Species In Aqueous Solution Research Articles

Effect of temperature and shear on the microstructure of a microbial polysaccharide secreted by Sphingomonas species in aqueous solution

Diutan gum is a biological polymer produced by Sphingomonas sp. In aqueous solution it shows gel-like structure under quiescent conditions. However, the flow-induced evolution of its viscoelastic properties and its microstructure are not known. In this work, the viscoelastic moduli were obtained under a flow field, applied in parallel, as a function of the temperature for 0.5 wt% diutan gum aqueous solutions. As both stress and temperature increase a decrease in the viscoelastic properties occurred, due to the fact that the molecular interactions decreased. Nevertheless, at stresses within the zero-shear viscosity region of the flow curves, no changes were observed. In addition, high stress values dampened the effect of the temperature. The results obtained are very interesting from an industrial application perspective.

Effect of cadmium sulphide precipitation on the partitioning of Cd isotopes: Implications for the oceanic Cd cycle

The biogeochemical cycling of cadmium (Cd) and its isotopes in the surface ocean is dominated by biological uptake into phytoplankton, while regeneration of the sinking particulate Cd governs the shapes of Cd profiles in the deeper ocean. Additionally, the water mass circulation plays an important role in the redistribution of Cd and its isotopes. Superimposed on this general cycle, it has recently been argued that cadmium sulphide (CdS) precipitation can occur in oceanic Oxygen Deficient Zones (ODZ). This has been proposed to account for the decrease in Cd/PO4 ratios and the positive Cd isotope excursion in seawater compared to sinking particles. To assess whether CdS precipitation results in a fractionation of Cd isotopes, we performed cadmium–sulphide precipitation experiments under controlled low-oxygen conditions in low (pure water) and high ionic strength (synthetic seawater) water, with variable reaction times and cadmium/sulphide ratios. Enrichment in light Cd isotopes is systematically observed in the precipitated CdS phase, in agreement with recent ab initio simulations of isotope effects associated with Cd speciation in aqueous solution. Our experimental results follow a closed-system Rayleigh fractionation model with the fractionation factor (αCdsol-CdS) for 112Cd/110Cd decreasing with increasing salinity – from 1.00026 for pure water to 1.00014 for a salinity twice that of modern seawater, indicating a salinity control on the magnitude of Cd isotope fractionation. We propose that this fractionation, varying with salinity, is controlled by isotope equilibrium between the various Cd aqueous species present in solution, with preferential involvement of free Cd2+ ion in CdS formation.The magnitude of Cd isotope fractionation in seawater (αCdsol-CdS = 1.00016) determined in our study is in accord with the Cd isotope shift observed in modern oceanic ODZ and attributed to removal by CdS. Our experiments show that CdS precipitation could have significant local impact on the cycling of Cd, and further demonstrates the utility of Cd isotopes as tracers of the sequestration of cadmium into sulphides in restricted euxinic basins, such as the Black Sea.

Complexity of Uranyl Peroxide Cluster Speciation from Alkali-Directed Oxidative Dissolution of Uranium Dioxide.

Solid UO2 dissolution and uranium speciation in aqueous solutions that promote formation of uranyl peroxide macroanions was examined, with a focus on the role of alkali metals. UO2 powders were dissolved in solutions containing XOH (X = Li, Na, K) and 30% H2O2. Inductively coupled plasma optical emission spectrometry (ICP-OES) measurements of solutions revealed linear trends of uranium versus alkali concentration in solutions resulting from oxidative dissolution of UO2, with X:U molar ratios of 1.0, showing that alkali availability determines the U concentrations in solution. The maximum U concentration in solution was 4.20 × 105 parts per million (ppm), which is comparable to concentrations attained by dissolving UO2 in boiling nitric acid, and was achieved by lithium hydroxide promoted dissolution. Raman spectroscopy and electrospray ionization mass spectrometry (ESI-MS) of solutions indicate that dissolution is accompanied by the formation of various uranyl peroxide cluster species, the identity of which is alkali concentration dependent, revealing remarkably complex speciation at high concentrations of base.

