Electrochemical reduction of uridine in dimethyl sulfoxide: effect of the ribose group

Abstract

Adam-The easier electrochemical reduction of uridme (I-/LLLtibofirranosylumcil) in dimethyl sulfoxide as compared to uracil (2, 4dihydroxypyrimidine) by ca. 0.1 V is exphcable on the basii of the electronwithdrawing effect of the ribose group. This effect and possible steric hindrance by the ribose group markedly affect the reaction sequence following the initial one-electron reduction to generate a radical anion, which abstracts a proton from the parent uridine (father-son reaction) to form the neutral uridine free radical and the uridme anion. With increasing &dine concentration, Further reduction and protonstion reactions are favored, resulting in an increase in the effective faradaic n from CLI. 0.5 to 0.8. The availability of only one proton-donating site on uridine, ie, that on N(3). allows explication of the behavior of other hydroxypyrimidiues such as uracil.

Electron Transfer in DNA and in DNA-Related Biological Processes. Electrochemical Insights

“…In aprotic solvents, for example, dimethylsulfoxide or acetonitrile (ACN), thymine is reduced at very negative potentials (in cyclic voltammetry experiments in ACN at glassy carbon electrode, the peak potential is close to −2.4 V vs SCE at 1 V s −1 ) with a consumption of ( 2 / 3 )e − per substrate molecule, as shown by Scheme . , Electron stoichiometry increases to 2e − per molecule in the presence of a weak acid, in line with the mechanistic scheme (the two protonation steps then involve the added acid and not thymine). Reduction of uracil, U (identical to thymine except that it has no methyl group at C 5 ), involves the exchange of half an electron per neutral substrate. , In this case, the radical anion U •− is protonated from neutral U, leading to the radical UH • . This radical, in contrast to • TH 2 , dimerizes before being reduced with a second electron, due to less steric hindrance at the C 6 position.…”

“…Reduction of uracil, U (identical to thymine except that it has no methyl group at C 5 ), involves the exchange of half an electron per neutral substrate. 91,92 In this case, the radical anion U •is protonated from neutral U, leading to the radical UH • . This radical, in contrast to • TH 2 , dimerizes before being reduced with a second electron, due to less steric hindrance at the C 6 position.…”

NAD/NADH as a model redox system: Mechanism, mediation, modification by the environment

“…The dimer can undergo a proton-assisted disproportionation to NAD+ and NADH [8], which is at least formally analogous to the disproportionation of a semiquinone:…”

“…The third step can follow two different paths. One involves a second heterogeneous electron transfer, NAD' tiNAD+ +e-UP (8) which is reversible. Although NAD' dimerizes very rapidly, the dimer is electrochemically oxidized at ca.…”