Solution Complexation Reactions Research Articles

ДОСЛІДЖЕННЯ КОМПЛЕКСОУТВОРЕННЯ ПОЛІЕТИЛЕНІМІНУ З ЙОНАМИ МІДІ (ІІ), НІКЕЛЮ (ІІ), КОБАЛЬТУ (ІІ)

There is described the influence of polyethylenimine globule structure on complexation with copper (II), nickel (II) and cobalt (II) ions. There are determined the values of the coordination number with the change of the pH of the solution for the complexes of ethylenediamine, diethylenetriamine and polyethylenimine with metal ions. It is investigated that the complexation of these metal ions with low molecular weight amines passes through three stages and with PEI through two stages. It is shown that the content of free nitrogen atoms in PEI, which do not react with metal ions, increases with increasing concentration of PEI in solution. The number of monomer units associated with metal ions depends on the size of the globule of the macromolecule, as well as the reaction process. The complexation reaction in solution is determined by the diffusion of metal ions into the polymer globule. If the reaction takes place in a diffusion field at a low polymer concentration, the rate of complexation is proportional to the concentration of macromolecules and the concentration of metal ions in solution.

Assessing the chemical behavior and spatial distribution of yttrium and rare earth elements (YREEs) in a coastal aquifer adjacent to the Urmia Hypersaline Lake, NW Iran.

This study aims to shed light on the seasonal behavior of yttrium and rare earth elements (YREEs) in the Urmia Aquifer (UA), in the immediate vicinity of Urmia Lake (UL) in Iran. Samples of groundwater, collected under dry and wet conditions in coastal wells of UA, suggest a large degree of variability in both YREE abundance and normalized patterns. Although weathering or water-rock interactions (between the surface/groundwater and rock samples) were predicted to be the most probable source in explaining YREEs in groundwater samples, results to the contrary indicate that the groundwater do not inherit aquifer rock-like YREE signatures in the study area; this might be due to the relative stability of YREEs during the process of water-rock interactions, which suggest that methods based on YREEs can be beneficial in discrimination of water sources. Furthermore, findings demonstrated no significant relationship between Ce/Ce* and salinity (0.08 and 0.05 in wet and dry seasons, respectively), and between Eu/Eu* and salinity (0.1 and -0.04 in wet and dry seasons, respectively). Dissimilarity of patterns of YREEs in rock and water samples reveals YREEs as no conservative tracers in determining the UL saltwater intrusion into coastal groundwater. Therefore, the groundwater YREE concentrations and fractionation patterns in UA warrant controlling by coastal aquifer need to be controlled by other chemical weathering, adsorption, desorption, and solution complexation reactions. Finally, comparison of REE concentration values in groundwater samples with corresponding indicative admissible drinking water concentrations (IAC) demonstrated their suitability for drinking purposes.

Rare earth elements adsorption onto Carrizo sand: Influence of strong solution complexation

To better understand the mobility and transport of rare earth elements (REE) in groundwater flow systems, the influence of carbonate ions as well as humic substances on REE adsorption onto Carrizo Aquifer sand was investigated as a function of CO 2 partial pressures ( P CO 2 ), pH, ionic strength, and initial REE concentrations. Batch adsorption experiments were carried out at room temperature (23° ± 1 °C) in a glove box under different P CO 2 (i.e., 0 < P CO 2 ≤ 10 − 1.3 atm). Our experiments show that carbonate ions can either increase or decrease REE adsorption depending on the carbonate ion concentrations or the initial REE concentrations. More specifically, the degree that REEs are adsorbed onto the aquifer sand is inversely related to the amount of carbonate species of REEs. For example, an increase of P CO 2 from 0 to 10 − 3.5 atm, or the presence of carbonate ions in low initial REE concentrations (e.g.,10 μg/kg), generally result in enhanced REE adsorption, owing to the low amount of carbonate species of REEs in solution. With further increase of P CO 2 at constant pH (7) and dissolved REE concentrations, solution complexation of REEs with carbonate ions increases and readily outcompetes mineral surface sites for REEs, leading to less REE adsorption. In addition, our experiments show that in the presence of carbonate ions, increasing pH from neutral pH to more alkaline pH leads to decreases in REE adsorption. The presence of humic substances can also either increase or decrease REE adsorption, depending on the pH range of the solution. Humic substances enhance REE adsorption at acidic pH range (i.e., pH < 4) and decrease REE adsorption when pH is above 4. Ionic strength has a negligible effect on REE adsorption in dilute solutions, and only when ionic strength was increased to 0.1 M was a decrease in REE adsorption noticeable. REE adsorption onto Carrizo sand can be successfully described by a model that considers both surface complexation and surface exchange reactions. Specifically, the modeling studies point out the important role that surface exchange reactions play in REE adsorption onto Carrizo sand at high REE loading conditions (i.e., high initial REE concentration at low solid/solution ratio). Model calculations show that strong solution complexation of dissolved REEs with carbonate ions competes for uncomplexed REE ions, [Ln 3+] F, where Ln is any of the lanthanides, and thus decreases REE adsorption at high P CO 2 levels (> 10 − 2.3 atm) or at high pH (> 8.0). Model calculations also indicate that competition between Na + and uncomplexed REE ions, [Ln 3+] F, for exchange sites results in less REE adsorption at high ionic strength (e.g., I = 0.1 M). Both experimental and modeling studies show that REE adsorption onto Carrizo sand is strongly influenced by REE solution complexation reactions, which are sensitive to P CO 2 levels, pH, and the amount and type of solution complexing ligands.

