Determination Of Complex Formation Constants Research Articles

Determination of complex formation constants of neptunium(V) with propionate and lactate in 0.5–2.6 m NaCl solutions at 22–60°C using a solvent extraction technique

Abstract Natural clay rocks like Opalinus (OPA) and Callovo-Oxfordian (COx) clay rock are considered as potential host rocks for deep geological disposal of nuclear waste. However, small organic molecules such as propionate and lactate exist in clay rock pore water and might enhance Np mobility through a complexation process. Therefore, reliable complex formation data are required in the frame of the Safety Case for a nuclear waste repository. A solvent extraction technique was applied for the determination of NpO 2 + ${\rm{NpO}}_2^ + $ complexation with propionate and lactate. Extraction was conducted from isoamyl alcohol solution containing 10−3 M TTA and 5 · 10−4 M 1,10-phenanthroline. Experiments were performed in 0.5–2.6 m NaCl solutions at temperatures ranging from 22 to 60 °C. Formation of 1:1 Np(V) complexes for propionate and lactate was found under the studied conditions. The SIT approach was applied to calculate equilibrium constants β°(T) at zero ionic strength from the experimental data. Log β°(T) is found linearly correlated to 1/T for propionate and lactate, evidencing that heat capacity change is near 0. Molal reaction enthalpy and entropy ( Δ r H m ∘ ${\Delta _{\rm{r}}}H_{\rm{m}}^ \circ $ and Δ r S m ∘ ${\Delta _{\rm{r}}}S_{\rm{m}}^ \circ $ ) could therefore be derived from the integrated van’t Hoff equation. Data for log β° (298.15 K) are in agreement with literature values for propionate and lactate. Np(V) speciation was calculated for concentrations of acetate, propionate and lactate measured in clay pore waters of COx. In addition, the two site protolysis non-electrostatic surface complexation and cation exchange (2SPNE SC/CE) model was applied to quantitatively describe the influence of Np(V) complexation on its uptake on Na-illite, a relevant clay mineral of OPA and COx.

Luminescence properties of uranium(VI) citrate and uranium(VI) oxalate species and their application in the determination of complex formation constants

AbstractFor the first time, the interaction of uranium(VI) with citric acid and oxalic acid in aqueous solution was investigated using time-resolved laser-induced fluorescence spectroscopy (TRLFS) between pH 2 and 4. The complex species UO2cit−and (UO2)2(cit)22−formed in citrate medium as well as UO2ox and UO2(ox)22−formed in oxalate medium show no luminescence emissions at room temperature. However, by coupling the fluorescence measurement technique with a low temperature system (−120 ºC, cryo-TRLFS), emission signals of the various complex species could be detected. The emission signals are bathochromic shifted in comparison to the emission maxima of the uncomplexed uranium(VI) cation. Using the spectroscopic data, the corresponding complex formation constants were calculated, which corroborate literature data.

Fluorescence spectroscopic study on complexation of uranium(VI) by glucose: a comparison of room and low temperature measurements

Cryogenic techniques are currently used in scanning tunnelling microscopy (STM) and single molecule spectroscopy. Recently such cryogenic devices have also been adapted to time resolved laser-induced fluorescence spectroscopy (TRLFS) systems applied to uranium(VI). In our study, we interpret TRLFS results obtained for the uranyl(VI) glucose system at room temperature (RT) and under cryogenic conditions of 153 K (cryo-TRLFS). A uranyl(VI) glucose complex was only identified by cryo-TRLFS measurements at pH 5 and not by RT measurements. The uranyl(VI) glucose complex was characterized by five emission bands at 499.0, 512.1, 525.2, 541.7, and 559.3 nm and a fluorescence lifetime of 20.9 ± 2.9 μs. The uranyl(VI) glucose complex formation constant was calculated for the first time to be logsI=0.1 M = 15.25 ± 0.96. Cryo-TRLFS investigation opens up new possibilities for the determination of complex formation constants since interfering quenching effects often encounter at RT are suppressed by measurements at cryogenic conditions.