The revised potential – pH diagram for Pb – H2O system

Abstract Thermodynamic properties of lead species in aqueous solution are collected. The chemical equilibria between various forms of Pb(II) are considered. The speciation diagrams for the equilibria 4[PbOH]+(aq) ⇄ [Pb4(OH)4]4+(aq) and 2[Pb3(OH)4]2+(aq) ⇄ [Pb6(OH)8]4+(aq), and the thermodynamic activity - pH diagram of Pb(II) species are plotted. Basic chemical and electrochemical equilibria for lead are calculated. The potential - pH diagram for Pb - H2O system is revised.

Retention and release of hexavalent and trivalent chromium by chitosan, olive stone activated carbon, and their blend.

Shrimp shells and waste of olive stones were used as feedstock for the preparation of chitosan and activated carbon. The adsorption of CrVI and CrIII species in aqueous solution by the materials prepared and their blend were studied by using the well-known kinetic and isotherm models, Fourier transform infrared spectroscopy and scanning electron microscope. It was demonstrated that the rates of adsorption were controlled by diffusion inside particles and throughout the liquid film, and adsorption occurred spontaneously (- 26 < ∆G° < - 15kJ/mol) in the range of 298-333K, except for that involving CrIII species and activated carbon. The maximum amounts of Cr species retained by the composite (146mg of CrVI/g and 33mg of CrIII/g at 298K) were three times greater than those of the basic constituents. Adsorption was markedly affected by temperature and pH, and CrVI species were substantially desorbed in acid mediums, particularly in acetic acid solution. The recovery of CrIII species varied according to the adsorbent and the solution used. The immobilization of CrVI species (HCrO4- and CrO42-) and CrIII species (Cr(OH)2+ and Cr3(OH)45+) by chitosan was accomplished by means of amine moieties and hydroxyls of D-glucosamine units of the biopolymer. The adsorption of CrVI species on activated carbon involved π electrons of aromatic rings as well as oxygenated sites (C-OH, C=O, C-O-C). In such a condition, CrVI was partially reduced into CrIII. For the composite, the amino functional groups of chitosan and hydroxyls of both constituents were implicated in the linkage of the biopolymer and activated carbon, and the C-O-H and C-O-C functional groups of chitosan were involved in the retention of CrVI species. For CrIII species, adsorption occurred preferentially on hydroxyls of the components, and consequently, the chains of the biopolymer recovered some flexibility.

Recovery of High-Purity Vanadium from Aqueous Solutions by Reusable Primary Amines N1923 Associated with Semiquantitative Understanding of Vanadium Species

The recovery of high-purity vanadium has attracted significant attention regarding both sustainability and environmental protection necessities. However, insufficient understanding of vanadium species in aqueous solution constrains further optimization of the vanadium recovery process. Here, a closed-loop technical route (extraction and stripping) was realized to recover high-purity vanadium products by in situ monitoring/controlling vanadium species. The evolution of vanadium species in the extraction reaction was semiquantitatively visualized by the system combined with annular centrifugal contactors (ACCs) and electrospray ionization time-of-flight mass spectrometry (ESI-TOF-MS), while the active (V4 and V10 species) and nonactive (H2VO4–) vanadium species were identified. In the stripping process, the behaviors of vanadium species have been described, which affected the morphology of recycled NH4VO3 products. As a result, the transformation pathway of vanadium species in the whole recovery process was...

Towards Identifying the Active Sites on Oriented Ruthenium Dioxide Surfaces in Catalyzing Oxygen Evolution

