Electrochemical and spectrophotometric determination of the formation constants of the ascorbic acid-��-cyclodextrin and dopamine-��-cyclodextrin inclusion complexes

From UV?Cvis spectrophotometry and cyclic voltammetry it is demonstrated the interaction of dopamine, DA, and ascorbic acid, AA, with ??-cyclodextrin, ??CD, in aqueous media at pH 3.0. The formation constants of the respective inclusion complexes were also determined. The spectrophotometry data fed into the data processing software SQUAD, allowed calculation of the said constants for the AA?C??CD complex (H₂AA?C??CD) giving a value of 3236 M^?1, while for the dopamine complex DA?C??CD (H₃DA+??CD) this was 5888 M^?1. From these results, the theoretical absorption spectra were generated which fitted quite well the experimental ones, thus indicating clearly that the constants are reliable. Moreover, from the cyclic voltammetry data, the stated constants were also calculated whereby that of the H₂AA?C??CD gave a value of 3981 M^?1 while for the dopamine complex DA?C??CD (H₃DA+??CD) it was 4898 M^?1. It is noteworthy to say that these values were similar to those found through spectrophotometry.