Effect of β-cyclodextrin on antioxidant activity of coumaric acids

Inclusion complexes of o-, m- and p-coumaric acid (CA) with beta-cyclodextrin (PCD) were prepared in stoichiometric ratios (1:1) and stability constants and antioxidant activity of the complexes were studied. The apparent stability constants in aqueous solution of 0.39 x 10(3) M-1, 2.81 X 10(3) M-1 and 49 x 10(3) M-1 for o-, m- and p-CA complexes, respectively, were determined by phase solubility tests. Different analytical techniques (IR, MS) in combination with different solvent washing procedures, were used for confirmation of the nature of the inclusion complexes. Dioxan was a suitable solvent for removal of only free CA and CA adsorbed on the surface of the PCD, while methanol removed absorbed, included and free CA from the complexes. In the case of o- and m-CA-beta CD complexes, antioxidant activity was significantly increased while, in p-CA-beta CD, it remained unchanged. The impact of complex structure on antioxidant activity of CA isomers was clarified. (C) 2008 Elsevier Ltd. All rights reserved.