Stability Constants Of Complexes Research Articles

Potentiometric, spectral characterization, and antioxidant activity studies of ternary complexes involving Cu(II) and carbamoylcholine chloride drug with amino acids

AbstractA potentiometric method was used to determine the stability constants for the various complexes of copper(II) with carbamoylcholine chloride (C) drug as a ligand in the presence of some biorelevant amino acid constituents like glycine (Gly), alanine (Ala), valine (Val), proline (Pro), β‐phenylalanine (Phe), S‐methylcysteine (Met), threonine (Thr), ornithine (Orn), lysine (Lys), histidine (Hisd), histamine (Hist), and imidazole (Imz) as ligands (L). Stability constants of complexes were determined at 25°C and I = 0.10 mol/L NaNO3. The relative stability of each ternary complex was compared with that of the corresponding binary complexes in terms of Δlog K and % R.S. values. Cu(II) complexes of drug C were synthesized in 1:1 and 1:1:1 M ratios of copper to drug [Cu(C)(NO3)2] (1) and copper to drug to glycine[Cu(C)(Gly)(NO3)].NO3 (2), respectively. Glycine ternary complex with drug and copper [Cu(C)(Gly)(NO3)].NO3 was considered as representative amino acid. The complexes 1 and 2 were isolated and characterized using various physicochemical and spectral techniques. Both complexes 1 and 2 were found to have magnetic moments corresponding to one unpaired electron. The possible square planar and square‐pyramidal geometries of the copper (II) complexes were assigned on the basis of electron paramagnetic resonance (EPR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), X‐ray powder diffraction (XRPD), ultraviolet–visible (UV–Vis) and infrared (IR) spectral studies, and the discrete Fourier transform method from DMOL3 calculations. Antioxidant activities of all the synthesized compounds were also investigated.

The interaction of morin and morin-5’-sulfonic acid with lead(II): Study of the 1:1 complex formation process in aqueous solution

Abstract This article focuses on the aqueous complexation between two flavonoids (morin and morinsulfonate) and Pb2+ at constant ionic strength I=0.5 M (NaClO4). The determination of stability constants of ML complexes were performed at wide pH range. Two obtained constants are 14.8 ± 0.1 and 15.2 ± 0.1 logarithmic units for morin and morin-5’-sulfonic acid, respectively. For estimating the thermodynamic stability of the complexes studied, the Def2-SV(P)/DFT/PBE0/SMD method has been used. Different computational models were tested to describe the data obtained. The theoretical values of logK reproduce the experimental parameters within reasonable errors.

Quantifying indium with ion chromatography in hydro- and biohydrometallurgical leaching solutions.

A methodology has been developed to chromatographically quantify indium in polymetallic (bio)hydrometallurgical processing solutions using the Dionex IonPac CS5A column and pyridine-2,6-dicarboxylic acid eluent. Cu(II) and In(III) could be separated by elevating the column temperature to 45°C. The comparatively low stability constant of the In-eluent complex (log K2 =3.8) required typical leaching samples to be diluted in the eluent rather than acid or water to overcome ligand competition between components of the sample solution and the eluent. The methodology was applied to leachates from (bio)hydrometallurgical processing of oxidic flue dust residues and sulfidic zinc ores, where both are promising candidates for the recovery of indium from low grade ores and metallurgical wastes. Indium, ferrous iron, ferric iron, copper, zinc, nickel, and manganese concentrations could be simultaneously quantified. The method was found suitable for samples containing at least 0.25mg/L indium and an iron to indium ratio of up to 100:1.

Potentiometric and spectroscopic studies of the complex formation between copper(II) and Gly-Leu-Phe or Sar-Leu-Phe tripeptides

