Addition Of Chelating Agent Research Articles

EDDS and EDTA-enhanced zinc accumulation by solanum nigrum inoculated with arbuscular mycorrhizal fungi grown in contaminated soil

The effect of two different chelating agents [EDTA and EDDS ( S, S-ethylenediaminedissucinic acid)] on Zn tissue accumulation in Solanum nigrum L. grown in a naturally contaminated soil was assessed. Under those conditions, the response of the plant to the inoculation with two different isolates of arbuscular mycorrhizal fungi (AMF) – Glomus claroideum and Glomus intraradices – was also studied. Plants grown in the local contaminated soil (Zn levels of 433 mg kg −1) accumulated up to 1191 mg kg −1 of Zn in the roots, 3747 mg kg −1 in the stems and 3409 mg kg −1 in the leaves. S. nigrum plants grown in the same soil spiked with extra Zn (Zn levels of 964 mg kg −1) accumulated up to 4735, 8267 and 7948 mg Zn kg −1 in the leaves, stems and roots, respectively. The addition of EDTA promoted an increase in the concentration of Zn accumulated by S. nigrum of up to 231% in the leaves, 93% in the stems and 81% in the roots, while EDDS application enhanced the accumulation in leaves, stems and roots up to 140, 124 and 104%, respectively. In the stems, the presence of Zn was predominantly detected in the cortex collenchyma cells, the starch sheath and the internal phloem and xylem parenchyma, and the addition of chelating agents did not seem to have an effect on the localisation of accumulation sites. The devise of a chelate-enhanced phytoextraction strategy, using chelating agents and AMF, is discussed.

Improved Understanding of Hyperaccumulation Yields Commercial Phytoextraction and Phytomining Technologies

This paper reviews progress in phytoextraction of soil elements and illustrates the key role of hyperaccumulator plant species in useful phytoextraction technologies. Much research has focused on elements which are not practically phytoextracted (Pb); on addition of chelating agents which cause unacceptable contaminant leaching and are cost prohibitive; and on plant species which offer no useful phytoextraction capability (e.g., Brassica juncea Czern). Nickel phytoextraction by Alyssum hyperaccumulator species, which have been developed into a commercial phytomining technology, is discussed in more detail. Nickel is ultimately accumulated in vacuoles of leaf epidermal cells which prevents metal toxicity and provides defense against some insect predators and plant diseases. Constitutive up-regulation of trans-membrane element transporters appears to be the key process that allows these plants to achieve hyperaccumulation. Cadmium phytoextraction is needed for rice soils contaminated by mine wastes and smelter emissions with 100-fold more soil Zn than Cd. Although many plant species can accumulate high levels of Cd in the absence of Zn, when Cd/Zn>100, only Thlaspi caerulescens from southern France has demonstrated the ability to phytoextract useful amounts of Cd. Production of element-enriched biomass with value as ore or fertilizer or improved food (Se) or feed supplement may offset costs of phytoextraction crop production. Transgenic phytoextraction plants have been achieved for Hg, but not for other elements. Although several researchers have been attempting to clone all genes required for effective hyperaccumulation of several elements, success appears years away; such demonstrations will be needed to prove we have identified all necessary processes in hyperaccumulation.

Enhancement of methane fermentation in the presence of Ni 2+ chelators

The enhancement of methane fermentation in the presence of Ni 2+ chelators, citric acid (CA), nitrilotriacetic acid (NTA), and ethylene diamine tetraacetic acid (EDAT) respectively, was investigated in this study. The results showed that the addition of chelating agents promoted methane fermentation of acetate. At a sodium acetate concentration of 7 g/L, temperature of 35 °C, and Ni 2+ concentration of 20 μM, methane production was enhanced 34.1%, 49.2%, and 38.6%, by the addition of 10 μM CA, NTA and EDTA, respectively. The formation of soluble complexes between chelating agents and Ni 2+ favored the dissolution of Ni 2+ from their sulfides, and the bioavailability of Ni 2+ was dramatically increased. By the addition of 10 μM NTA, the concentration of dissolved Ni 2+ was greatly increased from 58 to 1020 μg/L. Accompanying with that, the concentrations of F 430 and coenzyme M of the biomass increased 37% and by four-fold, respectively.

Large-scale purification and crystallization of the endoribonuclease XendoU: troubleshooting with His-tagged proteins.

