Iron Citrate Complexes Research Articles

The Direct Formation of an Iron Citrate Complex Using a Metallurgical Slag as an Iron Source for Micropollutant Removal via the Photo-Fenton Process

The Direct Formation of an Iron Citrate Complex Using a Metallurgical Slag as an Iron Source for Micropollutant Removal via the Photo-Fenton Process

Enhanced activation of sulfite by the iron-citrate complexes under NUV irradiation for metronidazole degradation: Kinetic, degradation mechanism and efficiency in real water

In the present study, a novel approach for the elimination of emerging pollutants through an advanced oxidation process has been developed by combining near ultraviolet (NUV) irradiation with an iron-citrate complex (Fe(III)-Cit) to overcome the defects of the traditional Fe(III)/sulfite system and enhance the activation of sulfite in a neutral aqueous solution. The performance of this system was studied using metronidazole (MTZ) as the target pollutant, and the impact of operational conditions such as initial pH, Fe(III)-Cit complex concentration, sulfite dose, metronidazole concentration and dissolved oxygen were studied. The rate constant of MTZ degradation at natural pH (7.0 ± 0.2) by the Fe(III)-Cit/sulfite/NUV system is over 12.72-times and 13.25-times higher than the sulfite/NUV and Fe(III)-Cit/NUV individual binary systems. The effectiveness of the system was further examined in various real water matrices. The latter proved to be effective in the following order: groundwater > ultra-pure water > > seawater, revealing that it was very effective in the former. Chemical probe experiments indicated that sulfate radicals and hydroxyl radicals were the principal reactive oxygen species involved in the photodegradation of MTZ. Additionally, dissolved oxygen played a crucial role in the reaction. MTZ degradation products were determined by HPLC/MS, leading to the identification of nine different by-products and the proposal of possible degradation pathways. Although further studies are required to better understand this system, this work paves the way for the application of activated sulfite-based processes for environmental remediation without pH adjustment, offering an alternative to the use of conventional oxidants.

Revealing the nuclearity of iron citrate complexes at biologically relevant conditions

Citric acid plays an ubiquitous role in the complexation of essential metals like iron and thus it has a key function making them biologically available. For this, iron(III) citrate complexes are considered among the most significant coordinated forms of ferric iron that take place in biochemical processes of all living organisms. Although these systems hold great biological relevance, their coordination chemistry has not been fully elucidated yet. The current study aimed to investigate the speciation of iron(III) citrate using Mössbauer and electron paramagnetic resonance spectroscopies. Our aim was to gain insights into the structure and nuclearity of the complexes depending on the pH and iron to citrate ratio. By applying the frozen solution technique, the results obtained directly reflect the iron speciation present in the aqueous solution. At 1:1 iron:citrate molar ratio, polynuclear species prevailed forming most probably a trinuclear structure. In the case of citrate excess, the coexistence of several monoiron species with different coordination environments was confirmed. The stability of the polynuclear complexes was checked in the presence of organic solvents.

Ingredient photostability as affected by iron: Colorant degradation

Understanding factors that affect food chemical stability is important for optimizing product quality and shelf life. The objective of this project was to investigate the role of iron and ultraviolet (UV) light on chemical stability by determining the degradation rate constants of Brilliant Blue, tartrazine, and Allura Red in pH 3 solutions of various compositions stored in the presence and absence of UV light. The storage of solutions in darkness at 30°C resulted in no observable loss of any colorant. Exposure to UV light significantly (p < .05) increased the degradation rate constants. Colorant degradation was fastest in the presence of citrate, iron, and UV light. Iron–citrate complexes are likely forming hydroxyl radicals upon UV exposure, which enhance colorant degradation. Photodegradation of food ingredients increases in the presence of iron and citrate buffer, resulting in a loss of shelf life. Practical applications The adverse effect of UV light on food chemical stability is enhanced by the presence of iron. Solutions containing iron and citrate buffer become decolorized rapidly when exposed to UV light. Thus, beverages packaged in light-permeable materials should not contain iron as a contaminant. Beverages fortified with iron should be placed in light-protective packaging to improve the storage stability of colorants and other ingredients.

