title: Speciation of phytate ion in aqueous solution. Protonation constants and copper(II) interactions in NaNO3aq at different ionic strengths.
abstract: The acid base behavior of phytate has been studied (at t=25 degrees C by potentiometry, ISE-H+ glass electrode) in NaNO3aq at different ionic strengths (0.1 < or = I/mol L(-1) < or = 1.0). The interactions with copper(II) were investigated in the same experimental conditions in different metal to ligand (Phy) ratios (1:1 < or = Cu2+ :Phy < or = 4:1), by using both ISE-H+ and ISE-Cu2+ electrodes. Phytate acid base behavior in sodium nitrate is very similar to that in sodium chloride, previously investigated. In the experimental conditions adopted, the formation of three CuiHjPhy(12-2i-j)- species is observed: the mononuclear CuH4Phy6- and CuH5Phy5-, and the dinuclear Cu2H5Phy3-. Analysis of complex formation constants at different ionic strengths reveals that both ISE-H+ and ISE-Cu2+ electrodes gave, within the experimental error, analogous values. Dependence of complex formation constants on ionic strength was modeled by EDH (Extended Debye-Hückel) and SIT (Specific ion Interaction Theory) equations. The sequestering ability of phytate toward copper(II) has been evaluated by the calculation of pL50 (the total ligand concentration, as -log CL, able to bind 50% of metal cation), an empirical parameter already proposed for an objective "quantification" of this ability. A thorough analysis of literature data on phytate-copper(II) complexes has been performed.
authors.affiliation: Dipartimento di Chimica Inorganica, Chimica Analitica e Chimica Fisica, Università di Messina, Salita Sperone, 31, I-98166 Messina Vill. S. Agata, Italy.
authors.forename: Pasquale
authors.initials: P
authors.lastname: Crea
authors.forename: Concetta
authors.initials: C
authors.lastname: De Stefano
authors.forename: Demetrio
authors.initials: D
authors.lastname: Milea
authors.forename: Nunziatina
authors.initials: N
authors.lastname: Porcino
authors.forename: Silvio
authors.initials: S
authors.lastname: Sammartano
mesh_terms: D003300:Copper / Q000737:chemistry*; D007477:Ions / Q000737:chemistry; D009566:Nitrates / Q000737:chemistry*; D009994:Osmolar Concentration; D010833:Phytic Acid / Q000737:chemistry*; D011522:Protons; D012996:Solutions / Q000737:chemistry
chemical_list: D007477:Ions; D009566:Nitrates; D011522:Protons; D012996:Solutions; D003300:Copper; D010833:Phytic Acid; C031618:sodium nitrate