Adenine electrochemical reaction

The initial electrochemical and biological oxidation with xanthine oxidase are essentially identical. However, electrochemically 2,8-dioxyadenine the final product in the presence of xanthine oxidase is much more readily oxidizable than adenine 59) so that considerable further oxidation occurs. To the authors knowledge, 2,8-dioxyadenine is not a major metabolite of adenine in man or other higher organisms. Accordingly, it is likely that other enzymes accomplish further degradation of 2,8-dioxyadenine. The relationship between the products so formed and the mechanism of the reaction to the related electrochemical processes has yet to be studied. 

XOD is one of the most complex flavoproteins and is composed of two identical and catalytically independent subunits each subunit contains one molybdenium center, two iron sulfur centers, and flavine adenine dinucleotide. The enzyme activity is due to a complicated interaction of FAD, molybdenium, iron, and labile sulfur moieties at or near the active site [260], It can be used to detect xanthine and hypoxanthine by immobilizing xanthine oxidase on a glassy carbon paste electrode [261], The elements are based on the chronoamperometric monitoring of the current that occurs due to the oxidation of the hydrogen peroxide which liberates during the enzymatic reaction. The biosensor showed linear dependence in the concentration range between 5.0 X 10 7 and 4.0 X 10-5M for xanthine and 2.0 X 10 5 and 8.0 X 10 5M for hypoxanthine, respectively. The detection limit values were estimated as 1.0 X 10 7 M for xanthine and 5.3 X 10-6M for hypoxanthine, respectively. Li used DNA to embed xanthine oxidase and obtained the electrochemical response of FAD and molybdenum center of xanthine oxidase [262], Moreover, the enzyme keeps its native catalytic activity to hypoxanthine in the DNA film. So the biosensor for hypoxanthine can be based on... 

G. Dryhurst and co-workers have investigated the electrochemistry of naturally occurring JV-heterocyclic molecules, including uric acid, xanthine, adenine, and guanine,5,402 in the expectation that the mechanisms observed electrochemically might lead to a more detailed understanding of the biological redox reactions of these molecules. 

G. Dryhurst and P.J. Elving, Electrochemical oxidation of adenine reaction products and mechanisms, J. Electrochem. Soc., 5 (1968) 1014-1022. 

When the dehydrogenases are used in analysis the method relies on measuring the change in the redox state of the cofactor, i.e. the change in the concentration of NAD or NADH. NADH is inherently more easily detected photometrically and electrochemically (see below) than its oxidized counterpart, NAD+ 13). When catalyzed by a dehydrogenase, the redox reaction of the nicotinamide adenine dinucleotides (NAD(P)+/NAD(P)H) is reversible, see Figure 1. A reaction catalyzed by a dehydrogenase can be schematically written as follows ... 

Amperometric biosensors based on flavin-containing enzymes have been studied for nearly 30 years. These sensors typically undergo several chemical or electrochemical steps which produce a measurable current that is related to the substrate concentration. In the initial step, the substrate converts the oxidized flavin adenine dinucleotide (FAD) center of the enzyme into its reduced form (FADH2). Because these redox centers are essentially electrically insulated within the enzyme molecule, direct electron transfer to the surface of a conventional electrode does not occur to a substantial degree. The classical" methods (1-4) of indirectly measuring the amount of reduced enzyme, and hence the amount of substrate present, rely on the natural enzymatic reaction ... 

Electrochemical oxidation of adenine and hydroxyadenines in aqueous solution at pH 3-11.2 using a pyrolytic graphite electrode gave after extended oxidation, a diimine species which undergoes a series of reactions to give various ring-opened products <9UCS(P2)1369> (see Section 7.11.5.2.4). 

The mechanism of electron transfer reactions in metal complexes has been elucidated by -> Taube who received the Nobel Prize in Chemistry for these studies in 1983 [xiv]. Charge transfer reactions play an important role in living organisms [xv-xvii]. For instance, the initial chemical step in -> photosynthesis, as carried out by the purple bacterium R. sphaeroides, is the transfer of electrons from the excited state of a pair of chlorophyll molecules to a pheophytin molecule located 1.7 mm away. This electron transfer occurs very rapidly (2.8 ps) and with essentially 100% efficiency. Redox systems such as ubiquinone/dihydroubiquinone, - cytochrome (Fe3+/Fe2+), ferredoxin (Fe3+/Fe2+), - nicotine-adenine-dinucleotide (NAD+/NADH2) etc. have been widely studied also by electrochemical techniques, and their redox potentials have been determined [xviii-xix]. 

Sodum, R.S., Fiala, E.S. (2001). Analysis of peroxynitrite reactions with guanine, xanthine, and adenine nucleosides by high-pressure liquid chromatography with electrochemical detection C8-nitration and oxidation. Chem. Res. Toxicol. 14 438-50. 

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. 

The electrochemical and enzymic (peroxidase) oxidations outlined in this section clearly support the view that electrochemical techniques can provide useful information regarding the pathways and mechanisms of enzymic redox reactions. Work currently underway in the author s laboratory on the electrochemical and enzymic oxidation of guanine, adenine, hypoxanthine, xanthine, and various nucleoside and nucleotide species indicates that there is a considerable parallelism between the electrochemical and enzyme-catalyzed processes. 

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... 

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