Spectrophotometric investigation of products formed following the initial one-electron electrochemical reduction of nicotinamide adenine dinucleotide (NAD+)

Abstract

On electrolysis of NAD+ in aqueous solution at a potential corresponding to the initial one-electron reduction of NAD+ to a free radical, a greenish-yellow color appears which fades when electrolysis is complete. Literature ultraviolet absorption data for the resulting dimer show considerable variation. When the electrolysis is conducted in darkness, the colored product has epsilon 340 of approx. 5700 M-1 . cm-1 and epsilon 259 of approx. 31000 M-1 . cm-1. On ultraviolet and visible illumination, the color disappears, the 340-nm peak decreases and the 259-nm peak increases. On only visible illumination, the color disappears, both peaks increase, the dimer's polarographic oxidation wave decreases and the wave due to 1-substituted nicotinamide reduction increases. The data suggest that the dimer decomposes to NAD+ and 1,4-NADH.

PHOTOCHEMICAL and ENZYMATIC REDOX TRANSFORMATIONS OF REDUCED FORMS OF COENZYME NADP+

“…, , 260 nm (E,,~,, = 32 X 107 M -' cm-I), A,,;,, 340 nm (6.8 x 10'): (NADP),, A , , , , 260 nm (33 X A n,dx 340 nm (6.1 x 10'); (NMN),, A ,,,' , 263 om (7.8 x lo3), A , , , 340 nm (7.4 x 10'); (1-methylnicotinamide),, A ,nilx 277 nm (6.1 x 10'). A,,,,, 360 nm (4.3 X lo'), in agreement with literature values (Burnett and Underwood, 1968;Chan ef al., 1975;Bresnahan and Elving, 1981;Miller el Irradiation of solutions (at p H 9.5 unless otherwise noted) was performed in 10, 5 or 2-mm pathlengths quartz cuvettes (fitted with inlet and outlet tubes) with an Osram HQV 125-W Woods lamp with major emission at 365 nm (and virtually negligible at 320 nm), so that absorption was due solely to the reduced nicotinamide moieties. The intensity incident at the cuvette surface was I,, = 6 x lo-" E min ' ern-?.…”

Anthracene‐based g‐C 3 N 4 photocatalyst for regeneration of NAD (P)H and sulfide oxidation based on Z‐scheme nature

“…The mechanistic pathway for the direct electrochemical reduction of NAD(P) + proceeds stepwise reaction pathways accompanying the free radical-type NAD(P) intermediates, which are dependent on many experimental factors such as the time-scale of experiment, existence of competing adsorption, and so on. 35,47,48 As shown in Scheme 3, the electrochemical reduction of radical form of NAD(P) can be completed by two possible expected routes; (a) protonation of free radical intermediate to form monomer and (b) radical coupling takes place to form dimer. Monomer and dimer forms ultimately yield in several NADH/NADPH isomers 3/3 0 and 4/4 0 [monomers, 3/3 0 , e.g., 1, 2-, 1, 4-, and 1, 6-NADH/NADPH (3a/3a 0 , 3b/3b 0 , and 3c/3c 0 ); and dimers, 4, 4 0 and 4, 6 0 NADH/NADPH (4a/4a 0 and 4b/4b 0 )].…”

Local redox conditions in cells imaged via non-fluorescent transient states of NAD(P)H

“…As a competing route, · NADH + can also return to 0 NADH, by recombining with a free electron, or taking up an electron from an electron donor. The short-lived · NAD radical was not explicitly included in the model, since although it can also dimerize, leading to a manifold of other reactions 57 , the one dominating process under our experimental conditions is the further oxidation to NAD + . Rate parameters: ground state excitation rate ( k 01 ), combined fluorescence and non-radiative decay rate ( k 10 ), intersystem crossing rate ( k isc ), triplet relaxation rate ( k T ), electron ejection rate from 1 NADH ( k ee ), electron ejection rate from n NADH ( k ee − n ), radical deprotonation rate ( k deprot ), radical reduction rate ( k red ).…”