In The Iron Research Articles

Metagenomic profiling of raw wastewater in Portugal highlights microbiota and resistome signatures of public health interest beyond the usual suspects

In response to the rapid emergence and dissemination of antimicrobial resistant bacteria (ARB) and genes (ARGs), integrated surveillance systems are needed to address antimicrobial resistance (AMR) within the One Health Era. Wastewater analyses enable biomarker monitoring at the sewershed level, offering timely insights into pathogen circulation and ARB/ARGs trends originating from different compartments. During two consecutive epidemic waves of the COVID-19 pandemic in Portugal, taxonomic and functional composition of raw urban wastewater from two wastewater treatment plants (WWTPs) representing one million in equivalent population, located in the main urban areas of the country, were profiled by shotgun metagenomics. Hospital wastewater from two central hospitals located in the WWTPs catchment areas were also sequenced. The resistome and virulome were profiled using metagenomic assemblies without taxonomic constraint, and then specifically characterized for ESKAPE pathogens.Urban and hospital wastewater exhibited specific microbiota signatures, Pseudomonadota dominated in the first and Bacteroidota in the latter. Correlation network analyses highlighted 85 (out of top 100) genera co-occurring across samples. The most frequent ARGs were classified in the multidrug, tetracyclines, and Macrolides, Lincosamides, Streptogramins (MLS) classes. Links established between AMR determinants and bacterial hosts evidenced that the diversity and abundance of ARGs is not restricted to ESKAPE, being also highly predominant among emergent enteropathogens, like Aeromonas and Aliarcobacter, or in the iron (II) oxidizer Acidovorax. The Aliarcobacter genus accumulated high abundance of sulphonamides and polymyxins ARGs, while Acinetobacter and Aeromonas hosted the highest abundance of ARGs against beta-lactams. Other bacteria (e.g. Clostridioides, Francisella, Vibrio cholerae) and genes (e.g. vanA-type vancomycin resistance) of public health interest were detected, with targeted monitoring efforts being needed to establish informative baseline data. Altogether, results highlight that wastewater monitoring is a valuable component of pathogen and AMR surveillance in healthy populations, providing a community-representative snapshot of public health trends beyond priority pathogens.

An electrochemical method for the regeneration of trivalent iron to increase the efficiency of in-situ leaching of uranium

Due to the increasing demand for electricity with the development of production and general infrastructure, increasing the production of uranium as an economically and environmentally efficient source of energy is an urgent problem. The purpose of this study is to develop an electrochemical method for the regeneration of iron (III) ions used as a uranium oxidizer in the process of in-situ leaching of uranium minerals with sulfuric acid solutions. Methods. The mechanism of reactions in the iron (II)-iron (III) redox system was studied by recording potentiodynamic polarization curves and conducting electrolysis of the oxidation of divalent iron ions under galvanostatic conditions. Results and discussion. Cathode-anodic and anodic-cathode cyclic polarization curves taken on platinum electrodes showed that the redox reactions of iron ions are reversible and these reactions occur at a slight overvoltage. The influence of the main electrochemical parameters (current density, concentrations of iron (II) ions and sulfuric acid) on the oxidation of divalent iron ions was studied for the first time using granular anode electrodes, the electrode spaces of which are separated by an anionite membrane. It has been found that the use of granular graphite electrodes in the oxidation divalent iron ions increases the current output by more than 2 times compared to a plate graphite electrode. Conclusion. According to the results of the study, it was noted that under optimal conditions, the current output of the oxidation of divalent iron ions exceeds 90%. Extensive research has shown that trivalent iron ions, widely used in the in-situ leaching process for uranium production, can be regenerated by electrochemical methods.

Controlling the Photophysical Properties of a Series of Isostructural d6 Complexes Based on Cr0, MnI, and FeII.

