EDTA Complex Research Articles

Investigations on the Interaction of EDTA with Calcium Silicate Hydrate and Its Impact on the U(VI) Sorption

The interaction of EDTA with calcium silicate hydrate (C-S-H) and its impact on the sorption of U(VI) by C-S-H in the presence of EDTA at varying concentrations has been investigated under N2 and ambient atmosphere. The solid phase characterization was performed by FTIR, XRD and TGA measurements and the uranium concentration in solution has been determined by alpha-spectroscopy. At increased EDTA concentrations ([EDTA] > 0.1 M) calcium is complexed and extensively extracted from the solid resulting in a quantitative dissolution of the Ca(OH)2 phase and deterioration of C-S-H. At lower EDTA concentrations ([EDTA] ≤ 0.01 M), EDTA is sorbed into the solid phase and the associated adsorption capacity (qmax = 0.67 mol/kg) has been evaluated by fitting the corresponding data with the Langmuir isotherm model. The incorporation of EDTA in the C-S-H matrix was corroborated by FTIR, XRD and TGA measurements. Regarding the effect of EDTA on the U(VI) sorption by C-S-H, evaluation of the experimental data reveal a significant decrease of the Kd values in the presence of EDTA most probably due to the stabilization of U(VI) in the form of U(VI)-EDTA complexes in solution. Under ambient conditions a further decrease of the Kd values is observed because of the formation of U(VI)-carbonato complexes related to CO2 dissolution and hydrolysis.

Oscillatory chemical reaction as a sensor of Cu(II)–EDTA complex formation and ligand degradation in copper ion‐catalyzed oxidation of thiocyanate ions with hydrogen peroxide

AbstractThe complex dynamics of the homogeneous H2O2–NaSCN–CuSO4–NaOH oscillator is influenced by the addition of EDTA, which manifests itself in the modification or complete suppression of the oscillations. However, depending on EDTA concentration, this effect can be reversible or not. Potentiometric and spectroscopic studies of these phenomena, together with recent discoveries about possible chemical interactions and compound formation in the Cu(II)–H2O2–EDTA system, resulted in the development of a new kinetic mechanism of the complex interaction of EDTA with this oscillatory system. The model involves 13 intermediates and is an extension of our former, 10‐variable mechanism of the H2O2–NaSCN–CuSO4–NaOH oscillator. Reliability of the proposed reaction scheme has been confirmed by numerical calculations, enabling also the estimation of appropriate reaction rate constants. The work is an example of the application of the chemical oscillatory reaction to study qualitatively and quantitatively the interactions of foreign species with the components of positive and negative feedback loops of a chemical dynamical system.

Novel access to ionic liquids based on trivalent metal–EDTA complexes and their thermal and electrochemical characterization

Two series of ionic liquids (ILs) consisting in metal-EDTA complex anions ([MEDTA], with V, Cr, Mn, Fe and Co as metal center) and 1-butyl-3-methylimidazolium ([BMIM]) or trioctylmethylphosphonium ([TOMP]) cations have been prepared via a new synthetic approach based on the related acidic EDTA complexes (HMEDTA). A strong influence of both the coordinated metal and the cation type on the thermal behavior of the obtained ILs was assessed through DSC and TGA, while the solubility features were found to be primarily affected by the cation nature. The observed solubility results for [TOMP] series ILs in organic solvents showed the preparation of ILs as an effective way to solubilize metal-EDTA complexes into non-aqueous solutions, opening new investigation potential and applicative perspectives. The electrochemical properties of the synthesized ILs have been studied both in aqueous and non-aqueous environments, providing insights on the strong solvent effect on metal-EDTA complexes electrochemistry and, for many of the ILs, showing promising characteristics for electrochemical applications both in water and in organic solvents.

