Ternary complexes in solution. Influence of 2,2′-bipyridyl on the stability of 1:1 complexes of Co2+, Ni2+, Cu2+, and Zn2+ with hydrogen phosphate, adenosine 5′-monophosphate, and adenosine 5′-triphosphate☆

Abstract

Ternary complexes of bivalent metal ions with 2,2′-bipyridyl and hydrogen phosphate, adenosine 5′-monophosphate, and adenosine 5′-triphosphate have been investigated by potentiometric titration and nuclear magnetic resonance spectrometry. Coordination of the phosphate compounds with 1:1 complexes of bipyridyl and Co 2+ or Zn 2+ occurs as readily as with the free metal ions; a stability increase is found with Cu 2+ . The ternary complex of Ni 2+ -bipyridyl-adenosine 5′-triphosphate is slightly less stable than the binary complex of Ni 2+ -adenosine 5′-triphosphate. From NMR spectra it is suggested that neither in the complex of Cu 2+ -bipyridyl- adenosine 5′-monophosphate nor in the Cu 2+ -bipyridyl-adenosine 5′-triphosphate any further interaction of metal ion with the adenyl moiety happens. Overall the results have considerable significance in terms of metal-activated enzymes and substrates wherein the usual formation of ternary complexes leads initially to greater stability and where the reactants are both brought together and activated at the same time. Some examples for biologically important ternary complexes are mentioned.