Species In Aqueous Solution Research Articles

The systematical detection and structure characterization of vanadium‐oxygen species in low concentration solutions by surface‐enhanced Raman spectroscopy experiments and density functional theory calculations

AbstractVanadium–oxygen species are very harmful to the environment and human health, and also some vanadium–oxygen species have good biological and biomedical effects to human beings. Thus, the study of vanadium–oxygen species is very significant. The types of V–O species are very complex. So far, however, the various structures of V–O species cannot be identified clearly. In this work, the surface‐enhanced Raman spectroscopy (SERS) was used to study vanadium–oxygen species in aqueous solution directly. The SERS spectra with high enhancement factor (EF) and detail information were obtained by the enhancement substrates such as gold nanoparticles (AuNPs), Ag mirror, the Au‐deposited Pt electrodes, and rough Au electrodes. The structures of vanadium‐oxygen species in solutions with different concentration and pH had been well‐characterized firstly by the combination of SERS experiments with density functional theory (DFT) calculations. This work will promote the basic study of the V–O species, and it is also a promotion for the SERS and analytical chemistry.

Speciation in CO2-loaded aqueous solutions of sixteen triacetoneamine-derivates (EvAs) and elucidation of structure-property relationships

The speciation in CO2-loaded aqueous solutions of 16 different derivates of triacetoneamine (EvAs) was investigated in a comprehensive NMR-spectroscopic study. About 350 experiments were carried out for CO2-loadings up to 3 moles CO2 per mole amine, temperatures between 20 °C and 100 °C, and a mass fraction of EvA in the unloaded solvent of 0.1 g/g. The observed CO2-containing species were primary and secondary carbamates, alkylcarbonate, (bi)carbonate, and molecular CO2. Some EvAs can form zwitterions with a ring structure, which have an important influence on the speciation. From the comprehensive set of data, relationships between the chemical structure of the EvAs and the observed speciation in aqueous solution were established. These results were related to application properties of the EvAs that were taken from previous work. Based on the findings, some general guidelines for the design of new amines were derived and applied for proposing new amines for CO2-absorption.

Formation of Heteropolynuclear Lanthanide Complexes Using Macrocyclic Phosphonated Cyclam-Based Ligands.

Ligands L1 and L2, respectively based on a cyclam and a cross-bridged cyclam scaffold functionalized at N1 and N8 by 6-phosphonic-2-methylene pyridyl groups, are described. While complexation of lanthanide (Ln) cations with L2 was not possible, a family of complexes has been prepared with L1, of the general formulae [LnL1H2]Cl (Ln3+ = Lu, Tb, Yb) or [LnL1H] (Ln3+ = Eu). The solution, structural, potentiometric, and photophysical data for these novel ligands and their complexes have been investigated, including a solid-state study by X-ray diffraction (L1, L2, and [EuL1H]), 1H NMR complexation investigations (Lu3+), as well as UV-vis absorption and luminescence spectroscopy in water and D2O (pH ≈ 7). L1 forms 1:1 metal-ligand stoichiometric octadentate complexes in solution. Importantly, the pyridyl phosphonate functions are capable of simultaneous chelation to the metal center and of interaction with a second metal center. 1H NMR (Lu3+) and spectrophotometric titrations of the isolated [TbL1]- complex by EuCl3 salts demonstrated the formation of high-order (hetero)polymetallic species in aqueous solution (H2O, pH = 7). Global analysis of the luminescence titration experiment points to the formation of 4:1, 3:1, and 3:2 [TbL1]/Eu heteropolynuclear assemblies, exhibiting a strong preference to forming [TbL1]3Eu2 at increased europium concentrations, with energy transfer occurring between the kinetically inert terbium complex and added europium cations.