The unique interaction between water and rutile Ruthenium Dioxide (RuO2) affords high pseudocapacitance and catalytic activities for a number of reactions such as the oxygen evolution reaction (OER)1,2,3. While the low energy, RuO2 (110) and (100) surfaces have been studied as model systems for gas phase catalysis and ultra high vacuum surface science studies4,5, the nature of adsorbed species in aqueous solutions remains to be understood. In this work, we examine the structural and chemical charge transfer processes occurring on oriented RuO2 single crystal surfaces as a function of potential, in acidic electrolyte, using in situ surface X-ray diffraction measurements. In order to validate experimentally observed changes in the nature of adsorbed oxygen, we use density functional theory to compute surface Pourbaix diagrams that show the most stable surface termination at any given potential. We start with the thermodynamically stable (110) surface, where we show that the coordinatively unsaturated sites (CUS) are the active sites for oxygen evolution. We also detect the formation of an –OO like group on the CUS site, which is the probable precursor of the evolved oxygen. We thus propose a four proton-electron mechanism for OER, where the final proton-electron removal is found to be rate limiting6. Using this evidence, we can rationally tune the oxygen evolution reaction (OER) activity of RuO2 surfaces by modifying the surface structure to increase the density of coordinatively unsaturated sites and optimize the binding strength of oxygenated species on the surface, in order to decrease the energetic barrier of the proposed rate-limiting step. We thus explore different orientations of RuO2, namely the (100), (101) and (001) terminations that have a higher CUS site density and lower oxygen binding energy compared to the (110) surface. Using in situ surface X-ray diffraction measurements we can detect the change in the nature of surface adsorbates just prior to OER for the different orientations. Probing the OER active state, supplemented by density functional theory calculations provides insight into the change of the rate limiting step and reaction mechanism for different orientations. Our work shows that modifying the surface orientation is an effective way to tune the active site density and energetics of key OER intermediates to obtain higher activities. Through this synergistic experimental and computational study, we provide an atomistic understanding of charge transfer processes prior to oxygen evolution and its implications on the oxygen evolution pathway on RuO2 for different surface orientations.

Evidence for the Heaviest Expected Halide Species in Aqueous Solution, At-, by Electromobility Measurements.

At- (astatide) is commonly expected to be the heaviest halide in the halogen group. However, there is no proof for the existence of this -1 charged species. Furthermore, investigations with astatine are restricted by its specific radioactive properties, which entail working at ultratrace concentrations (typically less than 10-10 M). In this work, an especially built electromigration device is applied to obtain information about the charge/size ratio characterizing an ion in aqueous solution. An anionic At species is observed in reducing conditions. Moreover, we propose the first absolute mobility value for the astatine species in acidic reducing condition: (-8.26 ± 0.59) × 10-4 cm2·V-1·s-1. This value appears close to that of I- ((-8.30 ± 0.33) × 10-4 cm2·V-1·s-1), which is obtained by the same method. The similar absolute mobilities obtained for both ions are coherent with theoretical calculations indicating similar diffusion behaviors for At- and I-. This good agreement confirms the existence of the At- species.

Highly selective fluorometric probes for detection of HClO in living cells

Due to the prominent photochemical and photophysical properties, the benzofurazan (NBD) fluorophore is a popular platform for constructing fluorescencet sensors. We reported herein a strategy to tune the fluorescence of NBD by modulating the push-pull pairs on the benzene ring, and obtained two novel fluorescent probes, MeS-DMAB and EtS-DMAB, which can selectively detect hypochlorous acid (HOCl) over other reactive oxygen species in aqueous solution with a large stokes shift (∼170 nm). The synthesis and optical properties of these two probes were described. The reaction products of HOCl with MeS-DMAB were isolated and characterized. It turns out that oxidation of the thioether to the corresponding sulfoxide accounts for the turn-on fluorescence. Finally, the probe EtS-DMAB was successfully applied to image exogenous and endogenous HOCl in live cells.

Reconciliation of pH, conductivity, total organic carbon with carboxylic acids detected by ion chromatography in solution after contact with multilayer films after γ-irradiation

The impact of γ-irradiation on polymers in multilayer films was studied by means of the study of the diffusion and release (spontaneous migration of the molecules from the container into the product) of chemical species in aqueous solution. A series of different measurements have been performed: pH, conductivity, total organic carbon (TOC) and ion chromatography (IC). Their evolution according to γ-irradiation dose was studied. More several rinsings made over several months allowed to quantify well the impact of the irradiation on these polymers. The samples are irradiated at several γ-doses, up to 270 kGy, and compared with a non-irradiated sample used as reference. It shows that quantity of generated carboxylic acids depends on the film material (PE/EVOH/PE and EVA/EVOH/EVA) and increases with γ-dose.