High redox potential promotes oxidation of pyrite under neutral conditions: Implications for optimizing pyrite autotrophic denitrification

Pyrite autotrophic denitrification (PAD) represents an important natural attenuation process of nitrate pollution and plays a pivotal role in linking nitrogen, sulfur, and iron cycles in a variety of anoxic environments. However, there are knowledge gaps about the oxidation mechanism of pyrite under anaerobic neutral conditions. This study explored the performance of PAD in the presence of EDTA and revealed the mechanism of anaerobic pyrite oxidation and microbial mineral transformation. It was demonstrated that ~200 mV was the electrochemical threshold for converting pyrite into bioavailable forms in PAD conditions, and accelerated pyrite oxidation by Fe3+-EDTA complexes can improve the performance of PAD effectively. Furthermore, genus related to sulfur and nitrogen cycle (Sulfurimonas, Denitrobacter) were found at higher abundances in cultures containing EDTA. The analysis of metagenomic binning showed that the microbial community in PAD culture with EDTA addition exhibited higher levels of functional diversity and redundancy. These results will further the understanding of the oxidation mechanism of pyrite under anaerobic neutral conditions and the corresponding microbial activities, and provide insights into the practical application of PAD.

Combined Effects of Fe(III)-Bearing Clay Minerals and Organic Ligands on U(VI) Bioreduction and U(IV) Speciation.

Reduction of U(VI) to U(IV) drastically reduces its solubility and has been proposed as a method for remediation of uranium contamination. However, much is still unknown about the kinetics, mechanisms, and products of U(VI) bioreduction in complex systems. In this study, U(VI) bioreduction experiments were conducted with Shewanella putrefaciens strain CN32 in the presence of clay minerals and two organic ligands: citrate and EDTA. In reactors with U and Fe(III)-clay minerals, the rate of U(VI) bioreduction was enhanced due to the presence of ligands, likely because soluble Fe3+- and Fe2+-ligand complexes served as electron shuttles. In the presence of citrate, bioreduced U(IV) formed a soluble U(IV)-citrate complex in experiments with either Fe-rich or Fe-poor clay mineral. In the presence of EDTA, U(IV) occurred as a soluble U(IV)-EDTA complex in Fe-poor montmorillonite experiments. However, U(IV) remained associated with the solid phase in Fe-rich nontronite experiments through the formation of a ternary U(IV)-EDTA-surface complex, as suggested by the EXAFS analysis. Our study indicates that organic ligands and Fe(III)-bearing clays can significantly affect the microbial reduction of U(VI) and the stability of the resulting U(IV) phase.

Electrochemistry of Ru(edta) complexes relevant to small molecule transformations: Catalytic implications and challenges

Electrochemistry of Ru(edta) complexes (edta4− = ethylenediaminetetraacetate) progressed over a period of several decades, with significant increase in understanding of the electro-catalytic processes involving the substrate coordinated to the metal center. While electrochemistry studies of many Ru(edta) complexes were published in several papers, no attempt has been made to provide a comprehensive and systematic overview of its electrochemical properties, evaluating its application to catalytic electrochemical transformation of small molecules. In this article, results of the electrochemical studies of both mononuclear and binuclear complexes of Ru(edta) are reviewed with regard to electron-transfer reaction mechanism and activity. Their potential to act as redox mediators or catalysts in electrochemical transformations of small molecules and enzymatic reactions, are highlighted. This review aims to contribute to the mechanistic understanding of Ru(edta) complexes in catalysis of such electrochemical transformations.

Antibiofilm properties of copper (II) and iron (III) complexes with an EDTA-based phenylene macrocycle and its acyclic analogue against food and clinical related pathogens

Bacterial food-borne and nosocomial infections are a public health issue around the world that is exacerbated by biofilm formation and acquired resistance to antibiotics. New therapies focusing on the prevention of biofilm formation may help to face these challenges. In this study, the antibiofilm activity of Cu2+ and Fe3+ complexes formed with an EDTA-based phenylene macrocycle and its acyclic analogue (edtaod and edtabz) was evaluated against Escherichia coli O157: H7, Listeria monocytogenes, Pseudomonas aeruginosa, Salmonella enterica sub. enterica serovar Typhimurium and Staphylococcus aureus. In general, edtabz ligand and complexes, at 0.25–1 mM, presented higher biomass reduction of biofilms than edtaod and its complexes against L. monocytogenes (edtabz and Fe-edtabz; 66.1–99.1% and 78.3–97.4%, respectively), P. aeruginosa (edtabz; 66.4–88.1%), S. aureus (Cu-edtabz; 27.4–73.9%) and Salmonella Typhimurium (Cu-edtabz; 19.4–75.5%). While biofilm formation of E. coli was inhibited by Cu-edtaod with a biomass reduction of 71.5–80.7%. Additionally, antibiofilm activity of edtaod was enhanced by Cu2+ or Fe3+ complexation. Correlation analysis showed that molecular properties such as molecular weight, volume and the number or rotatable bonds have a positive relationship with antibiofilm activity of compounds. Principal component analysis showed that biofilm inhibition patterns of Salmonella Typhimurium, L. monocytogenes and P. aeruginosa were similar and closely related with molecular volume of EDTA complexes. Overall, the results suggest that EDTA-based phenylene macrocycles and its Cu2+ and Fe3+ complexes with its antibiofilm activity can be useful to prevent biofilm related infections.

