Chemical Species In Solution Research Articles

Transformation of Engineered Copper Oxide Nanoparticles in Surface Waters.

Copper oxide nanoparticles (CuO-NPs) are widely used for their catalytic properties, conductive capacity, and innovations in the fields of superconductors, alloys, and solar energy sensors. To better understand the impact of water chemistry on the stability of CuO nanoparticles, a series of measurements were carried out on nanoparticles suspended in pure water, natural water, and water enriched with natural organic matter fulvic acid (FA). ICP-MS characterization in single-particle mode (SP-ICP-MS) was performed to determine the stability or transformation of nanoparticles in contrasting water conditions. We first observed that particle sedimentation was very fast in pure Milli-Q water. The addition of FA favored the dissolution of CuO-NPs with an increase in the dissolved copper concentration, for both Milli-Q water and natural water. The presence of FA also reduced the size of CuO-NPs (i.e., less aggregation) measured in natural water. By comparing signals of single particles, FA decreased nanoparticle numbers as well, confirming the increase in dissolution of CuO-NPs over time. The transformation products of CuO-NPs are important in the ecological context since the uptake and toxicity of parent nanoparticles differ from those of the chemical species in solution. Further considerations are needed on the fate of released NPs to better assess their exposure pathways to aquatic organisms and potential environmental risks.

Ecological regulation of chemical weathering recorded in rivers

We provide a new generalized framework accounting for the effects of water and nutrient uptake by roots in the weathering zone on broad patterns of solute concentration - discharge relationships in rivers. As plants withdraw water from the subsurface, they decrease the area-normalized fluid drainage rate. This results in a discharge flux to springs and streams which is a function of water use by plants, leading to ecosystem regulation of the characteristic timescales of chemical weathering reactions and fluid flow rate. Our predictive framework quantifies the pore water and river solute chemistry generated from water-rock interactions, regulated by the effects of vegetation on water flow rates. To this we add the capacity for vegetation to enrich, passively admit, or discriminate against a given dissolved solute based on ecophysiological needs, thus further modifying the local concentration of a given chemical species in solution across a weathering profile. This uptake flux is not lost to the atmosphere in the same manner as water is removed from the subsurface via evapotranspiration. Rather, these extracted chemical species become incorporated into the topsoil as litter which may be partially or fully resolubilized, creating an upper boundary condition which depends on the uptake and recycling characteristics of the ecosystem. These processes are united through a new solution to the advection-reaction equation which allows vegetation to regulate broad patterns of stream concentration - discharge relationships. We show that ecosystems are capable of both accelerating and impeding water-rock reaction rates across the weathering profile, ultimately leading to both thermodynamic and ecological controls on the baseflow concentration of rock-derived solutes in rivers.

Association constants of guanine oligomers with alkali-metal ions studied using atmospheric pressure droplet IR-laser ablation mass spectrometry

Abstract Guanine (G) molecules form a stable tetramer with a metal ion called a G-quartet. We observed G-quartets by using atmospheric pressure droplet Infrared-laser ablation mass spectrometry, which enables us to analyze the abundance of chemical species in solutions. We estimated the association constants of Gn and M+ (M+ = Li+, Na+, and K+) from the intensities of G1–5H+ and G1–4M+ in the obtained mass spectra. The larger association constants of G4 than those of Gn (n ≠ 4) indicate the stability of G-quartets.

Element distribution in electrochemically treated mine wastewater for efficient resource recovery and water treatment: A pilot study

The feasibility of recovering major and critical elements from acid mine drainage using a pilot-scale electrochemical reactor (ECR) was investigated by assessing elements concentration and species distribution in the liquid and solid phase (sludge) in multistage tests. These were carried out at different electrical currents (18–22 amps) and thus, pH (8–12). The results showed that major metals Al, Cu and Fe were removed from the liquid phase at pH 5.9 while remaining the majority of Zn (57.2 ppm). On the other hand, at pH 7, the effluent was mainly composed of Mn (7.3 ppm). These results were confirmed by the simulation results using the PHREEQC model, which also identified the main chemical species in solution and the precipitates formed after the treatment (oxyhydroxides/sulfates/oxides). The ECR treatment led to sludges with targeted critical elements, some up to 20 times (Co, Be and Sb) higher than their earth's crustal abundance. At pH 10, rare earth elements in the sludge targeted Ce, followed by Nd and La. This study is one of the few studies carrying a detailed analysis of the behavioural distribution pattern of these elements at each pH, which opens the door for the potential of recovering these elements.