Facile green synthesis of magnetic Fe3C@C nanocomposite using natural magnetite

One simple and environmental friendly synthesis strategy for preparing low-cost magnetic Fe3C@C materials has been facilely developed using a modified sol-gel approach, wherein natural magnetite acted as the iron source. A chelating polycarboxylic acid such as citric acid (CA) was employed as the carbon source, and it dissolved Fe very effectively, Fe3O4 and natural magnetite to composite an iron-citrate complex with the assistance of ammonium hydroxide. The core-shell structure of the as-prepared nanocomposites was formed directly by high-temperature pyrolysis. The Fe3C@C materials exhibited superparamagnetic properties (38.09 emu/mg), suggesting potential applications in biomedicine, environment, absorption, catalysis, etc.

Electrodeposition of Nanocrystalline Fe—W Coatings from a Citrate Bath

The electrode processes occurring during electrodeposition of nanocrystalline Fe-W alloy coatings from a citrate bath containing iron(II) sulfate and a tungstate (pH 6.9; 80°C, graphite anode) are studied by cyclic voltammetry. The current efficiency of alloy electrodeposition is up to 30%, if the applied current density is confined to the range of 2–5 A/dm2. The limitation on range of applied current densities is twofold: the lower limit is dictated by the diffusion-limited current density due to the reduction of the oxidized form of iron-citrate complex that forms at the bath preparation stage as a result of oxidation of Fe(II) species in a citrate solution; while the upper limit is imposed by the occurrence of side reactions such as the hydrogen evolution reaction and/or reduction of organic components of the bath. The use of an iron anode seems to be promising in this deposition process (the current efficiency of anodic dissolution of Fe in this bath is 93 ± 2%). The deposited coatings contain ~25 at % tungsten and their microhardness (which can be up to 900 kgF/mm2) depends on the volume current density. The studied system holds promise for application in mask-free localized electrodeposition.

Wavelength dependence of the efficiency of photocatalytic processes for water treatment

The main objective of this work is to present a novel approach to evaluate quantitatively the action spectra and energy efficiency for chemical oxidation and bacterial inactivation of photocatalytic processes using monochromatic LED sources. Two different catalysts with different absorption spectra (TiO2 and iron citrate complex) were used. In all cases, it was confirmed a direct relationship between the absorption spectrum of the catalyst and the spectral dependence of the photonic efficiency. The best alternative for TiO2 processes in terms of energy consumption when using artificial lighting is the use of 365nm. In contrast, for iron complexes it seems more economically feasible the use of longer wavelengths close to the visible range, because the lower absorption of the complex is counterbalanced by the higher energy efficiency of the LED devices. This can be obviously extrapolated to the use of sunlight, where the use of iron-based photocatalytic processes can harvest a higher fraction of the available light. Predictions of the process efficiency under solar irradiation based on the action spectra determined with LED at laboratory scale have been successfully validated by experimental data. The methodology proposed in this work could be easily extrapolated to other wavelength ranges required by novel catalysts or efficient short wavelength monochromatic LED sources available in the future.

111 - Early Administration of an NO Spin Trap Shortens the Survival and Reduces NO Production in Septic- Shocked Rat

