Iron Removal Rate Research Articles

Allosteric effects of sulfonate anions on the rates of iron release from serum transferrin

Serum transferrin is the protein that transports ferric ion through the bloodstream and is thus a potential target for iron chelation therapy. However, the release of iron from transferrin to low-molecular-weight chelating agents is usually quite slow. Thus a better understanding of the mechanism for iron release is important to assist in the design of more effective agents for iron removal. This paper describes the effect of sulfonate anions on the rates of iron removal from C-terminal monoferric transferrin by acetohydroxamic acid, deferiprone, nitrilotriacetic acid (NTA), and diethylenetriaminepentaacetic acid at 25 °C in 0.1 M N-(2-hydroxyethyl)piperazine-N′-(2-ethanesulfonic acid) (Hepes) buffer at pH 7.4. These ligands remove iron via a combination of pathways that show saturation and first order dependence on the ligand concentration. The kinetic effects of the anions methanesulfonate, methylenedisulfonate, and ethylenedisulfonate were evaluated. All these anions increase the overall rates of iron release, presumably by binding to an allosteric anion binding site on the protein. The two disulfonates produce a larger acceleration in iron release than the monosulfonate. More detailed studies using methylenedisulfonate show that this anion accelerates the rate of iron release via the saturation pathway. The addition of methylenedisulfonate results in the appearance of a large saturation pathway for iron release by NTA, which otherwise removes iron by a simple first-order process. The sulfonate group was selected for these studies because it represents an anionic functional group that can be covalently linked to a therapeutic ligand to accelerate iron release in vivo. The current studies indicate that the binding of the sulfonates to the allosteric site on the protein is quite weak, so that one would not expect a significant acceleration in iron release at clinically relevant ligand concentrations.

Efficacy, Compliance And Toxicity Factors Are Affecting The Rate Of Normalization Of Body Iron Stores In Thalassemia Patients Using The Deferiprone And Deferoxamine Combination Therapy

The international committee on chelation (ICOC) of deferiprone (L1) and deferoxamine (DFO) combination therapy was the first protocol reported to have achieved normal range body iron store levels (NRBISL) in β-thalassemia major (β-TM) patients. A follow-up study in eight β-TM patients has been designed to investigate the factors affecting the rate of iron removal leading to NRBISL. The patients had variable serum ferritin [mean ± SE (standard error) =1692 ± 366, range 539–3845 μg/L)] and magnetic resonance imaging (MRI) T2* relaxation times cardiac (mean ± SE =11.1 ± 2.5, range 4.5–24.2 ms) and liver (mean ± SE = 4.3 ± 1.8, range 1.4–14 ms). Organ function, blood and other biochemical parameters were regularly monitored for toxicity. The ICOC L1 (80–100 mg/kg/day) and DFO (40–60 mg/kg, at least 3 days per week) combination therapy caused an increase in cardiac (mean ± SE =30.2 ± 2.3, range 22–41 ms) and liver (mean ± SE =27.6 ± 2.8, range 9.1–35 ms) T2* and reduction in serum ferritin (mean ± SE = 158 ± 49, range 40–421 μg/L) to within the NRBISL. The rate of normalization was variable and in one case was achieved within 9 months, whereas the longest was about 3 years. The initial iron load, the rate of transfusions, the combination dose protocol and the level of compliance were the major factors affecting the rate of normalization of the iron stores. No serious toxicity was observed during the study period, which lasted a total of 24.7 patient years.

