Aqueous Complexes Research Articles

Adsorption of yttrium by the sodium-modified titanium dioxide: Kinetic, equilibrium studies and investigation of Na-TiO2 radiation resistance

The adsorption of yttrium cations from an aqueous solution of YCl3 by sodium-modified titanium dioxide (Na-TiO2) was investigated. The Na-TiO2 was obtained by impregnating Na+ cations into the surface layer of TiO2 nanoparticles. The synthesis of nanoparticle TiO2 was performed by a liquid-phase sol–gel method, using the aqua complex of [Ti(OH2)6]3+‧3Cl− as a precursor. Nanoheterostructured Na-TiO2 is an anatase modification of TiO2. The amount of incorporated sodium cations on the TiO2 surface is about 6%. The surface area of Na-TiO2 is 239 m2‧g−1; the volume of mesopores is 0.098 cm3‧g−1; that of micropores is 0.054 cm3‧g−1. Yttrium ion adsorption was investigated under batch conditions. Complexometric titration and mas-spectrometric analysis determined the initial and equilibrium concentration of yttrium. The radiation resistance of Na-TiO2 to the influence of beta irradiation was investigated as well. For this purpose, the radiation of β−-particles of the 90Sr-90Y source “Sirius” was used. The flux of β− – particles was 2.1 ‧ 108 electrons/sm2‧s; the maximal energy of incident electrons was 2.28 MeV. It was shown that the investigated adsorbent has a high adsorption capacity toward yttrium cations. The maximum adsorption is about 259 mg/g. The adsorption kinetic is fit well with the kinetic model based on the pseudo-second-order equation. The equilibrium adsorption of yttrium cations is described by Freundlich's theory with high reliability. The adsorbent is resistant to the influence of β− – irradiation. This is manifested in the invariance of its adsorption capacity toward yttrium cations after irradiation. Na-TiO2 is a promising material for the adsorption of yttrium and Rare Earth elements and can be used as the basis for the 90Y isotopic generator.

Specific features of lithium solvent extraction from perchlorate media with benzo-15-crown-5

The extraction of Li, Na, K perchlorates by the extraction system B15C5-CHCl3-H2O was studied in this work. It has been shown that the use of LiClO4 in extraction processes allows to prevent the accumulation of K+ in the extract and reduce the loss of the extractant. The dependences of the distribution coefficients of all three metals on temperature were established. It was found that, in contrast to the previously studied extraction systems with B15C5, lithium perchlorate is extracted as a complex with an atypical ratio of Li:crown ether = 1:2. The anhydrous complex [Li(B15C5)(ClO4)] and the aqueous complex [Li(B15C5)2(H2O)](ClO4) were isolated for the first time in crystalline form and characterized by X-ray diffraction. The isolated complexes and the lithium extract were studied by FTIR spectroscopy. A comparative analysis of these spectra made it possible to confirm the structure of not typical extracted lithium complex.

Copper–zinc/chitosan complex hydrogels: Rheological, degradation and biological properties

Polymer hydrogels crosslinked by therapeutic metal ions have attracted increased interest in recent years due to their unique and versatile properties. Chitosan hydrogels are widely investigated for various biomedical applications such as tissue engineering and drug delivery. Copper and zinc ions are considered as therapeutic metal ions, that have important roles in bone regeneration. The aim of this study was to investigate the physicochemical and biological properties of bimetallic–chitosan complex hydrogels with different cupric and zinc ions content. Scanning electron microscopy (SEM) revealed changes in the morphology from the microstructure with larger, tubular pores for aerogels with higher Zn content, to the sheets-like structure with long pores for samples with higher Cu content. FTIR analysis indicated the formation of bimetallic–chitosan aerogels. The obtained X-ray diffraction patterns showed a broadening of chitosan's characteristic diffraction maximum, while characterization of physical properties showed decreased swelling ability and increased shear modulus with higher Cu content. ICP-MS results showed a negligible amount of copper and zinc ions released under physiological conditions during 24 h indicating a strong physical crosslink between metal ions and chitosan chains. Furthermore, accelerated in vitro degradation showed that hydrogels maintained good stability during four weeks of lysozyme activity. The MTT assay indicated that the cytotoxicity of Cu2+–Zn2+/chitosan complexes could be adjusted by the amount of cupric ions. All results imply that Cu2+ and Zn2+ ions act as physical crosslinkers of the polymer network. Also, results are in agreement with the prediction of density functional theory (DFT) which indicated stronger chitosan–Cu tetrahedral aqua complex interactions in comparison to the chitosan–[Zn(H2O)4]2+ interactions.