XendoU is the first endoribonuclease described in higher eukaryotes as being involved in the endonucleolytic processing of intron-encoded small nucleolar RNAs. It is conserved among eukaryotes and its viral homologue is essential in SARS replication and transcription. The large-scale purification and crystallization of recombinant XendoU are reported. The tendency of the recombinant enzyme to aggregate could be reversed upon the addition of chelating agents (EDTA, imidazole): aggregation is a potential drawback when purifying and crystallizing His-tagged proteins, which are widely used, especially in high-throughput structural studies. Purified monodisperse XendoU crystallized in two different space groups: trigonal P3(1)21, diffracting to low resolution, and monoclinic C2, diffracting to higher resolution.

Influence of EDTA and citrate on thermal stability of whey protein stabilized oil-in-water emulsions containing calcium chloride

The influence of calcium ions and chelating agents on the thermal stability of model nutritional beverages was examined. Oil-in-water emulsions (6.94% (w/v) soybean oil, 0.35% (w/v) WPI, 0.02% (w/v) sodium azide, 20 mM Tris buffer, 0–10 mM CaCl 2, and 0–40 mM EDTA or citrate, pH 7.0) were stored at temperatures between 30 and 120 °C for 15 min. The particle size, particle charge, creaming stability, rheology, and free-calcium concentration of the emulsions were then measured. In the absence of chelating agents, appreciable droplet aggregation occurred in emulsions held at temperatures from 80 to 120 °C, which led to increased emulsion particle diameter, shear-thinning behavior, apparent viscosity, and creaming instability. Addition of chelating agents to the emulsions prior to heating decreased, but did not prevent, droplet aggregation in the emulsions. EDTA was more effective than citrate in decreasing droplet aggregation. Heat treatment increased the amount of chelating agents required to prevent droplet aggregation in the emulsions. Free-calcium concentration and droplet surface potential was independent of heat-treatment temperature, indicating that the performance of the chelating agents in binding calcium ions was not affected by the heat treatment. It was suggested that increased hydrophobic attractive interactions between the droplets occurred during heating, which induced droplet aggregation.

Influence of Chelating Agent Addition on Copper Distribution and Microbial Activity in Soil and Copper Uptake by Brown Mustard (Brassica juncea)

A pot culture experiment was conducted using a Cu-spiked soil to compare the effects of the application of ethylenediamine-N,N′-tetraacetate (EDTA) and [S,S]-ethylenediamine-N,N′-disuccinate (EDDS), a biodegradable chelating agent, on the soil Cu distribution, Cu uptake by brown mustard and on the metabolic activity of the soil microorganisms for substrate utilization. Seedlings of brown mustard were planted in the pots fitted with hollow fibers for soil solution suction, and cultivated for 12 weeks. Solutions of chelating agents with pH 6.0 at a concentration of 1.0 mmol kg−1 soil were supplied on the 35, 43, and 51 d after transplanting (total 3.0 mmol kg−1). The addition of EDTA and EDDS enhanced plant Cu uptake by 2.9 and 1.8 times compared with the uptake of the control plants which were grown without chelating agent supply. However, EDTA addition caused a significant growth reduction compared with the control, while the application of EDDS did not reduce the dry matter yield of the plants. The concentrations of Cu and chelating agent in the soil solution of the EDTA-amended soil were much higher than those in the EDDS treatment during the cultivation, especially at the late stage. The results of sequential extraction of Cu in soil after cultivation showed that the addition of both EDTA and EDDS decreased the amount of Cu in the Mn oxide-occluded fraction and increased the amount in the water-soluble and exchangeable fractions significantly, compared with the control soil. The amount of Cu in the acid-soluble and organically bound fractions of the soil supplied with both chelating agents was also lower than that in the control soil, although the value was not significant for the EDDS treatment. Based on the values of the average well color development (AWCD) on the Biolog ECO MicroPlates, the activity of the soil microorganisms for substrate utilization in the EDTA treatment after cultivation was lower than that in the EDDS treatment. These results suggested that the environmental risks caused by the leaching of Cu and Cu-chelate and the influence on soil microbial activity were less pronounced in the case of EDDS addition than EDTA. Therefore, EDDS could replace EDTA for chelate-assisted phytoremediation of soils contaminated with Cu, although the amount of Cu taken up by the plants was lower than that required for efficient reduction of the soil Cu content.