11 Platinum Speciation in Air Samples

Abstract The health effects of chloroplatinates are generally well recognised and acknowledged by regulators in both EU and USA (Platinum salt sensitivity). But what about Platinum species? Speciation is essential for valid toxicology assessments and speciation studies are lacking in this respect – it’s known that certain Platinum chloro complexes are more sensitising than others. A method for the separation of platinum chloro-complexes and their hydrolysis products has been developed. The different platinum chemical species are separated into their charged compounds in 0.07 M HCl: [PtCl4]2-, [PtCl6]2-, [PtCl3(H2O)]-, [PtCl5(H2O)]- and a zero charged/ bis-aquo compound. The separation was carried via an ion exchange chromatographic column coupled to a quadrupole ICP-MS for the detection of the different anionic platinum chloro-species. A gradient program consisting of a mixture of HCl and HClO4 was used as eluent to ensure the separation of the species. A process has been developed for the analysis of platinum species extracted from air filters in a PGM facility with JM. Although the methodology for speciation is robust, further work needs to be carried out in terms of alternative sample collection to the air filters such as bubblers as the process of sonication, drying and acid contact on the filters does adversely affect the chemical species in solution. A comparison between Platinum speciation in air filters collected form IOM samplers and bubblers will be included in this presentation. This work will generate data to help characterise different workplaces based on the types of task-based exposure.

Magnetic field-enhanced redox chemistry on-the-fly for enantioselective synthesis.

Chemistry on-the-fly is an interesting concept, extensively studied in recent years due to its potential use for recognition, quantification and conversion of chemical species in solution. In this context, chemistry on-the-fly for asymmetric synthesis is a promising field of investigation, since it can help to overcome mass transport limitations, present for example in conventional organic electrosynthesis. Herein, the synergy between a magnetic field-enhanced self-electrophoretic propulsion mechanism and enantioselective redox chemistry on-the-fly is proposed as an efficient method to boost stereoselective conversion. We employ Janus swimmers as redox-active elements, exhibiting a well-controlled clockwise or anticlockwise motion with a speed that can be increased by one order of magnitude in the presence of an external magnetic field. While moving, these bifunctional objects convert spontaneously on-the-fly a prochiral molecule into a specific enantiomer with high enantiomeric excess. The magnetic field-enhanced self-mixing of the swimmers, based on the formation of local magnetohydrodynamic vortices, leads to a significant improvement of the reaction yield and the conversion rate.

Surface Plasmon Photodetectors Based on Noble Metals

In this work, high sensitivity noble metals used in the Kretschmann configuration based photodetectors applied to detect the presence of biological and chemical species in solutions are investigated. The angle of incidence and film thickness dependencies of the surface plasmon polariton resonance (SPPR) of gold, silver and copper by the attenuated total reflection (ATR) method are studied to monitor and evaluate the SPR reflectance angle and reflectivity change. The analysis of the electric field of the surface plasmon wave which appears at the interface between the metallic layer and the air is carried out by the finite element method (FEM). The simulation is performed using COMSOL Multiphysics software which supports FEM. The aim of the present study is to find the most suitable noble metal and its optimum thickness to improve the performance of the SPR photodetector. Keywords: Attenuated total reflection method, FEM based COMSOL multiphysics software, Kretschmann configuration, noble metals, reflectivity.

Analyzing multi-step ligand binding reactions for oligomeric proteins by NMR: Theoretical and computational considerations

Solution NMR spectroscopy is widely used to investigate the thermodynamics and kinetics of the binding of ligands to their biological receptors, as it provides detailed, atomistic information, potentially leading to microscopic affinities for each binding event, and, to the development of allosteric pathways describing how the binding at one site affects distal sites in the molecule. Importantly, weak interactions that are often invisible to other biophysical methods can also be probed. Methodological advancements in NMR have enabled the investigation of high molecular weight, homo-oligomeric complexes that bind multiple ligand molecules, with increasing numbers of studies of the structural dynamics and binding properties of these systems. It therefore becomes of interest to consider how binding and kinetics parameters can be extracted from experiments on these more complicated molecules. Here we present the theoretical framework for analyzing binding reactions of homo-oligomeric complexes by NMR, taking into account all of the chemical species in solution and their corresponding NMR observables. A number of simulations are presented to illustrate the utility of the derived expressions.