The Comparison of Optimum Conditions for Lead (Pb) Analysis Method using DITHIZONE and EDTA Complex in Seaweeds (Eucheuma spinosum)

The comparison of optimum conditions for lead (Pb) analytical method using dithizone and EDTA complexes in Eucheuma Spinosum (Eucheuma Sp.) was measured using a standard addition method, where the standard solution of Pb2+ was added to the sample to reduce noise. Additionally, UV-Vis spectrophotometer was used with dithizone and EDTA complexes in Eucheuma Spinosum, where Pb2+ ions in both complexes were measured. Both complexes were first developed to determine the optimal pH that would measure Pb2+ level in Eucheuma Spinosum. The most favorable pH level for such measurement was pH 8, at which pH activity was most stable, and the most favorable complex was dithizone complex, with a regression value closer to one than that of EDTA complex.

Exploring the kinetics of actinyl-EDTA reduction by ferrous iron using quantum-mechanical calculations.

The reduction of An(vi) (An = U, Np, and Pu) to An(iv) significantly decreases its solubility and mobility. This reaction can be hindered by complexation with inorganic (e.g., carbonate) or organic ligands. Ethylenediaminetetraacetic acid (EDTA) is one such organic ligand that forms stable complexes with actinides. Therefore, it may enhance the mobility of actinides. However, the redox kinetics and mechanisms of actinyl (An(v/vi)O2+/2+)-EDTA are not well characterized yet and are thus studied here using quantum-mechanical calculations. The principle is to approach the actinyl-EDTA and Fe2+ (reductant) in small incremental steps and calculate the system energy at each distance. The overall reaction is then delineated into sub-processes (encounter frequency in bulk solution, formation of outer-sphere complex, transition from outer- to inner-sphere complex, and electron transfer), and reaction rates are determined for each sub-process. The formation of outer-sphere complexes occurs rapidly in microseconds to seconds over a wide range of actinyl concentrations (pM to μM); in contrast, the transition to the inner-sphere complex is relatively slow (milliseconds to a few seconds). Immediate electron transfer to form the pentavalent actinide is observed along the reaction path for Np(vi) and Pu(vi), but not for U(vi). Surprisingly, in acidic conditions, one of the carboxylic groups gets protonated in EDTA of [UO2(edta)]2- rather than one of the amino groups. This process-based series of calculations can be applied to any redox reaction and allows the prediction of changes to the rate law and rate-limiting step in a more fundamental way for different environments.

RuIII(edta) complexes as molecular redox catalysts in chemical and electrochemical reduction of dioxygen and hydrogen peroxide: inner-sphere versus outer-sphere mechanism

The reduction of molecular oxygen (O2) and hydrogen peroxide (H2O2) by [RuII(edta)(pz)]2− (edta4− = ethylenediaminetetraacetate; pz = pyrazine) has been studied spectrophotometrically and kinetically in aqueous solution. Exposure of the aqua-analogue [RuII(edta)(H2O)]2− to O2 and H2O2 resulted in the formation of [RuIII(edta)(H2O)]− species, with subsequent formation of the corresponding RuV Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> O complex. A working mechanism for the O2 and H2O2 reduction reactions mediated by the RuII(edta) complexes is proposed. The role of the coordinated water molecule (by its absence or presence in the primary coordination sphere) in controlling the mechanistic pathways, outer-sphere or inner-sphere, is discussed.

Hydroxyapatite of plate-like morphology obtained by low temperature hydrothermal synthesis

The morphology of hydroxyapatite crystals formed in hydrothermal reaction of calcium EDTA complex with KH2PO4 at 120 °C depends on the pH value of the reaction medium. Bone-like platy microcrystals were prepared at pH 6, while at higher pH values rod-like species were obtained.