Cadmium adsorption on hydrous aluminium (III) oxide: effect of adsorbed polyelectrolyte

Freshly precipitated hydrous oxides of Al (flocs) are important sorbents of heavy metal ions and are used in water treatment processes. The addition of chelating agents or polyelectrolytes can increase the efficiency of heavy metal removal by flocs. The polymer polyethylenimine is commonly used as a flocculant aid in water treatment and has been modified with phthalic acid. Adsorption studies have shown that the addition of millimolar concentrations of polyelectrolyte increases the removal of Cd ions from a 29.7 μM aqueous solution by aluminium flocs from ca. 40% to up to 75%. Experiments in which the pH was varied demonstrated that the observed enhancement of Cd adsorption is caused by a shift of the pH edge to lower pH values in the presence of polyelectrolyte. Maximum polyelectrolyte adsorption occurs between pH 6 and pH 7, corresponding to the point of enhanced Cd adsorption in the presence of polyelectrolyte. The enhancement of Cd adsorption observed below pH 7 is therefore likely to be due to the formation of a ternary surface complex. At pH values above pH 8 the polyelectrolyte forms a stable complex with Cd and Al ions in solution causing floc dissolution and decreased Cd adsorption.

Enhancement of Semiconductor Wafer Cleaning by Chelating Agent Addition

To realize environmental and cost benefits it is desirable to reduce the RCA cleaning sequence from its historical combination, in which the particle-removing SC1 solution deposits certain metals, necessitating the metal-removing SC2. One approach is to add a chelating agent to the SC1. Extensive testing of SC1 solutions with addition of the complexing agent 1,2-cyclohexanediaminetetraacetic acid (CDTA) were performed. CDTA was shown to be more stable than other complexing agents in SC1 solutions, facilitating significant bath life extension. Further, SC1 solutions with CDTA were shown to be capable of removing large quantities of metals from contaminated wafers, comparable to SC2, and preventing deposition of metals. An exception is aluminum, which can deposit from SC1 even with large amounts of added CDTA, but which can be removed by a subsequent dilute step. © 2001 The Electrochemical Society. All rights reserved.

Field validation of specific ecotoxicological tools for aquatic systems impacted with acid mine drainage

Acid mine drainage (AMD) is characterised by very low pH and high heavy metal concentrations. Serious ecotoxicological effects, often leading to the complete disruption of the ecosystem, can be observed at the regions suffering this kind of contamination. Those effects can be caused either by low pH itself or by other contaminants that emerge with water acidification (mobilisation and increased solubility of heavy metals). The discrimination between the toxicity due to each of these two factors is not possible with the existing toxicity tests; the addition of chelating agents or serial dilution methods seriously alter the chemical and physical properties of the effluent. A toxicity test, based on the survival time of Ceriodaphnia dubia (Crustacea, Cladocera) neonates exposed to the unchanged effluent, was developed and field validated, on an AMD contaminated site.

The effects and mechanism of chemical additives on the pyrolysis evolution and microstructure of sol–gel derived Ba 1− xSr xTiO 3 thin films

The dependence of phase evolution on preparation conditions of precursor sols were investigated by DSC and XRD experiments during the sol–gel processing for Ba 1− x Sr x TiO 3(BST) thin films. Two kinds of crystallization paths of perovskite BST were found during the annealing, which are closely dependent on chelating agent and solution aging. One path was the decomposition of all oxycarbonate intermediate, the other was the solid reaction between Ba/Sr carbonates and titanium oxides. For fresh sol, the addition of acetylacetone (HAcAc) as a chelating agent reduced the crystallization temperature by ∼70°C. Moreover, the back scattered scanning electron microscopy (BS-SEM) revealed that the HAcAc-derived films were homogeneous in composition in comparison with the heterogeneity of the films prepared with no chelating agent addition. The variations mentioned above were considered originating from different molecule structures of the precursors.