Chiral ligand induced geometrical type of isomerism in Schiff-base Copper(II) complexes with urease inhibitory activities

Enzyme urease plays a significant role in the pathogenesis of several diseases and has practical implications in fields such as agriculture and chemical analysis. Four new copper(II) complexes with Schiff-base ligands obtained from the template synthesis of 2-formylphenoxyacetic acid (fphaa) with DL-α-alanine, β-alanine, taurine, and γ-aminobutanoic acid were synthesized in addition to the previously described [Cu(fphaa-gly)(H2O)] derived from glycine. Crystallographic study of two solvates of Cu(fphaa-α-ala)⋅S (where S = H2O or DMSO) showed similarity of these complexes with the one derived from glycine. In addition, an E/Z isomerism originating in a different molecular arrangement of the aqua ligand with respect to the methyl group from alanine was described in the aqua complex. Only Z isomers were found in the complex with DMSO. All prepared complexes showed excellent inhibitory properties against jack bean urease (IC50 = 0.53–0.71 μmol/dm3), considerably better than the standard inhibitor acetohydroxamic acid (IC50 = 185 μmol/dm3).

Photocatalysts Based on Graphite-like Carbon Nitride with a Low Content of Rhodium and Palladium for Hydrogen Production under Visible Light.

In this study, we proposed photocatalysts based on graphite-like carbon nitride with a low content (0.01-0.5 wt.%) of noble metals (Pd, Rh) for hydrogen evolution under visible light irradiation. As precursors of rhodium and palladium, labile aqua and nitrato complexes [Rh2(H2O)8(μ-OH)2](NO3)4∙4H2O and (Et4N)2[Pd(NO3)4], respectively, were proposed. To obtain metallic particles, reduction was carried out in H2 at 400 °C. The synthesized photocatalysts were studied using X-ray diffraction, X-ray photoelectron spectroscopy, UV-Vis diffuse reflectance spectroscopy and high-resolution transmission electron microscopy. The activity of the photocatalysts was tested in the hydrogen evolution from aqueous and aqueous alkaline solutions of TEOA under visible light with a wavelength of 428 nm. It was shown that the activity for the 0.01-0.5% Rh/g-C3N4 series is higher than in the case of the 0.01-0.5% Pd/g-C3N4 photocatalysts. The 0.5% Rh/g-C3N4 sample showed the highest activity per gram of catalyst, equal to 3.9 mmol gcat-1 h-1, whereas the most efficient use of the metal particles was found over the 0.1% Rh/g-C3N4 photocatalyst, with the activity of 2.4 mol per gram of Rh per hour. The data obtained are of interest and can serve for further research in the field of photocatalytic hydrogen evolution using noble metals as cocatalysts.

Three-component deep eutectic solvent-based microextraction approach for biodiesel quality control: Determination of water and metals

Biodiesel is an important alternative fuel produced by blending biofuels with petroleum diesel. Biofuel production is usually carried out by catalytic interesterification of animal fats or vegetable oils, followed by the removal of by-products and catalysts through washing with water. Residual amounts of water and catalysts can accelerate fuel biodegradation and contribute to the corrosion of metal surfaces. Considering the need to control the quality of biodiesel fuel, a simple and environmentally friendly analytical approach was first developed for the determination of water and metals (sodium, potassium, magnesium, calcium as catalysts, and iron, copper, tin, zinc, lead as feedstock elements) using a deep eutectic solvent. The technique involved microextraction of analytes from biodiesel into a new three-component deep eutectic solvent (choline chloride, lactic acid, and cobalt chloride) using a laboratory vortex, followed by impregnating the filter paper with the obtained extract to determine the analytes. The colorimetric determination of water is based on a change in the color of the deep eutectic solvent, which goes from blue to pink due to the formation of cobalt aqua complexes. The detection of water on the filter paper was carried out using a conventional scanner. The content of metals on the filter paper was determined by X-ray fluorescence spectrometry. Under optimal conditions, the detection limit was 100 mg kg−1 for water and 0.03–3 mg kg−1 for metals. The technique enabled multicomponent analysis to be carried out without the use of dangerous Karl Fischer reagents (for water determination) and microwave mineralization of samples (for elemental analysis). The enrichment factor ranged from 290 to 330, and the RSD was less than 15%.