Iron crystallization in a fluidized-bed Fenton process

The mechanisms of iron precipitation and crystallization in a fluidized-bed reactor were investigated. Within the typical Fenton’s reagent dosage and pH range, ferric ions as a product from ferrous ion oxidation would be supersaturated and would subsequently precipitate out in the form of ferric hydroxide after the initiation of the Fenton reaction. These precipitates would simultaneously crystallize onto solid particles in a fluidized-bed Fenton reactor if the precipitation proceeded toward heterogeneous nucleation. The heterogeneous crystallization rate was controlled by the fluidized material type and the aging/ripening period of the crystallites. Iron crystallization onto the construction sand was faster than onto SiO 2, although the iron removal efficiencies at 180 min, which was principally controlled by iron hydroxide solubility, were comparable. To achieve a high iron removal rate, fluidized materials have to be present at the beginning of the Fenton reaction. Organic intermediates that can form ferro-complexes, particularly volatile fatty acids, can significantly increase ferric ion solubility, hence reducing the crystallization performance. Therefore, the fluidized-bed Fenton process will achieve exceptional performance with respect to both organic pollutant removal and iron removal if it is operated with the goal of complete mineralization. Crystallized iron on the fluidized media could slightly retard the successive crystallization rate; thus, it is necessary to continuously replace a portion of the iron-coated bed with fresh media to maintain iron removal performance. The iron-coated construction sand also had a catalytic property, though was less than those of commercial goethite.

Small City Tackles Radium in Well Water

This article discusses a pilot study by the city of Goodview, Minnesota, for the removal of radium with hydrous manganese oxide (HMO) and coprecipitation with iron from its well water. Dual media, sand, and manganese greensand media were tested in the pilot plant, and results showed that the manganese greensand media had the lowest filter headloss buildup and would produce the longest filter runs. The media also produced the best quality water with the highest removal rate of radium and iron.

Estimating iron and aluminum removal rates in the eastern equatorial Pacific Ocean using a box model approach

Iron limitation plays an important role in maintaining the high-nitrate low-chlorophyll (HNLC) condition in the equatorial upwelling zone. The rate and depth of upwelling control Fe supply to the euphotic zone. This study constrains the transport fluxes and budget of two trace metals, Fe and Al, in the upper ocean. They are co-delivered to the eastern equatorial Pacific surface waters via the Equatorial Undercurrent and upwelling but show distinct biogeochemical cycling processes. We combine the results of the in situ measurements of dissolved Fe and Al (dFe and dAl) with the modeled velocity fields to calculate the physical fluxes. The model calculations are evaluated with the conservation of heat, volume transport, NO 3 and Si(OH) 4 budgets for the equatorial Pacific. The vertical flux due to upwelling provides averaged dFe and dAl supply rates of 1.45 μmol m −2 d −1 and 11.51 μmol m −2 d −1, respectively. The sum of the net physical fluxes in the eastern equatorial Pacific for dFe and dAl are 0.41 μmol m −2 d −1 and 2.77 μmol m −2 d −1, respectively. These estimates are equal to the net biological and chemical removal rates of dFe and dAl. The calculated dFe:C net removal ratio is in the range of 3-9 μmol:mol, which agrees with most other estimates. This suggests that the majority of net dFe removal is due to biological uptake in the upper water column. The results of this box model approach illustrate the usefulness of combining the modeled outputs and in situ measurements, which provide additional constraints on Fe transport and cycling in the equatorial Pacific and possibly other HNLC regions.

Introduction of higher doses of deferasirox: better efficacy but not effective iron removal from the heart and increased risks of serious toxicities

Importance of the field: Thousands of iron loaded patients are using deferasirox, who are not aware of the new, fatal and irreversible serious toxic side effects, the need for prophylaxis and the availability of more effective and less toxic chelation therapies.Areas covered in this review: Updating on efficacy issues in relation to the introduction of higher deferasirox doses and comparison to existing chelation therapies. A new maximum dose of 40 mg/kg/day has been introduced for deferasirox in an attempt to achieve negative iron balance in thalassemia and other transfused iron loaded patients. A marginal increase in cardiac iron removal using doses of 30 – 40 mg/kg/day suggests that the rate of iron removal by deferasirox is insufficient by comparison to the deferiprone/deferoxamine combination, where total and rapid clearance of excess cardiac iron and normalization of the body iron stores could be achieved.What the reader will gain: Identification of drug interactions and new fatal and permanent toxic side effects of deferasirox and implications on efficacy, toxicity and cost of using higher doses. Deferasirox has been identified to cause fatal gastrointestinal hemorrhages, renal tubulopathy, hepatic and renal failure, alopecia and anaphylactic reactions in addition to previously reported fatal or serious toxic side effects such as agranulocytosis, renal and hepatic toxicity, skin rash and gastric intolerance. Interactions with UDP-glucuronosyl transferase inducers, CYP2C8 and CYP3A4 substrates and drugs affecting enterohepatic recycling are likely to affect deferasirox's efficacy and toxicity. Increased toxicity is expected from the use of higher doses of deferasirox and regular prophylactic monitoring is required to avoid fatal and permanent toxicity incidences. The increased costs from higher doses of deferasirox will mostly affect patients living in the developing countries.Take home message: Only few patients may benefit from the introduction of higher doses of deferasirox. There is a need for introducing more effective prophylactic measures. Safer, more effective and less costly chelation treatments are available using deferiprone, deferoxamine and their combination.

