1H NMR spectroscopic study of complexation of citalopram with beta-cyclodextrin in aqueous solution

(1)H NMR spectroscopic study of citalopram (CT) in the absence as well as in the presence of beta-cyclodextrin (beta-CD) in aqueous solution revealed the formation of four 1:1 beta-CD-CT inclusion complexes. The stoichiometry of the complexes was determined by the continuous variation (Job) method, which was further confirmed by Scott's method. The binding constants (K(R) and K(R, S)) were calculated using Scott's method. The structures of all the complexes have been proposed as shown in the diagrams. All the CT proton resonances showed splitting in the presence of beta-CD, owing to chiral discrimination by the beta-CD, between the two enantiomers. The chiral discrimination appears to be due to different modes of binding of the R- and S-CT in the complexes involving a CN-containing aromatic ring.