Experimental and theoretical evidence of a persistent radical-cation dimer generated during the electrooxidation of an N-glucosamine-pyrrole derivative

The results of the electrochemical characterization by cyclic voltammetry of 1,3,4,6-tetra-O-acetyl-2-amino-2-deoxy-2-(pyrro-1-yl)-β-d-glucopyranose (Py-GSATA) are presented. This compound was analyzed in acetonitrile containing 0.1 M tetrabutylammonium perchlorate, using a platinum disk electrode as the working electrode. Py-GSATA showed two irreversible oxidation signals, the first at 1.24 and the second at 1.54 V vs Fc(+)/Fc. After successive cyclic voltammetry, under different experimental conditions, it was shown that it is not possible to electropolymerize this pyrrole derivative. Surprisingly, the bulk anodic electrolysis of Py-GSATA generated a single electroactive soluble product with an electrochemical cathodic signal located at -0.35 V vs Fc(+)/Fc. Mass spectrometry of the solution showed the presence of a dimeric species of the parent compound. ESR spectroscopy of the electrolysis solution showed a persistent radical species stable at least for 6 months (4 °C). UV-vis spectroscopy was consistent with low chain cation-radical oligomers. In order to propose an explanation to the dimer cation stability in solution, molecular modeling using a B3LYP/6-31+G** level of theory was used to analyze the stability and feasibility of the electrogenerated species.