Development of first-row transition metal complexes with similar luminescence and photoredox properties as widely used RuII polypyridines is attractive because metals from the first transition series are comparatively abundant and inexpensive. The weaker ligand field experienced by the valence d-electrons of first-row transition metals challenges the installation of the same types of metal-to-ligand charge transfer (MLCT) excited states as in precious metal complexes, due to rapid population of energetically lower-lying metal-centered (MC) states. In a family of isostructural tris(diisocyanide) complexes of the 3d6 metals Cr0, MnI, and FeII, the increasing effective nuclear charge and ligand field strength allow us to control the energetic order between the 3MLCT and 3MC states, whereas pyrene decoration of the isocyanide ligand framework provides control over intraligand (ILPyr) states. The chromium(0) complex shows red 3MLCT phosphorescence because all other excited states are higher in energy. In the manganese(I) complex, a microsecond-lived dark 3ILPyr state, reminiscent of the types of electronic states encountered in many polyaromatic hydrocarbon compounds, is the lowest and becomes photoactive. In the iron(II) complex, the lowest MLCT state has shifted to so much higher energy that 1ILPyr fluorescence occurs, in parallel to other excited-state deactivation pathways. Our combined synthetic-spectroscopic-theoretical study provides unprecedented insights into how effective nuclear charge, ligand field strength, and ligand π-conjugation affect the energetic order between MLCT and ligand-based excited states, and under what circumstances these individual states become luminescent and exploitable in photochemistry. Such insights are the key to further developments of luminescent and photoredox-active first-row transition metal complexes.

Electron Correlation in the Iron(II) Porphyrin by Natural Orbital Functional Approximations.

The relative stability of the singlet, triplet, and quintet spin states of iron(II) porphyrin (FeP) represents a challenging problem for electronic structure methods. While it is currently accepted that the ground state is a triplet, multiconfigurational wave function-based methods predict a quintet, and density functional approximations vary between triplet and quintet states, leading to a prediction that highly depends on the features of the method employed. The recently proposed Global Natural Orbital Functional (GNOF) aims to provide a balanced treatment between static and dynamic correlation, and together with the previous Piris Natural Orbital Functionals (PNOFs), allowed us to explore the importance of each type of correlation in the stability order of the states of FeP with a method that conserves the spin of the system. It is noteworthy that GNOF correlates all electrons in all available orbitals for a given basis set; in the case of the FeP with a double-ζ basis set as used in this work, this means that GNOF can properly correlate 186 electrons in 465 orbitals, significantly increasing the sizes of systems amenable to multiconfigurational treatment. Results show that PNOF5, PNOF7s, and PNOF7 predict the quintet to have a lower energy than the triplet state; however, the addition of dynamic correlation via second-order Møller-Plesset corrections (NOF-MP2) turns the triplet state to be lower than the quintet state, a prediction also reproduced by GNOF that incorporates much more dynamic correlation than its predecessors.

Chemiluminescence quenching capacity as a surrogate for total organic carbon in wastewater

Total organic carbon (TOC) is a valuable indicator to evaluate the degree of organic pollution in wastewater. Real-time analysis of TOC in wastewater can allow the wastewater treatment plants to manage the treatment process efficiently, avoid violations of the discharge regulations, and eliminate overtreatment. However, traditional methods for TOC determination are time-consuming. Benefitting from the rapid generation of SO4•− in the iron(II)-activated peroxymonosulfate (Fe(II)/PMS) system and the high reactivity of SO4•− towards naproxen as a chemiluminescence (CL) probe, a surrogate for TOC based on the determination of CL quenching capacity (CLQC) of organics in the Fe(II)/PMS-naproxen system was developed. According to the derived equation by considering both non-fluorescent and fluorescent quenching, the CLQC of organics in the Fe(II)/PMS-naproxen system was highly dependent on their TOC, making it to be a potential surrogate for TOC. The interferences of ubiquitous inorganic ions in wastewater on the determination of CLQC were leveled by adjusting electrical conductivity and adding mercury ions. Finally, the feasibility of CLQC as a surrogate for TOC in two real wastewaters containing different concentrations of inorganic anions was confirmed. This work can provide a TOC value within several seconds by determining the CLQC of wastewater with Fe(II)/PMS-naproxen system.