Metal complexes involving a chelation between copper(II) and the tripeptides, sarcosyl-l-leucyl-phenylalanine (Sar-Leu-Phe) and glycyl-l-leucyl-phenylalanine (Gly-Leu-Phe), have been identified as potential therapeutic drugs for rheumatoid arthritis. However, in solution the speciation and exact coordination of these tripeptides to copper(II) is unknown and as a result this was investigated using glass electrode potentiometry, ultraviolet–visible spectrophotometry, infrared spectroscopy and 1H NMR and CW EPR spectroscopies. The same basicity was found for the terminal amine of both tripeptides, but the methyl group on Sar decreased the copper(II) complex stability constants by 0.38–1.67 log units. Four species: ML, MLH-1, ML2H-1 and MLH-2 were found for both tripeptides in the pH range 2–11. The dissociated protons are from the amide groups. Room temperature and frozen solution EPR spectra support the existence of MLH-1, MLH-2 and ML2H-1 (a large excess was required for the ML2H-1 species). The two species, MLH-2 and ML2H-1, have a CuN3O equatorial chromophore, which therefore produce similar room temperature EPR spectra, with similar magnetic parameters. Frozen solution EPR spectra revealed different anisotropic magnetic parameters in axial symmetry, thus suggesting the presence of two different geometries. The lower g|| and the higher A|| values indicate that the geometry of the MLH-2 complexes tends more towards square planar, instead of the usual expected tetragonally elongated octahedral geometry. Copper(II) could coordinate to each tripeptide via an amine-N, two amide-Ns, two carbonyl-Os and a carboxyl-O. The proposed coordination modes were validated using quantum mechanical calculations.

Anion Exchange Behaviour of Zr, Hf, Nb, Ta and Pa as Homologues of Rf and Db in Fluoride Medium

Studies of the chemical property of transactinide elements are very difficult due to their short half-lives and extremely small production yields. However it is still possible to obtain considerable information about their chemical properties, such as the most stable oxidation states in aqueous solution, complexing ability, etc., comparing their behaviour with their lighter homologous in the periodic table. In order to obtain a better knowledge of the behavior of rutherfordium, Rf (element 104), dubnium, Db (element 105) in HF medium, the sorption properties of Zr, Hf, Nb, Ta and Pa, homologues of Rf and Db, were studied in NH4F/HClO4 medium in this work. Stability constants of the fluoride complexes of these elements were experimentally obtained from Kd obtained at different F- and H+ concentrations. The anionic complexes: [Zr(Hf)F5]-, [Zr(Hf)F6]2-, [Zr(Hf)F7]3-, [Ta(Pa)F6]-, [Ta(Pa)F7]2-, [Ta(Pa)F8]3-, [NbOF4]- and [NbOF5]2- are present as predominant species in the HF range over investigation.
 

Tales of the Unexpected: The Case of Zirconium(IV) Complexes with Desferrioxamine.

The Zr4+ complexes with desferrioxamine (H3DFO) and its derivatives are the only 89Zr-based imaging agents for proton emission tomography (PET) that have been used so far in clinical trials. Nevertheless, a complete speciation of the Zr4+/H3DFO system in solution has never been performed and the stability constants of the relevant complexes are still unknown. Here we report, for the first time, the speciation of this system in water, performed by potentiometric titrations, and the determination of the stability constants of all complexes formed in the pH range 2.5–11.5. Surprisingly, although desferrioxamine gives rise to very stable 1:1 complexes with Zr4+ (logK = 36.14 for Zr4+ + DFO3− = [ZrDFO]+), 2:2 and 2:3 ones are also formed in solution. Depending on the conditions, these binuclear complexes can be main species in solution. These results were corroborated by small-angle X-ray scattering (SAXS) and MALDI mass spectrometry analyses of complex solutions. Information on complex structures was obtained by means of density functional theory (DFT) calculations.

Insight into the interaction mechanism of iron ions with soil humic acids. The effect of the pH and chemical properties of humic acids.

