The electrochemical oxidation of the antioxidant drug dipyridamole at glassy carbon and graphite electrodes in micellar solutions

The anodic oxidation of dipyridamole (DIP) has been studied in micellar solutions of the anionic surfactant sodium dodecylsulfate (SDS), the cationic cetyltrimethylammonium bromide (CTAB) and the neutral t-octyl phenoxy polyethoxyethanol (Triton X-100). The oxidation reaction was studied by employing cyclic voltammetry at a glassy carbon, and rotating disc voltammetry which allowed the estimation of the diffusion coefficients, DI for DIP in the presence of the micelles. The values of D in the case of CTAB (0.42 x 10(-6) cm(2) s(-1)) and Triton X-100 (0.39 x 10(-6) cm(2) s(-1)) at pH 7.0 are consistent with DIP being transported to the electrode together with the micelle - so, for nonionic and cationic micelles the oxidation of DIP is diffusion controlled by drug micelle binding. In the case of SDS the values of D (0.16 x 10(-7) cm(2) s(-1) at pH 7.0) are significantly lower than those expected for the pure SDS micelles. Furthermore, the interaction of SDS with the electrode surface could also contribute to preclude the efficient transport of DIP to the electrode surface, explaining the low diffusion constant found. In acid solution, at pH 3.0 or below, the oxidation of DIP is characterized by a single two-electron wave. Upon alkalinization to a more physiological pH range(pH 6-9) a two step oxidation behavior is found only in the presence of anionic SDS. Diffusion coefficients for both waves are very similar suggesting that both processes are governed by the same mechanism. (C) 2000 Elsevier Science Ltd. All rights reserved.