Sealing of porous YSZ samples with Gd-doped CeO2 film produced using aqueous metal-EDTA complex solution

In this study, we propose a method for sealing porous samples using aqueous solutions of metal-ethylenediaminetetraacetic acid (EDTA) complexes. Gd-doped ceria (GDC) films were synthesized on porous NiO-mixed yttria-stabilized zirconia (YSZ) samples by coating them with a (Ce, Gd)-EDTA complex solution and subsequently sintering them in air at 850 °C for 1 h. When the Ce/Gd ratio in EDTA was 0.8:0.2, only a crystalline Ce0.8Gd0.2O1.9 phase was formed on the surface. The obtained results confirmed that the proposed treatment is effective for sealing the surfaces and open pores of porous samples. Finally, it was observed that a GDC layer was formed both at the sample surface and within the pores smaller than 1.7 μm.

Effect of EDTA-2Na modification on Fe-Co/Al2O3 for hydrogenation of carbon dioxide to lower olefins and gasoline

Capturing and utilization of carbon dioxide (CO2) not only leads to effective use of carbon resources, but also alleviates environmental pollution caused by increasing concentration of CO2, thus making it a hot research topic in recent years. In this study, a series of highly dispersed iron-cobalt (Fe-Co) catalysts was prepared by ethylenediaminetetraacetic acid disodium salt (EDTA-2Na) modification, which could efficiently convert CO2 into high value-added chemicals (C2-C4= and C5-C11). X-ray diffraction (XRD) analysis showed that the addition of a small amount of Co and EDTA-2Na contributed to enhance the sintering resistance of Fe species. During the calcination process, EDTA4− can be decomposed into small organic molecules with reducibility, thus promoting the reduction of iron species. The CO temperature-programmed desorption (CO-TPD) results showed that cobalt enhanced the adsorption and activation of intermediate CO on NaxFe-Co catalyst, thereby promoting the catalytic conversion of CO2. The complexation of EDTA promotes the synergistic effect of Fe-Co bimetals, enhances the chemical adsorption of CO2. Sodium in EDTA-2Na promotes the surface basicity of the catalysts, which is favored for improving the product distribution of hydrocarbons. At lower H2/CO2 (1/1) ratio, the EDTA-2Na modified Fe-Co/Al2O3 catalyst exhibited high conversion of CO2 (32.8 %) and excellent selectivity toward high value-added chemicals. The selectivity of by-product CO was only 8.1 %; and C2-C4= (32.5 %) and C5-C11 (46.3 %) accounted for ∼79 % selectivity among the hydrocarbons generated.

New insights in the slow ligand exchange reaction between Cr(III)-EDTA and Fe(III), and direct analysis of free and complexed EDTA in tannery wastewaters by liquid chromatography - Tandem mass spectrometry

EDTA and soluble Cr(III) are usually both present in wastewaters coming from treatment plants handling tannery effluents. A well-established method to determine EDTA is based on the conversion of free and complexed EDTA into its Fe(III) complex. This procedure gives inconsistent data when Cr(III)-EDTA is present. This fact was here demonstrated by studying the kinetics of the exchange reaction between Fe(III) and Cr(III)-EDTA at 90 °C and various pH values, from acidic to neutral. The reaction is very slow (several weeks); the slow kinetics of conversion of Cr(III)-EDTA to Fe(III)-EDTA is even more accentuated at room temperature and the low concentrations of reactants in wastewaters. The presence of EDTA complexes of Fe(III) and Cr(III) was demonstrated in industrial effluents and wastewaters by developing a selective method based on liquid chromatography-tandem mass spectrometry (LC-MS/MS), which was able to detect free and complexed EDTA at concentration levels <1 μM. A systematic underestimation of the EDTA expressed as Fe(III) complex was demonstrated in samples containing Cr(III)-EDTA. Cr(III)-EDTA was identified for the first time as a component of wastewater samples at a concentration level of about 2 μM and turned out to be an inert species that significantly contributes to the final soluble Cr amount. This study gives new insights into the inertness of Cr(III) toward metal exchange equilibria of EDTA complexes, resolves a bias in the analysis of total EDTA in samples containing Cr(III)-EDTA, allowing the direct determination of free and complexed EDTA by LC-MS.

