Electrochemical Oxidation of Guanine at the Pyrolytic Graphite Electrode

Abstract

The electrochemical oxidation of guanine at the pyrolytic graphite electrode was investigated by linear and cyclic scan voltammetry between pH 0–12.5 and by controlled electrode potential electrolysis in aqueous 1M acetic acid solution. Guanine is oxidized by an initial 2normale/2H+ potential determining attack at the −Nfalse(7false)=Cfalse(8false)− double bond followed by a further 2normale/2H+ oxidation of the −Cfalse(4false)‒Cfalse(5false)− double bond to give 2‐amino‐6,8‐dioxypurine ‐4,5‐diol which, being unstable, undergoes further reaction by two routes: (a) further electrochemical oxidation to parabanic acid, guanidine, and carbon dioxide; and (b) hydrolysis to oxalyl guanidine and carbon dioxide. The exact nature of intermediate species in the electro‐oxidation of guanine and uric acid were more thoroughly established by extensive use of fast sweep cyclic voltammetry. In particular it appears that in ammonia buffers at moderately high pH, the intermediate is a 4,5‐diamine rather than a 4,5‐diol.

Additions of water, hydroxide ions, alcohols and alkoxide ions to carbonyl and azomethine bonds

“…On the other hand, some oxidation products of purines may be hydrated. In particular the species bearing two imino groups assumed to be formed as an intermediate in the electrooxidation of uric acid 157 [163][164][165] , xanthine 158 165,166 , adenine 159 167 and guanine 160 168 were anticipated to add one or two molecules of water. This assumption was based on identification of products of cleavage of such intermediates and was supported by the decrease of the reduction current attributed to the diimine with increasing concentration of methanol, added to the aqueous solution.…”

Direct Electrochemical Oxidation of DNA on Polycrystalline Gold Electrodes

“…Thus, it can be supposed that the efficiency of the DNA oxidation is determined by the duration of the applied overvoltage. Therewith, non-complete 2e À oxidation, possibly accompanied by the formation of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG, a sugar containing analogue of 8-oxoguanine, 8-oxoG) occurs at high scan rates, and complete 4e À oxidation of guanine residues is achieved at low scan rates, in the same manner as was demonstrated for pure guanine at pyrolytic graphite electrodes (see later) [36]. Guanine has been shown to be electrochemically oxidized on pyrolytic graphite by a mechanism implying its primary sufficiently slow 2e…”

“…Contrary to ssDNA-modified electrodes, no electrochemical response was obtained with Au electrodes modified with ssDNA containing no guanines, ssDNA(-G). Thus the peak at 730/ 780 mV virtually relates to the oxidation of DNA through the guanine residues, as this potential corresponds to the potential of guanine oxidation, E peak (V) 1.115 ± 0.065 pH [2,36], or, specifically, 634 mV at pH 7.4. More positive potentials of the oxidation process observed with the DNA-modified electrodes compared to the oxidation of pure guanine [2,36] could be connected with the possible oxidation of the guanine residues not only exposed to the electrode surface, but buried into the DNA structure as well.…”

“…oxidation of 8-oxoG at À C(4) C(5)À position yielding 2-amino-6,8-dioxypurine-4,5-diol [2,36]. A similar mechanism can be assumed for the oxidation of guanine residues in DNA at gold electrodes.…”

Electrochemistry of Purine Derivatives 1: Direct Determination for the Antiviral Drug 9-[(1,3-Dihydroxy-2-propoxy)methyl]guanine by Anodic Differential Pulse Voltammetry

“…Compound 1 gave a single, well-defined oxidation peak over the pH range (2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12) investigated ( Fig. 1).…”