Spectrophotometric Determination of Complex Formation Constants Between a New Schiff Base and Some Transition Metals by Rank Annihilation Factor Analysis

Rank annihilation factor analysis (RAFA) was used for the spectrophotometric studies of complex formation between a new Schiff base derived from 3,6-bis((aminoethyl)thio)pyridazine and some transition metals in dimethylformamide (DMF). Formation constants of these complexes were derived using RAFA on spectrophotometric data. According to molar ratio data and Job’s plot, the stoichiometry of complexation between the Schiff base and the Ni2+, Co2+, Cu2+, and Zn2+ cations was 1:1 and for Pd2+ was 2:1. The logarithm of the complex formation constants was found to be 5.66 for Ni2+, 5.1 for Co2+, 7.08 for Cu2+, 6.73 for Zn2+, and 7.77 for Pd2+.

Modern Potentiometry

For most chemists, potentiometry with ion-selective electrodes (ISEs) primarily means pH measurements with a glass electrode. Those interested in clinical analysis might know that ISEs, routinely used for the determination of blood electrolytes, have a market size comparable to that of glass electrodes. It is even less well known that potentiometry went through a silent revolution during the past decade. The lower detection limit and the discrimination of interfering ions (the selectivity coefficients) have been improved in many cases by factors up to 10(6) and 10(10), respectively, thus allowing their application in fields such as environmental trace analysis and potentiometric biosensing. The determination of complex formation constants for lipophilic hosts and ionic guests is also covered in this Minireview.

Determination of complex formation constants by phase sensitive alternating current polarography: Cadmium–polymethacrylic acid and cadmium–polygalacturonic acid

The use of phase sensitive alternating current polarography (ACP) for the evaluation of complex formation constants of systems where electrodic adsorption is present has been proposed. The applicability of the technique implies the previous selection of the phase angle where contribution of capacitive current is minimized. This is made using Multivariate Curve Resolution by Alternating Least Squares (MCR-ALS) in the analysis of ACP measurements at different phase angles. The method is checked by the study of the complexation of Cd by polymethacrylic (PMA) and polygalacturonic (PGA) acids, and the optimal phase angles have been ca. −10° for Cd–PMA and ca. −15° for Cd–PGA systems. The goodness of phase sensitive ACP has been demonstrated comparing the determined complex formation constants with those obtained by reverse pulse polarography, a technique that minimizes the electrode adsorption effects on the measured currents.

Enhanced kinetic inertness in the electrochemical interconversion of Cu(i) double helical to Cu(ii) monomeric complexes

Three new ligands made of two iminoquinoline halves separated by an (R,R)-trans-1,2-cyclohexenediyl spacer have been synthesized. These ligands feature –OR functions appended in the 8-positions of the quinoline rings (R = n-alkyl). The ligands display a behaviour similar to that of their analogues that contain unsubstituted quinolines, forming a bistable system with copper. [Cu2L2]2+ helicates are obtained with Cu+ and [CuL]2+ monomers with Cu2+, as shown by UV/Vis titrations, determination of complex formation constants, mass and NMR measurements, and X-ray crystallographic analysis. The OR groups are found to be non-coordinating, but the presence of such substituents on the quinoline rings slows the electrochemical interconversion of [Cu2L2]2+ into [CuL]2+. In particular, oxidation of [Cu2L2]2+ gives a reversible two-step profile in cyclic voltammetry experiments, due to the formation of the Cu2+ helicate [Cu2L2]4+, that does not evolve into [CuL]2+in the CV experiment time scale.

Determination of the complex formation constants for some water-soluble polymers with trivalent metal ions by differential pulse polarography

The formation of metal complexes between water-soluble polymers, poly(vinyl alcohol) [PVA], poly(N-vinylpyrrolidone) [PVP], poly(acrylamide) [PAAm] and poly(ethylene oxide) [PEO] with trivalent metal ions, Fe3+, Cr3+, and V3+ were studied by using differential pulse polarography (DPP). The general experimental observation is the shift of totally reversible reduction peaks (M3++Hg+e−⇌M2++Hg) towards more negative potentials when the complexing water-soluble polymers are added to the solution of trivalent metal ions. The negative shift in potential permitted the determination of complex formation constants (Kf) between trivalent metal ions and water soluble polymers. The complex formation constants for Fe3+, Cr3+, and V3+ ions with these polymers increased in the order of V3+>Cr3+>Fe3+.

Interlaboratory comparability of copper complexation capacity determination in natural waters.