Enantioselective Aldol Reaction with Difluoroenoxysilanes Catalyzed by Cationic Palladium Aqua Complexes

AbstractThe enantioselective addition of difluoroenoxysilanes to aromatic aldehydes, catalyzed by cationic palladium aqua complexes, has been described. The reaction is operationally simple, does not require anhydrous conditions and performs at room temperature. The palladium catalysts, previously discovered and reported by Sodeoka, are easily prepared in two steps from PdCl2(MeCN)2. The aldol compounds were obtained in good yields and with enantiomeric ratios up to 93 : 7, the reaction being more efficient using electron‐rich aldehydes.

Density Functional Theory Based Protocol to Calculate the Redox Potentials of First-row Transition Metal Complexes for Aqueous Targeting Redox Flow Batteries.

Transition metal complexes are a promising class of redox mediators for targeting redox flow batteries due to the tunability of their electrochemical potentials. However, reliable time-efficient tools for the prediction of their reduction potentials are needed. In this work, we establish a suitable density functional theory protocol for their prediction using an initial experimental data set of aqueous iron complexes with bidentate ligands. The approach is then cross-validated using different complexes found in the redox-flow literature. We find that the solvation model affects the prediction accuracy more than the functional or basis set. The smallest errors are obtained using the COSMO-RS solvation model (mean average error (MAE) = 0.24 V). With implicit solvation models, a general deviation from experimental results is observed. For a set of similar ligands, they can be corrected using simple linear regression (MAE = 0.051 V for the initial set of iron complexes).

A combined spectroscopic and theoretical study to investigate the coordination modes of 2,3- and 3,4-pyridine dicarboxylates with Eu(III)

The complex formation of Eu(III) with 2,3-pyridine dicarboxylic acid (23PDCA) and 3,4-pyridine dicarboxylic acid (34PDCA) has been studied by luminescence spectroscopy in aqueous medium. About three orders of luminescence enhancement of Eu(III) was observed in Eu(III)-PDCA complexes compared to its aqua complex, Eu(H2O)93+. Stability constant values (Log KMLi) were obtained for various metal–ligand (MLi (i = 1–3)) complexes formed in the aqueous medium. Complexation studies along with luminescence lifetime data suggested that both the ligands bind with Eu(III) in a bidentate fashion. Interestingly, the bi-dentate mode of 23PDCA interaction with Eu(III) is dominantly through nitrogen atom of pyridyl and the oxygen atom of nearby carboxylate group, whereas in case of 34PDCA, the bi-dentate coordination is through the two oxygen atoms of both the carboxylate groups. The density functional theory (DFT) calculations provided insights into the complex formation at the molecular level and the theoretical results show excellent agreement with the experimental observations.

Кормление личинок судака (Sander lucioperca Linnaeus, 1758) при их подращивании в установке замкнутого водоснабжения

The article presents materials on optimizing the conditions for growing pike-perch during the larval period of development in an artificially created environment. The problems associated with the complexity of embryonic and post-embryonic development, the transition of larvae from endogenous to exogenous food, their rearing on artificial feed, and the causes of cannibalism have been described. The goal was to obtain and analyze the results of growing pike-perch larvae in conditions of closed water supply using living organisms as starter feed. The results of a study of the reproduction of pike-perch in industrial conditions of the aqua complex of the Coastal Scientific Expeditionary Base “Kagalnik” of the SSC RAS (Rostov Region, Azov District) are presented, describes the results of rearing pike-perch larvae in a recirculating aquaculture system. The values of the main hydrochemical parameters of the environment in fish tanks, necessary to ensure the normal growth and development of pike-perch larvae, as well as the characteristics of growth and survival during the experiments, are given. As a result, biotechnical standards for the reproduction of pike-perch by the intensive method have been developed. For high survival of pike-perch larvae, it is necessary to ensure timely feeding of larvae – after filling the swim bladder and switching to active feeding. The diet should be varied in terms of species composition of zooplankton. To prevent cannibalism among farmed fish, it is important to maintain the hydrochemical parameters at an optimal level, and the presence of food organisms in the fish tank is also necessary.