The main aim of this work was to study the mechanisms of interaction between iron(II) ions and humic acids as a function of pH, iron concentration and various humic acids chemical properties, including the degree of humification, elemental composition, aromaticity and content of acidic functional groups. The results indicated that iron was bound by humic acids at pH 7 in amounts ∼2 times higher than at pH 5 (averaged capacities: 117 and 57 cmol/kg, respectively). Iron binding at pH 7 increased with increasing the total carboxylic and phenolic groups content and the degree of humification of humic acids (R-coefficients: 0.99 and 0.95, respectively). The stability of humic acid-iron complexes at pH 7 were only slightly lower than at pH 5 due to iron hydroxides formed at pH > 5 (averaged stability constants: 5.18 and 5.26, respectively). Iron coordination mode varied depending on pH: at pH 5, the bidentate (chelate) mode dominated, whereas at pH 7 the bridging mode appeared prevalent. The total amount of bound iron was much smaller than the content of the carboxylic and phenolic groups in humic acids, on average by ∼80 (pH 7) and ∼90.1% (pH 5) indicating the occurrence of steric effects in humic acid structure i.e. the reduction of the complexation capacity of free functional groups by adjacent groups occupied by iron and/or the formation of intramolecular aggregates with iron hindering the access of further metal ions. At pH 5 the complexes were soluble in the iron concentration range positively correlated to carboxylic and phenolic groups content, showing the protective nature of negatively charged functional groups on the stability of the solution. At this pH, the destabilization of the system was governed by the neutralization of humic acid charged structures by metal cations and the compression of the double electric layer. At pH 7 the stability of the humic acid-iron solution was largely determined by the form of iron, mainly by the precipitation of metal hydroxides acting as a flocculant destabilizing the solution by co-precipitation of humic acid-iron complexes.

Ultra trace level square wave anodic stripping voltammetric sensing of mercury(II) ions in environmental samples using a Schiff base-modified carbon paste electrode

ABSTRACT In this approach, a new carbon paste electrode modified with N,N′-bis(5-bromo-2-hydroxybenzylidene)-2,2-dimethylpropane-1,3-diamine Schiff base ligand (L) was synthesised for selective and effective determination of Hg2+ ions in aqueous environmental samples using cyclic and square wave anodic stripping voltammetric methods. First, the selective detection of mercury ion was confirmed by evaluating the stability constants of metal complexes formed between the Schiff base ligand (L) and some desired cations by conductometric measurements. Afterwards, by preparing an effective carbon paste electrode modified with L, the experimental and instrumental parameters affecting the performance of modified electrode were investigated. Square wave anodic stripping voltammograms were obtained after applying an accumulation potential −0.5 V and accumulation time 150 s in Britton–Robinson buffer solution at pH 2.0. The optimal square wave parameters found are pulse amplitude 75 mV, frequency 50 Hz and step potential 6 mV. The procedure exhibited linear range from 0.4 to 120 μg L−1 Hg2+ with a limit of detection of 0.042 μg L−1. The proposed electrode was proved to be highly selective in the presence of various cations and anions and was successfully used for determination of mercury in tobacco and several water samples.

Novel QSPR modeling of stability constants of metal-thiosemicarbazone complexes by hybrid multivariate technique: GA-MLR, GA-SVR and GA-ANN

The quantitative structural property relationship (QSPR) models of the logβ11 stability constants of M:L complexes of the structurally diverse thiosemicarbazones and several metal ions (M = Ag+, Cd2+, Co2+, Cu2+, Fe3+, Mn2+, Cr3+, La3+, Mg2+, Mo6+, Nd3+, Ni2+, Pb2+, Zn2+, Pr3+, Dy3+, Gd3+, Ho3+, Sm3+, Tb3+, V5+) in aqueous solution have been constructed by combining the genetic algorithm with multivariate linear regression (QSPRGA-MLR), support vector regression (QSPRGA-SVR) and artificial neural network (QSPRGA-ANN). The multi-levels optimization for grid search technique is used to find the best QSPRGA-SVR model with the optimized parameters capacity C = 1.0, Gamma, γ = 1.0 and Epsilon, ε = 0.1. The quality of the QSPR models presented in statistical values as training R2 in range 0.9148–0.9815, validation Q2 in range 0.7168–0.9669 and MSE values in range 0.2742–2.4906. The new two thiosemicarbazone reagents were designed and synthesized based on the lead thiosemicarbazone reagents. The logβ11 values of new complexes Cu2+L, Ni2+L, Cd2+L and Zn2+L derived from the QSPRGA-SVR and QSPRGA-ANN model turn out to be in a good agreement with experimental data.