Free radical generation by non-equilibrium atmospheric pressure plasma in alcohol–water mixtures: an EPR-spin trapping study

Free radical species in aqueous solution—various alcohol–water reaction mixtures—by exposure to non-equilibrium cold atmospheric pressure Ar plasma (CAP), were monitored using electron paramagnetic resonance spin-trapping techniques with 3, 5-dibromo-4-nitrosobenzene sulfonate as a water soluble nitroso spin trap. The major radical species were formed by H-abstraction from alcohol molecules due to ·OH radicals. In the ethanol–water mixture ·CH2CH2OH produced by H abstraction from CH3 group of the ethanol and ·CH3 radicals were detected. The latter was due to the decomposition of unstable CH3·CHOH to form the ·CH3 radicals and the stable formaldehyde by C–C bond fission. These intermediates are similar to those observed by reaction with ·OH radicals generation in the H2O2–UV photolysis of the reaction mixtures. The evidence of ·CH3 radical formation in the pyrolytic decomposition of the reaction mixtures by exposure to ultrasound or in methane irradiated with microwave plasma have been reported previously. However, the pyrolytic ·CH3 radicals were not found in both plasma and H2O2–UV photolysis condition. These results suggests that free radicals produced by Ar-CAP are most likely due to the reaction between abundant ·OH radicals and alcohol molecules.

Amperometric Sensor Based on Au/MWCNT for Simultaneous Speciation of Cr(III) and Cr(VI) Ionic Species

In this paper, the simultaneous speciation of the Cr(VI) and Cr(III) ionic species in aqueous solutions was achieved by measuring the current of a cyclic voltammogram at determined potential, under mass transport limiting conditions, using a rotatory disk electrode. The influence of the sensor interface, the rotation speed, and the scan rate potential on the sensibility and time analysis were studied. Quantification of Cr(III) is related to the oxidation process to Cr(VI), while quantification of Cr(VI) is associated to reduction process to Cr(III). From the analysis of cyclic voltammograms at different rotation speed and scan rate, were determined that Cr(III) is controlled by electric charge transference, on the other hand, Cr(VI) is controlled by mass transference. The sensor was modified with ultra-low loading of Au nanoparticles on the carbon nanotubes (CNT), whose improve the quantification of Cr(VI) and Cr(III) compared with the conventional materials.

Simulation of Calcium Phosphate Species in Aqueous Solution: Force Field Derivation.

A new force field has been derived for the aqueous calcium phosphate system that aims to reproduce the key thermodynamic properties of the system, including free energies of hydration of the ions and the solubility of the solid mineral phases. Interactions of three phosphate anions (PO43-, HPO42-, and H2PO4-) with water were calibrated through comparison with the results obtained from ab initio molecular dynamics using both GGA and hybrid density functional theory with dispersion corrections. In the solid state, the force field has been evaluated by benchmarking against experiment and other existing models and is shown to reproduce the structural and mechanical properties well, despite the primary focus being on thermodynamics. To validate the force field, the thermodynamics of ion pairing for calcium phosphate species in water has been computed and shown to be in excellent agreement with experimental data.

Levaquin drug complexing property towards platinum and palladium metal ions: Thermodynamic studies in aqueous solutions

The experimental protonation and complex formation equilibrium constants of levaquin (LFX) with platinum(II) and palladium(II) metal ions have been investigated at 310.15K in water solutions at ionic strength of I=0.16mol·dm−3 NaNO3 using pH-potentiometric and cyclic voltammetry techniques, and by means of Hyperquad 2008 estimation model program. Also, the dissociation constants of LFX and the equilibrium constants of its binary complexes with the studied platinum(II) and palladium(II) metal ions in I=0.16mol·dm−3 NaNO3 water solutions were observed at different temperatures such as 298.15, 310.15, 318.15 and 328.15K. The theoretical calculations of overall protonation and stability constants of the metal ion-LFX complex species in aqueous solutions were predicted as the free energy change associated with the LFX protonation, and metal ion – LFX complex formation equilibria using ab initio and density function theory calculations by applying Gaussian 09 software molecular modeling. The determination of equilibrium constants were confirmed by the spectrophotometric method with the refinement by using the HypSpec program. The usage of the experimental potentiometry/spectrophotometry techniques and theoretical predictions provides a complete picture of the microscopic equilibria of the studied systems (metal ions -LFX). Precisely, this theoretically predications could be useful to control the most real protonation constants of levaquin ligand in which the binding sites changes due to the ligand protonation/deprotonation equilibria. Also, the complexing capacities of different platinum(II) and palladium(II) metal ions towards LFX in solutions were evaluated and discussed. From the determined experimental stability constants of different metal complex species, the concentration distribution diagrams of the various metal ions - LFX complex species in solutions were estimated using HySS 2009 software.