Natural and induced cadmium-accumulation in poplar and willow: Implications for phytoremediation

Potentially poplars and willows may be used for the in situ decontamination of soils polluted with Cd, such as pasturelands fertilised with Cd-rich superphosphate fertiliser. Poplar (Kawa and Argyle) and willow (Tangoio) clones were grown in soils containing a range (0.6–60.6 μg g−1 dry soil) of Cd concentrations. The willow clone accumulated significantly more Cd (9–167 μg g−1 dry matter) than the two poplar clones (6–75 μg g−1), which themselves were not significantly different. Poplar trees (Beaupre) sampled in situ from a contaminated site near the town of Auby, Northern France, were also found to accumulate significant quantities (up to 209 μg g−1) of Cd. The addition of chelating agents (0.5 and 2 g kg−1 EDTA, 0.5 g kg−1 DTPA and 0.5 g kg−1NTA) to poplar (Kawa) clones caused a temporary increase in uptake of Cd. However, two of the chelating agents (2 g kg−1 EDTA and 0.5 g kg−1 NTA) also resulted in a significant reduction in growth, as well as abscission of leaves. If the results obtained in these pot experiments can be realised in the field, then a single crop of willows could remove over 100 years worth of fertiliser-induced Cd contamination from pasturelands.

Toxicity of Organic and Inorganic Mercury to Saccharomyces cerevisiae

In this study the effect if six different forms of mercury on the growth of the yeast Saccharomyces cerevisiae is presented. Five kinds of strains of S. cerevisiae were used. They were a wild type, a mercury-resistant type, and three mutants: mutation repair-deficient mutant, excision repair-deficient mutant, and recombination repair-deficient mutant. In terms of EC50 toward the wild-type strain, the toxicity order for the inorganic forms was Hg(NO3)2>HgSO4>HgCl2. Monovalent nitrate mercury Hg(NO3)2 was more toxic than bivalent Hg(NO3)2. The toxicity of organic mercury CH3HgCl on cell growth was two orders of magnitude higher than that of inorganic HgCl2. Between the two organic forms, CH3HgCl was more toxic than CH3HgOH. The survival rate in the presence of a certain concentration of CH3HgCl was about one-hundredth of the survival in presence of the same concentration of HgCl2. On the other hand, the concentration of CH3HgCl in the cell was about 170 times that of HgCl2. The addition of chelating agents, EDTA and methyl-penicillamine, to the medium did not reduce the toxicity of mercury. Among the three mutants tested, the one deficient in recombination repair systems was the most sensitive to mercury.

The Effect of Acidification and Chelating Agents on the Solubilization of Uranium from Contaminated Soil

AbstractThe role of acidification and chelating agents in the solubilization of uranium (U) from contaminated soil was examined in a series of experiments. Soil acidification and the addition of chelating agents were the two methods compared initially. The results indicated that the addition of citric acid solubilized more U than acidification or the other amendments tested. This increase in U solubility was, however, transitory. A subsequent experiment indicated that citrate concentration had a more dramatic effect on U solubility than did acidification. The greatest soluble U concentration during this experiment (775 mg kg−1 soil, or ∼85% of the total U) was observed after 24 h in the presence of 20 millimoles citrate kg−1 soil at pH 5. The persistence of U solubility over the 96‐h experimental period was primarily a function of pH and citrate degradation. In a separate experiment, in which citric acid rather than citrate was added to contaminated soil, the soluble U concentrations observed were generally lower than those observed in the presence of citrate. Citric acid decreased soil pH to values ≤3.6, and solubilized higher concentrations of Al and Fe than observed in the presence of citrate. Since the maximum solubilization of U was observed at pH 5, the implication of these results is that a combined approach, using both soil acidification and citric acid addition, may be necessary to maximize the phytoextraction of U from soils with a pH > 6.0.

Characterization of a G M1-dependent surface interaction for alcohol with DPPC membranes

A unique surface interaction for perdeuterated ethanol and 1-butanol with dipalmitoylphosphatidylcholine (DPPC)/monosialoganglioside (G M1) multilamellar vesicles can be detected from the fast exchange averaging of the nuclear quadrupole coupling constant of the alcohol in the free and bound states using deuterium NMR. At 1.0% perdeuterated ethanol or 0.5% perdeuterated 1-butanol, a small splitting of the alcohol resonance(s) was detected in the liquid-crystalline phase, but not in the gel phase of the bilayer. The observed splitting is proportional to the fraction of alcohol bound and is dependent on temperature, alcohol, and G M1 concentrations. The splitting was only observed in the presence of negatively charged G M1 but not neutral asialoganglioside (asialo-G M1) in DPPC multilamellar vesicles. The observed splitting decreased with the addition of Ca 2+ or Mg 2+ ions. This effect was reversed upon the addition of chelating agents. It is proposed that the unique surface interaction for alcohol may result from small surface perturbations of the phosphatidylcholine head groups by the negatively charged sialic moieties of neighboring G M1 molecules in the bilayer.

