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

Abstract

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 ³¹P-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 (Mg²⁺) 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. ³¹P NMR study showed in the presence of Spm ³¹P 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 Mg²⁺ in neutral pH indicated the importance of polyamine as a stabilizer of phosphate compounds.