Interaction of Phytatewith Ag+, CH3Hg+, Mn2+, Fe2+, Co2+, and VO2+: StabilityConstants and Sequestering Ability.

The stability of M/Phy species (M = Ag+, CH3Hg+, Mn2+, Fe2+, Co2+, VO2+, and Phy = Phytate) was determined in NaNO3, at I= 0.10 mol·dm–3and T= 298.15 K, potentiometrically. For the VO2+/Phy system, the measurements were performed at differentionic strengths (to 0.45 mol·dm–3) and ionicmedia (NaNO3and Na2SO4). In general,the formation of six MHqPhy (with 0 ≤ q≤ 5) species was observed. For the CH3Hg+/Phy system, the formation of three polynuclear species,M2HqPhy (with 2 ≤ q≤ 4), was also evidenced. The general stabilitytrend is: VO2+∼ CH3Hg+>Co2+> Mn2+∼ Fe2+>Ag+. The sequestering ability of phytate toward the consideredmetal cations was evaluated at different pH values and increased withincreasing pH, except for methylmercury and vanadyl. Literature valueswere critically compared, where possible, with data reported in thiswork. The dependence of the formation constants of the MHqPhy species on the number of protons and on the firstmetal hydrolysis constants was modeled. Furthermore, a relationshipbetween the stability of the mononuclear MHqPhy and the polynuclear MpHqPhy species was found. These three relationshipswere then combined, for testing and predictive purposes. The lastcontribution of this research group to the series entitled “Speciationof phytate ion in aqueous solution” is reported in ref 1. [ABSTRACT FROM AUTHOR]