Equilibrium study on the interaction of phytic acid with polyamines and metal ions

Interaction of phytic acid (myo-inositolhexakisphosphoric acid, IP) and polyamines (A = en, tn, Put, dien, 2,3-tri, 3,3-tri, Spd, 3,3,3-tet, spermine(Spm)) have been studied by potentiometric and (31)P-NMR techniques. The non-covalent interactions have led to the formation of stable molecular complexes of (IP)H(n)(A) type at the 1:1 molar ratio of the ligands, but of different numbers of protons. The IP protonation constants, stability constants of the molecular complexes and metal (Mg(2+)) complexes have been determined. The structural and pH dependences of stability constants showed the interactions between IP and A have the acid-base character determining their effectiveness, although the IP structure (5ax1eq, 5eq1ax) in molecular complexes should be also taken into account. (31)P NMR study showed in the presence of Spm (31)P highfield shifts and high pH shift of signal broadening due to chemical exchange between 5ax1eq and 5eq1ax. The preferable binding of Spm to IP over Mg(2+) in neutral pH indicated the importance of polyamine as a stabilizer of phosphate compounds.