Kompleks Besi(II) dengan ligan 3-bpp: review

The change of two different spin electronic states under the influence of temperature, pressure and light irradiation is known as the Spin Transition or Spin Crossover (SCO) phenomenon.  Spin transition exists on octahedral complexes with an intermediate ligand field, one of the ligands is 2,6-bis (pyrazol-3-yl)pyridine or 3-bpp. Spin transition complexes were intensively investigated because they are highly potential candidates for electronic materials, such as sensors, molecular switches and information storages.  The iron(II) complex with 3-bpp ligand has shown SCO characteristics including different transition pattern and transition temperature which were influenced by type of the counter anions.  The iron(II) complexes with different types of counter anions have exhibited SCO phenomenon, due to the effect of temperature with abrupt transition.  However, the presence of hydrate water in the iron(II) complex results in the higher temperature transition.  In addition of that, the transition pattern has changed from the abrupt transition into the gradual transition types.  Several studies of SCO properties of the complex Fe(II)-3-bpp reported that the transition type and the temperature transition were influenced by the type of counter anion and the amount of hydrate molecules.  With various transition patterns and transition temperatures, the potential of Fe(II)-bpp complexes as SCO materials is more interesting to explored.   Keywords: Iron(II) Complex, 3-bpp Ligand, Spin Crossover

Concentration of Iron(II) in Fresh Groundwater Controlled by Siderite, Field Evidence

Iron(II) concentrations in fresh groundwater in Dutch aquifers range from absent up to 50 mg/l. Evaluation of extensive chemical data sets learned that the maximum logarithmic concentration of iron(II) in aquifers, between ± 6.5 < pH < ± 8, is a linear function of pH, governed by Siderite. It is a broad relation due to oversaturation with respect to Siderite and to variation in alkalinity. Iron(II) is continuously supplied to groundwater by reduction of hydrous ferric oxides (HFO), until becoming saturated with respect to Siderite, and from then on, HFO reduction and Siderite precipitation occur simultaneously. In Dutch aquifers, the electron supply rate (equivalent to the organic matter oxidation rate) apparently exceeds the HFO electron uptake rate (equivalent to the HFO reduction rate) and the excess supply is taken up by sulfate (equivalent to the sulfate reduction rate): HFO reduction, sulfate reduction and FeS precipitation occurring simultaneously, where the presence of Siderite prevents a dip in the iron(II) concentration. After sulfate becomes exhausted, the excess electron supply is transferred to methane production: HFO reduction and methane production occurring simultaneously. This evaluation also demonstrated that the organic matter oxidation rate and the HFO reduction rate decrease over time. The results of this study are also relevant for the behavior of As and of Co, Ni and Zn in groundwater, as HFO, Pyrite and Siderite may contain variable contents of these elements.

South Ural State University, Chelyabinsk, Russian Federation

A method for the kinetic photometric determination of oxalate ion in aqueous solutions, in-cluding extracts from foodstuffs, has been suggested. The initial rate method has been used: the straight parts of kinetic curves (approximately 5 min) are processed by the least square method to get the slope coefficients used as analytical signals. The procedure is based upon the oxalate ion action as an activator in the iron(II)-catalyzed reaction of iodide oxidation by potassium bromate. Unlike the previously used light absorbance in the UV region, the suggested procedure controls the rate of the iodine-starch complex formation at 590 nm. The greatest initial rate for the reaction is at pH 5.05 of the acetate buffer solution and the optimal concentration of soluble starch 0.30 mg/mL. The calibration graph is linear in the oxalate concentration range (0.1–10) mg/mL. In this interval precision error varies between 0.67 % and 4.71 %, accuracy error is within (0.22–9.30) %. The procedure has been applied to food analysis by the standard addition method. Aqueous extract has been obtained from 2.5 g of finely chopped sample of raw beet, stirred with 100 mL of water for 1 h, centrifuged, filtered, and quantitatively transferred to 250-mL volumetric flask. Determination of oxalate in 1-mL aliquot has required the same volume of colored beet extract for a reference solution, but otherwise the procedure stands valid. The oxalate content has been found to equal (379 ± 2) mg/g of the raw beet (P = 0,95; n = 4), with 0.6 % precision error and 3.0 % accuracy error.

Spin-crossover in the iron(II) complex based on dihydro-bis(pyrazolyl)borate and 1,10-phenanthroline-5,6-dione

A novel mixed-ligand Fe(II) complex based on dihydro-bis(pyrazolyl)borate and 1,10-phenanthroline-5,6-dione Fe[(H2B(Pz)2]2[phen-dione] was synthesized. Its local atomic structure and magnetic properties were characterized by means of X-ray absorption and Mössbauer spectroscopies in the temperature range of 8–300 K. According to the experimental data, the transition of iron ions from high-spin to low-spin configuration is observed in the Fe[(H2B(Pz)2]2[phen-dione] complex when the temperature decreases. The obtained experimental data are in a good agreement with the results of quantum chemical calculations.