The role of nitric oxide (NO) in shock depends on its evolution. It seems that an early NO increment compensates for systemic vasoconstriction whereas a late massive production participates in vasoplegia. NO spin traps are used to form short life time adducts with NO, and evidence for NO by electron paramagnetic resonance. The goal of this study was to evaluate the early administration of sodium diethyldithiocarbamate (DETC, an NO spin trap) on survival and NO production in septic shock. Septic shock was induced in Male Wistar rats through the iv administration of lipopolysaccharide (LPS, 5 mg/Kg). To assess their survival the animals were divided into two groups (n=6) which were treated at exactly the same time as the LPS with either: 1) Isotonic saline solution (ISS, 600 µl ip, and 600 µl sc) or 2) DETC (500 mg/Kg, diluted in 600 µl of ISS, ip) and iron citrate complex (iron sulfate and sodium citrate diluted in 600 µl of ISS, sc). Survival times were recorded and differences evaluated by the Mantel Cox Test. Two more groups (the same treatments as above) were used to measure NO2/NO3 ions (indirect NO measurement, modified Griess reaction) in arterial blood samples (1ml, replaced with 3ml of Hartman solution) before (time 0) and after (1, 2 and 6 h) LPS. The animals were sacrificed by anesthesia overdose after the last blood sample was taken. Differences were evaluated by two way ANOVA testing. Survival was significantly shorter (p=0.01) and NO2/NO3 concentration was significantly smaller (p This study was supported by CONACYT 216184 and 225115 Grants.

Photo-Fenton degradation of the pharmaceuticals ciprofloxacin and fluoxetine after anaerobic pre-treatment of hospital effluent.

This work evaluated the photo-Fenton degradation of two pharmaceuticals extensively used in human medicine, ciprofloxacin (CIP), and fluoxetine (FLU) when present in an anaerobic pre-treated hospital effluent (HE) at low concentration (100μgL-1). Operational parameters such as concentration of hydrogen peroxide, iron, and initial pH as well as the effect of iron citrate complex were evaluated considering the degradation of the pharmaceuticals. Iron citrate complex (Fecit) influenced significantly FLU degradation at pH 4.5 achieving 80% after 20min, while with iron nitrate only 36% degradation was obtained after the same time. However, only a slight effect was observed on CIP degradation, achieving 86% with Fecit and 75% with Fe(NO3)3, after 20min. Samples of HE used in this work were previously treated in an anaerobic reactor followed by sand filtration; however, the presence of pharmaceuticals was detected. Degradation of both FLU and CIP was significantly hindered when present in HE, due to the relatively high content of organic (39.6mgL-1) and inorganic (12.5mgL-1) carbon, which may have consumed ·OH in side reactions. However, the iron cycle reduction was not affected by the matrix in the presence of citrate. Despite the recalcitrance of the matrix (no total organic carbon removal), it was possible to achieve over 50% degradation of both pharmaceuticals after 90min.

Bacterial inactivation with iron citrate complex: A new source of dissolved iron in solar photo-Fenton process at near-neutral and alkaline pH

This study reports the first application of Fe–citrate-based photo-Fenton chemistry for the inactivation of Escherichia coli. Promising results of bacterial inactivation at near-neutral and alkaline pH conditions were obtained, while using low iron concentration (Fe–citrate concentration: 0.6mg/L, relative to the Fe content) and avoiding precipitation of ferric hydroxides. The effects of the solution pH and Fe–citrate complex concentration on E. coli inactivation during the photo-Fenton reaction were investigated. The efficiency of the homogeneous photo-Fenton process using Fe–citrate complex as a source of iron strongly improved bacterial inactivation as compared with the heterogeneous photo-Fenton treatment (FeSO4 and goethite as sources of iron) at near-neutral pH. The bacterial inactivation rate increased in the order of goethite<FeSO4<Fe–citrate, which agreed well with the trend for the HO radical formation, monitored by ESR. Encouraging results were also obtained while applying this treatment for bacterial inactivation in natural water samples from Lake Geneva (Switzerland) at pH 8.5, since no bacterial reactivation and/or growth were observed after photo-Fenton treatment. This type of application is promising, considering the simplicity of the installations and procedures, the ability to use the Sun as the light source, and the safety of all of the chemicals in this system.