Influence of the Microbial Community in the Treatment of Acidic Iron-Rich Water in Aerobic Wetland Mesocosms

ABSTRACT Microbial communities certainly have an influence on the treatment performance of constructed wetlands (CWs); however, microbial community structure or microbial activity (MA) is rarely concurrently or comparatively quantified in relation to treatment performance. The objective of this study was to better understand the influence of the resident CW microbial community on water treatment performance in CWs. Using laboratory-scale mesocosm wetlands, several CW design variables and water chemistry variables were quantitatively and comparatively determined to assess their role in Fe(II) removal from simulated acid mine drainage (AMD). Initial AMD pH, initial AMD Fe(II) concentration, and overall wetland MA had a significant effect on an apparent first-order iron removal rate constant. Under the aerobic conditions used in this study, the presence of Phragmites australis did not have a significant effect on treatment performance. Of all the factors studied, the MA associated with the fixed microbial community had the greatest influence on the rate of iron removal. The presence of a microbiological component was shown to increase the first-order iron removal rate by a factor of 10. Following exposure to AMD, partial detachment of the fixed microbial regime was also observed, highlighting the potential consequences of AMD on the microbial community.

Removal of iron from acidic leach liquor of lateritic nickel ore by goethite precipitate

The separation of high levels of iron from acid leaching liquor is a difficult task, especially in the atmosphere acid leaching process for laterite ore. In this paper the removal of iron by goethite precipitation from the leach liquor of reduced laterites is reported. The goethite precipitation process uses air as oxidation agent, that is, V.M. method, and does not need the pre-reduction of ferric iron since the soluble iron in leach liquor is mainly ferrous ion. The effects of pH value on the rate of iron removal and the loss of nickel to the residue were investigated. It was found the pH value had remarkable influence on the nickel loss during goethite precipitation. By carefully controlling the pH value to less than 2.5 the loss of nickel could be restricted to below 5%. Attempts of recover the nickel lost to the goethite residue through weak acid washing were unsuccessful, suggesting the retention of nickel by the goethite.

The Unique Kinetics of Iron Release from Transferrin: The Role of Receptor, Lobe–Lobe Interactions, and Salt at Endosomal pH

Transferrins are a family of bilobal iron-binding proteins that play the crucial role of binding ferric iron and keeping it in solution, thereby controlling the levels of this important metal. Human serum transferrin (hTF) carries one iron in each of two similar lobes. Understanding the detailed mechanism of iron release from each lobe of hTF during receptor-mediated endocytosis has been extremely challenging because of the active participation of the transferrin receptor (TFR), salt, a chelator, lobe–lobe interactions, and the low pH within the endosome. Our use of authentic monoferric hTF (unable to bind iron in one lobe) or diferric hTF (with iron locked in one lobe) provided distinct kinetic end points, allowing us to bypass many of the previous difficulties. The capture and unambiguous assignment of all kinetic events associated with iron release by stopped-flow spectrofluorimetry, in the presence and in the absence of the TFR, unequivocally establish the decisive role of the TFR in promoting efficient and balanced iron release from both lobes of hTF during one endocytic cycle. For the first time, the four microscopic rate constants required to accurately describe the kinetics of iron removal are reported for hTF with and without the TFR. Specifically, at pH 5.6, the TFR enhances the rate of iron release from the C-lobe (7-fold to 11-fold) and slows the rate of iron release from the N-lobe (6-fold to 15-fold), making them more equivalent and producing an increase in the net rate of iron removal from Fe2hTF. Calculated cooperativity factors, in addition to plots of time-dependent species distributions in the absence and in the presence of the TFR, clearly illustrate the differences. Accurate rate constants for the pH and salt-induced conformational changes in each lobe precisely delineate how delivery of iron within the physiologically relevant time frame of 2 min might be accomplished.