Direct and indirect impact of the bacterial strain Pseudomonas aeruginosa on the dissolution of synthetic Fe(III)- and Fe(II)-bearing basaltic glasses

This study investigates the direct and indirect bacterial contributions that influence the dissolution of basaltic glass. In this regard, three different types of glasses – with or without Fe, in the reduced Fe(II) or oxidized Fe(III) states – were prepared on the basis of a simplified basaltic glass composition. In order to prevent the direct contact between the glasses and the model siderophore-producing strain Pseudomonas aeruginosa, the glass samples were isolated in dialysis bags and immersed at 25 °C and pH 6.5 in bacterial cultures. Throughout the dissolution experiments, the following parameters were monitored: determination of bacterial growth, quantification of siderophore (i.e. pyoverdine) production, microscopic observation of the glass surface and determination of dissolution kinetics.Isolating the glass from the bacterial suspension only triggered the biosynthesis of siderophores in the Fe(III)-bearing glass dissolution experiments. Siderophores were produced in the presence of Fe(II)-bearing and Fe-free glass, independently on the experimental setup. The siderophore production appeared to be either continuous in the absence of Fe (glass-free control, Fe-free glass dissolution experiments) or stopped as soon as the bacteria entered their stationary phase when an Fe source was present (Fe(II) and Fe(III)-bearing glass dissolution experiments). The increase in the dissolution rates of each glass was correlated to the complex stability constants of the siderophore with the metallic cations in presence (KFe2+ < KAl3+ ≪ KFe3+). Among the three glasses, only the Fe(III)-bearing one seemed to be significantly impacted by the dialysis process: its dissolution rate was doubled by isolating the glass grains from the cells. These results particularly allow to separate the impact of such bacterial exudates from physical contact effects: they showed the efficiency of pyoverdine in increasing the dissolution of an Fe(III)-bearing glass and evidenced that a direct bacterial cell attachment to the surface of such a glass results in a more moderate enhancement of its dissolution process. This work is a new contribution regarding the high affinity of microorganisms for basaltic glasses as an Fe-source. It highlights the role of Fe(III) accessibility upon the bacterial cells as a key parameter regulating their activity and their efficiency in accelerating the dissolution.

Affinity capillary electrophoresis employed for determination of stability constants of antamanide complexes with univalent and divalent cations in methanol.

Affinity capillary electrophoresis (ACE) and pressure-assisted ACE were employed to study the noncovalent molecular interactions of antamanide (AA), cyclic decapeptide from the deadly poisonous fungus Amanita phalloides, with univalent (Li+ , Na+ , K+ , and NH4+ ) and divalent (Mg2+ and Ca2+ ) cations in methanol. The strength of these interactions was quantified by the apparent stability constants of the appropriate AA-cation complexes. The stability constants were calculated using the nonlinear regression analysis of the dependence of the effective electrophoretic mobility of AA on the concentration of the above ions in the BGE (methanolic solution of 20mM chloroacetic acid, 10mM Tris, pHMeOH 7.8, containing 0-50mM concentrations of the above ions added in the form of chlorides). Prior to stability constant calculation, the AA effective mobilities measured at actual temperature inside the capillary and at variable ionic strength of the BGEs were corrected to the values corresponding to the reference temperature of 25°C and to the constant ionic strength of 10mM. From the above ions, sodium cation interacted with AA moderately strong with the stability constant 362±16 L/mol. K+ , Mg2+ , and Ca2+ cations formed with AA weak complexes with stability constants in the range 37-31 L/mol decreasing in the order K+ > Ca2+ > Mg2+ . No interactions were observed between AA and small Li+ and large NH4+ cations.

Precious metal-free molecular machines for solar thermal energy storage.

Four benzothiazolium crown ether-containing styryl dyes were prepared through an optimized synthetic procedure. Two of the dyes (4b and 4d) having substituents in the 5-position of the benzothiazole ring are newly synthesized compounds. They demonstrated a higher degree of trans–cis photoisomerization and a longer life time of the higher energy forms in comparison with the known analogs. The chemical structures of all dyes in the series were characterized by NMR, UV–vis, IR spectroscopy and elemental analysis. The steady-state photophysical properties of the dyes were elucidated. The stability constants of metal complexes were determined and are in good agreement with the literature data for reference dyes. The temporal evolution of trans-to-cis isomerization was observed in a real-time regime. The dyes demonstrated a low intrinsic fluorescence of their Ba2+ complexes and high yield of E/Z photoisomerization with lifetimes of the higher energy form longer than 500 seconds. Density functional theory (DFT) calculations at the B3LYP/6-31+G(d,p) level were performed in order to predict the enthalpies (H) of the cis and trans isomers and the storage energies (ΔH) for the systems studied.

