J.A.P. Piedade

Electrochemical oxidation mechanism of guanine and adenine using a glassy carbon microelectrode

The electrochemical oxidation mechanism of guanine and adenine was investigated using a glassy carbon microelectrode and cyclic and differential pulse voltammetry. It is pH-dependent and the electron transfer process occurs in consecutive steps with the formation of strongly adsorbed dimers on the electrode surface for both compounds.

Electrochemical Oxidation of 8‐Oxoguanine

Electrochemical oxidation of DNA can occur at each of the four bases and guanine is the one that can suffer the easiest oxidative damage. The occurrence of the guanine oxidation product, 8-oxoguanine, as a consequence of DNA damage caused by DNA oxidation causes important mutagenic lesions and hence it is very important to develop reliable methods for its quantification. Electrochemical study of the mechanism of oxidation of 8-oxoguanine on glassy carbon shows that it is a reversible electrode process, pH dependent, and involves several reaction products. Electroanalytical determinations of 8-oxoguanine were carried out and the detection limit was 8×10–7 M.

Electrochemical detection of in situ adriamycin oxidative damage to DNA

Adriamycin intercalation and in situ interaction with double helix DNA was investigated using a voltammetric DNA-biosensor. Oxidation and reduction of adriamycin molecules intercalated in double helix DNA were investigated in order to understand the in vivo mechanism of action with this anti-neoplasic drug. The results showed that the interaction of adriamycin with DNA is potential-dependent causing contact between DNA guanine and adenine bases and the electrode surface such that their oxidation is easily detected. A mechanism for adriamycin reduction and oxidation in situ when intercalated in double helix DNA immobilised onto the glassy carbon electrode surface is presented and the formation of the mutagenic 8-oxoguanine explained.

Electrochemical sensing of DNA–adriamycin interactions

Adriamycin, a cancerostatic anthracycline antibiotic, causes considerable death of tumour cells, together with the induction of breaks in DNA single and double strands. The interaction of this compound with DNA was investigated using an electrochemical DNA-biosensor. Adriamycin intercalation in DNA disrupts the double helix and the detection of guanine and 8-oxoguanine could mimic one possible mechanism for the in vivo adriamycin drug action.

Anodic voltammetry and AFM imaging of picomoles of adriamycin adsorbed onto carbon surfaces

Adriamycin adsorbs strongly and irreversibly onto surfaces and this enabled electrochemical detection of in situ adriamycin oxidative damage to DNA. The adsorption of adriamycin onto glassy carbon and highly oriented pyrolytic graphite (HOPG) electrodes was studied by voltammetry and mode atomic force microscopy (MAC). At a glassy carbon electrode (GCE), the adsorbate has similar voltammetric behaviour to adriamycin in solution, which enabled the cyclic, differential pulse and square wave voltammetric study of the electron transfer reaction. The total surface concentration of adriamycin adsorbed onto GCE, from a 50 nM adriamycin solution during 3 min, was calculated to be 2.57� /10 � 12 mol cm � 2 . The oxidation of adsorbed adriamycin is pHdependent and corresponds to a two electron/two proton mechanism, and the detection limit for adriamycin adsorbed onto the GCE was 3.33� /10 � 10 M. In situ AFM images show quick and spontaneous adsorption of the adriamycin onto a HOPG surface. Adriamycin forms a stable monolayer when adsorbed from different concentrations of adriamycin solutions and for short adsorption times. The strong and irreversible chemisorption of adriamycin onto carbon electrodes enables detection limits of the order of picomolar, which is much lower than the detection limits attainable by voltammetric methods for most organic compounds. # 2002 Elsevier Science B.V. All rights reserved.

Procedure 29 Electrochemical sensing of DNA damage by ROS and RNS produced by redox activation of quercetin, adriamycin and nitric oxide

Publisher Summary This chapter presents the electrochemical study of the in situ interaction of quercetin, adriamycin, DETA/NO and their metabolites with double-stranded DNA (dsDNA) immobilized on a glassy carbon electrode (GCE) surface. For construction of DNA-biosensors the GCE is polished using diamond spray before every electrochemical assay. After polishing, the electrode is rinsed thoroughly with Milli-Q water for 30 s. After this mechanical treatment the GCE is placed in pH 4.5 0.1M acetate buffer electrolyte and record various DP voltammograms until a steady-state baseline voltammogram is obtained. This procedure is fundamental to obtain reproducible experimental results. The electrical transduction of DNA damage is monitored by differential pulse voltammetry. All the voltammograms presented are background-subtracted and baseline-corrected using the moving average application with a step window of 5 mV included in GPES version 4.9 software. This mathematical treatment improves the visualization and identification of peaks over the baseline without introducing any artefact, although the peak intensity is in some cases reduced (o10%) relative to that of the untreated curve.