Interactions of Inosine 5′-Monophosphate with Ca2+ and Mg2+: A Thermodynamic and Spectroscopic Study in Aqueous Solution

A thermodynamic and spectroscopic study is reported on the interactions between inosine 5′-monophosphate (IMP), a ribonucleotide of hypoxanthine, and Ca2+ and Mg2+, metal cations naturally occurring in biological fluids. Thermodynamic parameters concerning protonation and complex formation equilibria were determined. For both systems, the speciation model involved the formation of the MLH+ and ML0 species (M = Ca2+ or Mg2+), whose stability constants were determined in NaCl at different ionic strengths (I = 0.1−1 mol·kg−1) and temperatures (T = 288.15−318.15 K). In order to gain more information about the reliability of the speciation model obtained from potentiometric investigations and to get deeper insight on the interactions between ligand and metals, 1H NMR spectroscopy was employed. Finally, the binding ability of IMP toward Ca2+ and Mg2+ was evaluated in terms of pL0.5 (the ligand total concentration required to “sequester” the 50% of the metal cation). Examples of calculation in the conditions of some biological fluids are reported.