85289-84-5Relevant articles and documents
Oxygen-initiated chain mechanism for hydride transfer between NADH and NAD+ models. Reaction of 1-benzyl-3-cyanoquinolinium ion with N -methyl-9,10-dihydroacridine in acetonitrile
Hao, Weifang,Parker, Vernon D.
, p. 9286 - 9297 (2013/01/15)
A reinvestigation of the formal hydride transfer reaction of 1-benzyl-3-cyanoquinolinium ion (BQCN+) with N-methyl-9,10- dihydroacridine (MAH) in acetonitrile (AN) confirmed that the reaction takes place in more than one step and revealed a new mechanism that had not previously been considered. These facts are unequivocally established on the basis of conventional pseudo-first-order kinetics. It was observed that even residual oxygen under glovebox conditions initiates a chain process leading to the same products and under some conditions is accompanied by a large increase in the apparent rate constant for product formation with time. The efficiency of the latter process, when reactions are carried out in AN with rigorous attempts to remove air, is low but appears to be much more pronounced when MAH is the reactant in large excess. On the other hand, the intentional presence of air in AN ([air] = half-saturated) leads to a much greater proportion of the chain pathway, which is still favored by high concentrations of MAH. The latter observation suggests that a reaction intermediate reacts with oxygen to initiate the chain process in which MAH participates. Kinetic studies at short times show that there is no kinetic isotope effect on the initial step in the reaction, which is the same for the two competing processes. Our observation of the chain pathway of an NADH model compound under aerobic conditions is likely to be of importance in similar biological processes where air is always present.
The tightness contribution to the Bronsted α for hydride transfer between NAD+ analogues
Lee, In-Sook Han,Chow, Kim-Hung,Kreevoy, Maurice M.
, p. 7755 - 7761 (2007/10/03)
It has been shown that the rate of symmetrical hydride transfer reaction varies with the hydride affinity of the (identical) donor and acceptor. In that case, Marcus theory of atom and group transfer predicts that the Bronsted α depends on the location of the substituent, whether it is in the donor or the acceptor, and the tightness of the critical configuration, as well as the resemblance of the critical configuration to reactants or products. This prediction has now been confirmed for hydride transfer reactions between heterocyclic, nitrogen-containing cations, which can be regarded as analogues of the enzyme cofactor, nicotinamide adenine dinucleotide (NAD+). A series of reactions with substituents in the donor gives Bronsted α of 0.67 ± 0.03 and a tightness parameter, τ of 0.64 ± 0.06. With substituents in the acceptor α = 0.32 ± 0.03 and τ = 0.68 ± 0.08. The reactions are all spontaneous, with equilibrium constants between 0.4 and 3 x 104, and the two sets span about the same range of equilibrium constants. The two τ values are essentially identical with an average value of 0.66 ± 0.05. These results can be semiquantitatively mimicked by rate constants calculated for a linear, triatomic model of the reaction. Variational transition state theory and a physically motivated but empirically calibrated potential function were used. The computed rate constants generate an α value of 0.56 if the hydride affinity of the acceptor is varied and an α of 0.44 if the hydride affinity of the donor is varied. The calculated kinetic isotope effects are similar to the measured values. A previous error in the Born charging term of the potential function has been corrected. Marcus theory can be successfully fitted to both the experimental and computed rate constants, and appears to be the most compact way to express and compare them. The success of the linear triatomic model in qualitatively reproducing these results encourages the continued use of this easily conceptualized model to think about group, ion, and atom transfer reactions.
Steric and kinetic isotope effects in the deprotonation of cation radicals of NADH synthetic analogues
Anne, Agnès,Fraoua, Sylvie,Hapiot, Philippe,Moiroux, Jacques,Savéant, Jean-Michel
, p. 7412 - 7421 (2007/10/02)
The deprotonation rate constants and kinetic isotope effects of the cation radicals have been determined by combined use of direct electrochemical techniques at micro- and ultramicroelectrodes, redox catalysis, and laser flash photolysis, over a extended
