Speciation of phytate ion in aqueous solution.: Non covalent interactions with biogenic polyamines

The noncovalent interactions of phytate (Phy(6-)) with biogenic amines were studied potentiometrically in aqueous solution, at t = 25degreesC. Several species are formed in the different H(+)-Phy(6-)-amine (A) systems, which have the general formula A(p)(Phy)H(q)((12-q)-), with pless than or equal to3 and 6less than or equal toqless than or equal to10. The stability of these species is strictly dependent on the charges involved in the formation equilibria. For the equilibrium pH(i)A(i+) + H(j)(Phy)((12-j)-) = A(p)(Phy)H(q)((12-q)-), (q = pi + j) we found the relationship logK = azeta(zeta is the charge product of reactants), where a = 0.35(0.03, valid for all the amines; this roughly indicates an average free energy contribution per bond -DeltaG(0) = 4.0 +/- 0.2 kJ mol(-1). A slightly more sophisticated equation is also proposed for predicting the stability of these species. Owing to the quite high (partially protonated) phytate charge, the stability of Ap([)(Phy)H(q)((12-q)-) species is quite high, making phytate a strong amine sequestering agent in a wide pH range.