Spin crossover in homo- and heteroligand iron(II) complexes with tris(pyrazol-1-yl)methane derivatives

The studies concerning coordination compounds of various salts of iron(II) with tris(pyrazol-1-yl)methane derivatives (HC(pz)3) are discussed. The results of a number of studies on the synthesis and investigation of the homo- and heteroligand iron(II) complexes with tris(3,5- dimethylpyrazol-1-yl)methane (HC(3,5-Me2pz)3) are considered. The study of the temperature dependence μeff (T) showed that the spin crossover (SCO) 1A1↔5T2 observed in a series of the compounds discussed is accompanied by thermochromism (color change pink (purple) ↔ colorless). Specific features of the SCO and their dependence on the outer-sphere anion in the iron(II) complexes are discussed. The data of the recently published work devoted to the synthesis of the iron(II) complexes with three N-substituted HC(pz)3 derivatives (general formula xL, where x = H, CH2C6H5 (Bn) and p-SO3C6H4CH3 (Ts)) are considered.

Block Copolymerization of Lactide and an Epoxide Facilitated by a Redox Switchable Iron‐Based Catalyst

AbstractA cationic iron(III) complex was active for the polymerization of various epoxides, whereas the analogous neutral iron(II) complex was inactive. Cyclohexene oxide polymerization could be “switched off” upon in situ reduction of the iron(III) catalyst and “switched on” upon in situ oxidation, which is orthogonal to what was observed previously for lactide polymerization. Conducting copolymerization reactions in the presence of both monomers resulted in block copolymers whose identity can be controlled by the oxidation state of the catalyst: selective lactide polymerization was observed in the iron(II) oxidation state and selective epoxide polymerization was observed in the iron(III) oxidation state. Evidence for the formation of block copolymers was obtained from solubility differences, GPC, and DOSY‐NMR studies.

Block Copolymerization of Lactide and an Epoxide Facilitated by a Redox Switchable Iron-Based Catalyst.

A cationic iron(III) complex was active for the polymerization of various epoxides, whereas the analogous neutral iron(II) complex was inactive. Cyclohexene oxide polymerization could be "switched off" upon in situ reduction of the iron(III) catalyst and "switched on" upon in situ oxidation, which is orthogonal to what was observed previously for lactide polymerization. Conducting copolymerization reactions in the presence of both monomers resulted in block copolymers whose identity can be controlled by the oxidation state of the catalyst: selective lactide polymerization was observed in the iron(II) oxidation state and selective epoxide polymerization was observed in the iron(III) oxidation state. Evidence for the formation of block copolymers was obtained from solubility differences, GPC, and DOSY-NMR studies.

Photodegradation of olive mill effluent with hydrogel-coated Fe3O4 magnetite composite

In this study, hydrogel-coated Fe3O4 magnetite composite was used for the photocatalytic degradation of pollutant parameters [polyphenols, chemical oxygen demand (COD) components, total aromatic amines (TAAs) ] from the olive mill effluent wastewater at different pH (4.0–7.0–9.0) conditions, at temperatures (21, 30, and 40°C), at different H2O2 concentrations (50, 100, 200, and 1,000 mg/l), at different retention times (15, 30, 45, and 60 min), and increasing hydrogel-coated Fe3O4 magnetite composite concentrations under 100W ultraviolet (UV) and 29W sunlights. The maximum CODtotal, polyphenols, and TAAs yields were 96%, at between 88 and 94%, and at between 83 and 94%, respectively, at 3 g/l of hydrogel-coated Fe3O4 magnetite nano composite concentration, at 100W UV light irradiation, at pH 4.0, after 60 min retention time, respectively. At the lowest molar ratio of 1/5 in the iron(II) chloride tetrahydrate and iron(III) chloride hexahydrate to hydrogel the highest photodegradation obtained at 30°C. When the molar ratio of the iron(II) chloride tetrahydrate and iron(III) chloride hexahydrate to hydrogel was 1/3 to the maximum photodegradation reached at 40°C. At the higher molar ratio of 1/2, the best photodegradation yields were obtained at 40°C. The maximum CODtotal, polyphenols, and TAAs yields were obtained at acidic pH, and at 50 mg/l H2O2 concentration. The Fe3O4 nanoparticles exhibited high catalytic recyclability under magnetic conditions resulting in significant decrease in treatment costs.