Using Proteins in a Bioinorganic Laboratory Experiment: Iron Loading and Removal from Transferrin

With the increasing availability of metalloproteins it is now possible to incorporate them into bioinorganic laboratory experiments. Thus, we have developed a laboratory experiment where students use UV–vis spectroscopy to determine the rate of iron removal from transferrin by a well-known, commercially-available iron chelating drug, Deferiprone. Students gain experience in both chemical and biological laboratory techniques, while assessing the efficacy of a drug that is physiologically relevant to humans.

Fe (II) and Mn (II) removal from drilled well water: A case study from a biological treatment unit in Harbin

Two parallel pilot-scale biological filters which used manganese sand and silica sand as media respectively were tested for the removal of iron and manganese from drilled well water in Harbin. Iron and manganese oxidizing bacteria were isolated and used as inoculums for filter start-up. Manganese sand filter and silica sand filter can remove 3–6 mg/L of ferrous iron 0.9 mg/L and 0.6 mg/L of manganese respectively under the operation conditions of DO (5 mg/L), pH 7.2, and flow rate 3.9 m/h. The kinetics analysis indicated that the iron removal versus flow rate followed the first-order reaction. This kinetics model also demonstrated that a manganese sand filter had higher removal efficiency than a silica sand filter. Gallionella sp. was found in the backwashing water after 6 months of operation.

Modeling of Iron Removal from Spent Passivation Baths by Ion Exchange in Fixed-Bed Operation

In this work the mathematical model that describes the kinetics of the fixed-bed ion exchange iron separation from chromium(III) passivating baths is presented. Passivation is a common step in the zinc electrodeposition galvanic process. The removal of iron species from the passivation baths allows the extention of their life, thus reducing the amount of waste to be managed and the consumption of raw materials. A commercial chelating resin, Purolite S-957, containing sulfonic and phosphonic acid functional groups was employed. Equilibrium experiments, carried out under isothermal conditions at 20 °C, were correlated to the Freundlich equation, with the following parameters KF ) 25 700((mg (n-1)/n L 1/n )/kgdry_resin) and n ) 2.45. A simple mathematical model assuming a reversible chemical reaction as the rate-controlling step has been developed to describe the fixed-bed iron removal rate in the media solutions under study. The value of the unknown parameter, the rate coefficient for the forward reaction, kd ) 10 660[(mg (n-1)/n L 1/n )/(kgdry_resin h)] was obtained from experimental data of iron uptake employing parameter estimation software. The proposed model offers a satisfactory description of the behavior of the iron loading curves for three different types of real passivation baths under variable feed iron concentration and loading flow rate, using only one estimated parameter.