Lability of metal complexes at spherical sensors. Dynamic voltammetric measurements

The diffusive-kinetic steady-state (dkss) approximation is applied to the case of a metal ion reaching a transforming/consuming spherical surface (sensor) when the ion is involved in a complexation reaction in solution. Simple time-dependent expressions for the surface metal flux, the lability degree and the half-wave potential are presented, valid for any value of the ratio of concentrations at the surface and the sensor radius. The solution presented is compared with other theoretical approaches, such as the kinetic steady state (kss) and the total steady state (tss), pointing out that the easy dkss approach is much more accurate than the tss one to study the metal flux and the lability degree for any value of the radius, from ultramicro to planar sensors.

Thermodynamics of the Interaction of the Ni2+ Ion with the L-β-Phenyl-α-Alanine Anion in Aqueous Solution

The enthalpies of the interaction of the L-β-phenyl-α-alanine anion with the Ni2+ ion in aqueous solution were measured by calorimetry for the ionic strength I = 0.5, 1.0, and 1.5 (KNO3 as a supporting electrolyte) at 298.15 K. The thermodynamic parameters of the formation of Ni(II) complexes with phenylalanine in aqueous solution were calculated. The effect of the ligand structure on the thermodynamic parameters of complexation reactions in solution was discussed.

Account of Analytical Techniques Employed for the Determination of Thermodynamics of Inclusion Complexation of Drugs with Cyclodextrins

AbstractFor Abstract see ChemInform Abstract in Full Text.

A model describing the interactions between anaerobic microbiology and geochemistry in a soil amended with glucose and nitrate

SummaryUnder anaerobic conditions, microbes closely interact with geochemical reactions and can have an impact on the soil, the deep vadose zone, the underlying aquifer and the atmosphere. We have designed a model combining anaerobic microbial activities with geochemical reactions in the soil, and assessed it in batch experiments. The model describes the dynamics of six functional microbial communities, their decomposition after death, and the catabolism of carbohydrates through denitrification, dissimilatory NH4+ production, Fe(III) reduction, fermentation, acetogenesis, and SO42– reduction. It was combined with a model that thermodynamically describes acid–base, reduction–oxidation and complexation reactions in solution, and kinetic precipitation and dissolution. Batch incubations were done on a Calcic Cambisol, either without amendment, or after supplying (i) glucose or (ii) glucose and NO3–. Gases, mineral cations and anions, glucose, fatty acids and alcohols were measured during incubation. Net production of CO2 was similar for both glucose treatments, about 40 times larger than in the control. For the glucose treatments, the main microbial activities were fermentation, acetogenic transformation of ethanol, and oxidation of H2. When the soil was enriched with NO3–, no H2 was produced, and microbial activities were rapidly inhibited by NO2–. The model shows these trends as well as geochemical characteristics including pH and reduction–oxidation potential.

Modeling of the Sorption Dynamics in Multicomponent Ion-Exchange Systems with Consideration of Complexation Reactions on the Basis of the Surface Complexation Theory

The sorption dynamics in multicomponent ion-exchange systems with consideration of complexation reactions in solution is theoretically described by solving (on a computer) nonlinear material balance equations and kinetic equations of internal diffusion. Equilibria in multicomponent ion-exchange systems are characterized using the surface complexation theory. According to this theory, fixed groups of an ion exchanger and counterions form complexes located in different layers (Stern layers) at different distances from the surface. These layers constitute a circuit of series-connected capacitors. The fundamental advantage of such an approach is the fact that equilibria in multicomponent systems can be described in terms of a set of parameters obtained for binary systems. Additional account is taken of complexation reactions in the solution in the space between sorbent grains in an ion-exchange column. The H+–A–B three-component metal-ion exchange in various systems (A, B = Zn2+, Co2+, Ni2+, Cd2+, Ca2+, and Na+) is studied. Comparison is made between the results of numerical calculations of the characteristics of the H+–An+–Bn+ ion exchange in multicomponent systems containing metal ions with and without consideration of chemical reactions.

