H-1 NMR spectroscopy was used to evaluate the effects of biologically active anions Cl- and Br- in inclusion complex formation of alpha-cyclodextrin with some aromatic carboxylic acids. It was demonstrated that presence of Br- anions induces the decrease in alpha-cyclodextrin binding affinity to carboxylic acids, while Cl- has no a noticeable effect. The observed difference was discussed in terms of selective interactions of alpha-cyclodextrin with Br- and Cl-. Only Br- anions are able to penetrate into alpha-cyclodextrin cavity and compete with carboxylic acid molecule for the macrocyclic cavity. This competition shifts the alpha-cyclodextrin/acid equilibrium in the direction of complex dissociation. (C) 2012 Elsevier B.V. All rights reserved.