Different metal coordination in sub- and super-critical fluids: Do molybdenum(IV) chloride complexes contribute to mass transfer in magmatic systems?

Molybdenum (Mo) is extracted predominantly from magmatic-hydrothermal ore deposits, and knowledge of the thermodynamic properties of aqueous Mo complexes over a wide range in pressures (P) and temperatures (T) is required to predict the transport and deposition of Mo in ore-forming environments. These properties are usually derived from experimental studies conducted over a limited P-T range, with uncertainties increasing as temperature and pressure increase, because of inherent technical difficulties and decreasing number of studies. There is a discrepancy between numerous experimental studies at T < 400 °C and a handful of studies at magmatic-hydrothermal conditions. The low T (<400 °C) experiments suggested that Mo(VI) chloride complexes are unlikely to play a significant role in nature, whereas some studies in magmatic-hydrothermal conditions showed the predominance of Mo(VI) chloride complexes. In an attempt to resolve these inconsistencies, we investigated Mo(VI)-Cl complexations from 350 to 750 °C (500 to 2000 bar) using ab initio molecular dynamics (MD) simulations. The simulations reveal that in high-temperature magmatic-hydrothermal fluids (750 °C, 2000 bar), a tetrahedral Mo(VI) chloride complex, MoO2(OH)Cl(aq), becomes stable; this coordination differs from the octahedral Mo(VI)-chloride complexes identified in highly acidic sub-critical fluids. The ab initio thermodynamic integration method was employed to calculate the equilibrium constants of the reaction.MoO2(OH)Cl(aq) + H2O = MoO2(OH)2(aq) + HCl(aq)Thermodynamic modelling of the speciation using the calculated equilibrium constants shows that at lower temperatures (350 °C, 500 bar), Mo(VI)-chloro complexes are only important at highly acidic conditions (pH < 1), in accordance with previous studies. However, the MD results show that at higher temperatures, Mo-chloro-complexes may be important in transporting Mo in mildly acidic conditions up to the quartz-muscovite-K-feldspar buffered pH. Hence, Mo(VI) chloro-complexes could play an important role in the formation of magmatic-hydrothermal Mo deposits (e.g., Climax-type Mo deposits). We conclude that the mode of metal transport can change dramatically at high temperatures as a result of coordination changes caused by changes in the solvation properties of water; and that quantitative MD is an important tool to support the interpretation of scant experimental results available for magmatic-hydrothermal systems.

Using continuous electrical conductivity measurements to derive major solute concentrations in karst systems

AbstractHydrochemical data of karst springs provide valuable insights into the internal hydrodynamical functioning of karst systems and support model structure identification. However, the collection of high‐frequency time series of major solute species is limited by analysis costs. In this study, we develop a method to retrieve the individual solute concentration time series and their uncertainty at high temporal resolution for karst springs by using continuous observations of electrical conductivity () and low‐frequency ionic measurements. Due to the large ion content and non‐negligible concentrations of aqueous complexes in karst systems, the concentration of each solute species occurring as free ion and as part of aqueous complexes are computed separately. The concentration of species occurring as free ions are computed considering their contributions to the total , whereas the concentration of the species as part of complexes are obtained from speciation calculations. The pivotal role of the complexation processes for the reconstruction of solute concentration time series starting from the signal is investigated in two karstic catchments with different geologies and temporal resolution of the available hydrochemical datasets, that is the Kerschbaum dolostone system in Austria and the Baget limestone system in France. The results show that complexation processes are significant and should be considered for the estimation of the total solute concentration in case of SO4, Ca, Mg and HCO3. The signal of a karst spring can be used to interpolate and quantify the dynamics of those solutes characterized by large contribution (approximately &gt;6%) to the total and low relative variability, that is HCO3, Ca and Mg. Moreover, the presented method can be used to estimate concentrations of solutes when applied to karst systems with stationary and hydrogeochemical homogeneous contributing area. On the contrary, the method is affected by large uncertainty in case of dynamic systems characterized by varying contributions of water from different geological areas. This study aims to contribute to the problem of hydrogeochemical data availability and to support future works on karst systems conceptualization.

