Kinetic and Equilibrium Constants of Phytic Acid and Ferric and Ferrous Phytate Derived from Nuclear Magnetic Resonance Spectroscopy

Abstract

Inositol phosphates are metabolically derived organic phosphates (P) that increasingly appear to be an important sink and source of P in the environment. Salts of myo-inositol hexakisdihydrogen phosphate (IHP) or more commonly phytate are the most common inositol phosphates in the environment. IHP resists acidic dephosphorylation and enzymatic dephosphorylation as ferric or ferrous IHP. Mobility of IHP iron complexes is potentially pH and redox responsive, making the time scale and environmental fate and transport of the P associated with the IHP of interest to the mass balance of phosphorus. Ferric and ferrous complexes of IHP were investigated by proton nuclear magnetic resonance spectroscopy ( (1)H NMR) and enzymatic dephosphorylation. Ferrous IHP was found to form quickly and persist for a longer period then ferric IHP. Dissociation constants derived from (1)H NMR experiments of chemically exchanging systems at equilibrium were 1.11 and 1.19 and formation constants were 0.90 and 0.84 for ferric and ferrous IHP, respectively. The recovery of P from enzymatic dephosphorylation of ferric and ferrous IHP was consistent with the magnitude of the kinetic and equilibrium rate constants.

Soil Phosphorus Forms in Hydrologically Isolated Wetlands and Surrounding Pasture Uplands

“…In addition, the marked lack of the distinctive peak signature associated with the various isomers of inositol hexakisphosphate, even in upland pasture samples, was in contrast to other studies of upland grasslands (Tate and Newman, 1982; Turner et al, 2003b; McDowell and Stewart, 2006; Murphy et al, 2009). The abiotic sorption and stabilization of inositol phosphates in such environments is attributed to their interaction with clay minerals and amorphous Fe and Al oxides (Celi and Barberis, 2007; Heighton et al, 2008). In addition to data presented, which report the low Fe and Al concentrations throughout the system (Table 2), existing soil surveys (Lewis et al, 2003) and detailed particle‐size distribution analysis (Bhadha and Jawitz, 2010) show only minimal clay content (<2.5%) in the uplands.…”

Voltammetric Investigation of Iron(III) Interactions with Phytate

“…Fe(II) phytates were investigated by many authors [9,20,21,24,47]. Torres et al [24] reported that the highest protonation degree of iron(III) phytate species formed in acidic media is i = 5 and log of the stability constant …”

“…Among a number of artificially produced as well as in the nature occurring ligands with high affinity to iron ions, inositol hexaphosphate (IP6) possess a specific role. Phytic acid, myo-inositol 1,2,3,4,5,6 hexakis (dihydrogen phosphate) and its salts (phytates) are synthetized in terrestrial ecosystems by plants, and form the dominant class of organic phosphorus [8,9].…”

“…Coordination of Fe(III) with phytate does not influence only mineral bioavailability but also exhibits antioxidant properties [7]. Many studies were reported on iron(III) complexation by phytate studied mainly by 31 P NMR, and potentiometric or spectrophotometric techniques [9,20,[23][24][25]. Characterization of either chelates in solution or solid Fe(III)-IP6 precipitate is a complex task that was not fully explained.…”

Probing the pH Dependent Optical Properties of Aquatic, Terrestrial and Microbial Humic Substances by Sodium Borohydride Reduction

“…It has been suggested that soil humic material is capable of forming micelles that can provide protection to labile moieties (Sutton & Sposito, 2005). Formation of micelles is unlikely due to the Beer Lambert behavior seen in all HS in this study (Table 2) but other forms of protection such as encapsulation or association with cations or clays is known to provide protection from enzymatic attack (Heighton et al, 2008;Hedges et al 2000;Baldock & Skjemstad, 2000). The soil humic acids EHA and LHA have a higher percentage of black carbon or conjugated cyclic carbon (Skjemstad et al, 2002).…”