Solution Studies and Crystal Structures of Heteropolynuclear Potassium/Copper Complexes with Phytate and Aromatic Polyamines: Self-Assembly through Coordinative and Supramolecular Interactions.

Phytate (L12- ) is a relevant natural product. It interacts strongly with biologically relevant cations, due to the high negative charge exhibited in a wide pH range. The synthesis and crystal structures of the mixed-ligand Cu(II) polynuclear complexes K(H2 tptz)0.5 [Cu(H8 L)(tptz)] ⋅ 3.6H2 O (1), K(H2 O)3 {[Cu(H2 O)(bpca)]3 (H8 L)} ⋅ 1.75H2 O (2), and K1.5 (H2 O)2 [Cu(bpca)](H9.5 L) ⋅ 8H2 O (3) (tptz=2,4,6-tri(pyridin-2-yl)-1,3,5-triazine; Hbpca=bis(2-pyridylcarbonyl) amine) are reported herein. They were obtained by the use of an aromatic rigid amine, which satisfies some of the metal coordination sites and promotes the hierarchical assembly of 2D polymeric structures. Speciation of phytate-Cu(II)-Hbpca system and determination of complex stability constants were performed by means of potentiometric titrations, in 0.15 M NMe4 Cl at 37.0 °C, showing that, even in solution, this system is able to produce highly aggregated complexes, such as [Cu3 (bpca)3 (H7 L)]2- . Furthermore, the Cu(II)-mediated tptz hydrolysis was studied by UV-vis spectroscopy at room temperature in 0.15 M NMe4 Cl. Based on the equilibrium results and with the aid of molecular modelling tools, a plausible self-assembly process for 2 and 3 could be proposed.

Quantifying correlations of metal ionic characters with ecological soil screening levels (Eco-SSLs) of metals using QICAR models

Soil pollution by heavy metals is a major challenge for soil ecosystems; therefore, many countries have published thresholds or standards for protecting soil organisms based on toxicity testing. However, there have been few studies on the mechanism of metal toxicity on organisms in soils, especially relationships between metal's ionic properties and its toxicity. Herein, we selected environmental soil screening levels (Eco-SSLs), which are internationally recognized ecotoxicity values recommended by the United States Environmental Protection Agency (USEPA), and investigated relationships between Eco-SSLs and metal ionic characteristics. The results showed that several ionic characteristics were significantly correlated with Eco-SSL using a classification of metal ions according to hard and soft acids and bases. Electrochemical potential, atomic ionization potential, the first hydrolysis constant, the maximum complex stability constant, a polarization force parameter and covalent radius showed significant correlations with Eco-SSLs for borderline plus hard ions, while the soft index exhibited significant fitting for borderline plus soft ions, suggesting that ionic bonding and covalent bonding played important roles in metal toxicity on borderline plus hard ions and soft ions, respectively. Then, we chose characteristics that had the strongest correlations with Eco-SSLs, and developed quantitative ion character–activity relationship (QICAR) for soil organisms. The QICARs predicted Eco-SSLs for metals that were reasonably consistent with those recommended by USEPA, with differences between them generally <0.5 orders of magnitude. Overall, QICAR provide a basis for ecological risk assessment and could be useful to interpret relationships between metal's ionic properties and its toxicity.

The complexation of Eu(III) and Cm(III) with polyacrylate as a model compound for complex polycarboxylates studied by laser fluorescence spectroscopy

The complexation of the trivalent heavy metals Eu(III) and Cm(III) with polyacrylate as a model ligand is investigated by time-resolved laser fluorescence spectroscopy (TRLFS) and subsequent thermodynamic modelling (charge neutralization model). The aqueous speciation of both metals is investigated as a function of temperature (20–60 °C) and ligand concentration (0–0.4 g/kg) in 0.1 mol/kg NaCl solution ([H+]total ≈ 10−4 mol/kg). Only one complex species is observed at all experimental conditions. With increasing temperature the aqueous Eu(III) and Cm(III) speciation is slightly shifted towards the complexes species. This effect is attributed to the stronger deprotonation of the polymer, which is also reflected by an increase of its loading capacity. The complex stability constants, however, show no visible temperature dependency. Log β’(T) ranges between 5.8 and 5.9 for both Eu(III) and Cm(III) over the whole range of experimental conditions.

