by β-cyclodextrin as well as the topology and geometry of interaction between curcumin and carrier. For this purpose, the phase solubility of curcumin was assessed using Higuchi and Connors method, and the inclusion complex was characterised by 1D 1H and 2D ROESY NMR analysis, and finally confirmed by molecular modelling. The phase solubility diagram demonstrated the AL-type which confirms an increase in curcumin solubility by increasing the concentration of β-cyclodextrin. 1H NMR and ROESY spectra results showed a cross-peak between H-3 proton of β-cyclodextrin and the aromatic rings group of curcumin. This revealed the hydrophobic interactions between aromatic rings of curcumin and the cavity of β-cyclodextrin. Finally, the enthalpy of formation was obtained from molecular modelling results which in turn indicated that the process is exothermic and low-energy interactions are involved in the inclusion complex formation.