Distinctive hydration dynamics around highly coordinated Cu2+/Zn2+-chloride complexes: A molecular dynamics simulation study

The existence of highly coordinated dication-chloride complexes and hydration characteristics around these species remain controversial. In this work, molecular dynamics simulations were used to investigate the stability of [CuCl4]2− and [ZnCl4]2− complexes in aqueous solution at various temperatures and electric fields. The results exhibit the presence of [CuCl4]2− and [ZnCl4]2− complexes in aqueous solution. For [CuCl4]2− and [ZnCl4]2− complexes, there is no overlap of the inner hydration shells, which is different from [CaClx]2-x (x = 4– 6) complexes. Our results show that the existence of [CuCl4]2− and [ZnCl4]2− species can be attributed to the hydration dynamics of their second shell. The dynamic rotation of hydration bonds between water molecules and Cl− ions of [CuCl4]2− or [ZnCl4]2− clusters can prolong the residence of the water molecules in the second shell, and promote the presence of [CuCl4]2− and [ZnCl4]2− species in aqueous solution. The dynamic rotation of water molecules also results in the relative separation of [CuCl4]2− or [ZnCl4]2− clusters with the bulk phase. Compared with hydrated Cu2+ ion, the fast diffusion of [CuCl4]2− cluster indicates that the interaction of hydrated [CuCl4]2− cluster with bulk phase is relatively weak.

Formation of Functional Cyclooctadiene Derivatives by Supramolecularly‐ Controlled Topochemical Reactions and Their Use as Highly Selective Fluorescent Biomolecule Probes†

Summary of main observation and conclusionControlling the regio‐ and stereochemistry of the photoproducts in solution is far more challenging for polyenes than for monoalkenes. Herein, a supramolecularly‐controlled topochemical reaction of conjugated dienes in homogeneous system is developed, ultimately providing two cyclooctadiene‐cored tetraimidazolium molecular receptors exclusively. These cyclooctadiene derivatives exhibited highly sensitive and selective fluorescence sensing for thymine relative to other biologically relevant species in aqueous solution at physiological pH. Both the cyclooctadiene moieties and imidazolium units play important roles in the selective recognition observed. The presented supramolecularly‐controlled method allows the simple yet rare selective photoconversion of flexible cyclooctadiene derivatives in solution. This study offers a new synthetic strategy for the preparation of functional molecules with potential for use in biological applications.

Pressure Induced Wetting and Dewetting of the Nonpolar Pocket of Deep-Cavity Cavitands in Water.

Hydrophobic interactions drive the binding of nonpolar ligands to the oily pockets of proteins and supramolecular species in aqueous solution. As such, the wetting of host pockets is expected to play a critical role in determining the thermodynamics of guest binding. Here we use molecular simulations to examine the impact of pressure on the wetting and dewetting of the nonpolar pockets of a series of deep-cavity cavitands in water. The portals to the cavitand pockets are functionalized with both nonpolar (methyl) and polar (hydroxyl) groups oriented pointing either upward or inward toward the pocket. We find wetting of the pocket is favored by the hydroxyl groups and dewetting is favored by the methyl groups. The distribution of waters in the pocket is found to exhibit a two-state-like equilibrium between wet and dry states with a free energy barrier between the two states. Moreover, we demonstrate that the pocket hydration of the cavitands can be collapsed onto a unified adsorption isotherm by assuming the effective pressures within each cavitand pocket differ by a shift pressure that depends on the chemical identity and number of functional groups placed about the portal. These observations support the development of a two-state capillary evaporation model that accurately describes the equilibrium between states and naturally gives rise to the effective shift pressures observed from simulation. This work demonstrates that the hydration of host pockets can be tuned following simple design rules that in turn are expected to impact the thermodynamics of guest complexation.

Complexation of As(III) by phosphonate ligands in aqueous fluids: Thermodynamic behavior, chemical binding forms and sequestering abilities

