Solution ³¹P NMR Investigation of Inositol Hexakisphosphate Surface Complexes at the Amorphous Aluminum Oxyhydroxide–Water Interface

Abstract

Phytate (myo-inositol hexakisphosphate, myo-IHP) is one of the most common organic phosphorus (P) species in soils and sediments which can be mineralized to increase the concentration of dissolved phosphate in pore water. Because of its six phosphate functional groups, functional group-specific adsorption mechanisms in reactive soil minerals become important in predicting solubility. In this study, solution 31 P NMR was used to elucidate the functional groupspecific adsorption mechanisms of myo-IHP at the amorphous Al hydroxide (AAH)−water interface at pH 6.5 in conjunction with batch adsorption experiments and Zetasizer measurements. The adsorption maximum of myo-IHP with AAH was ∼312.50 mmol kg −1 , and the charge reversal effects in IHP-reacted AAH particles suggested the presence of inner-sphere surface species. The upfield shifts of various phosphate groups in the NMR spectra further supported the formation of inner-sphere IHP complexes at the AAH−water interface. When the initial myo-IHP/AAH (mol kg −1 ) was decreased from 2.5 to 1.25−1.67, P1,3 and P4,6 functional groups were coordinated in addition to P2; P5 became reactive with the ratio being decreased to <0.84, P5. This multifunctional group coordination increased aggregate size. The study showed that the availability of surface sites of adsorbents influenced the functional group-specific myo-IHP adsorption.

Direct Nanoscale Imaging Reveals the Mechanism by Which Organic Acids Dissolve Vivianite through Proton and Ligand Effects

“…The peaks assigned to vibrations of −COO – of the vivianite-OA complex underwent a blue shift to 1426 and 1616 cm –1 (Figure A), indicating the formation of inner-sphere surface complexes on the vivianite surface through chemisorption. This blue shift of Raman characteristic peaks caused by inner coordination has been well reported. ,, In this study, the blue shift of −COO – peaks in CA before and after adsorption indicated the formation of surface complexes through chemisorption (Figure B). It was noteworthy that the peaks at 1407 and 1597 cm –1 , assigned to the symmetric and asymmetric vibrations of −COOH at pH 4.0 and 6.0, respectively, disappeared when the pH increased to 8.0 because of CA deprotonation.…”

“…This blue shift of Raman characteristic peaks caused by inner coordination has been well reported. 6,64,65 In this study, the blue shift of −COO − peaks in CA before and after adsorption indicated the formation of surface complexes through chemisorption (Figure 6B). It was noteworthy that the peaks at 1407 and 1597 cm −1 , assigned to the symmetric and asymmetric vibrations of −COOH at pH 4.0 and 6.0, 66 The blue shift of the −COO − peak in Raman spectra was due to the formation of an inner-sphere surface complex through chemisorption, indicating that −COO − significantly altered the interfacial hydration environment on a vivianite surface, thus reducing the energy barrier required for pit dissolution, thereby accelerating the release of iron and phosphorus.…”

Enhancing Phytate Availability in Soils and Phytate-P Acquisition by Plants: A Review

“…11,58 Besides, phytate stability varies with metal oxides, especially amorphous Fe and Al. 78 For example, phytate is sorbed onto goethite via four of the 6-phosphate groups, with the remaining two being free. 68 This explains the 3:2 sorption ratio between phytate and P in soils.…”

Spectroscopic Investigation of Phosphorus Mineralization as Affected by the Calcite–Water Interfacial Chemistry

“…Proteins like phytase bear multiple functional groups and are known to interact with mineral surfaces via, for example, electrostatic interaction, hydrophobic interaction, van der Waals force, and conformational entropy. ,, Therefore, a similar kinetics experiment was conducted between phytase-reacted calcite and phytic acid (i.e., calcite-phytase and InsP6 (aq) , Figure B–D), and the results showed impaired P mineralization. With multiple phosphate groups and thus strong chelating ability, phytic acid also actively interacts with clay minerals like calcite. − Therefore, another kinetics experiment between phytic acid-reacted calcite and phytase was conducted (i.e., calcite-InsP6 and phytase­(aq) , Figure B–D), and inhibited phytase activity was observed. Although P mineralization was suppressed for all three addition sequences, released [phosphate] generally followed the order calcite-phytase and InsP6 (aq) > calcite-phytase-InsP6 > calcite-InsP6 and phytase (aq) , indicating that calcite–phytase interaction did not affect the catalytic ability of phytase as much as the calcite–phytic acid interaction.…”