Hydroxylated Polyoxometalate with Cu(II)- and Cu(I)-Aqua Complexes: A Bifunctional Catalyst for Electrocatalytic Water Splitting at Neutral pH.

A sole inorganic framework material [Li(H2O)4][{CuI(H2O)1.5} {CuII(H2O)3}2{WVI12O36(OH)6}]·N2·H2S·3H2O (1) consisting of a hydroxylated polyoxometalate (POM) anion, {WVI12O36(OH)6}6-, a mixed-valent Cu(II)- and Cu(I)-aqua cationic complex species, [{CuI(H2O)1.5}{CuII(H2O)3}2]5+, a Li(I)-aqua complex cation, and three solvent molecules, has been synthesized and structurally characterized. During its synthesis, the POM cluster anion gets functionalized with six hydroxyl groups, i.e., six WVI-OH groups per cluster unit. Moreover, structural and spectral analyses have shown the presence of H2S and N2 molecules in the concerned crystal lattice, formed from "sulfate-reducing ammonium oxidation (SRAO)". Compound 1 functions as a bifunctional electrocatalyst exhibiting oxygen evolution reaction (OER) by water oxidation and hydrogen evolution reaction (HER) by water reduction at the neutral pH. We could identify that the hydroxylated POM anion and copper-aqua complex cations are the functional sites for HER and OER, respectively. The overpotential, required to achieve a current density of 1 mA/cm2 in the case of HER (water reduction), is found to be 443 mV with a Faradaic efficiency of 84% and a turnover frequency of 4.66 s-1. In the case of OER (water oxidation), the overpotential needed to achieve a current density of 1 mA/cm2 is obtained to be 418 mV with a Faradaic efficiency of 80% and turnover frequency of 2.81 s-1. Diverse electrochemical controlled experiments have been performed to conclude that the title POM-based material functions as a true bifunctional catalyst for electrocatalytic HER as well as OER at the neutral pH without catalyst reconstruction.

Nuclear spin relaxation in aqueous paramagnetic ion solutions.

A Brownian shell model describing the random rotational motion of a spherical shell of uniform particle density is presented and validated by molecular dynamics simulations. The model is applied to proton spin rotation in aqueous paramagnetic ion complexes to yield an expression for the Larmor-frequency-dependent nuclear magnetic resonance spin-lattice relaxation rate T_{1}^{-1}(ω) describing the dipolar coupling of the nuclear spin of the proton with the electronic spin of the ion. The Brownian shell model provides a significant enhancement to existing particle-particle dipolar models without added complexity, allowing fits to experimental T_{1}^{-1}(ω) dispersion curves without arbitrary scaling parameters. The model is successfully applied to measurements of T_{1}^{-1}(ω) from aqueous manganese(II), iron(III), and copper(II) systems where the scalar coupling contribution is known to be small. Appropriate combinations of Brownian shell and translational diffusion models, representing the inner and outer sphere relaxation contributions, respectively, are shown to provide excellent fits. Quantitative fits are obtained to the full dispersion curve of each aquoion with just five fit parameters, with the distance and time parameters each taking a physically justifiable numerical value.

Dinuclear platinum(II) complexes with 1,5-nphe bridging ligand: Spectroscopic and molecular docking study of the interactions with N-acetylated L-methionylglycine and human serum albumin

The hydrolysis of N-acetylated L-methionylglycine dipeptide (Ac-L-Met-Gly) in the presence of dinuclear platinum(II)-aqua complexes with general formula [{Pt(L)(H2O)}2(μ-1,5-nphe)]4+ (1,5-nphe is 1,5-naphthyridine; L is bidentately coordinated ethylenediamine (1w), (±)-1,2-propylenediamine (2w) and 1,3-propylenediamine (3w)) is described in detail. The hydrolytic activity of these complexes was monitored by 1H NMR spectroscopy, which confirmed the regioselective cleavage of the Met-Gly-amide bond in this peptide. Quantum-chemical calculations revealed the primary reaction path with coordination of dipeptide via the terminal amide nitrogen of methionine followed by its coordination for the sulphur atom, in which the decomposition of the resulted platinum(II)-dipeptide complex and the coordination of its glycine residue precedes the hydrolytic cleavage of the Met-Gly amide bond. In the secondary reaction path, in which Ac-L-Met-Gly is coordinated via the methionine sulphur atom, the decomposition of the starting [{Pt(L)(H2O)}2(μ-1,5-nphe)]4+ complex is followed by the regioselective hydrolysis of the investigated dipeptide. The binding affinity of the chloride derivatives of the corresponding dinuclear platinum(II)-aqua complexes, [{Pt(L)Cl}2(μ-1,5-nphe)]2+ (1–3) towards the human serum albumin (HSA), a transport protein, was investigated using electronic absorption and fluorescence emission measurements, and results indicated the static interactions between these complexes and HSA. A docking study revealed a unique binding site on HSA, based on the electrostatic and the hydrogen bonding, which does not have a methionine residue nearby, therefore does not exist danger of HSA hydrolysis by these complexes.