In recent years, the contamination of water by arsenic reached alarming levels in many countries of the world, attracting the interest of many researchers engaged in testing methodologies able to remove this harmful pollutant. An important aspect that must be taken into consideration is the possibility to find arsenic in different chemical forms which could require different approaches for its removal. At this aim, a speciation analysis appears to be crucial for better understanding the behavior of arsenic species in aqueous solutions, especially in presence of compounds with marked chelating properties. Phosphonates can be identified as good sequestering agents and, at this purpose, this manuscript intends to investigate the interaction of As(III) with three phosphonic acids derived from nitrilotriacetic acid (NTA) by replacements of one (N-(Phosphonomethyl) iminodiacetic acid, NTAP), two (N,N-Bis-(phosphonomethyl) glycine, NTA2P) and three (Nitrilotri(methylphosphonic acid), NTA3P) carboxylic groups with the same number of phosphonate groups. An in-depth potentiometric and calorimetric investigation allowed to determine speciation models featured by simple ML, MLHi and ML(OH) species. A complete thermodynamic characterization of the systems is reported together with the definition of coordination mode by mass spectrometry measurements. On the light of the speciation models, the possibility of using these ligands in arsenic removal techniques was assessed by determining the pL0.5 (the concentration of ligand able to remove the 50% of metal ion present in trace). All ligands show a good sequestering ability, in particular under the conditions of fresh water, following the trend NTA3P > NTA2P > NTAP.

Evaluation of influence of cold atmospheric pressure argon plasma operating parameters on degradation of aqueous solution of Reactive Blue 198 (RB-198)

The intention of this work is to remove Reactive Blue 198 (RB-198) dye components from simulated water solution using cold atmospheric pressure argon plasma jet. Aqueous solutions of RB-198 dye were treated as a function of various operating parameters such as applied potential, reaction time and distance between the plasma jet and surface of the liquid. The efficiency of the degradation of RB-198 molecules was explored by means of UV-Vis spectroscopy. The reactive species involved during the treatment process were examined by optical emission spectra (OES). The present hydroxyl radicals (OH• radical) and hydrogen peroxide (H2O2) in the plasma-treated aqueous dye solutions were investigated using various spectroscopic techniques. The other parameters such as total organic carbon (TOC), conductivity and pH were also reviewed. The toxicity of plasma-treated RB-198 solution was finally studied by diffusion bacterial analysis and by tracking seed germination processes. The results show that a higher degradation percentage of 99.27% was acquired for the RB-198 treated at higher reaction time and applied potential, and shorter distance between the plasma jet and water surface. This may be due to the formation of various reactive oxygen (OH• radical, atomic oxygen (O) and H2O2) and nitrogen species (nitric oxide (NO) radicals and N2 second positive system (N2 SPS)) during the processes as confirmed by OES analysis and other spectroscopy analysis. TOC (17.7% – 81.8%) and pH (7.5 – 3.4) values of the plasma-treated RB-198 decreased significantly with respect to various operation parameters, which indicates the decomposition of RB-198 molecules in the aqueous solution. Moreover, the conductivity of plasma-treated RB-198 aqueous solutions was found to have increased linearly during the plasma treatment due to the formation of various ionic species in aqueous solution. The toxicity analysis clearly exhibits the non-toxic behavior of plasma-treated RB-198 aqueous solution towards the bacterial growth and germination of seeds.

Thermodynamic and experimental analysis of Ni-Co-Mn carbonate precursor synthesis for Li-rich cathode materials

The Eh-pH diagrams for Ni-Co-Mn-CO3-H2O system at various temperatures and ion concentrations are simulated via OLI studio based on the fundamentals of thermodynamic equilibrium. A co-existence area for NiCO3, CoCO3, and MnCO3 is observed visually from the Eh-pH diagrams, which thermodynamically proves the stability of these species in aqueous solutions, and the possibility of co-precipitating polymetallic carbonate. The simulation results also demonstrate that a higher temperature and/or a more dilute solution are not in favor of the co-precipitation. With the predicted pH ranges from the Eh-pH diagrams, a confirmative experiment was conducted to synthesize Ni0.13Co0.13Mn0.54(CO3)0.8, the precursor for preparing Li1.2Ni0.13Co0.13Mn0.54O2, which is a promising cathode material for next-generation LIBs. The physical properties of both materials are characterized in detail, and the electrochemical performance for the final cathode material was tested. The results show that Ni2+, Co2+, and Mn2+ ions in solution are homogeneously co-precipitated in the form of polymetallic carbonate. The Li1.2Ni0.13Co0.13Mn0.54O2 material obtained from the carbonate precursor has a typical structure of Li- and Mn-rich cathodes and yields an initial discharge capacity of 296.0 mAh g−1 at 0.1 C and 188.1 mAh g−1 after 100 cycles at 1 C rate. It was verified that the OLI-assisted Eh-pH simulation is consistent with the experimental measurements.