QUESTIONING THE RELEVANCE OF SOLUTION pH CALCULATION

A brief discussion on the unnecessary calculation of pH in solution was done, as the historical reasons for this need before the invention of commercial pH meter was widely diffused. An alternative approach for acid-base equilibrium evaluation was proposed, without approximation or need of application only for simple solutions. The central aspect for the new approach is the determination of equilibrium concentration of all chemical species in solution, including the strong acid or base concentration for adjusting of pH of solutions. Therefore, the proposed method allowed the calculation in a mixture, including several polyprotic systems. Two detailed examples were presented. The effective electrical charge parameter was formally defined.

Nuclear magnetic shielding of molecule in solution based on reference interaction site model self-consistent field with spatial electron density distribution.

A new method for calculating nuclear magnetic shielding in solutions is developed based on the reference interaction site model self-consistent field (RISM-SCF) with spatial electron density distribution (SEDD). In RISM-SCF-SEDD, the electrostatic interaction between the solute and the solvent is described by considering the spread of electron to obtain more realistic electronic structure in solutions. It is thus expected to allow us to predict more quantitative chemical shifts of a wide variety of chemical species in solutions. In this study, the method is applied to a water molecule in water and is validated by examining the dependence of the solvent temperature and density on chemical shifts. The dependence of solvent species is also investigated, and more accurate results are obtained for polar solvents compared to the previous RISM-SCF study. Another application example of this method is the 15N chemical shifts of two azines in water, which is difficult to predict with the polarizable continuum model (PCM). Our results are in good agreement with the previous quantum mechanical/molecular mechanics study and experimental results. It is also shown that our method gives more realistic results for methanol and acetone than the PCM.

DESCRIPTION OF PROCESS IN AQUEOUS SOLUTIONS: DIFFERENCES BETWEEN XIX AND XX CENTURIES CONCEPTIONS

The development of studies of Chemical solutions occurred with two distinct concepts, the XIX century concept, and the XX century concept. XIX century concept was created before the Arrhenius’ electrolytic theory and it did not consider the real chemical species in solution. The differences between these concepts can seem subtle at a glance, but some examples are shown to clarify them, as well as the problems with use the XIX century concept. The examples involve differences in chemical equations, Henderson-Hasselbach Equation, Arrhenius’ Ionization degree, Acid-base and solubility equilibria.

How Solvent Dynamics Controls the Schlenk Equilibrium of Grignard Reagents: A Computational Study of CH3MgCl in Tetrahydrofuran.

The Schlenk equilibrium is a complex reaction governing the presence of multiple chemical species in solution of Grignard reagents. The full characterization at the molecular level of the transformation of CH3MgCl into MgCl2 and Mg(CH3)2 in tetrahydrofuran (THF) by means of ab initio molecular dynamics simulations with enhanced-sampling metadynamics is presented. The reaction occurs via formation of dinuclear species bridged by chlorine atoms. At room temperature, the different chemical species involved in the reaction accept multiple solvation structures, with two to four THF molecules that can coordinate the Mg atoms. The energy difference between all dinuclear solvated structures is lower than 5 kcal mol-1. The solvent is shown to be a direct key player driving the Schlenk mechanism. In particular, this study illustrates how the most stable symmetrically solvated dinuclear species, (THF)CH3Mg(μ-Cl)2MgCH3(THF) and (THF)CH3Mg(μ-Cl)(μ-CH3)MgCl(THF), need to evolve to less stable asymmetrically solvated species, (THF)CH3Mg(μ-Cl)2MgCH3(THF)2 and (THF)CH3Mg(μ-Cl)(μ-CH3)MgCl(THF)2, in order to yield ligand exchange or product dissociation. In addition, the transferred ligands are always departing from an axial position of a pentacoordinated Mg atom. Thus, solvent dynamics is key to successive Mg-Cl and Mg-CH3 bond cleavages because bond breaking occurs at the most solvated Mg atom and the formation of bonds takes place at the least solvated one. The dynamics of the solvent also contributes to keep relatively flat the free energy profile of the Schlenk equilibrium. These results shed light on one of the most used organometallic reagents whose structure in solvent remains experimentally unresolved. These results may also help to develop a more efficient catalyst for reactions involving these species.