Redox Properties and Activity of Iron–Citrate Complexes: Evidence for Redox Cycling

Iron in iron overload disease is present as non-transferrin-bound iron, consisting of iron, citrate, and albumin. We investigated the redox properties of iron citrate by electrochemistry, by the kinetics of its reaction with ascorbate, by ESR, and by analyzing the products of reactions of ascorbate with iron citrate complexes in the presence of H2O2 with 4-hydroxybenzoic acid as a reporter molecule for hydroxylation. We report -0.03 V < E°' > +0.01 V for the (Fe(3+)-cit/Fe(2+)-cit) couple. The first step in the reaction of iron citrate with ascorbate is the rapid formation of mixed complexes of iron with citrate and ascorbate, followed by slow reduction to Fe(2+)-citrate with k = ca. 3 M(-1) s(-1). The ascorbyl radical is formed by iron citrate oxidation of Hasc(-) with k = ca. 0.02 M(-1) s(-1); the majority of the ascorbyl radical formed is sequestered by complexation with iron and remains EPR silent. The hydroxylation of 4-hydroxybenzoic acid driven by the Fenton reduction of iron citrate by ascorbate in the presence of H2O2 proceeds in three phases: the first phase, which is independent of the presence of O2, is revealed as a nonzero intercept that reflects the rapid reaction of accumulated Fe(2+) with H2O2; the intermediate oxygen-dependent phase fits a first-order accumulation of product with k = 5 M(-1) s(-1) under aerobic and k = 13 M(-1) s(-1) under anaerobic conditions; the slope of the final linear phase is ca. k = 5 × 10(-2) M(-1) s(-1) under both aerobic and anaerobic conditions. Product yields under aerobic conditions are greater than predicted from the initial concentration of iron, but they are less than predicted for continuous redox cycling in the presence of excess ascorbate. The ongoing formation of hydroxylated product supports slow redox cycling by iron citrate. Thus, when H2O2 is available, iron-citrate complexes may contribute to pathophysiological manifestations of iron overload diseases.

Combination of photocatalytic and photoelectro-Fenton/citrate processes for dye degradation using immobilized N-doped TiO2 nanoparticles and a cathode with carbon nanotubes: Central composite design optimization

In this report, commercial TiO2 nanoparticles were doped with nitrogen by a manual grinding method using urea. The prepared catalyst was characterized by X-ray diffraction (XRD), diffuse reflectance spectra (DRS), and transmission electron microscopy (TEM). N-doped TiO2 was immobilized on ceramic plates by methyl tri-methoxy silane. Next, multi-walled carbon nanotubes (CNTs) were stabilized on carbon paper to fabricate the cathode. Scanning electron microscopy (SEM) was employed to confirm stabilization of the CNTs. The prepared cathode and immobilized catalyst were utilized for the degradation of C.I. Direct Red 23 (DR23) by the photoelectro-Fenton (PEF) process in the presence of citrate (Cit) combined with a photocatalytic process. The coupled PEF/Cit/N-TiO2 process could be performed under visible light, not only due to the formation of iron–citrate complexes, but also because of the incorporation of nitrogen to the crystalline structure of TiO2 and the generation of TiO2 complexes with electrogenerated H2O2. Results demonstrated that the degradation efficiency of DR23 (20mg/L) using the identical operational conditions, followed a decreasing order of: PEF/Cit/N-TiO2>PEF/Cit>PEF>EF>N-TiO2. Eventually, a model was developed by the central composite design (CCD) method, describing the degradation efficiency as a function of the operational parameters.

Yeast Stress, Aging, and Death

Yeast Stress, Aging, and Death

One-step synthesis of yttrium orthoferrite nanocrystals via sol–gel auto-combustion and their structural and magnetic characteristics