A molecular dynamics investigation of actinyl-ligand speciation in aqueous solution.

Actinyl ions (AnO2n+), the form in which actinides are commonly found in aqueous solution, are important species in the nuclear fuel cycle. These ions can form stable complexes with ionic ligands such as OH-, NO3-, Cl-, and even other actinyl ions in the aqueous phase. Knowledge of the relative stabilities of these complexes is important for the efficient design of separation processes used in recycling. These complexes also play a major role in the formation of actinide nanoclusters. A quantitative treatment of the stability of these actinyl ion complexes is therefore warranted. In the present work, molecular dynamics (MD) simulations have been performed to calculate the potential of mean force (PMF) between two actinyl ions (UO22+ and NpO2+) and various ligands (F-, Cl-, OH-, NO3-, SO42-, CO32-, Na+, and H2O) in explicitly-modeled aqueous solution. Equilibrium constants were calculated from the PMFs, and are consistent with experimental trends. Dication actinyls show stronger affinity for anions compared to monocation actinyls, whereas the opposite is true for cation-cation interactions between actinyls. Finally, the dynamics of actinyl-ligand contact ion pair (CIP) dissociation were characterized by calculating rate constants from transition state theory. The transmission coefficient, a dynamical correction factor used to correct for reaction barrier recrossing, was calculated for each actinyl-ligand CIP dissociation event.

Transport and accumulation of plasma generated species in aqueous solution.

The interaction between cold atmospheric pressure plasma and liquids is receiving increasing attention for various applications. In particular, the use of plasma-treated liquids (PTL) for biomedical applications is of growing importance, in particular for sterilization and cancer treatment. However, insight into the underlying mechanisms of plasma-liquid interactions is still scarce. Here, we present a 2D fluid dynamics model for the interaction between a plasma jet and liquid water. Our results indicate that the formed reactive species originate from either the gas phase (with further solvation) or are formed at the liquid interface. A clear increase in the aqueous density of H2O2, HNO2/NO2- and NO3- is observed as a function of time, while the densities of O3, HO2/O2- and ONOOH/ONOO- are found to quickly reach a maximum due to chemical reactions in solution. The trends observed in our model correlate well with experimental observations from the literature.

Thermodynamic studies on metal ions – Ninhydrin – Glycine interactions in aqueous solutions

The experimental protonation and complex formation equilibrium constants of ligands (ninhydrin (NHN) and glycine (Gly)) with trivalent (iron(III), aluminium(III), and chromium (III)), divalent (copper(II), cobalt(II), nickel(II), strontium(II), manganese(II), and mercury(II)) and monovalent silver(I) metal ions have been investigated at 310.15 K in water solutions at ionic strength of 13.60 g·dm−3 NaNO3 using pH-potentiometric, UV–visible spectrophotometric, and cyclic voltammetry techniques, and by means of Hyperquad 2008 estimation model program. Also, the dissociation constants of NHN and the equilibrium constants of its binary complexes and ternary complexes with the studied metal ions in 13.60 g·dm−3 NaNO3 water solutions were observed at different temperatures such as (298.15, 310.15, 318.15 and 328.15) K. The theoretical calculations of overall protonation and stability constants of the metal ion-ninhydrin complex species in aqueous solutions were predicted as the free energy change associated with the ninhydrin protonation, and metal ion – ninhydrin – glycine complex formation equilibria using ab initio and density function theory calculations by applying Gaussian 09 software molecular modelling. The convention of the experimental Potentiometry/Spectrophotometry techniques and theoretical calculations provide a complete picture of the microscopic equilibria of the studied metal ions – ninhydrin – glycine systems. Precisely, this theoretical predication could be useful to control the most real protonation constants of ninhydrin and glycine ligands in which the binding sites change due to the ligand protonation/deprotonation equilibria. Also, the complexing capacities of different metal ions towards ninhydrin and glycine in solutions were evaluated and discussed. From the determined experimental stability constants of different metal complex species, the concentration distribution diagrams of the various metal ions – ninhydrin – glycine complex species in solutions were estimated using HySS 2009 software.