Distribution of the rare earth elements in porewaters from a clay-rich aquitard sequence, Saskatchewan, Canada

A 91.4-m thick porewater profile of the rare earth elements (REEs) is presented from a thick clay-rich Pleistocene till (0–80 m) and Cretaceous clay (80–156 m) aquitard sequence, Saskatchewan, Canada. The upper 3–4 m of till is weathered. Absolute aqueous concentrations of the REEs vary by more than one order of magnitude. Aqueous REE concentrations decrease with depth through the weathered till to a depth of about 15 m below ground, below which, the concentrations in the unweathered till remain relatively consistent. The only porewater sample from the clay (91.4 m) has the highest total REE concentration. Elevated REE concentrations in the oxidized zone attributed to geochemical weathering. There is no significant seasonal variation in aqueous REE concentrations within the water columns in the piezometers. Redox conditions and solution complexation reactions exert predominant controls on the aqueous REE concentrations. The majority of REE patterns are coherent, characterized by overall negatively fractionated REE, with convex-down profiles from La to Pr or Nd, and convex-up from Nd to Tb. In the porewater sample from the clay, the LREEs are an exception, with a flat normalized profile. HREE/LREE fractionations in the porewaters are depth-dependent and are mainly controlled by solution complexation with dissolved sulfate, phosphate, free carbonate ions and DOC. Porewaters in the unweathered till (5–76.2 m) are characterized by negative Ce anomalies, which may reflect in part, negative Ce anomalies in the host till geochemistry. The negative Ce anomalies are magnified relative to the host tills during water–rock interaction and REE transportation. Porewaters from the weathered till exhibit strong positive Ce anomalies relative to PAAS, the host rocks and their leachates. The Ce anomalies are predominantly controlled by the redox conditions and solution complexation. The large positive Ce anomalies in these porewaters are probably caused by the oxidation of Ce(III) to Ce(IV) that was stabilized in solution through complexation with high contents of inorganic and organic ligands. Positive Eu anomalies relative to PAAS, the host rocks and leachates of the host rocks, result from hydrolysis of plagioclase feldspar. The limited depth profile for total dissolved REEs across the weathered–unweathered till boundary is retarded with respect to that previously established for Na +, K +, Mg 2+, SO 4 2−, and TDS, suggesting that chemical reactions control the migration of dissolved REEs.

Determination of Binding Selectivities by Electrospray lonization Mass Spectrometry

Electrospray ionization mass spectrometry is used for the measurement of binding selectivities of four model hosts, 18-crown-6, dibenzo-18-crown-6, dicyclohexano-18-crown-6, and 1,4,10,13-tetraoxa-7,16-diazacyclooctadecane, for both alkali and transition metal ions. Based on the intensities of the metal complexes observed in the mass spectra, the relative binding selectivities can be directly estimated. Results are compared to theoretical selectivities obtained by solving simultaneous equilibria equations that define the competing complexation reactions in solution. Good agreement is found in most cases, thus allowing rapid determination of binding selectivities of hosts in a variety of solvents.

Origin of middle rare earth element enrichments in acid waters of a Canadian High Arctic lake

–Middle rare earth element (MREE) enriched rock-normalized rare earth element (REE) patterns of a dilute acidic lake (Colour Lake) in the Canadian High Arctic, were investigated by quantifying whole-rock REE concentrations of rock samples collected from the catchment basin, as well as determining the acid leachable REE fraction of these rocks. An aliquot of each rock sample was leached with 1 N HNO 3 to examine the readily leachable REE fraction of each rock, and an additional aliquot was leached with a 0.04 M NH 2OH · HCl in 25% (v/v) CH 3COOH solution, designed specifically to reduce Fe-Mn oxides/oxyhydroxides. Rare earth elements associated with the leachates that reacted with clastic sedimentary rock samples containing petrographically identifiable Fe-Mn oxide/oxyhydroxide cements and/or minerals/amorphous phases, exhibited whole-rock-normalized REE patterns similar to the lake waters, whereas whole-rock-normalized leachates from mafic igneous rocks and other clastic sedimentary rocks from the catchment basin differed substantially from the lake waters. The whole-rock, leachates, and lake water REE data support acid leaching or dissolution of MREE enriched Fe-Mn oxides/oxyhydroxides contained and identified within some of the catchment basin sedimentary rocks as the likely source of the unique lake water REE patterns. Solution complexation modelling of the REEs in the inflow streams and lake waters indicate that free metal ions (e.g., Ln 3+, where Ln = any REE) and sulfate complexes (LnSO 4 +) are the dominant forms of dissolved REEs. Consequently, solution complexation reactions involving the REEs during weathering, transport to the lake, or within the lake, cannot be invoked to explain the MREE enrichments observed in the lake waters.

