Electrochemical oxidation-reduction paths for pyrimidine, cytosine, purine and adenine Correlation and application.

In order to evaluate the striking discrepancy between the experimental ease of polarographic reduction of adenine and cytosine, and that predicted by molecular orbital calculation, the electrochemical oxidation-reduction behaviour of pyrimidine, cytosine, purine, adenine and related compounds was investigated at both mercury and graphite electrodes. Information was obtained on the specific adsorption of reactant and product species on the electrode, the reversibility of the energy-controlling electron-transfer step, and accompanying chemical reactions. Triangular sweep voltammetry, a.c. and d.c. polarography, and electrocapillary data, in particular, were utilized. The first three techniques were critically examined for their potential analytical utility. The results were compared with previously obtained electrochemical data and the sequence of electron-transfer and various non-electron transfer steps was more firmly established. It became clear that in order validly to correlate quantum mechanically calculated data for the energy required to add or remove an electron to or from the outermost electron level of each molecule (in the gas phase), with electrochemical redox potentials (in solution), the effects of adsorption, electron-transfer reversibility and solvation energy must be considered.