Equilibrium Studies of Phytate Ions. 1. Equilibria Between Phytate Ions and Protons in 3 M (Na)ClO4 Medium.

Potentiometric Determination of Phytic Acid and Investigations of Phytate Interactions with Some Metal Ions

“…In the region before first EP 1 a group of strong acidic protons exists with an average dissociation constants pK a around 2.6 ± 0.1, the second group appears between EP 1 and EP 2 with an average pK a of 7.2 ± 0.2, and a third group of protons can be predicted at an average pK a of 11.5 ± 0.5. Interestingly, these values are very close to that of ortophosphoric acid, 14,20 but the titration curve of H 3 PO 4 shown in Fig. 3 (curve b), reveals due to a low number of protons a much sharper pH transition in the range around both equivalence points, and its content can be determined very accurately by an alkalimetric titration.…”

“…The solution of this complex task was found in the interaction between phytate and metallic ions and formation of a relatively strong complexes of the alkaline cations with phytates. 14,[24][25][26] As mentioned above sodium ions significantly increase acidity of phytate due to complexation (Fig. 2, curve a), but at this low concentration of titrant (low ionic strength, I), complete deprotonation to its final 12 th step does not occur.…”

“…This effect is known well and is due to the complexation of Na + ions with phytate as phytic acid obtains an enhanced acidic character in the presence of alkali ions due to exchange of protons with Na + ions. 14,[24][25][26] However, in both cases only two EPs (EP 1 at pH 5.3 and EP 2 at pH 8.5-9.5) can be determined unambiguously. Further from the course of the titration curves is evident that phytic acid contains three categories of protons.…”

“…32 To stimulate deprotonation of phytic acid therefore the exchange with sodium or other alkaline ions should be exploited. 14,24 In Fig. 4A alkalimetric titration of phytic acid in the presence of 1 M NaCl is shown.…”

“…1 Inositol phosphates (IP x , 1 ≤ x ≤ 6) are naturally occurring compounds synthetized by plants and widely found in natural environment. Many papers deal with antioxidative [2][3][4] and anticorrosion [5][6][7] properties of phytates and their role in the environment, 8 biological functions, 9 human nutrition, [10][11] and interactions with protons [12][13][14] and metallic ions 1,[15][16][17] in aqueous solutions. The magnitude of the interaction between metal ions and chelating agents is defined by the corresponding equilibrium constants, and nowadays most of them are determined experimentally by spectrophotometry, potentiometry and other techniques (NMR) in combination with computational analysis of data.…”