Kinetics of the oxidation of NADH by methylene blue in a closed system

Abstract

correction is only partially cancelled by the higher order corrections determined in the coupled cluster procedure. In spite of such a cancellation, the cumulative electron correlation contribution is large and amounts to almost 40% of the tautomer relative stability. This seems to suggest that one cannot obtain a correct relative energy of tautomers of 2( 1 H)-pyridinethione at the lower orders of the many-body perturbation theory because of cancellations of lower order terms with higher order terms. We conclude that the large contribution to the relative stability of the tautomers arising from the low-order (e.g., from second order) perturbation theory may be considerably reduced by higher order terms. As a consequence, the relative stability estimated with the S C F + scaled ZPE + MBPT(2) + higher order coorelation methods would fall closer to the experimentally derived values than the MBPT(2) result, as is probably true for diazinethiones. However, the inclusion of the higher order correlation terms does not seem to be enough to compensate for the systematic discrepancy between the theoretical and the experimental estimates of the relative stability of the tautomers. ConclusionsThe gas-phase and matrix isolation experiments showed that 4(3H)-pyrimidinethione exists, under conditions where intermolecular interactions are minimized, as a mixture of thiol and thione tautomers. The relative concentration of tautomers, in the gas phase ([thiol]/[thione] -3 at 483 K) and in matrix experiments ([thiol]/[thione] -5 at 350 K), depends on the temperature. In both cases, the experimentally derived value of the free energy difference was similar (AF N 4.5 kJ/mol).

Coupled Electron‐Proton Transport in Electropolymerized Methylene Blue and the Influences of Its Protonation Level on the Rate of Electron Exchange with β‐Nicotinamide Adenine Dinucleotide

“…The inset in Figure 10 exhibits a plot of 1/k a against c b at pH 7, showing a straight line as expected from Equation 13. This linear relationship strongly supports the assumption that the coenzyme and the mediator form a 1 : 1 complex [2]. The slope and intercept of the straight line allow us to estimate values of k þ2 and K M .…”

“…12). PMB had two to three times the slope k ob of poly(Meldolas blue), whereas monomeric Meldolas blue in solution contrarily oxidized the coenzyme much more rapidly than MB þ did: its firstorder rate constant ¼ 2.63 Â 10 À3 s À1 at a NADH concentration of 1 mM [2]. This reversal of electrocatalytic activity can result from a change in the E 1/2 of the mediators with electropolymerization ( Table 2).…”

A Model of the Oscillatory Metabolism of Activated Neutrophils

“…The reaction is slow at pH around 7, but it may be catalyzed by a number of organic substances, e.g., methylene blue (Sevcik and Dunford, 1991). Here the reaction is modeled as a second order reaction with a very low rate constant (of the order of 1 M ÿ1 s ÿ1 ).…”

Elucidation of the Role of the Complex in Hydride Transfer Reaction between Methylene Blue and 1-Benzyl-1,4-dihydronictinamide by Effect of γ-Cyclodextrin

“…Sevcik and Dunford studied the kinetics of the oxidation of dihydronicotinamide adenine dinucleotide (NADH) by MB + [26]. They obtained a saturation curve by plotting the observed rate constant against [NADH] 0 , and proposed mechanisms which include the formation of a 1:1 complex between NADH and MB + .…”