The Heaviest Possible Ternary Trihalogen Species, IAtBr−, Evidenced in Aqueous Solution: An Experimental Performance Driven by Computations

AbstractEvidencing new chemical species in solution is particularly challenging when one works at ultra‐trace concentrations, as is likely to happen with radioelements such as astatine (Z=85). Herein, quantum mechanical calculations were used to predict the narrow experimental domain in which it is possible to detect the presence of an exotic ternary trihalogen anion, IAtBr−, and thus to guide a series of experiments. By analyzing the outcomes of competition experiments, we show that IAtBr− exists and can even predominate in aqueous solution. The equilibrium constant associated with the reaction At++I−+Br−⇌IAtBr− was determined to be 107.5±0.2, which is in fair agreement with that predicted by density functional theory (106.9). This system not only constitutes the very first example of a ternary trihalogen species that involves the element astatine but is also the first trihalogen species reported to predominate in solution. Moreover, we show that the oxidation number of At is zero in this species, as in the other molecules and anions that At+ can form with Cl−, Br−, and I− ligands.

The Heaviest Possible Ternary Trihalogen Species, IAtBr- , Evidenced in Aqueous Solution: An Experimental Performance Driven by Computations.

Evidencing new chemical species in solution is particularly challenging when one works at ultra-trace concentrations, as is likely to happen with radioelements such as astatine (Z=85). Herein, quantum mechanical calculations were used to predict the narrow experimental domain in which it is possible to detect the presence of an exotic ternary trihalogen anion, IAtBr- , and thus to guide a series of experiments. By analyzing the outcomes of competition experiments, we show that IAtBr- exists and can even predominate in aqueous solution. The equilibrium constant associated with the reaction At+ +I- +Br- ⇌IAtBr- was determined to be 107.5±0.2 , which is in fair agreement with that predicted by density functional theory (106.9 ). This system not only constitutes the very first example of a ternary trihalogen species that involves the element astatine but is also the first trihalogen species reported to predominate in solution. Moreover, we show that the oxidation number of At is zero in this species, as in the other molecules and anions that At+ can form with Cl- , Br- , and I- ligands.

Reversed Janus Micro/Nanomotors with Internal Chemical Engine.

Self-motile Janus colloids are important for enabling a wide variety of microtechnology applications as well as for improving our understanding of the mechanisms of motion of artificial micro- and nanoswimmers. We present here micro/nanomotors which possess a reversed Janus structure of an internal catalytic “chemical engine”. The catalytic material (here platinum (Pt)) is embedded within the interior of the mesoporous silica (mSiO2)-based hollow particles and triggers the decomposition of H2O2 when suspended in an aqueous peroxide (H2O2) solution. The pores/gaps at the noncatalytic (Pt) hemisphere allow the exchange of chemical species in solution between the exterior and the interior of the particle. By varying the diameter of the particles, we observed size-dependent motile behavior in the form of enhanced diffusion for 500 nm particles, and self-phoretic motion, toward the nonmetallic part, for 1.5 and 3 μm ones. The direction of motion was rationalized by a theoretical model based on self-phoresis. For the 3 μm particles, a change in the morphology of the porous part is observed, which is accompanied by a change in the mechanism of propulsion via bubble nucleation and ejection as well as a change in the direction of motion.

Chemical Changes in Nonthermal Plasma-Treated N-Acetylcysteine (NAC) Solution and Their Contribution to Bacterial Inactivation.

In continuation of our previous reports on the broad-spectrum antimicrobial activity of atmospheric non-thermal dielectric barrier discharge (DBD) plasma treated N-Acetylcysteine (NAC) solution against planktonic and biofilm forms of different multidrug resistant microorganisms, we present here the chemical changes that mediate inactivation of Escherichia coli. In this study, the mechanism and products of the chemical reactions in plasma-treated NAC solution are shown. UV-visible spectrometry, FT-IR, NMR, and colorimetric assays were utilized for chemical characterization of plasma treated NAC solution. The characterization results were correlated with the antimicrobial assays using determined chemical species in solution in order to confirm the major species that are responsible for antimicrobial inactivation. Our results have revealed that plasma treatment of NAC solution creates predominantly reactive nitrogen species versus reactive oxygen species, and the generated peroxynitrite is responsible for significant bacterial inactivation.

Control of crystallite and particle size in the synthesis of layered double hydroxides: Macromolecular insights and a complementary modeling tool

Zinc–aluminum layered double hydroxides with nitrate intercalated (Zn(n)Al–NO3, n=Zn/Al) is an intermediate material for the intercalation of different functional molecules used in a wide range of industrial applications. The synthesis of Zn(2)Al–NO3 was investigated considering the time and temperature of hydrothermal treatment. By examining the crystallite size in two different directions, hydrodynamic particle size, morphology, crystal structure and chemical species in solution, it was possible to understand the crystallization and dissolution processes involved in the mechanisms of crystallite and particle growth. In addition, hydrogeochemical modeling rendered insights on the speciation of different metal cations in solution. Therefore, this tool can be a promising solution to model and optimize the synthesis of layered double hydroxide-based materials for industrial applications.