2‐Amino‐5‐(2‐pyridyl)‐thiadiazole as Bidentate Ligand

AbstractThe amino substituted bidentate chelating ligand 2‐amino‐5‐(2‐pyridyl)‐1,3,4‐thiadiazole (H2L) was used to prepare 3:1‐type coordination compounds of iron(II), cobalt(II) and nickel(II). In the iron(II) perchlorate complex [FeII(H2L)3](ClO4)2·0.6MeOH·0.9H2O a 1:1 mixture of mer and fac isomers is present whereas [FeII(H2L)3](BF4)2·MeOH·H2O, [CoII(H2L)3](ClO4)2·2H2O and [NiII(H2L)3](ClO4)2·MeOH·H2O feature merely mer derivatives. Moessbauer spectroscopy and variable temperature magnetic measurements revealed the [FeII(H2L)3]2+ complex core to exist in the low‐spin state, whereas the [CoII(H2L)3]2+ complex core resides in its high‐spin state, even at very low temperatures.

Spin Density Distribution in a MOF presenting electric and magnetic order

One of the main features of molecular compounds is the possibility of combining different properties in a synergic way giving a multifunctional material. Here we will discuss the case of a compound combining electric and magnetic order, thus giving a "multiferroic" molecular material. The disorder-order of the dimethylammnoium molecule in the Iron(II)-Iron(III) system [NH2(CH3)2]n[FeIIIFeII(HCOO)6]n is in the origin of the observed electric transition from paraelectric to antiferroelectric. In combination with the mentioned electric properties, this compound shows also magnetic order in the form of Nel N-Type ferrimagnetism [1]. The structure of [NH2(CH3)2]n[FeIIIFeII(HCOO)6]n has been characterized by means of neutron diffraction at VIVALDI and D19 instruments at Institut Laue-Langevin (ILL, Grenoble, France), where a crystallographic phase transition was observed from the high temperature structure [P-31c; a =b=8.2550(12) and c=13.891(3) at room temperature] to a lower symmetry one [R-3c; a = b=14.2600(17) and c=41.443(8) at low temperature]. On the other hand, the magnetic behaviour of this compound can be described as a result of two sublattices anti-ferromagnetically coupled, containing different spin carriers FeIII and FeII, respectively, with an ordering temperature of 37 K, and which are responsible of the different magnetic behaviours at low temperature.[2] The different spins of the neighbouring ions [S=5/2 and S=2] result in a ferrimagnetic state. Polarized neutron diffraction measurements aimed at clarifying the spin density map in order to understand the influence of the counter ion in the magnetic properties were carried out at D3 instrument (ILL). Measurements of the flipping ratios were performed with magnetic field of 9 Tesla at 45K, over the magnetic ordering temperature. The results point to an unusual weak spin density located around the counterions which suggests a non-negligible role in the magnetic behavior for the amine group.

Dissipative structure in the photo-induced phase under steady light irradiation in the spin crossover complex

We report the spatial and temporal dynamics of the photo-induced phase in the iron (II) spin crossover complex Fe(ptz)(6)(BF(4))(2) studied by image measurement under steady light irradiation and transient absorption measurement. The dynamic factors are derived from the spatial and temporal fluctuation of the image in the steady state under light irradiation between 65 and 100 K. The dynamic factors clearly indicate that the fluctuation has a resonant frequency that strongly depends on the temperature, and is proportional to the relaxation rate of the photo-induced phase. This oscillation of the speckle pattern under steady light irradiation is ascribed to the nonlinear interaction between the spin state and the lattice volume at the surface.

