Adenine electrochemical reduction

The electrochemical reductions of purine, adenine, and related compounds involve two consecutive steps as shown in Scheme 138 for adenine [251]. 

The electrochemical reduction of pyridinium cations and other positively charged A-het-eroaromatic systems has received considerable attention as models for nicotinamide adenine dinucleotide (NAD" ) and nicotinamide adenine dinucleotide phosphate (NADP ). 

Under specific conditions, adenine forms an intermediate Cu(l)-adenine species which is sparingly soluble and adsorbs strongly on the mercury surface [53-55]. The reaction involves electrochemical reduction of Cu(ll) to Cu(l) at a suitable potential and the reaction... 

W. T. Bresnahan, P. J. Elving, The role of adsorption in the initial one-electron electrochemical reduction of nicotinamide adenine-dinucleotide (NAD ), /o mi / of the American Chemical Society 1981, 103, 2379. 

Boldrin Zanoni MV, Rogers El, Hardacre C, Compton RG (2010) The electrochemical reduction of the purines guanine and adenine at platinum electrodes in several room temperature ionic liquids. Anal Chim Acta 659(1-2) 115-121... 

Electrochemical reduction of natural and biosynthetic nucleic acids at a dropping mercury electrode [1, 3, 73] showed that adenine and cytosine residues, as well as guanine residues in a polynucleotide chain, are reducible. The CV of DNA at a hanging mercury drop electrode showed a cathodic peak due to irreversible reduction of cytosine and adenine moieties. The reduction of the guanine moiety occurs at very negative potentials, but a peak due to the oxidation of the reduction product of the guanine moiety (7,8-dihydroguanine moiety) could be detected in the reverse scan [3]. 

The electrochemistry of this cofactor in both oxidized and reduced forms is irreversible and conveys an additional complexity in fuel cell design. Electrochemical reduction of NAD requires specific conditions in order to limit or avoid adsorption of NAD that causes enzyme inhibition, reportedly due to the adenine moiety of the cofactor [27-32]. 

Figure 12 shows a proposed reaction pathway for the electrochemical reduction of the Ni(I) adenine complex assuming octahedral coordination is retained following the reduction of Ni(II). During controlled potential electrolysis at -1.75 V, the adenine ligand undergoes intracomplex proton transfer and a 4 electron reduction (per formula unit) forming 1,2,3,6-tetrahydroadenine with Ni(I) as shown. 

Figure 13. General reaction pathway for electrochemical reduction and reoxidation of metal adenine complexes (MAd) not containing aqueous ligand(s).

The oxidation of guanine (G) and adenine (A) follows a two-step mechanism involving the total loss of four electrons and four protons showing current peaks at approximately 0.9 and 1.2 V, respectively. However, the redox properties are dependent on the pH, the ionic strength of the electrolyte, and the electrode material.2 The reader is referred to a recent review by Palecek and coworkers for a more comprehensive discussion regarding the electrochemical mechanism of the oxidation and reduction of DNA bases on carbon and mercury electrodes.3 4 Guanine oxidation is irreversible and occurs in two consecutive steps (Fig 10.1).5... 

G. Dryhurst and P.J. Elving, Electrochemical oxidation-reduction paths for pyrimidine, cytosine, purine and adenine. Correlation and application, Talanta, 16 (1969) 855-874. 

Electrochemical oxidation of the reduced form (NADH) of nicotinamide adenine dinucleotide and its analogs has been investigated [262] best results are obtained using a carbon felt electrode. The results are consistent with an ECE mechanism yielding the pyridinium salt. Indirect oxidation of NADH (and reduction of NAD" ) is treated in Chapters 27 and 29. 

Some oxidoreductases require nicotine adenine dinucleotide (NADH) as a cofactor.146 To use them in organic synthesis, as in the reduction of a ketone to an alcohol, it is necessary to have an efficient system to continuously regenerate them. A common way is to include in the same reaction formic acid and formate dehydrogenase, the byproduct being carbon dioxide.147 The regeneration of the cofactor can also be done electrochemically with or without the addition of a hydrogenase.148 The use of whole organisms eliminates this need. 

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