The results of a test of interlaboratory comparability for the determination of copper complexation capacity and copper-ligand complex formation constant are presented. Eight water samples comprising, six natural waters, a synthetic ligand solution and a blank solution were analysed by seven laboratories using their own methods of complexation titration. Given the wide variation that might have been possible, relatively good comparability was demonstrated amongst the variety of methods for determining copper complexation capacity. The complexation capacity data largely satisfied the predefined criterion of agreement to within 50%. This provides support for the use of metal speciation criteria in the regulation of copper in the environment. Data for the determination of complex formation constants were of poorer comparability, ranging between 10(7) and 10(12) for the same water.

Determination of complex formation constants of 18 neutral alkali and alkaline earth metal ionophores in poly(vinyl chloride) sensing membranes plasticized with bis(2-ethylhexyl)sebacate and o-nitrophenyloctylether

A segmented sandwich membrane method is used to determine complex formation constants of 18 electrically neutral ionophores in situ in solvent polymeric sensing membranes. These ionophores are commonly used in potentiometric and optical sensors, and knowledge of such binding information is important for ionophore and sensor design. In this method, two membrane segments are fused together, with only one containing the ionophore, to give a concentration-polarized sandwich membrane. Unlike other approaches, this method does not require the use of a reference ion in the sample and/or a second ionophore in the membrane, and is typically pH insensitive. The following ionophores responsive for the common cations lithium, sodium, potassium, magnesium and calcium are characterized and discussed: valinomycin, BME-44, bis[(benzo-15-crown-5)-4′-ylmethyl]pimelate, ETH 157, ETH 2120, bis[(12-crown-4)methyl]dodecylmethylmalonate], 4- tert-butylcalix [4] arene tetraacetic acid tetraethyl ester, ETH 149, ETH 1644, ETH 1810, 6,6-dibenzyl-14-crown-4, N, N, N′, N′, N″, N″-hexacyclohexyl-4,4′,4″-propylidyne tris(3-oxabutyramide), ETH 1117, ETH 4030, ETH 1001, ETH 129, ETH 5234, and A23187. The logarithmic complex formation constants range from 4.4 to 29 and compare well to published data for ionophores that were characterized earlier. From the observed complex formation constants, maximum possible selectivities are calculated that would be expected if interfering ions show no binding affinity to the ionophore, and the values are compared with experimental findings. Each ionophore is characterized in poly(vinyl chloride) membranes plasticized either with a polar (NPOE) or a nonpolar plasticizer (DOS). Membranes based on NPOE always show larger complex formation constants of the embedded ionophore.

Determination of complex formation constants of lipophilic neutral ionophores in solvent polymeric membranes with segmented sandwich membranes.

A potentiometric method to determine ionophore complex formation constants in solvent polymeric membrane phases, proposed originally by Russian researchers, is critically evaluated and compared to other established methods. It requires membrane potential measurements on two-layer sandwich membranes, where only one side contains the ionophore. The resulting initial membrane potential reflects the ion activity ratio at both aqueous phase--membrane interfaces and can be conveniently used to calculate complex formation constants in situ. This method is potentially useful, since it does not require the use of a reference ion or second ionophore in the measurement. In this paper, the five ionophores valinomycin, BME-44, ETH 2120, tert-butylcalix[4]arene tetraethyl ester, and S,S'-methylenebis(diisobutyldithiocarbamate) are characterized in poly(vinyl chloride) (PVC) plasticized with dioctyl sebacate (DOS) and compared with other established methods. The resulting formation constants correspond well to literature values. The influence of varying membrane concentrations and different anionic site additives is studied and found to be relatively small. Experiments are also performed with and without lipophilic inert electrolytes and with ionophore-free sandwich membranes to illustrate the effect of ion pairing and the membrane internal diffusion potential on the response of such sandwich membranes. These experiments suggest that ions are completely associated in PVC-DOS membranes, but that such ion pairs are rather nonspecific. Diffusion potentials seem to play a minor role with these systems. The results are explained with theory. This work indicates that the characterization of electrically charged ionophores, anion-selective ionophores, and ionophores in membrane matrixes other than PVC plasticized with DOS may now be experimentally accessible.