A Couple of Tripodal and Dipodal Fluorescent Sensors for Sequential “On‐Off‐On” Response to Cu2+ and ATP/ADP Recognition in Aqueous Solution

AbstractA couple of tripodal (1) and dipodal (2) probes having tris(2‐aminoethyl) amine (tren) / N′‐Methyl‐2,2′‐diaminodiethylamine as core moiety, Boc‐L‐alanine as binding group and anthracene as signaling unit have been synthesized for the recognition of cations and anions. For 1 and 2, their recognition behaviors towards metal ions are similar, and both of them show selective recognition towards Cu2+ over other metal ions with a fluorescence “switch‐off” response. Notably, for in situ generated 1‐Cu2+ and 2‐Cu2+ ensembles, their responses towards polyphosphate anions are different. 1‐Cu2+ exhibits a more significant fluorescence “switch‐on” response towards ATP than other anionic species in aqueous solution (H2O/DMSO 9:1, HEPES buffer, 0.01 M, pH 7.4). While 2‐Cu2+ shows a better sensitivity to ADP than ATP under the same conditions. Sequential “on‐off‐on” fluorescence responses of 1 and 2 to Cu2+ and ATP/ADP are successfully applied in HeLa cells.

Adsorption of Scandium and Neodymium on Biochar Derived after Low-Temperature Pyrolysis of Sawdust

The objective of this study was to investigate the adsorption of two rare earth elements (REEs), namely scandium (Sc) and neodymium (Nd), on biochar produced after low temperature pyrolysis (350 °C) of wood sawdust. The biochar was characterized with the use of several analytical techniques, namely X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and thermogravimetric (TG) analysis, while the pH at point of zero charge (pHPZC) was also determined. The experimental conditions were: absorbent concentration 1–10 g·L−1, REE concentration in solution 20 mg·L−1, contact time for equilibrium 24 h, temperature 25 °C and stirring speed 350 rpm. The efficiency of biochar was compared to that of a commercial activated carbon. Geochemical modelling was carried out to determine speciation of Nd and Sc species in aqueous solutions using PHREEQC-3 equipped with the llnl database. The experimental results indicated the potential of low temperature produced biochar, even though inferior to that of activated carbon, to adsorb efficiently both REEs. The equilibrium adsorption data were very well fitted into the Freundlich isotherm model, while kinetic data suggested that the removal of both REEs follows the pseudo-second order kinetic reaction. Finally, the most probable adsorption mechanisms are discussed.

Structure, acidity, and metal complexing properties of oxythioarsenites in hydrothermal solutions

In the pursuit of understanding the aqueous chemistry of oxythioarsenites (i.e., H3AsO2S and H3AsOS2) on a microscopic scale, first principles molecular dynamics (FPMD) simulations were performed to investigate the hydration structures, acidity constants, and metal-complexing properties of these species in aqueous solutions at temperatures up to 573K. The simulations showed that the oxythioarsenite species are stable and have trigonal pyramidal structures in both low- and high-temperature fluids. Their solvated structures were characterized in detail and it was found that the S or H atoms of the SH ligands form very weak H-bonds with the solvating water molecules and the OH ligands form H-bonds with water as both donors and acceptors. Furthermore, the dangling S or O sites act as strong acceptors to form H-bonds. Their acidity constants were calculated by using the FPMD-based vertical energy gap method. Together with our previous work (Liu et al., 2015, Chemical Geology, 411, 192–199), we found that in the arsenite-thioarsenite series (i.e., H3AsO3−xSx for x varying from 0 to 3), the pKa values of the oxythioarsenite species (H3AsO2S and H3AsOS2) were always located between those of the end members, H3AsO3 and H3AsS3, and decreased with the increasing temperature up to 573K. Based on the calculated acidity constants, the speciation versus pH distributions were obtained at temperatures ranging from ambient temperature to 573K. It was found that both H2AsO2S− and H2AsOS2− are the predominant species at near neutral pH for H3AsO2S and H3AsOS2 species, respectively. In addition, the structures and the dissociation free energy of the oxythioarsenite-metal complexes at 573K indicated that these As-S moieties are effective ligands for complexing with ore-forming metals in geological fluids.