title: Sequestering ability of phytate toward biologically and environmentally relevant trivalent metal cations.
abstract: Quantitative parameters for the interactions between phytate (Phy) and Al(3+), Fe(3+), and Cr(3+) were determined potentiometrically in NaNO(3) aqueous solutions at I = 0.10 mol L(-1) and T = 298.15 K. Different complex species were found in a wide pH range. The various species are partially protonated, depending on the pH in which they are formed, and are indicated with the general formula MH(q)Phy (with 0 ≤ q ≤ 6). In all cases, the stability of the FeH(q)Phy species is several log K units higher than that of the analogous AlH(q)Phy and CrH(q)Phy species. For example, for the MH(2)Phy species, the stability trend is log K(2) = 15.81, 20.61, and 16.70 for Al(3+), Fe(3+), and Cr(3+), respectively. The sequestering ability of phytate toward the considered metal cations was evaluated by calculating the pL(0.5) values (i.e., the total ligand concentration necessary to bind 50% of the cation present in trace in solution) at different pH values. In general, phytate results in a quite good sequestering agent toward all three cations in the whole investigated pH range, but the order of pL(0.5) depends on it. For example, at pH 5.0 it is pL(0.5) = 5.33, 5.44, and 5.75 for Fe(3+), Cr(3+), and Al(3+), respectively (Fe(3+) < Cr(3+) < Al(3+)); at pH 7.4 it is pL(0.5) = 9.94, 9.23, and 8.71 (Al(3+) < Cr(3+) < Fe(3+)), whereas at pH 9.0 it is pL(0.5) = 10.42, 10.87, and 8.34 (Al(3+) < Fe(3+) < Cr(3+)). All of the pL(0.5) values, and therefore the sequestering ability, regularly increase with increasing pH, and the dependence of pL(0.5) on pH was modeled using some empirical equations.
authors: Dipartimento di Chimica Inorganica, Chimica Analitica e Chimica Fisica, Università di Messina, Viale Ferdinando Stagno d'Alcontres 31, I-98166 Messina (Vill. S. Agata), Italy.
authors: Clemente
authors: C
authors: Bretti
authors: Rosalia Maria
authors: RM
authors: Cigala
authors: Gabriele
authors: G
authors: Lando
authors: Demetrio
authors: D
authors: Milea
authors: Silvio
authors: S
authors: Sammartano
mesh_terms: D000535:Aluminum / Q000737:chemistry; D002412:Cations / Q000737:chemistry*; D002857:Chromium / Q000737:chemistry; D036262:Empirical Research; D006863:Hydrogen-Ion Concentration; D007501:Iron / Q000737:chemistry; D008024:Ligands; D008670:Metals / Q000378:metabolism*; D010833:Phytic Acid / Q000378:metabolism*; D011199:Potentiometry / Q000295:instrumentation / Q000379:methods
chemical_list: D002412:Cations; D008024:Ligands; D008670:Metals; D002857:Chromium; D010833:Phytic Acid; D000535:Aluminum; D007501:Iron