Single phase yttrium orthoferrite (YFeO3) nanocrystals have been one-step synthesized by a sol–gel auto-combustion method using nitrates of iron and yttrium as raw materials, citrate acid (CA) and ethylene glycol (EG) as chelating agents and nitrate ammonium as oxidant. The effects of CA/M and the pH value of the solutions on the concentrations of yttrium– and iron–citrate complex species were quantitatively studied to ensure the formation of chemically homogenous gels. The auto-combustion of the dried gels and the microstructural features and magnetic properties of as-synthesized YFeO3 nanocrystals were characterized and investigated by using XRD, FT-IR, TG-DTA, FESEM and VSM. It has been shown that a hexagonal YFeO3 can be formed during the auto-combustion of gels with CA/M = 1.5, EG/CA = 1.5, pH = 6.0 and Q = 35%, the molar ratio of the oxygen available from nitrates (NO3−) to the oxygen required for complete oxidation of fuels to CO2, H2O and N2, while single phase orthorhombic YFeO3 nanocrystals of ∼90 nm in average diameter may be one-step synthesized from the gels with Q = 80%, and show an enhanced weak ferromagnetism characterized with a RT magnetization of 0.45 emu g−1 at the magnetic field 0.35T, a paramagnetism with the susceptibility χ = 2.27 × 10−5 emu g−1 Oe−1, and an extremely low coercive field of 245 Oe.

Low temperature and in-field Mössbauer spectroscopic studies of ε-Fe3N particles synthesized from iron–citrate complex

The Mössbauer spectra of ε-Fe3N at 5 K show several sextets which indicate a disordered arrangement of nitrogen atoms. Even though the 5 K spectra hints out a distribution for the Fe atoms coordinated with two nitrogen atoms (Fe(II)), the in-field spectrum showed that the Fe(II) atoms are magnetically different. It is found that the arrangements of magnetic spins with the direction of easy magnetic axis are different for the two Fe(II) sites. In addition to this, the presence of an antiferromagnetic phase is revealed in an in-field Mössbauer spectrum at 5 K.

Sulfate radical-based ferrous–peroxymonosulfate oxidative system for PCBs degradation in aqueous and sediment systems

Polychlorinated biphenyls (PCBs) in the environment pose long-term risk to public health because of their persistent and toxic nature. This study investigates the degradation of PCBs using sulfate radical-based advanced oxidation processes (SR-AOPs). These processes are based on the generation of sulfate radicals through iron (Fe(II), Fe(III)) mediated activation of peroxymonosulfate (KHSO5, PMS) or persulfate (Na2S2O8, PS). This study is the first instance for coupling of Fe(II)/Fe(III) with PMS for PCB degradation in aqueous and sediment systems. The high oxidation efficiencies of the free radicals (SO4−), in combination with the slow rate of consumption of the oxidants, make these processes very effective for the degradation of recalcitrant organic compounds. The effectiveness of the process was evaluated based on the degradation of a model polychlorinated biphenyl, 2-chlorobiphenyl and total organic carbon (TOC) removal. The kinetics of 2-chlorobiphenyl degradation along with the effect of oxidant and catalyst concentrations on the degradation efficiency was studied. Near complete removal of 2-chlorobiphenyl was observed when Fe(II) was used with PMS or PS. Fe(II) acts as a sulfate radical scavenger at higher concentrations indicating that there is an optimum concentration of Fe(II) that leads to most effective degradation of the target contaminant. A chelating agent, sodium citrate, was used to control the quantity of iron in the solution for activation of the oxidant. For the first time, we studied the feasibility of the activation of PMS using iron citrate complexes for PCB degradation. In the presence of sodium citrate, increase in degradation efficiency was observed up to a metal:ligand ratio of 1:2, after which the increase in citrate concentration led to a decrease in removal efficiency. Fe(II)/PMS systems were found to be very effective in degrading PCB in a sediment-slurry system with more than 90% PCB removal being observed within 24h.

