Preparation and spectral investigation of inclusion complex of caffeic acid with hydroxypropyl-β-cyclodextrin

The inclusion complexation behavior of caffeic acid (CA) with hydroxypropyl-β-cyclodextrin (HP-β-CD) was studied by UV–vis, fluorescence spectroscopy and nuclear magnetic resonance spectroscopy (NMR). Experimental conditions including the concentration of HP-β-CD and media acidity were investigated in detail. The result suggested HP-β-CD was more suitable for including CA in acidity solution. The binding contants (K) of the inclusion complexes were determined by linear regression analysis and the inclusion ratio was found to be 1:1. The water solubility of CA was increased by inclusion with HP-β-CD according to the phase-solubility diagram. The spatial configuration of complex has been proposed based on 1H NMR and two-dimensional (2D) NMR, the result suggested that CA was entrapped inside the hydrophobic core of HP-β-CD with the lipophilic aromatic ring and the portion of ethylene.