Inclusion complexation of N-substituted phenothiazines and their radical cations generated electrochemically with β-cyclodextrin

The interactions of beta-cyclodextrin (beta-CD) with phenylphenothiazine (1), N-benzylphenothiazine (2) and N-phenethylphenothiazine (3) were studied by cyclic voltammetry. In aqueous solutions, increasing the amount of beta-CD caused negative shifts in the anodic peaks and an increase in the current of the 1/1(+)* and 3/3(+)*, couples owing to the fact that more 1 and 3 were included in the beta-CD cavities. However, compound 2 neither gave an anodic nor a cathodic wave in the presence of beta-CD because the oxidization reactions on the surface of electrode were controlled by the conformations of the N-substituted phenothiazines in the cavity of beta-CD. In 1 : 9 methanol/water binary solutions, 1 and 3 were investigated by fast scan cyclic voltammetry which showed that the irreversible waves became quasi-reversible waves in the presence of P-CD, confirmed the stabilization of cation radical intermediates by beta-CD. The electrochemical and absorption spectral data indicated 1:1 inclusion complex formation of beta-CD with I and 3 cation radicals in methanol/water binary solutions and the binding constants of 1(+)* and 3(+)* were very large under this condition.