A thermodynamic and temperature-jump kinetic study has been carried out for the interactions of Ni(II) with the coenzymes flavin adenine mononucleotide (FMN) and flavin adenine dinucleotide (FAD) at 15 °C and I = 0.1 M. For the former, two relaxation times (~ 10-3 and 10-4 s) were characterized as a function of concentration and pH. These were attributed to the formation of nickel phosphate and nickel phosphate-adenine (back-bound) complexes, respectively. For the NiFAD system, four distinct relaxation times were observed, which ranged from about 100 μs to 35 ms. These were interpreted on the basis of a multistep complexation mechanism involving the initial interaction of Ni(II) with the phosphate moiety, followed by a sequence of back-bound complexes involving interactions with the adenine and isoalloxazine ring systems. The nickel phosphate interactions were kinetically consistent with solvent exchange rates from the primary coordination sphere of Ni(II). To the best of our knowledge, the NiFAD system is the only one for which four relaxation times have been observed and characterized.
ASJC Scopus subject areas
- Colloid and Surface Chemistry