A computational insight on the noncovalent interactions of aminothiazole-based palladium(II) complexes with DNA as a potent anticancer agent

In recent times, cancer has been reported as one of the largest growing deadly diseases in humankind. The use of cisplatin for oncological treatment has been known for a long time. However, no other suitable solutions have been extensively explored to substitute highly potent yet toxic cisplatin. In the current work, we have computationally investigated five experimentally synthesized Pd(II) complexes (Nn, n = 1–5), along with their positively charged aqua derivatives (NnW, n = 1–5), having aminothiazole analogues that may act as a potent inhibitor(s) of cancer. The interaction of the Pd(II) complexes with the B-DNA (1BNA) and preformed intercalation site DNA (1XRW) was explored by implementing the molecular docking with clustering protocol to generate the most probable docked conformers. From the docking analyses, we found that the Pd(II) complexes bind to the minor groove of the DNA in a parallel fashion. Moreover, the results suggested that the minor groove binding moderately dominates the intercalation mode of binding besides having aromatic rings. The results also implied that the aqua derivatives of the Pd(II) complexes undergo strong binding (both minor groove and intercalation) due to the higher positive charge than their corresponding chloride derivatives. Furthermore, the aqua complexes with fluorinated aromatic rings (N1W and N5W) have a lower binding affinity for intercalation than for binding in the minor groove. Additionally, we performed the independent gradient model (IGM) analysis for the minor groove binding only from the first seed of the most probable docked conformers, for which our study confirmed the presence of hydrogen bonding and van der Waals interactions. Altogether, our results provide good insights into the fate of the chosen complexes and may act as a potent alternative(s) to cisplatin.

Mechanism of selective transportation of metal ions across chelating membranes in electrodialysis

The presented research explains the mechanism of selective transportation mass in electrodialysis by chelating membrane according to the electrosorption and specific diffusivity. The Nernst-Planck equation was applied for modelling and defining the character of mass transportation. The chelating membrane is developed by the chemical grafting of hydroxyquinoline (HQ), which guarantees selectivity. The investigation of mass transportation was determined using a single-component solution of transition metal cations like Co2+, Mn2+and Ni2+, as well as from alkaline metal classes like Li+ and Mg2+. Finally, the multi-component solutions were tested to confirm the chelating membrane's specific character and mass transportation mechanism. The chemical and electrochemical investigations like FTIR and EIS confirmed the appearance of the chelating reactions between membrane and cobalt cations only. According to the creation of aqua complexes of HQ and Co2+, the PAN-5C8Q membrane could transport in a significant majority only Co2+ against other mono- and divalent cations. The transport number against the Mn2+, Ni2+, Mg2+ and Li+ for Co2+got over 0.6.

Inorganic polyphosphate accumulation protects a marine, filamentous cyanobacterium, Anabaena torulosa against uranium toxicity