Ion‐Chromatographic Analysis of Low Molecular Weight Organic Acids in Spodosol Forest Floor Solutions

AbstractLow molecular weight organic acids (LMWOA) from root exudates, decomposing organic matter, and other sources are important lignads involved in solution complexation reactions as well as ligand exchange reactions at mineral surfaces. The purpose of this study was to (i) develop an ion chromatography method that could be used to determine LMWOA in soil solutions from Spodosols, (ii) assess methods for preserving LMWOA in soil solutions, and (iii) evaluate LMWOA concentrations in forest floor solutions during a growing season. Solutions were collected weekly from zero‐tension lysimeters installed within the forest floor (forest floor leachate collectors). Limits of quantitation for acetic, formic, malonic, oxalic, phthalic, and citric acids were 0.35, 0.14, 0.43, 0.41, 0.07, and 0.04 µM, respectively, which in some cases are an order of magnitude lower than reported in previous studies. Freezing soil solutions after filtering resulted in the best recoveries (between 90 and 100% for all LMWOA); other methods of preservation, such as filtering alone and filtering and storing at 4°C, resulted in lower recoveries. The average concentrations of LMWOA in the forest floor solutions were 10 µM acetic acid, 0.7 µM formic acid, and 3.3 µM oxalic acid. Dissolved organic C from the forest floor contained a maximum concentration of 2.0% acetic acid, 0.01% formic acid, and 0.15% oxalic acid. There were no apparent temporal patterns in LMWOA concentrations, except for a decrease in LMWOA concentrations from late September to a minimum in October.

Kinetics of Complexation Reactions at Surfaces and in Solution: Implications for Enhanced Radionuclide Migration

Enhanced mobility of radionuclides has been observed at several waste disposal sites; radioactive wastes have often contained strong, organic complexing agents as co-contaminants. Adsorption at mineral-water interfaces is one of the types of reactions by which radionuclides may become immobilized in the subsurface environment. For a contaminant metal introduced into the subsurface in organically-complexed form, such immobilization requires either adsorption of the intact complex or displacement of the contaminant metal from the complex. Comparison with complexation reactions in solution suggests that, in the tatter case, immobilization of the contaminant metal may be subject to kinetic limitations. A comparative discussion of the mechanisms of complexation reactions in solution and at surfaces serves as background for examination of laboratory studies of competitive- and co-adsorption and field studies of metal mobility.

Equilibrium and spectral studies of putrescine complexes with copper(II)

It has been found that in the putrescine-copper system several types of complex compounds (MHL,ML,ML2,ML2OH) are formed. In thepH range of 7–9, despite a multiple excess of ligand, a precipitation occurs. When adenosine is introduced to the system, the ability to observe the complexation reaction in solution is largely increased, because the additional ligand prevents precipitation. On the basis of computer analysis of potentiometric titration data the stability constants of the compounds have been determined. The coordination mode of the complexes is discussed.

Role of complexation processes in cadmium mobilization during estuarine mixing

Complexation reactions with ligands in solutions1 and on solid surfaces2–4 are essential features of the biogeochemical cycling of trace metals such as cadmium5. Field studies6–8 and laboratory experiments8–11 show that cadmium can be mobilized from riverine participate matter when river water mixes with sea water. Although this mobilization is often attributed to the formation of cadmium chloro complexes in solution6,9,11, the role of these competitive complexation processes has not been quantified. Moreover, there is controversy concerning the reversibility of the interaction of cadmium with particulates11–13, which is an essential factor controlling the amount of cadmium that can be mobilized. Here we report the results of laboratory experiments and equilibrium calculations which demonstrate that cadmium partition between suspended particles and solution is completely reversible, and that complexation reactions in solution can completely account for the amount of cadmium released from suspended particles. Apparently, this toxic metal is not irreversibly fixed on particles, but can be released in response to changes in the aquatic environment. This may have important implications for the bioavailability of particle-bound cadmium.

