Investigation on the Inclusion Behavior of Caffeic Acid with Cyclodextrin

Abstract

The formation of the inclusion complex of caffeic acid with cyclodextrin (β-CD) was studied by fluorescence, absorption spectroscopy, nuclear magnetic resonance (NMR) and the binding constant (K) of the inclusion complexes was obtained by steady-state fluorescence measurements. Experimental conditions including concentrations of β-CD and media acidity were investigated for the inclusion formation in detail. The results suggested that caffeic acid exists in four molecular forms in aqueous solution, (charged forms and neutral form) and β-CD were most suitable for inclusion of one of the charged forms of caffeic acid and could cause enhanced fluorescence emission and absorption of caffeic acid. Moreover, the spatial information of complexes have been investigated by NMR. The related mechanism is proposed to explain the inclusion process.

Keywords:

• β-Cyclodextrin
• Caffeic acid
• Fluorescence
• Absorption
• Nuclear magnetic resonance

Acknowledgements

The work was supported by the Foundation of Shanxi Province (No. 20041102 and 2006011017).