β-NaYF4:Yb,Er,Gd nanorods@1T/2H-MoS2 for 980 nm NIR-triggered photocatalytic bactericidal properties

Fabrication of β-NaYF4:Yb,Er,Gd@1T/2H-MoS2 nanocomposites for NIR-driven photocatalytic sterilization of Escherichia coli.

Trends and new directions in the crystal chemistry of actinide oxo-clusters incorporated in polyoxometalates

This highlight article reports the synthetic methods, the structural topologies and the behaviour of actinide-polyoxometalate species in aqueous solution.

Synthesis and structural characterization of a series of ternary copper(II)-L-dipeptide-neocuproine complexes. Study of their cytotoxicity against cancer cells including MDA-MB-231, triple negative breast cancer cells

This work presents the synthesis and characterization of eight copper complexes [Cu(L-dipeptide)(neo)]·nH2O (neo = neocuproine) and their cytotoxic activities against tumor cell lines. The crystalline structure of [Cu(gly-val)(neo)]·3H2O, [Cu(gly-leu)(neo)]·H2O, [Cu(ala-gly)(neo)]·4H2O, [Cu(val-phe)(neo)]·4.5H2O and [Cu(phe-phe)(neo)]·3H2O were determined by single crystal X-ray diffraction. In all of them, the Cu(II) is pentacoordinated, in a square pyramidal environment. The coordination observed in solid state was retained in the major species in aqueous solution, as suggested by Electronic Paramagnet Resonance and UV–vis spectroscopies. The complexes were shown to have affinity for isolated DNA, as determined by Circular Dichroism experiments. Furthermore, biological experiments showed that all the complexes present high cytotoxic activity against the cell lines: MDA-MB-231, MCF-7 (human metastatic breast adenocarcinomas, the first triple negative), MCF-10A (human normal breast cells), A549 (human lung epithelial carcinoma) and MRC-5 (human lung epithelial cells). Together, these results suggest that these compounds are promising steps towards new effective drugs to treat cancer.

Hydrothermal liquefaction of microalgae for biofuel production: the recycling of nutrients from an aqueous solution after HTL

Microalgae are an alternative source for the renewable biofuels production. One of the promising technologies of microalgae fuel production is the hydrothermal liquefaction (HTL) with obtaining bio-oil as the target product. We have carried out a number of experiments on the hydrothermal liquefaction the biomass of blue-green microalgae Arthrospira platensis rsemsu 1/02-P (collection of Renewable Source Energy Laboratory at Lomonosov Moscow State University). For the HTL of arthrospira biomass the reactor of the Institute of High Temperatures RAS have been used. The outputs of bio-oil, gaseous products, solid residue and aqueous solution were 34-46%, 12-18%, 26-30%, 10-24% respectively. The aqueous solution hydrothermal liquefaction is a by-product, it has a limited energy value and needs to be recycled. Aqueous solution contains the nutrients necessary for growing algae but in quantities that are orders of magnitude higher than the standard ones. Studies growth of different algae species in aqueous solution after HTL have shown that in order to prevent the growth inhibitors toxic effect intensive its dilution is necessary. Microalgae strains, which can be cultivated in 500-fold diluted aqueous solution (Galdieria sulphuraria rsemsu G-1, Chlorella vulgaris rsemsu Chv-20/11-Ps), have been experimentally selected. It allows partially recycling the by-product of bio-oil from microalgae

Formation of metal-organic ligand complexes affects solubility of metals in airborne particles at an urban site in the Po valley.