Nature of non-transferrin-bound iron: studies on iron citrate complexes and thalassemic sera

Despite its importance in iron-overload diseases, little is known about the composition of plasma non-transferrin-bound iron (NTBI). Using 30-kDa ultrafiltration, plasma from thalassemic patients consisted of both filterable and non-filterable NTBI, the filterable fraction representing less than 10% NTBI. Low filterability could result from protein binding or NTBI species exceeding 30 kDa. The properties of iron citrate and its interaction with albumin were therefore investigated, as these represent likely NTBI species. Iron permeated 5- or 12-kDa ultrafiltration units completely when complexes were freshly prepared and citrate exceeded iron by tenfold, whereas with 30-kDa ultrafiltration units, permeation approached 100% at all molar ratios. A g = 4.3 electron paramagnetic resonance signal, characteristic of mononuclear iron, was detectable only with iron-to-citrate ratios above 1:100. The ability of both desferrioxamine and 1,2-dimethyl-3-hydroxypyridin-4-one to chelate iron in iron citrate complexes also increased with increasing ratios of citrate to iron. Incremental molar excesses of citrate thus favour the progressive appearance of chelatable lower molecular weight iron oligomers, dimers and ultimately monomers. Filtration of iron citrate in the presence of albumin showed substantial binding to albumin across a wide range of iron-to-citrate ratios and also increased accessibility of iron to chelators, reflecting a shift towards smaller oligomeric species. However, in vitro experiments using immunodepletion or absorption of albumin to Cibacron blue-Sepharose indicate that iron is only loosely bound in iron citrate-albumin complexes and that NTBI is unlikely to be albumin-bound to any significant extent in thalassemic sera.

Iron-citrate complexes and free radicals generation: Is citric acid an innocent additive in foods and drinks?

The generation of free radicals (Fenton chemistry) from various iron citrate complexes has been studied. Spin trapping methods have been used. The results can question concerning the innocence of added citric acid in foods and cold drinks. We concluded that in absence of pathological situation citric acid is probably not dangerous but it may become dangerous in situation of oxidative stress and/or iron overload.

Photodegradation of a ternary iron(III)-uranium(VI)-citric acid complex.

The mechanisms of photodegradation of binary iron- and uranium-citrate and ternary iron-uranium-citrate complexes were elucidated. Citric acid degradation products were identified by HPLC and GC, and the metal precipitates were identified by XRD and EXAFS. Photodegradation of a binuclear iron-citrate complex occurred as a result of two one-electron oxidations of citric acid with the formation of 3-oxoglutarate and two ferrous ions. The ferrous ions were reoxidized by a photo-Fenton reaction, resulting in the precipitation of iron as two-line ferrihydrite Fe(OH)3. The citric acid in the uranium-citrate complex underwent a two-electron oxidation to acetoacetate with the concomitant reduction of U(VI) to U(IV). The U(IV) was subsequently photooxidized in the presence of dioxygen with precipitation of uranium as the mineral schoepite (UO3 x 2H2O). A two-step electron reduction of two ferric ions to two ferrous ions wasthe primary mechanism for photodegradation of the ternary iron-uranium-citrate complex with oxidation of citric acid to 3-oxoglutarate; reduction of uranium was not observed. The iron precipitated as ferrihydrite and the uranyl ion as a uranyl hydroxide species. These results show the potential application of photochemical treatment of wastewater and decontamination solutions containing binary and ternary iron- and uranium-citrate complexes.

Complexation of iron(III) and iron(II) by citrate. Implications for iron speciation in blood plasma

Estimates of the concentrations and identity of the predominant complexes of iron with the low-molecular-mass ligands in vivo are important to improve current understanding of the metabolism of this trace element. These estimates require a knowledge of the stability of the iron–citrate complexes. Previous studies on the equilibrium properties of the Fe(III)–citrate and Fe(II)–citrate are in disagreement. Accordingly, in this work, glass electrode potentiometric titrations have been used to re-determine the formation constants of both the Fe(III)– and Fe(II)–citrate systems at 25 °C in 1.00 M (Na)Cl and the reliability of these constants has been evaluated by comparing the measured and predicted redox potentials of the ternary Fe(III)–Fe(II)–citrate system. The formation constants obtained in this way were used in computer simulation models of the low-molecular-mass iron fraction in blood plasma. Redox equilibria of iron are thus included in large models of blood plasma for the first time. The results of these calculations show the predominance of Fe(II)–carbonate complexes and a significant amount of aquated Fe(II) in human blood plasma.