Synthesis, microstructure, anti-corrosion property and biological performances of Mn-incorporated Ca-P/TiO2 composite coating fabricated via micro-arc oxidation.

In this work, a Mn-incorporated Ca-P/TiO2 composite coating was produced through the facile one-step micro-arc oxidation (MAO) method. It is revealed that only when the concentration of Na2Mn-EDTA reaches 0.02mol/L, the Ca-P phase could form on Mn-incorporated TiO2 coating, which is associated with the combined effect of EDTA complex and Mn species. The Ca-P phase is amorphous, which may contain hydroxyapatite phases whereas the underlying Mn-incorporated TiO2 coating contains two separate layers, including the Mn-rich outer layer and Mn-depleted inner layer. The biological investigation of the Mn-incorporated Ca-P/TiO2 composite coating suggests that it exhibits desirable osteogenesis with certain capability to inhibit the growth of S. aureus bacteria. Hence, a promising composite coating with superior bone formability could be produced using the one-step micro-arc oxidation method in the electrolyte containing Na2Mn-EDTA.

Arsenite oxidation and arsenic adsorption on birnessite in the absence and the presence of citrate or EDTA.

Birnessite not only oxidizes arsenite into arsenate but also interacts with organic matter in various ways. However, effects of organic matter on interaction between As and birnessite remain unclear. This study investigated effects of citrate and EDTA (3.12 and 2.05mM, respectively) on oxidation of As(III) (1.07mM) and adsorption of As(V) (0.67mM) on birnessite (5.19mM as Mn) at near-neutral pH. We found that As(V) adsorption on birnessite was enhanced by citrate and EDTA, which resulted from the increase in active adsorption sites via dissolution of birnessite. In comparison with citrate batches, more As was adsorbed on birnessite in EDTA batches, where dissolved Mn was mainly presented as Mn(III)-EDTA complex. Citrate or EDTA-induced dissolution of birnessite did not decrease the As(III) oxidation rate in the initial stage where As(III) oxidation rate was rapid. Afterwards, As(III) oxidation was conspicuously suppressed in citrate-amended batches, which was mainly attributed to the decrease in adsorption sites by adsorption of citrate/Mn(II)-citrate complex. This suppression was enhanced by the increase in concentrations of dissolved Mn(II). Citrate inhibited As adsorption after As(III) oxidation due to the strong competitive adsorption of citrate/Mn(II)-citrate complex. However, the As(III) oxidation rate was increased in EDTA-amended batches in the late stage, which mainly derived from the increase in the active sites via birnessite dissolution. The strong complexation ability of EDTA led to formation of Mn(III)-EDTA complex. Arsenic adsorption was not affected due to the limited competitive adsorption of the complex on the solid. This work reveals the critical role of low molecular weight organic acids in geochemical behaviors of As and Mn in aqueous environment.

Sorption of Complex Co(II)-EDTA by Anion Exchange Resin AB-17-8 from Model Deactivating Solutions Containing Fe(III)-EDTA

The results of studies of the sorption of EDTA complexes with ions Co(II) and Fe(III) on anion exchange resin AB-17-8 used in mixed filters of special water treatment apparatus of NPP are presented. The character of the sorption process of complexes Co(II)-EDTA and Fe(III)-EDTA in acidic media depending on the pH and salt background of solutions simulating deactivating solutions formed after the dissolution of iron oxide compounds containing cobalt radionuclides was studied. It has been shown that upon deactivation of spent ion-exchanged resins with acid solutions of EDTA salts, the secondary sorption of EDTA complexes with cobalt radionuclides on anion exchange resin can be reduced by lowering the pH of the deactivating solutions and increasing the concentration of competing inorganic anions, with no noticeable competing effects of the complexes Fe(III)-EDTA.