English

At the 2008 ASMR conference, data from the initial two months of operation of a U.S. EPA pilot biochemical reactor (BCR) was reported. The BCR was designed and constructed in August, 2007 to treat mining influenced water (MIW) emanating from an adit at a remote site in southern Colorado. The original objective of the study was to operate and monitor a BCR on a year-round basis in a harsh mountain environment. In the second year, a pilot chitin reactor was constructed for manganese removal. The treatment results from 13 months of BCR operation and 2 months of chitin reactor are presented. The treatment goal for the two pilot reactors was to determine compliance with the applicable surface water quality standards for the State of Colorado. Several attributes of the treatment and monitoring system were unique. It was constructed at an elevation of 11,000 feet a.m.s.l. (3,353 meters), was designed to operate year-round, and was totally passive, using solar energy for the monitoring system and pump power. Due to the site being inaccessible during winter months, this remote monitoring system was designed to collect samples and monitor field variables through the winter months. Field variables were measured and stored by Hydrolab™ sondes. Influent and effluent water quality samples were collected and stored in Teledyne™ ISCO™ 6712 samplers. For the first year of operation, the field variable data were transmitted via Stratolink™ satellite communicators. Due to operational issues, the Stratolink™ units were replaced with satellite phones in September 2008. The contaminants of concern (COCs) in the MIW are cadmium, copper, iron, lead, manganese, and zinc. BCR metal removal rates averaged approximately 98% over the first year of operation for cadmium, copper, lead, and zinc. Despite these high removal rates, the BCR effluent exceeded the applicable water quality standards for cadmium, lead, and zinc. Iron and manganese removal rates varied over the first year of BCR operation and were not sufficient to achieve the applicable water quality standards. The removal of manganese by the chitin reactor was inconsistent with an average percent removal rate of 23% over the first two months of operation. Since data are limited on biochemical and chitin reactors operating in elevated and harsh winter locations, the acquired data are unique for MIW remediation. Additional Keywords: ARD, MIW, biochemical reactor, BCR, sulfate reducing bioreactor, SRB, chitorem® BCR , chitin, satellite data transmission, heavy metals remediation, passive treatment, Green Remediation

Recovery of Copper from Acid Mine Drainage by an Integrated Sulphate Reducing Process

An integrated sulfate reducing process was used to treat Acid Mine Drainage with high concentrations of Cu2+, Fe and SO42-. The water treatment system integrated a sulfidogenic UASB bioreactor with a precipitation reactor which was used to recover copper. Sodium lactate was used as energy source. The effective volume of the UASB reactor was 2 L and the hydraulic retention time was 12.57h. In the sulphate removal reactor, sulphate was removed from 21160 to 195 mg/L with a rate of 4427.8 mg/L/d. Cu2+ and Fe was removed by biologically generated S2- and OH- from 360 and 6520 to 0.049 mg/L and less than 10 mg/L respectively. The average COD, copper and iron removal rate was 2523.2, 15.21 and 274.98 mg/L/d separately. The effluent pH reached 6.0-7.0. The results showed potential usage of this bioreactor in treating Acid Mine Drainage.

Determination of Hydraulic Residence Times in Several UK Mine Water Treatment Systems and their Relationship to Iron Removal

In the UK, the Coal Authority has more than 40 mine water treatment systems, most of which are wetland systems with settlement lagoon pretreatment. The purpose of treatment in wetlands is the oxidation of ferrous to ferric iron and the subsequent hydrolysis and precipitation of ferric hydroxide within the wetland. It is generally accepted (Hedin et al., Passive treatment of coal mine drainage, 1994, p 35; Skousen and Ziemkiewicz, Acid mine drainage control and treatment, 1996, p 362; Younger et al., Mine water: hydrology, pollution, remediation, 2002, p 442) that this process proceeds by a first-order rate law, although most systems are designed based on an areal removal rate (10 g/m2/day) developed by the U.S. Bureau of Mines (Hedin et al., Passive treatment of coal mine drainage, 1994, p 35); this design guideline inherently assumes a constant removal rate. Given the actual kinetics of iron removal in wetlands, it follows that residence time will control iron removal; given the wide range of system geometries and aspects, it is logical to ascertain the actual hydraulic residence time of wetlands and settlement lagoons and determine the effect this has on iron removal. To make a preliminary assessment of this link, hydraulic residence time of two Coal Authority wetlands (Lambley and Whittle) and two Coal Authority settlement lagoons (Acomb East, Acomb West and Whittle) were measured using bromide tracer tests. Water samples for iron analysis and flow measurements were taken during each tracer test. The Lambley wetland performs well in terms of residence time, and, as reeds become established and adsorptive processes increase, its iron removal performance (currently 58% removal) may improve, but the low influent iron concentration appears to be a significant impediment to meeting the original performance target. In contrast, the hydraulic performance of the Whittle wetland system is poor, which appears to be due to accumulation of dead plant material coupled with a high length to width ratio. However, performance in terms of iron removal is good (92% removal), which appears to be due to the higher influent iron concentration, and especially the fact that the iron enters the wetland largely in particulate form. The longer residence time of water within the Acomb lagoons (≈12 h) resulted in far more effective iron removal (72% in the east lagoon and 85% in the west lagoon) than the shorter residence time at Whittle (24% iron removal, ≈5 h residence time). Performance (in terms of iron removal) of the settlement lagoon systems appears to be far more closely related to the hydraulic residence time (albeit this conclusion must be tentative, given that only three systems have been investigated, and the Acomb system receives chemical addition). Based on this study, treatment system sizing using 100 m2 lagoon area per 1 L/s flow appears to be a more appropriate basis for design rather than an areal iron removal rate.