Soil solution concentrations and chemical species of copper and zinc in a soil with a history of pig slurry application and plant cultivation

Successive pig slurry applications may increase soil copper (Cu) and zinc (Zn) concentrations and change the proportions of free chemical species in solution when combined with plant cultivation. The aim of this study was to assess the soluble, available, and total Cu and Zn concentrations and the distribution of their chemical species in the solution in a Hapludalf soil with a history of pig slurry application and plant cultivation. The study was conducted in undisturbed soil columns that originated from an 8-year-long experiment conducted at the experimental unit of the Federal University of Santa Maria in Santa Maria, southern Brazil. The soil was a Typic Hapludalf soil fertilized with pig slurry at rates of 0, 20, 40, and 80m3ha−1. The soil was collected from depth intervals of 0–0.05, 0.05–0.1, 0.1–0.2, 0.2–0.3, 0.3–0.4, and 0.4–0.6m before and after cultivation with black oat and maize in a greenhouse to assess the total and available Cu and Zn concentrations and to extract the solution. The soil solution concentrations of the main cations, anions, and dissolved organic carbon (DOC) and pH were assessed. The distribution of Cu and Zn chemical species was assessed using the Visual Minteq software. The history of 21 pig slurry applications increased the concentration of Cu and Zn in surface soil intervals, but the concentration of Cu also increased in the soil solution at depth. The phytotoxicity caused by Cu and Zn may not occur even after several years of pig slurry application because the plants provide soil conditions in which chemical species complexed with dissolved organic carbon predominate and Cu and Zn in free forms are present only in small amounts.

Selective porous gates made from colloidal silica nanoparticles.

Highly selective porous films were prepared by spin-coating deposition of colloidal silica nanoparticles on an appropriate macroporous substrate. Silica nanoparticles very homogenous in size were obtained by sol–gel reaction of a metal oxide silica precursor, tetraethyl orthosilicate (TEOS), and using polystyrene-block-poly(ethylene oxide) (PS-b-PEO) copolymers as soft-templating agents. Nanoparticles synthesis was carried out in a mixed solvent system. After spin-coating onto a macroporous silicon nitride support, silica nanoparticles were calcined under controlled conditions. An organized nanoporous layer was obtained characterized by a depth filter-like structure with internal porosity due to interparticle voids. Permeability and size-selectivity were studied by monitoring the diffusion of probe molecules under standard conditions and under the application of an external stimulus (i.e., electric field). Promising results were obtained, suggesting possible applications of these nanoporous films as selective gates for controlled transport of chemical species in solution.

The potential of ball-milled South African bentonite clay for attenuation of heavy metals from acidic wastewaters: Simultaneous sorption of Co2+, Cu2+, Ni2+, Pb2+, and Zn2+ ions

Adsorption of Co2+, Cu2+, Ni2+, Pb2+, and Zn2+ by bentonite clay from polycationic solution was investigated. Mineralogical composition of clay was done using X-ray diffraction (XRD), elemental composition using X-ray fluorescence (XRF) and morphology using scanning electron microscopy (SEM) and electron dispersion X-ray (EDX). Optimum adsorption conditions were evaluated using batch experimental procedures. Parameters optimized included: adsorbent dosage, shaking time, ion’s concentration and pH. Interaction of bentonite clay with acidic wastewaters led to an increase in pH and significant reduction in metal species concentration. Optimization experiments revealed that 60min of equilibration, 1g of clay dosage, 50mgL−1 of polycations, pH 6, 250rpm and 26°C were the optimum condition for removal of heavy metals from the acidic wastewaters. Removal of metals was >99% for all chemical species in solution. The metal species sorption affinity varied as follows: Co>Cu>Ni=Zn>Pb. Kinetic studies showed that adsorption by bentonite clay fitted to the pseudo-second-order model with pore diffusion also acting as a major rate governing step. The adsorption data fitted well to Freundlich adsorption isotherm than Langmuir adsorption isotherm hence confirming multilayer adsorption. This comparative study proved that bentonite clay can increase the pH and effectively remove metal species from acidic and metalliferous wastewaters.