Simultaneous Adsorption of Zn(II) and Hg(II) Ions on Selective Adsorbent of Dithizone-Immobilized Bentonite in the Presence of Mg(II) Ion

Sequential desorption of adsorbed Zn(II) and Hg(II) ions using distilled water (physical interaction), 1 M KNO 3 (electrostatics), HONH 2 HCl in 25% (v/v) CH 3 COOH (hydrogen bond) and 0.1 M Na 2 EDTA (complexation) • Selective adsorbent of heavy metals based on dithizone immobilization on bentonite. • Significant enhanced performance of the adsorbent towards Hg(II) and Zn(II) ions. • Simultaneous adsorption kinetics of Hg(II) and Zn(II) follow pseudo-2 nd order model. • Isotherm adsorption of Zn(II) follows Langmuir, Hg(II) fits well Freundlich model. • Electrostatic interactions for Zn(II), hydrogen bond and complexation for Hg(II). Simultaneous adsorption of Zn(II) and Hg(II) in the presence of alkaline earth metal, Mg(II) on dithizone-immobilized bentonite has been done by batch method. The study was begun by activation of natural bentonite with HCl followed by immobilization of dithizone on bentonite surface. Some parameters influencing the adsorption such as pH, interaction time and initial concentration of metal ions were optimized. Types of interaction between metal ions and adsorbent were assessed by conducting sequential desorption of the adsorbed metals using H 2 O, KNO 3 , HONH 2 HCl and Na 2 EDTA. XRD and FTIR characterizations suggest that dithizone has been successfully immobilized on the surface of bentonite. Optimum conditions for simultaneous adsorption of Hg(II) and Zn(II) in the presence of Mg(II) are at pH 6 and interaction time of 60 minutes. Capacity, affinity and selectivity of dithizone immobilized bentonite towards Hg(II) and Zn(II) are better than those of non-immobilized activated natural bentonite, but the interaction types of the two metal ions with adsorbents are different. Zn(II) ion mostly interacts with adsorbents through physical and electrostatic interactions, while Hg(II) ion interacts via hydrogen bond and complexation. Upon immobilization of dithizone on the surface of bentonite, the interaction of Hg(II) with adsorbent changes significantly from hydrogen bond to complexation. Moreover, the presence of Mg(II) ion gives no significant influence on metal adsorption, indicating that dithizone-immobilized bentonite is quite selective towards heavy metal ions.

A Highly Selective Complexometric Determination of Mercury(II) using L-Tyrosine as a Masking agent

Determination of mercury in the existence of various other metal ions, a transparent speedy and accurate complexometric method is described, depending on the selective masking ability of L-Tyrosine towards Hg (II). Along with other associated metal ions, Hg (II) present in a given sample solution is first complexed with an surplus of EDTA and the leftover EDTA is titrated with Zinc sulfate solution in the presence of xylenol orange as an indicator at pH 5.0-6.0.A known excess of 0.02M L-Tyrosine solution is then added to discharge the EDTA from Hg (II)-EDTA complex and then it is mixed well. The displaced EDTA is again titrated with a Zinc sulfate solution. The method goes well in the range 4-80 mg of mercury (II) with the relative error ±0.4 and standard deviation ≤0.05 mg. The issue of the existence of various metal ions on the exactitude of the results has been studied. And the method can be applied for the determination of Mercury in alloys, in its synthetic mixtures of ions and its complexes.

Luminescence properties of the Ln-EDTA complexes covalently linked to the chitosan biopolymers containing β-diketonate as antenna ligands.

This paper reports on the preparation, characterization, and photoluminescence properties of novel hybrid materials, in which the EDTA-Ln-L complexes (where L: H2 O, acac, bzac, dbm, and tta ligands, and Ln: Eu, Gd, and Tb) were covalently linked to the precursor medium molecular weight chitosan surface (CS) matrices or on the chitosan surfaces previously crosslinked with epichlorohydrin (CSech). The emission spectra of these materials were characterized by intraconfigurational-4fN transitions centred on the Eu3+ and Tb3+ ions. Some broad bands from the polymeric matrix were also observed in the emission spectra, however the relative intensities of the intraconfigurational bands increased significantly for systems containing diketonate ligands when the antenna effect became more efficient. The values of the radiative rates (Arad ) were higher for crosslinked hybrid systems with epichlorohydrin, while nonradiative rates (Anrad ) presented the opposite behaviour. These data contributed to an increase in the values of emission quantum efficiency (η) for crosslinked materials. The effect of the modification process and antenna ligand on the values of intensities, intensity parameters Ω2 e Ω4 of the Eu3+ complexes were also investigated. The results showed that the crosslinked biopolymer surfaces have great potential for applications in molecular devices light converters.