One-electron reactions in biochemical systems as studied by pulse radiolysis. I. Nicotinamide-adenine dinucleotide and related compounds.

The oxidation of a reduced pyridine nucleotide analog by flavins

I. INTRODUCTION The senior author and his collaborators have long been concerned with the use of analytical chemical techniques – more specifically, experimental approaches and methodologies primarily based on polarography – to study problems of general chemical interest. Currently, electroanalytical approaches are being used in a systematic investigation of chemical phenomena involving biologically significant compounds, where such approaches seem to offer distinct advantages. Attention has been focused on the behavior of nucleic acid components, pyridine coenzymes, and relevant model compounds in solution as well as the electron-transfer interface. Behavior at the interface involves (a) adsorption of original, intermediate, and product species, (b) association in the adsorbed state, (c) mechanisms and kinetics of electron-transfer (redox) processes, and (d) chemical reactions (kinetics and mechanisms) involving reactant, intermediate (free radical, carbanion), and product species preceding, accompanying...

Nicotinamide-Nad Sequence: Redox Processes and Related Behavior: Behavior and Properties of Intermediate and Final Products

On the mechanism of pyridine nucleotide reduction by dithionite.

Über den Mechanismus der Wasserstoffübertragung mit Pyridinnucleotiden, XI Die nichtenzymatische Reduktion von Chinonen mit DPNH‐Modellen

The reversible reduction of nicotinamide methiodide and methochloride has been studied using cathodic reduction at a mercury surface, sodium dithionite, hydrogen and colloidal platinum, and various leuco-dyes. The method of cathodic reduction was the most satisfactory. Polarography showed a 2-step reduction. Macro-reductions at a mercury surface suggested dimerization of the intermediate free radical. The behaviour of dihydromethylnicotinamide towards hydrogen ions, oxygen, iodine, potassium ferricyanide, ferric iron, and various dyes has been examined. Although it is not readily oxidized by oxygen it is capable of reducing most other systems with a higher Eo?:. Two methods of estimating the reduced compound are suggested and involve (a) the potentiometric titration of potassium ferricyanide at pH 9.1 and (b) the reduction and decolourization of 2.6-dichlorophenolindophenol at pH 4.7. The oxidation-reduction potential of nicotinamide methiodide has been measured by oxidative titration of the dihydro-compound at pH 9.1 and 30±0.01 °C and found to be -0.36 ± 0.02 V against the normal hydrogen electrode. The titration curve does riot show a separation of the two reduction steps. Evidence is discussed for the production of both o- and p-dihydromethylnicotinamide during reduction.

The redox properties of Nicotinamide Methohalides

The rates of oxidation of N-methylacridan by 2,6-dichlorophenolindophenol have been measured between pH 2.74 and 6.91 at 20 to 22 °C in the presence of 8 to 22 per cent. ethanol. The reaction was of the second order and was found to proceed by ' two simultaneous mechanisms, both involving the conjugate acid of N-methylacridan. The oxidation of this cation by the indophenol anion proceeded at a rate which was 19 times greater than the oxidation by the uncharged indophenol molecule. It is shown that oxidation probably occurs by hydrogen atom transfer rather than electron transfer. A similar mechanism for the oxidation of dihydro-coenzyme I would account for its slow reactivity towards molecular oxygen and the biological necessity for mediating systems involving both hydrogen atoms and electrons.

JH Baxendale

Papers

The redox properties of Nicotinamide Methohalides

The kinetics of Oxidation of N-Methylacridan: A Model for Coenzyme 1

Mechanism of hydrogen transfer in model dehydrogenase systems.