Guanine electrochemical oxidation

Eskiocak, U., Ozkan-ariksoysal, D., Ozsoz, M. and Oktem, H.A. (2007) Label-free detection of telomerase activity using guanine electrochemical oxidation signal. Anal. Chem.,19 (22), 8807-8811. 

Fig. 17. Mechanism for the electrochemical oxidation of guanine at the PGE. Molar amounts of products are those formed in 1 M HOAc...

There is really too little information on the biological oxidation of guanine to attempt to compare it with the electrochemical oxidation. It might be useful to bear in mind the electrochemical mechanism when further studies of the biological oxidation of this compound are carried out. 

The electrochemical behaviour and the adsorption of nucleic acid molecules and DNA constituents have been extensively studied over recent decades [1-6]. Electrochemical studies demonstrated that all DNA bases can be electrochemically oxidized on carbon electrodes [7-13], following a pH-dependent mechanism. The purines, guanine (G) and adenine (A), are oxidized at much lower positive potentials than the pyrimidines, cytosine (C) and thymine (T), the oxidation of which occurs only at very high positive potentials near the potential corresponding to oxygen evolution, and consequently are more difficult to detect. Also, for the same concentrations, the oxidation currents observed for pyrimidine bases are much smaller than those observed for the purine bases. Consequently, the electrochemical detection of oxidative changes occurring in DNA has been based on the detection of purine base oxidation peaks or of the major... 

Electrochemical oxidation of natural and synthetic DNA performed at pyrolytic graphite [16] and glassy carbon [3-6,17,18] electrodes showed that at pH 4.5 only the oxidation of the purine residues in polynucleotide chains is observed. Using differential pulse voltammetry, the less positive peak corresponds to the oxidation of guanine residues and the peak at more positive potentials is due to the oxidation of adenine residues. 

Guanine, with a formal potential at pH 7 of 1.3 V vs. normal hydrogen electrode (NHE) (1.06 V vs. saturated calomel electrode (SCE)), is the most easily oxidized of the four DNA bases/331 The other bases have formal potentials up to 0.5 V more positive. Detecting nucleic acids by electrochemical oxidation depends on structure, with double-stranded (ds) DNA giving only trace oxidation peaks at best and single-stranded (ss) DNA giving irreversible oxidation peaks at about 1.0-1.2 V vs. SCE on carbon electrodes. 

Enhanced electrochemical signals for DNA can be obtained by catalytic electrochemical oxidation using transition metal complexes/341 Studies by Thorp et al/35 01 showed that Ru(bpy)f+ (bpy=2,2 -bipyridine) is an efficient electrochemical catalyst that oxidizes only guanine bases in DNA and oligonucleotides. The reaction follows the catalytic pathway below ... 

Fig. 6 Label-free electrochemical detection of DNA hybridization. The inosine (I) substituted probe shows no electrochemical signals, since inosine is not electroactive (a) After hybridization with the target DNA, the appearance of the guanine (G) oxidation signal (around + 1 V vs. Ag/AgCl) provides specific detection (b)...

Guanine and guanosine can be electrochemically oxidized at a pyrolytic graphite electrode [86, 96,97] with Epn = -f-1.02 V in 2 M H2SO4. Uracil and thymine. Uracil and thymine are not reducible polarographically under normal conditions [78, 86,95], but in alkaline media they yield an anodic wave caused by the formation of a mercury salt [98]. 

An extremely powerful approach developed by Thorp and coworkers over the last decade uses a transition-metal mediator to facilitate the catalytic oxidation of DNA. " In a typical assay, RuCbpyXa is electrochemically oxidized to Rulbpyls , which rapidly oxidizes guanine residues in DNA to... 

Figure 7.1 Label-free voltammetric detection of aptamer-protein interactions. (A) The electrochemical oxidation response from the guanine bases in the aptamer is observed at about 1 V (peak G) on the surface of the screen-printed electrodes. (The inset shows gold and carbon-based screen-printed electrodes with a three-electrode system.) (B) After the binding event with the target protein, an oxidation signal appears at about 0.6 V (peak P), and the oxidation signal of the aptamer decreases.

S. (2005). Allele-specific genotyping by using guanine and gold electrochemical oxidation signals. Bioelectrochemistry 67, 199-203. 

On the other hand, changes to the electrical properties of an interface, change in flexibility from ssDNA to the rigid dsDNA, or the electrochemical oxidation of guanine bases are used approaches for label-free methods for detection of DNA hybridization. There... 

Nucleosides and nucleotides derived from adenine and guanine are electrochemically oxidized at graphite electrodes at more positive potentials than their parent bases [145, 146]. No details of the products or mechanism associated with electrochemical oxidation of the base derivatives have been published. An analytical method has been developed... 

Fig. 11. Primary electrochemical oxidation of bases at the graphite electrodes. A adenine, B guanine.

The inherent electrochemical activity of DNA is utilized in processes without reporter molecules. It is well known that the guanine base of DNA can be oxidized at moderate potentials. This property can be utilized if the molecules constituting the probe are not oxidizable themselves. For that purpose, oligonucleotides are synthesized which contain inosine instead of guanine base molecules. Inosine is practically inert at potentials where guanine is oxidized. If the target molecule combines with the synthetic probe during... 

Correlation between Electrochemical and Biological Oxidation Guanine... 

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