Metals in atmospheric aerosols play potentially an important role in human health and ocean primary productivity. However, the lack of knowledge about solubility and speciation of metal ions in the particles or after solubilisation in aqueous media (sea or surface waters, cloud or rain droplets, biological fluids) limits our understanding of the underlying physico-chemical processes. In this work, a wide range of metals, their soluble fractions, and inorganic/organic compounds contained in urban particulate matter (PM) from Padua (Italy) were determined. Metal solubility tests have been performed by dissolving the PM in water and in solutions simulating rain droplet composition. The water-soluble fractions of the metal ions and of the organic compounds having ligand properties have been subjected to a multivariate statistical procedure, in order to elucidate associations among the aqueous concentrations of these PM components in simulated rain droplets. In parallel, a multi-dimensional speciation calculation has been performed to identify the stoichiometry and the amount of metal-ligand complexes theoretically expected in aqueous solutions. Both approaches showed that the solubility and the aqueous speciation of metal ions were differently affected by the presence of inorganic and organic ligands in the PM. The solubility of Al, Cr, and Fe was strongly correlated to the concentrations of oxalic acid, as their oxalate complexes represented the expected dominant species in aqueous solutions. Oxalates of Al represented ∼98% of soluble Al, while oxalates of Cu represented 34-75% of the soluble Cu, and oxalates of Fe represented 76% of soluble Fe. The oxidation state of Fe can strongly impact the speciation picture. If Fe is present as Fe(II) rather than Fe(III), the amount of Cr and Cu complexed with diacids can increase from 75% to 94%, and from 32% to 53%, respectively. For other metals, the solubility depended on the formation of soluble aquo-complexes, hence with a scarce effect of the organic ligands. An iron-oxalate complex was also directly detected in aerosol sample extracts.

Emissive carbon dots derived from natural liquid fuels and its biological sensing for copper ions

Liquid fuels rich in aliphatic and aromatic carbon compounds are utilized as the carbon precursors for the production of carbon dots (CDs) for the first time. Herein we demonstrate the preparation of liquid fuels derived CDs (d-CDs and f-CDs) via chemical oxidation approach and the subsequent application for cerebral copper ions (Cu2+) sensing in rat brain microdialysate. The as-prepared CDs exhibits different morphology and photoluminescence properties depending on the different component of precursors. The luminescence of the as-prepared d-CDs can be significantly quenched upon addition of Cu2+, in which Cu2+ are trapped by the oxygen and nitrogen functional groups surrounding the emissive d-CDs. Moreover, the fluorescence intensity of d-CDs is sensitive to the concentration of Cu2+ with a linear relationship in the range of 0–4 μM, and a detection limit was estimated to be 0.039 μM. Simultaneously, we found out that the luminescent d-CDs manifests an extraordinarily high selectivity which can clearly discriminate Cu2+ from other interference species in aqueous solution and therefore substantially endows d-CDs as a fluorescent sensing platform for Cu2+. According to this nature, we employed d-CDs for the in vivo analysis of Cu2+ in the rat brain microdialysate and the measured basal level of Cu2+ was estimated to be 2.82 ± 0.16 μM (n = 3) even in the presence of other metal ions, biological substances and amino acids that commonly existing in the rat brain.

Study and modeling of the liquid–solid equilibrium of the KCl–KNO3–HCl–H2O system at 283.15 K

AbstractIn this work, the liquid–solid equilibrium of the KCl–KNO3–HCl–H2O system at 283.15 K was investigated. To calculate the solubility product constants of KCl and KNO3 in HCl solution, the Pitzer equation was used to calculate the activity coefficient of the ionic species in aqueous solution. In addition, the thermodynamic model with the Pitzer equation was constructed to regress the temperature coefficient parameters for HCl and HNO3. The calculation and prediction of the KCl–KNO3–HCl–H2O system using the results of the regression confirmed that the regression was successful and the Pitzer equation was suitable. For the reaction KCl(s) + HNO3 → KNO3(s) + HCl, the equilibrium constant K can be obtained from the solubility product constants of KCl and KNO3. Eutectic points for the KCl–KNO3–HCl–H2O system were also predicted. These equilibrium data could be expressed by the triangular phase diagram. The process of the reaction to produce KNO3 could be explained through this triangular phase.

