Voltammetric and spectroscopic studies of the oxidation of the anti-oxidant drug dipyridamole in acetonitrile and ethanol

The eletrochemical oxidation of dipyridamole DIP was studied by cyclic voltammetry with ultramicroelectrodes, electronic absorption and fluorescence spectroscopies, and ESR spectroscopy in acetonitrile and ethanol. Extensive electrolysis of DIP was performed in these solvents and the progress of the oxidation reaction as a function of time was monitored through cyclic voltammetry, absorption and fluorescence optical spectroscopies, taking advantage of the fact that DIP is a highly fluorescent compound. Voltammograms at high and low scanning rates showed a similar behavior in the different solvents characterized by two almost reversible voltammetric waves corresponding to the consecutive one-electron release. The corresponding E-1/2 were 120 and 400 mV in acetonitrile and 470 and 680 mV in ethanol. The release of one electron produces a radical cation which is readily detected by ESR spectroscopy. The oxidation is accompanied by the decrease of fluorescence intensity and significant changes in the optical absorption spectrum of DIP with the appearence of the characteristic absorption of the radical in the blue spectral region. The oxidation in ethanol seems to be affected by the solvent in the sense that it is not as easy as in acetonitrile and longer reaction times are required to complete the process. The relative ease of oxidation is in agreement with its reported anti-oxidant activity both in model systems and in physiological media. (C) 1998 Elsevier Science B.V. All rights reserved.