Prevention of toxicity of metal ions to Aeromonas and other bacteria in drinking-water samples using nitrilotriaceticacid (NTA) instead of ethylenediaminetetraaceticacid (EDTA)

The addition of chelating agent to drinking-water samples reduces die-off, due to the toxic effect of metal ions, of bacteria such as Aeromonas. The use of ethylenediaminetetraaceticacid (EDTA) is undesirable since it is a highly persistent chemical which contributes to environmental pollution. This study shows that the less persistent nitrilotriaceticacid (NTA) is a suitable alternative. No significant differences (P < 0.001) were detected between EDTA and NTA in protecting bacteria.

Effect of zinc binding on the structure and stability of fibrolase, a fibrinolytic protein from snake venom.

Fibrolase is a metalloprotease with potential use as a fibrinolytic agent. Loss of the intrinsic zinc atom leads to a rapid decrease in enzymatic activity. Circular dichroism measurements indicate that there is a partial unfolding of an alpha-helical section of the protein concomitant with the loss of zinc. Removal of zinc can be affected by elevated temperatures, acidic pH values, and addition of chelating agents. At low molar concentrations, both ethylenediaminetetraacetic acid (EDTA) and dithiothreitol (DTT) were found to remove zinc efficiently. Analysis of the sequence of fibrolase identified a segment which possessed a high degree of homology with the metal binding site of other zinc proteases, such as thermolysin and the collagenases. However, the putative zinc binding site in fibrolase lacks the additional glutamate ligand found in thermolysin and subtilisin. This sequence is also predicted to adopt an alpha-helical conformation. Together, these data indicate that there is a well-defined metal binding site in fibrolase and that metal binding is the most important factor governing the stability of this protein.

Sol-gel thin films of SrTiO 3 from chemically modified alkoxide precursors

SrTiO 3 alkoxide precursor was chemically modified through the addition of chelating agents, diisopropanolamine, triethanol-amine and acetylacetone. The effects of chelation on the crystallization and microstructures of SrTiO 3 sol-gel films on fused silica substrates were studied. Microstructural studies indicated segregation of small crystallites of SrTiO 3 for thin films obtained from triethanolamine and acetylacetone chelated precursor solutions. On the other hand, diisopropanolamine chelated solution yielded dense and smooth films.

The effect of free radicals induced by paraquat and copper on the in vitro development of Plasmodium falciparum.

The role of transition metals in paraquat toxicity was studied in cultures of Plasmodium falciparum. We showed that addition of copper led to an enhancement of the plasmodium killing, whereas addition of chelating agents, such as desferrioxamine and diethylenetriamine pentaacetic acid markedly reduced the toxic effects. Parsitized G6PD deficient erythrocytes were more sensitive than parasitized normal erythrocytes to copper and to the combination of copper and paraquat.

Bioconversion of chicken wastes to value-added products

Increasing quantities of chicken waste concerns the poultry industry because of escalating disposal costs and the potential for environmental pollution. Biological conversion of these wastes to valuable products such as methane and/or chemical feed-stocks appears to be feasible. Biomethanation of chicken waste by a sewage sludge microbial consortium produced as much as 69 mol% methane in the gas phase. Acetic and propionic acids were the major acids produced during the bioconversion. Addition of chelating agents and other micronutrients enhanced methane production and shifted the ratios of intermediates accumulated. Preliminary data indicate that more than 60% of the chicken waste carbon was converted and that the nitrogen-rich residue may have potential as a soil additive.

Titanium gel made from metallic titanium and hydrogen peroxide

Various titanium-peroxo intermediates may be formed in the Ti-H 2O 2 redox process. In a catalytically decomposed Ti-H 2O 2 system, an oxidizing transparent yellow-green gel with a final pH between 3 and 4 is typically formed within 48 h without addition of chelating agents. The redox potential of the gel is larger than that of the Fe(II)/Fe(III) system. The total Ti concentration in the studied gel was spectro-photometrically determined to be about 45 m M. The oxidizing component was determined to be about 15 m M with the use of iodometric titration. A model for the catalytic H 2O 2 decomposition is discussed, and an explanation for the existence of an ESR-active radical component in the gel is suggested. The possible relation of the gel formation to the known biocompatibility of titanium is speculated on.