Adsorption of hydrolyzable surfactants: effect of precipitation on adsorption of oleate on hematite

Adsorption of surfactant at the solid-liquid interface plays a governing role in many separation techniques including the concentration of mineral values by flotation. Good correlation has been obtained between collector adsorption and flotation recovery in a number of mineral-surfactant systems. However, several investigators have not found this to be the case in the hematite-oleate system. We have shown that precipitation and complexation reactions in solution contribute significantly to oleate abstraction. When these are taken into account, pH-dependent adsorption density (under flotation conditions) does show the same trend as flotation recovery. Equilibrium abstraction and adsorption are examined and evidence for specific contribution from dissolved mineral species to surfactant depletion is found. Unexpectedly, a strong effect of S/L ratio on adsorption density has been identified indicating that measured precipitation is underestimated. A method of data handling is suggested to extract adsorption density from total depletion, eliminating the effect of the presence of the mineral bed. Adsorption density is found to be quite low, less than 1 % surface coverage. To explain the high hydrophobicity at such low adsorption, a mechanism involving two-point attachment is proposed.

Adsorption of hydrolyzable surfactants: Effect of precipitation on adsorption of oleate on hematite

Adsorption of surfactant at the solid-liquid interface plays a governing role in many separation techniques including the concentration of mineral values by flotation. Good correlation has been obtained between collector adsorption and flotation recovery in a number of mineral-surfactant systems. However, several investigators have not found this to be the case in the hematite-oleate system. We have shown that precipitation and complexation reactions in solution contribute significantly to oleate abstraction. When these are taken into account, pH-dependent adsorption density (under flotation conditions) does show the same trend as flotation recovery. Equilibrium abstraction and adsorption are examined and evidence for specific contribution from dissolved mineral species to surfactant depletion is found. Unexpectedly, a strong effect of S/L ratio on adsorption density has been identified indicating that measured precipitation is underestimated. A method of data handling is suggested to extract adsorption density from total depletion, eliminating the effect of the presence of the mineral bed. Adsorption density is found to be quite low, less than 1% surface coverage. To explain the high hydrophobicity at such low adsorption, a mechanism involving two-point attachment is proposed.

Effects of hydrostatic pressure on lipid bilayer membranes. II. Activation and reaction volumes of carrier mediated ion transport

Measurements of voltage relaxations following brief charge-pulses applied to lipid bilayers have been performed at different hydrostatic pressures in the presence of the neutral carriers cyclo (D-Val-L-Pro-L-Val-D-Pro)3(PV) and valinomycin. From double-exponential relaxations observed in membranes containing PV-K+ complexes estimates were obtained of the amount of membrane absorbed complexes, NMS, and of the rate of complex translocation, kMS. The pressure dependence of kMS corresponded to an activation volume for translocation of approximately 12 cm3/mol independent of ionic strength and K+ concentration. The pressure dependence of NMS strongly varied with K+-concentration suggesting a major role of ion-complexation in solution which is estimated to involve a reaction volume of 25.5 cm3/mol, while the volume of absorption of a PV-K+ complex by the membrane was estimated -7.5 cm3/mol. The relaxations observed in the presence of valinomycin contained three exponentials and could be used to estimate four rate constants and one absorption parameter which characterize the valinomycin-mediated transport. When the transport of Rb+ was tested, the rate constant for the complex dissociation, kD, and the total concentration of free and complexed carriers in the membrane, No, were found to be pressure insensitive. The translocation rates for the complex, kMS and for the free carrier, kS, were instead markedly pressure dependent according to estimated activation volumes in the range of 11 to 18 cm3/mol. The recombination rate constant kR was also pressure dependent according to an activation volume of 12-14 cm3/mol. The study of the valinomycin-K+ transport yielded similar results as far as N.,ks, and kms are concerned, but in this case kR was pressure independent, while kD was increased by pressure. The net volume change associated with the transfer of a free ion to the membrane in the form of a valinomycin-ion complex was nevertheless very similar for K+ and Rb+. It is concluded that pressure affects the transmembrane mobility of liposoluble molecules, whether charged or not, mostly by increasing the effective viscosity of the hydrocarbon core of the bilayer. The pressure dependence of the membrane uptake of amphipathic compounds seems also to obey the general rule: that of involving a negative volume change. However, when the compounds arise from a complexation reaction in solution or at the membrane solution interface possible positive volumes of complexation may make effective uptake to be reversed rather than increased by pressure.