The equilibria and kinetics of Ni(II) interactions with the two pyridine coenzymes NAD and NADP were investigated by the temperature-jump relaxation technique. Three relaxation times for each system were detected, of which the two slower were characterized in detail as a function of metal ion and ligand concentrations and pH. The two slow times, τ2 and τ3, were in the 10−3 and 10−1 s time regions, respectively. Both times for NAD were only slightly concentration and pH dependent; those for NADP were strongly pH dependent. These results were found to be consistent with a mechanism involving sequential formation of several different 1:1 metal ion complexes, including those in which the various ring systems participated with phosphate bonding. For NADP, a parallel series of steps involving the phosphate-protonated coenzyme was also present. Rate constants were compared to those for corresponding steps in simpler nucleotide and phosphate systems. A major conclusion from this study was that the kinetic behavior of the simpler systems was retained even in the largest metal ion complexes. We call this behavior “kinetic integrity”.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Inorganic Chemistry