Complexation of nicotinamide adenine dinucleotide with ferric and ferrous ions.

Motivated by the observed influence of stainless steel and ferric and ferrous ions on the behavior of the peroxidase/oxidase oscillator, the mechanism and kinetics of interaction of 1,4-dihydronicotinamide adenine dinucleotide (NADH) with iron ions in 0.1 M acetic acid/sodium acetate buffer with pH 5.1 and with the solution/stainless steel interface were extensively studied. The character of a possible mutual influence of NADH/acetate buffer solution and Type 316 stainless steel has been investigated. We also suggest the mechanism of stainless steel corrosion inhibition by NADH. It was determined that fast complexation of ferric and ferrous ions with NADH occurred with rate constant kcompl = 4.0 x 10(9) +/- 0.2 x 10(9) M-1 s-1. The composition of the product complex is [Fe-(NADH)2] for both Fe2+ and Fe3+. A previously unreported complex of ferrous ion and NADH was discovered, determined, and separately investigated. Kinetic and equilibrium constants for reactions of iron ions-NADH complexation and following redox processes of the complex decomposition were determined from spectrophotometric and electrochemical experiments.