Complex Formation of Phytic Acid With Selected Monovalent and Divalent Metals

Abstract

The formation of metal complexes with phytic acid is a complex process that depends strongly on the metal-to-ligand molar ratio, pH value and consequent protonation level of the phytate ligand as well as accompanying side reactions, in particular metal hydrolysis and precipitation of the formed coordination compounds. In the present work, the potentiometric titration technique was used in combination with a detailed analysis of the equivalent point dependencies for selected biologically relevant monovalent and divalent cations from the groups of alkaline earths and transition metals, namely: Mg(II), Zn(II), Fe(II), Cu(I), and Cu(II) ions. The investigation of complex formation mechanism, the evaluation of the species formed, and the identification of other side reactions was based on the examination of three distinct equivalent points, which were detectable by alkalimetric titrations of phytic acid in the presence of selected metal ions. It has been demonstrated that alkaline earth metals interact with different binding site(s) than the transition metals, and experiments with both oxidation states of copper revealed similar complexing characteristics, which depend mainly on the ionic radius (and not on the ionic charge as initially expected). Quantitative data on phytate complexation, hydroxide formation and complex precipitation are presented herein for all metals studied, including Cu(I), which was investigated for the first time by means of alkalimetric titration.

Long-Term Biosolids Application on Land: Beneficial Recycling of Nutrients or Eutrophication of Agroecosystems?

“…One likely mechanism of P toxicity in crops triggered by luxury uptake of phosphate is the accumulation of high levels of phytate [63], the prevalent storage form of P in plants. Phytate complexes Fe, Zn, Cu, and Mn strongly, reducing the bioavailability of these trace metals [64,65]. It is reasonable to suggest that complexation of these metal cations by phytate accumulated in roots could reduce their translocation to shoots and cause micronutrient deficiencies.…”

Analytical Methods for Determination of Phytic Acid and Other Inositol Phosphates: A Review

“…However, due to the problematic determination of the initial phytate protonation level which can lead to higher experimental errors, the differential (two-point) alkalimetric determination, introduced by Marolt and Pihlar [ 50 ] (2015), proved as a reliable standardization procedure of phytic acid ( Figure 2 ). The method was later applied in the study of the phytate complexation with monovalent and divalent metals by Marolt et al [ 14 ] (2020) and for the investigation of the removal of dissolved organic phosphorous (in the form of phytate) from wastewaters by Petzoldt et al [ 51 ] (2020).…”

“…Numerous publications regarding their antinutritional effects can be found in the literature due to their strong binding interactions with essential minerals, such as Ca 2+ , Mg 2+ , Zn 2+ , Fe 2+ , Fe 3+ , Cu 2+ , and Mn 2+ [ 12 ], proteins, carbohydrates and lipids [ 13 ]. This is mostly due to the electrostatic interactions which arise from the (partial) deprotonation of phytic acid in the wide range of pH and consequent negative charge of phytate anion in the range from −1 to −12 [ 14 ]. Formation of (un)soluble coordination compounds decreases the bioavailability of minerals in food and hinders their absorption [ 15 ].…”

“…On the other hand, strong interactions with heavy metals [ 1 ], particularly with iron and copper ions [ 14 ], exhibit also an antioxidant [ 25 ] and anticancer effects [ 26 ] of phytates alone or in combination with other inositol phosphates as reviewed by Vučenik and Shamsuddin [ 27 ] (2006). A specific coordination site between phosphate groups 1, 2, and 3 (see Figure 1 ) causes a significant negative shift of reversible redox potential of the redox couple Fe 2+ /Fe 3+ [ 28 ] and even more importantly the removal of all available (six) coordination sites of iron, and therefore completely inhibiting its ability to catalyze Fenton reaction and hydroxyl radical ( • OH) formation [ 29 ].…”

Current Perspectives on the Physiological Activities of Fermented Soybean-Derived Cheonggukjang

“…Phytic acid is known as a harmful substance that suppresses the absorption of cations in the intestine by chelation, especially divalent cations in the following order of decreasing affinity: copper, zinc, cobalt, manganese, iron, and calcium [ 98 , 99 ]. However, the chelating activity of phytic acid also contributes to its anticancer effects and other physiological activities that prevent free radical-mediated diseases, such as inflammation [ 98 , 100 , 101 , 102 , 103 ]. Isoflavone, which contributes to the astringency of soybeans, has already been verified to have anticancer effects in several epidemiological, animal, and in vitro studies.…”