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This work presents a study of the electrochemical oxidation of 7‐methylguanine (7‐mGua) in aqueous solution at glassy carbon electrode by cyclic voltammetry, differential pulse voltammetry, square wave voltammetry and electrochemical impedance spectrometry. The anodic behaviour of 7‐mGua was compared with the electro‐oxidation of guanine and 7‐methylguanosine. The results demonstrated that the methyl and ribose groups are not electroactive but strongly influence the oxidation mechanism of these species. The oxidation of 7‐mGua occurred in a single pH‐dependent step, with the withdrawal of two electrons and two protons of C8, to form 8‐oxo‐7‐methylguanine, while the electro‐oxidation of 7‐methylguanosine also occurred in a single pH‐dependent step, however, with the withdrawal of one electron and one proton of C8 to form a hydroxylated product, since its oxidation to 8‐oxo‐7‐methylguanosine is hindered by the presence of the pendant groups. In addition, the oxidation of 7‐mGua was investigated in the presence of DNA and DNA‐bases, leading to the conclusion that the formation of 7‐mGua, from an interaction of DNA with an alkylating agent, would cause an increase on the deoxyguanosine peak current of the DNA‐biosensor, with no interference of any free DNA bases, which demonstrated that DNA‐electrochemical biosensors find application on detecting DNA methylation, opening a new avenue for applications of DNA biosensors.

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The electrochemical oxidation of 3‐nitro‐tyrosine (3‐NO2‐Tyr) was studied in aqueous media at metallic electrodes (platinum and gold), using voltammetric techniques. The interaction between 3‐NO2‐Tyr and double helix DNA (dsDNA) in a physiological medium was also investigated. Electro‐oxidation of 3‐NO2‐Tyr occurs in one single irreversible pH‐dependent step with the transfer of one electron and one proton from the phenolic group to the formation of radicals, which preferably dimerize, fouling the electrode surfaces. The differential pulse voltammetry and gel electrophoresis results clearly demonstrated a strong interaction of 3‐NO2‐Tyr with the dsDNA for the formation of a stable 3‐NO2‐Tyr‐dsDNA complex.

The anodic behaviour of 1‐methyl‐tryptophan (1‐mTrp) in aqueous electrolytes was investigated on a glassy carbon electrode (GCE), using voltammetric techniques. The oxidation of 1‐mTrp was associated with an electrochemical‐chemical (EC) mechanism: one electron and one proton were removed of C2 to form an intermediate radical, 1‐mTrp⋅. This was followed by a two‐way reaction, producing a 1‐mTrp dimer and/or reaction with water to form a final hydroxylated product. The oxidation mechanism of 1‐mTrp proposed was also compared with the anodic oxidation Trp on GCE. Differential pulse voltammetry was also explored for quantification of Trp and 1‐mTrp in neutral medium with low detection limits, on an anodically pre‐treated GCE.