Ferritin Contains Less Iron (59Fe) in Cells When the Protein Pores Are Unfolded by Mutation

Ferric minerals in ferritins are protected from cytoplasmic reductants and Fe2+ release by the protein nanocage until iron need is signaled. Deletion of ferritin genes is lethal; two critical ferritin functions are concentrating iron and oxidant protection (consuming cytoplasmic iron and oxygen in the mineral). In solution, opening/closing (gating) of eight ferritin protein pores controls reactions between external reductant and the ferritin mineral; pore gating is altered by mutation, low heat, and physiological urea (1 mm) and monitored by CD spectroscopy, protein crystallography, and Fe2+ release rates. To study the effects of a ferritin pore gating mutation in living cells, we cloned/expressed human ferritin H and H L138P, homologous to the frog open pore model that was unexpressable in human cells. Human ferritin H L138P behaved like the open pore ferritin model in vitro as follows: (i) normal protein cage assembly and mineralization, (ii) increased iron release (t1/2) decreased 17-fold), and (iii) decreased alpha-helix (8%). Overexpression (> 4-fold), in HeLa cells, showed for ferritin H L138P equal protein expression and total cell 59Fe but increased chelatable iron, 16%, p < 0.01 (59Fe in the deferoxamine-containing medium), and decreased 59Fe in ferritin, 28%, p < 0.01, compared with wild type. The coincidence of decreased 59Fe in open pore ferritin with increased chelatable 59Fe in cells expressing the ferritin open pore mutation suggests that ferritin pore gating influences to the amount of iron (59Fe) in ferritin in vivo.

Gated pore mutation affects ferritin iron in vivo

Ferritins, spherical protein cages, concentrate iron and oxidants as ferric oxy biominerals. Eight pores, formed by junctions of three subunits, have crucial roles in iron removal from ferritin minerals based on the coincidence of pore unfolding (X‐ray crystallography, CD spectroscopy in mutant and wild type proteins) and changes in iron removal rates in frog model ferritins. Sequence similarity between human and frog ferritins is 65%, but quaternary structure and pore gates are the same. To examine the effects of pore mutations in human cell lines we made the analogous mutation in human H ferritin: L138P (L134P in horse/frog numbering). We observed, as in the frog mutant, there was no effect on cage assembly (gel filtration), and the initial rate of Fe removal from the mineral was faster (4.9‐fold, P&lt;0.01), with 50% Fe removed from L138P in 2.2 min vs. 46.6 min from the wild type (WT). To study the pores in vivo, HeLa cells were transiently transfected with plasmids encoding H‐WT or H‐L138P ferritin, with comparable increases in ferritin protein (8 fold). When the retention of Fe in ferritin (cpm/ng ferritin protein) was compared, using cells incubated two hours with 59Fe‐transferrin, H‐L138P had only 25% (P&lt;0.01) as much 59Fe as WT; the background used was 59Fe in endogenous ferritin (mock transfection). The data on ferritin pores in cultured cells, together with a study identifying a ferritin binding peptide with effects similar to L134 mutation in vitro, (Liu et al, JBC, 282:31821), suggest that cytoplasmic factors regulate recovery of iron from ferritin in vivo by pore folding/unfolding. Part support (NIH Grant DK20251).