Determination of complex formation constants for Cu(II)–Alizarin complexone with amines by capillary zone electrophoresis

Complex formation constants between Cu(II)–Alizarin complexone (Cu(II)–ALC) and amines were investigated by capillary zone electrophoresis. The electrophoretic mobility ( μ ep) of Cu(II)–ALC was obtained from the migration time of 3 μg ml −1 Cu(II) in a borate buffer in the presence of 1 × 10 −3 mol dm −3 ALC of pH 9.1 at 20 kV. The μ ep value decreased with increasing amine concentration as additive in the buffer. This indicates coordination of the amines with Cu(II)–ALC. The first and second coordination equilibrium constants (dm 3 mol −1) were 1 ± 1 and (3.33 ± 0.01) × 10 6, 100 ± 1 and (4.73 ± 0.01) × 10 6, 69 ± 4 and (1.21 ± 0.07) × 10 5, 2 ± 1 and (2.74 ± 0.06) × 10 5, 150 ± 20 and 74 ± 7, 5 ± 1 and 74 ± 3, 42 ± 1 and 12 ± 3, 57 ± 1 and 9 ± 2, (2.9 ± 0.2) × 10 8 and 990 ± 90, and 7900 ± 200 and 780 ± 70 for ammonia, methylamine, ethylamine, n-propylamine, pyridine, 2-methylpyridine, 3-methylpyridine, 4-methylpyridine, imidazole, and 1-methylimidazole, respectively.

Scanning Chronopotentiometry as a Method for the Determination of Complex Formation Constants

The complex formation of cadmium(II) with ethylenediaminetetraacetate (H4Y) in aqueous solutions has been studied using scanning chronopotentiometry. It has been found that in the acid medium region (pH < 3) free (hydrated) cadmium ions and the two complex ion species CdHY− and CdY2− are in equilibrium in the case of excess cadmium ions. Scanning chronopotentiometry is shown to enable one to easily determine the equilibrium concentrations of essentially all electroactive metal ion species. This feature of the method makes it very promising for studying complex formation in solutions and for determining the stability constants of unprotonated and protonated metal complexes, especially in the case of their joint presence in the solution under investigation.

Scanning Chronopotentiometry as a Method for the Determination of Complex Formation Constants

The complex formation of cadmium(II) with ethylenediaminetetraacetate (H4Y) in aqueous solutions has been studied using scanning chronopotentiometry. It has been found that in the acid medium region (pH < 3) free (hydrated) cadmium ions and the two complex ion species CdHY− and CdY2− are in equilibrium in the case of excess cadmium ions. Scanning chronopotentiometry is shown to enable one to easily determine the equilibrium concentrations of essentially all electroactive metal ion species. This feature of the method makes it very promising for studying complex formation in solutions and for determining the stability constants of unprotonated and protonated metal complexes, especially in the case of their joint presence in the solution under investigation.

Self Diffusion of Diastereomeric Complexes

Abstract For systems in which a chiral substrate and a different chiral metal chelate are forming a diastereomeric complex it is often not possible to determine the complex formation constant using chemical shift data only. It is shown that an unambigu - ous determination of complex formation constants is possible by combining data obtained from chemical shift measurements and self diffusion measurements.

Ion association studies in aqueous NiSO4 solutions by positron lifetime spectroscopy

Abstract Ion association has been studied by positron lifetime spectroscopy in aqueous solutions containing the Ni2+ and SO 4 2– ions at 294 K with the double aim of assessing the reliability of the method for quantitative determination of complex formation constants and of probing the validity of various expressions to calculate single-ion activity coefficients at high ionic strength. The existence of two complexes, identified as NiSO4 and Ni2SO 4 2+ , is shown by the data analysis. Considering the formation constant of the former, KI=(196±10)M–1, determined in previous works leads to discarding several of the expressions commonly used for activity corrections. Two possible values are retained for KI, (193±20)M–1 and (179±20)M–1, while KII related to Ni2SO 4 2+ is better defined, as (2.57±0.14)M–1.

Spectrophotometric determination of complex formation constants by estimation of free ligand concentration

Determination des constantes de stabilite des complexes 1:1 pour Zn et La avec PAP. La methode est basee sur l'estimation indirecte des complexes, mesure de l'absorption du pic du coordinat qui diminue avec une augmentation de la concentration du metal

Ion-selective electrode determination of complex formation constants in submicromolar silver nitrate solution

Ion-selective electrode determination of complex formation constants in submicromolar silver nitrate solution