Solvophobic effect of 1-alkyl-3-methylimidazolium chloride on the thermodynamic of complexation between β-cyclodextrin and dodecylpyridinium cation

Preferential solvation participate in various supramolecular self-assembly processes, whose thermodynamic properties can be modulated by the addition of ionic liquids (ILs). However, the effects of these liquids on the thermodynamics of the host-guest complexation process remain unexplored. In this study, the thermodynamic properties of the complexation between 1-dodecylpyridinium cations (C12Py+) and β-cyclodextrin (βCD) species in aqueous solutions with different concentrations of 1-alkyl-3-methylimidazolium halides (CnmimX) were investigated by isothermal titration calorimetry. In water, C12Py+ and βCD form a 1:1 inclusion complex, which is enthalpically (ΔHico= −9.2 ± 0.1 kJ mol−1) and entropically (TΔSico= 16.1 ± 0.2 kJ mol−1) favorable. However, in IL aqueous solutions, all the βCD―C12Py+ thermodynamic parameters of the complexation change and this IL effect is dependent on the carbon chain length of Cnmim+ cations. ILs with shorter alkyl chains (Cnmim+, n ≤ 4) decreases the system entropy, while ILs with longer alkyl chains (Cnmim+, n ≥ 6) reduce the enthalpy values. These effects are attributed to i) preferential solvation of surfactant tails by ILs; ii) ability of the ILs to modify the 3D water structure and iii) inclusion of IL molecules into the inner cavities of βCD.

Antimony speciation in aqueous solution followed with AGNES

Determining antimony speciation is essential to understand its environmental behaviour and potential (eco)toxicological effects. Absence of Gradients and Nernstian Equilibrium Stripping (AGNES) is an electroanalytical technique that has been applied up to date to the determination of the free metal ion concentrations of Zn(II), Cd(II), Pb(II) and In(III). In this work, the first application of AGNES to the measurement of the concentration of one particular species of Sb(III) in aqueous solution is developed. The extensive hydrolysis of this element, even at low pH, suggests the convenience of performing calibrations and AGNES measurements in terms of the Sb(OH)3(aq) concentration, rather than the “free” ion. A new preconcentration factor, Y′, is also introduced as the ratio between [Sb0] in the amalgam and [Sb(OH)3(aq)] in the solution. Y′ dependence on pH is evaluated with calibrations at different pH values. The experimental values of Sb(OH)3(aq) obtained with AGNES in the titration of antimony with the organic ligand oxalate agree very well with the values predicted with the complexation constants recently reported. This promising methodology opens the way to tackle antimony speciation with AGNES in other systems.

Supramolecular copolymers predominated by alternating order: Theory and application.

We investigate the copolymerization behavior of a two-component system into quasilinear self-assemblies under conditions that interspecies binding is favored over identical species binding. The theoretical framework is based on a coarse-grained self-assembled Ising model with nearest neighbor interactions. In Ising language, such conditions correspond to the antiferromagnetic case giving rise to copolymers with predominantly alternating configurations. In the strong coupling limit, we show that the maximum fraction of polymerized material and the average length of strictly alternating copolymers depend on the stoichiometric ratio and the activation free energy of the more abundant species. They are substantially reduced when the stoichiometric ratio noticeably differs from unity. Moreover, for stoichiometric ratios close to unity, the copolymerization critical concentration is remarkably lower than the homopolymerization critical concentration of either species. We further analyze the polymerization behavior for a finite and negative coupling constant and characterize the composition of supramolecular copolymers. Our theoretical insights rationalize experimental results of supramolecular polymerization of oppositely charged monomeric species in aqueous solutions.

Interaction between As(III) and Simple Thioacids in Water: An Experimental and ab Initio Molecular Dynamics Investigation.

Albeit arsenic compounds are ubiquitous in aqueous solutions, the speciation of such a pollutant in natural water mainly depends on its binding capabilities with specific molecules. The features of most of the interactions of arsenic complexes can be established in solution, but the data related to the stability of the formed species, essentially depending on the concentration of the ligands, are elusive. For this reason, here, we report on a series of investigations where diverse approaches are combined together in order to characterize the behavior of As(III) species in aqueous solutions where simple chelating agents, such as thiolactic and thiomalic acids, are solvated. By synergistically exploiting potentiometric, calorimetric, and spectroscopic measurements along with ab initio molecular dynamics, the stability and the underlying formation mechanisms of specific species, along with the arsenic coordination modalities with the ligands, have macroscopically and microscopically been assessed. Furthermore, vibrational modes of the complexes formed by arsenic and simple thioacids have been assigned by means of Raman experiments.