Understanding Electrochemical Oxidation of Methylguanines -Theory and Experiment
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| Year of publication | 2020 |
| Type | Conference abstract |
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| Citation | |
| Description | The oxidation of guanine (G) plays a majorrole in the redox processes of DNA due to the relative ease with which this nucleobase may be oxidized [1,2]. The general mechanism of G oxidation has been examinedon different graphiteelectrodes depending on the environment, such as pH, ionic strength, and the type of a supporting electrolyte[3-5].In our study, we show how the established mechanism ischangingwhen G will bemethylated. We investigated the oxidation processes of four N-methyl derivatives of G (1N, 3N, 7N, and 9N)on a polymer pencil graphite electrode (pPeGE) [6]to ascertain the relationship between the position of the methyl group and the corresponding oxidation behaviour.In the context of the oxidation peak potentialsit was found that energetically easieroxidationcan be expected in the case of methyl substitution at the pyrimidine ring rather than at the imidazole one.The position of the methyl affects the rapid protonation/deprotonation and tautomeric equilibria that are present in the oxidation processes.The assumption was proved by our theoretical study. The voltammetric data were completed withquantum chemical calculations:(i) the HOMO energies of all N-methylGs, (ii) the SOMO energies of the corresponding cations, and (iii) the theoretical oxidation potentials obtained from thermochemical cycles. Possible tautomeric structures of all the methylderivatives were optimized using COSMO solvation models at B3LYP/6-31+G(d) level [7]. While 1-, 7-and 9-mG tautomers of lowest energy resemble G, guanosine and GMP derivatives in the sense that their species have hydrogen atoms located on N1 and N9 atoms [8], 3-mG prefers to have N7 atom protonated. This finding will be discussed in more detail with respect to specific electrochemical properties of 3-mG reported from experiments |
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