Kinetics of Iron (II) Removal from Aqueous Solution Using Activated Dolomite

Experimental investigations were undertaken in batch kinetic systems, for the removal of iron (II) from aqueous solutions using activated dolomite. The effect of the extent dolomite activation on the dissolution of magnesium and calcium from the dolomite lattice was determined. Under optimum experimental conditions there was a direct linear relationship between magnesium dissolution and iron (II) removal from bulk solution. The experimental data were mathematically described using empirical external mass transfer and pseudo-intra-particle diffusion models. The data show conformity with a three stage process, with the iron (II) removal rate showing good correlation with external mass transfer (t &lt; 1 min) and two rates of pseudo-intra-particle diffusion (1 &lt; t &lt; 90mins, and t &lt; 90mins).

Terephthalamide-containing ligands: fast removal of iron from transferrin

The mechanism and effectiveness of iron removal from transferrin by three series of new potential therapeutic iron sequestering agents have been analyzed with regard to the structures of the chelators. All compounds are hexadentate ligands composed of a systematically varied combination of methyl-3,2-hydroxypyridinone (Me-3,2-HOPO) and 2,3-dihydroxyterephthalamide (TAM) binding units linked to a polyamine scaffold through amide linkers; each series is based on a specific backbone: tris(2-aminoethyl)amine, spermidine, or 5-LIO(TAM), where 5-LIO is 2-(2-aminoethoxy)ethylamine. Rates of iron removal from transferrin were determined spectrophotometrically for the ten ligands, which all efficiently acquire ferric ion from diferric transferrin with a hyperbolic dependence on ligand concentration (saturation kinetics). The effect of the two iron-binding subunits Me-3,2-HOPO and TAM and of the scaffold structures on iron removal ability is discussed. At the low concentrations corresponding to therapeutic dose, TAM-containing ligands exhibit the fastest rates of iron removal, which correlates with their high affinity for ferric ion and suggests the insertion of such binding units into future therapeutic chelating agents. In addition, urea polyacrylamide gel electrophoresis was used to measure the individual microscopic rates of iron removal from the three iron-bound transferrin species (diferric transferrin, N-terminal monoferric transferrin, C-terminal monoferric transferrin) by the representative chelators 5-LIO(Me-3,2-HOPO)(2)(TAM) and 5-LIO(TAMmeg)(2)(TAM), where TAMmeg is 2,3-dihydroxy-1-(methoxyethylcarbamoyl)terephthalamide. Both ligands show preferential removal from the C-terminal site of the iron-binding protein. However, cooperative effects between the two binding sites differ with the chelator. Replacement of hydroxypyridinone moieties by terephthalamide groups renders the N-terminal site more accessible to the ligand and may represent an advantage for iron chelation therapy.

Influence of Chelators on Iron Solubilization from Quartz and Feldspars by Bioleaching

Ultra-fine iron particles are difficult to treat by conventional mineral processing methods. Thus bioleaching is an attractive alternative for effective removal of iron minerals. The removal of oxidic Fe-phases from industrial silicates via bioleaching needs to be optimized with regard to the rate of iron reduction and dissolution. A new role for chelators as the low addition of AQDS or NTA during bacterial quality improvement of non-metallics, resulted in stimulating of Fe dissolution under non-controlled anaerobic conditions. AQDS stimulated bacterial iron reduction and Fe2+ concentration in solution was higher than Fe3+. However, NTA non-stimulated iron reduction, but increased bacterial iron dissolution in form of Fe3+. Changes in iron removal from samples were used to assess the chelator effectiveness of the heterotrophic bioleaching process. Chelators might be added to iron-contaminated non-metallics during bioleaching processes for stimulation of rate of iron removal.