The intricate dynamics of inorganic polyphosphate (polyP) in response to phosphorus (P) limitation and metal exposure typical of contaminated aquatic environments is poorly understood. Cyanobacteria are important primary producers in aquatic environments that are exposed to P stringency as well as metal contamination. There is a growing concern regarding migration of uranium, generated as a result of anthropogenic activities, into the aquatic environments owing to high mobility and solubility of stable aqueous complexes of uranyl ions. The polyP metabolism in cyanobacteria in context of uranium (U) exposure under P limitation has hardly been explored. In this study, we analyzed the polyP dynamics in a marine, filamentous cyanobacterium Anabaena torulosa under combination of variable phosphate concentrations (overplus and deficient) and uranyl exposure conditions typical of marine environments. Polyphosphate accumulation (polyP+) or deficient (polyP−) conditions were physiologically synthesized in the A. torulosa cultures and were ascertained by (a) toulidine blue staining followed by their visualization using bright field microscopy and (b) scanning electron microscopy in combination with energy dispersive X-ray spectroscopy (SEM/EDX). On exposure to 100 μM of uranyl carbonate at pH 7.8, it was observed that the growth of polyP+ cells under phosphate limitation was hardly affected and these cells exhibited larger amounts of uranium binding as compared to polyP− cells of A. torulosa. In contrast, the polyP− cells displayed extensive lysis when exposed to similar U exposure. Our findings suggest that polyP accumulation played an important role in conferring uranium tolerance in the marine cyanobacterium, A. torulosa. The polyP-mediated uranium tolerance and binding could serve as a suitable strategy for remediation of uranium contamination in aquatic environments.

Geochemical Equilibrium Modelling of the Aqueous Speciation of Select Trace Elements in the Great Lakes

The behaviour and fate of trace elements in surface waters are greatly affected by their chemical form in solution, but the aqueous speciation of dissolved trace elements in the North American Great Lakes has received relatively little attention. Here, we present results from geochemical equilibrium modelling with 2021 surface water quality data to examine the spatiotemporal dynamics of trace element speciation in the Great Lakes. The relative abundance of aqueous trace element species appeared consistent with variability in solution chemistry and followed basin-wide trends in pH, alkalinity, salinity, and nutrient levels. The speciation of alkali metals was dominated by free monovalent cations, and that of oxyanion-forming elements by oxoacids, whereas significant fractions (&gt;1%) of other aqueous complexes were also evident for rare earth elements (e.g., Ce and Gd as carbonates), alkaline earth metals (e.g., Sr as sulfates), or transition metals (e.g., Zn as phosphates). Spatially, differences in the relative abundance of aqueous trace element species were &lt;2 orders of magnitude, with the highest variation (~50-fold) occurring for select chloride-complexes, resulting from upstream-to-downstream salinity increases in the basin. Finally, simulations of various future water quality scenarios (e.g., decreasing P levels, increasing temperature and salinity) suggest that the speciation of most trace elements is robust temporally as well. This study demonstrates how considering aqueous speciation may help improve the understanding of trace element dynamics and support water quality management in the Great Lakes.

Relevance of Surface Adsorption and Aqueous Complexation for the Separation of Co(II), Ni(II), and Fe(III)

During the solvent extraction of metal ions from an aqueous to an organic phase, organic-soluble extractants selectively target aqueous-soluble ions for transport into the organic phase. In the case of extractants that are also soluble in the aqueous phase, our recent studies of lanthanide ion-extractant complexes at the surface of aqueous solutions suggested that ion-extractant complexation in the aqueous phase can hinder the solvent extraction process. Here, we investigate a similar phenomenon relevant to the separation of Co(II), Ni(II), and Fe(III). X-ray fluorescence near total reflection and tensiometry are used to characterize ion adsorption behavior at the surface of aqueous solutions containing water-soluble extractants, either bis(2-ethylhexyl) phosphoric acid (HDEHP) or 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (HEHEHP), as well as adsorption to a monolayer of water-insoluble extractant dihexadecyl phosphoric acid (DHDP) at the aqueous-vapor interface. Competitive adsorption of Ni(II) and Fe(III) utilizing either HDEHP or DHDP illustrates the essential feature of the recent lanthanide studies that the ion, which is preferentially extracted in liquid-liquid extraction, Fe(III), is found preferentially adsorbed to the water-vapor interface only in the presence of the water-insoluble extractant DHDP. A more subtle competition produces comparable adsorption behavior of Co(II) and Ni(II) at the surfaces of both HDEHP- and HEHEHP-aqueous solutions in spite of the known preference for Co(II) under solvent extraction conditions. Comparison experiments with a monolayer of DHDP reveal that Co(II) is preferentially adsorbed to the surface. This preference for Co(II) is also supported by molecular dynamics simulations of the potential of mean force of ions interacting with the soluble extractants in water. These results highlight the possibility that complexation of extractants and ions in the aqueous phase can alter selectivity in the solvent extraction of critical elements.