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

The noncovalent interactions of phytate (Phy12−) with biogenic amines were studied potentiometrically in aqueous solution, at t=25°C. Several species are formed in the different H+-Phy12−-amine (A) systems, which have the general formula Ap(Phy)Hq(12-q)−, with p≤3 and 6≤q≤10. The stability of these species is strictly dependent on the charges involved in the formation equilibria. For the equilibrium pHiAi++Hj(Phy)(12-j)−=Ap(Phy)Hq(12-q)−, (q=pi+j) we found the relationship logK=aζ (ζ 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 −ΔG0=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)Hq(12-q)− species is quite high, making phytate a strong amine sequestering agent in a wide pH range