Iron(II) closo-borate complexes with 1,2,4-triazole derivatives: Spin crossover in the iron(II) closo-borate complexes with tris(pyrazol-1-yl)methane

Methods of synthesis of iron(II) complexes containing cluster closo-borate anions—[Fe(Htrz)3]B10Cl10 (I) (HTrz is 1,2,4-triazole), [Fe(NH2Trz)3]B10Cl10 · 2H2O (II) (NH2Trz is 4-amino-1,2,4-triazole), [Fe{HC(pz)3}2]B10Cl10 (III), [Fe{HC(pz)3}2]B10H10 (IV), and [Fe{HC(pz)3}2]B12H12 · 2H2O (V) (HC(pz)3 is tris(pyrazol-1-yl)methane)—have been developed. The compounds have been studied by the static magnetic susceptibility method (78–500 K) and electronic, IR, and EXAFS spectroscopy. Complexes I and II in the temperature range under consideration remain in the high-spin state. Low-spin complex III shows incomplete spin crossover and decomposes on heating above 440 K. Complexes IV and V are characterized by reversible spin crossover 1 A 1 ⇔ 5 T 2 accompanied by thermochromism (the pink ⇔ white color change). The crossover temperature (T c) for IV and V is 375 and 405 K, respectively.

How Do the Thiolate Ligand and Its Relative Position Control the Oxygen Activation in the Cysteine Dioxygenase Model?

In the iron(II)-thiolate models of cysteine dioxygenase, the thiolate ligand is a key factor in the oxygen activation. In this contribution, four model compounds have been theoretically investigated. This comparative study reveals that the thiolate ligand itself and its relative position are both important for the activation of O(2). Before the O(2) binding, the thiolate ligand must transfer charge to Fe(II), and the effective nuclear charges of Fe(II) is decreased, which results in a lower redox potential of compounds. In other words, the thiolate ligand provides a prerequisite for the O(2) activation. Furthermore, the relative position of the thiolate ligand is discovered to determine the reaction path of O(2) activation. The amount of charge transfer is crucial for these reactions; the more charge it transfers, the lower the related redox potentials. This work really helps think deeper into the O(2) activation process of mononuclear nonheme iron enzymes.

Copper(I)-promoted halogen exchange in the iron(II) dichloroclathrochelate

Abstract The halogen exchange reaction of the macrobicyclic iron(II) complex FeBd2(Cl2Gm)(BF)2 (where Bd2– and Cl2Gm2– are α-benzyldioxime and dichloroglyoxime dianions, respectively) with two-fold excess of CuI and stoichiometric amounts of NaI in NMP gave the mixture of initial compound with diiodo- and iodochloroclathrochelates as well as the small amounts of the cage by-products of side hydrodehalogenation and homo-coupling reactions of this precursor. The chromatographically isolated complex FeBd2(IGmCl)(BF)2 has been characterized using elemental analysis, MALDI-TOF mass spectrometry, IR, UV–vis, 1H and 13C{1H} NMR spectroscopies, and X-ray diffraction crystallography. This clathrochelate possess a geometry intermediate between that of a trigonal prism and a trigonal antiprism (the distortion angle φ = 23.6°). The Fe–N distances vary in a narrow range (1.91–1.92 A), the height h of the FeN6-coordination polyhedron and the averaged bite angle α are equal to 2.34 A and 39.2°, respectively. The reaction studied occurs only in the case of the vic-dihalogenosubstituted macrobicycles with CuI as both the catalyst and the reagent, and with iodide anions coordinated to the copper(I) ions. The proposed mechanism of this reaction is similar to that for copper-catalyzed Finkelstein-type reactions of aryl halides and the intermediate anion-radical species are effectively generated with CuI–N-methylpyrrolidone complex.

High-temperature spin transition in the iron(II) trifluoromethylsulfonate, perrhenate, and tetraphenylborate complexes with tris(pyrazol-1-yl)methane

New coordination compounds of iron(II) trifluoromethylsulfonate, perrhenate, and tetraphenylborate with tris(pyrazol-1-yl)methane (HC(Pz)3) of the composition [Fe(HC(Pz)3)2]A2 (A = CF3SO3− (I), ReO4− (II), and B(C6H5)4− (III)) were synthesized and studied by the method of static magnetic susceptibility and IR and electronic spectroscopies. The crystal and molecular structures of compounds I and II were determined by X-ray diffraction analysis. The magnetochemical study of complexes I—III in the interval from 275 to 500 K showed that they possessed the high-temperature spin transition 1A1 ⇄ 5T2 accompanied by thermochromism.