Characterization by Potentiometric Procedures of the Stability Constants of the Binary and Ternary Complexes of Cu(II) and Duloxetine Drug with Amino Acids

Potentiometric titration method has been used to define stoichiometries and stability constants of ternary complexes of Cu(II) with duloxetine (D) and some selected amino acids (L). The protonation constants of the ligands and the stability constants of the binary and ternary complexes of Cu(II) with the ligands were calculated from the potentiometric data using the HYPERQUAD program. The formation constants of the complexes formed in aqueous solutions and their concentration distributions as a function of pH were evaluated at 25°C and ionic strength 0.10 mol·L−1NaNO3. Respective stabilities of ternary complexes have been determined compared with the corresponding binary complexes in terms ofΔlog Kand %R.S. values. A novel binary and ternary duloxetine (D) drug with glycine and its Cu(II) complexes has been synthesized and characterized by several spectroscopic methods. Electronic spectra and magnetic susceptibility measurements reveal square planar geometry for both complexes. The elemental analyses and mass spectral data have justified the [Cu(D)(Gly)] and [Cu(D)Cl(H2O)] composition of complexes, where D = duloxetine and Gly = glycine. The EPR spectra of Cu(II) complexes support the mononuclear structures. Thermal properties and decomposition kinetics of Cu(II) complexes are investigated.

Low-Molecular-Weight Organic Acid Complexation Affects Antimony(III) Adsorption by Granular Ferric Hydroxide.

Antimony(III) mobility in natural aquatic environments is generally enhanced by dissolved organic matter. Tartaric acid is often used to form complexes with and stabilize dissolved Sb(III) in adsorption studies. However, competition between such low-molecular-weight organic acid complexation and adsorption of Sb(III) has received little attention, which prompted us to measure Sb(III) adsorption by iron oxyhydroxide adsorbents commonly used in water treatment plants. Sb K-edge X-ray absorption fine structure (EXAFS) spectra gave Sb-O and Sb-Fe distances and coordinations compatible with a bidentate binuclear inner-sphere complex with trigonal Sb(O,OH)3 polyhedra sharing corners with Fe(O,OH)6 octahedra and a bidentate mononuclear inner-sphere complex but with Sb(O,OH)4 tetrahedra at alkaline pH. Experimental batch titration data were fitted using the charge-distribution multisite surface complexation (CD-MUSIC) model, constrained by the EXAFS molecular level information and taking competitive effects by the organic ligand into consideration. The proportion adsorbed at acid to neutral pH decreased as the Sb(III) concentration increased. The CD-MUSIC adsorption model indicates that this was solely caused by strong competition from tartrate complexation in solution, which leads to adsorption constants higher than those derived without taking this competition into account. The adsorption model results allow for calculating a pe-pH predominance diagram using the USGS PhreePlot code. The study provides consistent surface complexation stability constants, allowing the new database to be used also to reliably model adsorption of toxic oxyanions in anoxic aqueous environments: for example, to accurately simulate competition between Sb(III) and As(III).

1,5-Bis[2-(Dioxyphosphoryl)-4-ethylphenoxy]-3-oxapentane and Its Analogs: Acidity and Complexation in Aqueous Media Containing Copper(II) Cation

Dissociation and complexation with Cu(II) cation is studied for phosphoryl-containing podands (tetrabasic 1,5-bis[2-(dioxyphosphoryl)-4-ethylphenoxy]acidic-type-3-oxapentane (H4LP) and dibasic 1,5-bis[2-(oxyethoxyphosphoryl)-4-ethylphenoxy]-pentane (H2LP)) and their carbonyl analog (polyether dibasic acid 1,5-bis[2-(oxycarbonylphenoxy)]oxapentane (H2LC) in water in the presence of 5% dimethylformamide potentiometrically, spectrophotometrically, and conductometrically. Phosphoryl podands exhibit good complexing properties and can selectively bind metal cations. The dissociation constants are determined and the distribution diagram of ionized species of the compounds under study depending on pH is plotted. The molar ratio between the metal and podand in all complexes is found to be 1 : 1. The stability constants of complexes with Cu2+ cation are calculated. The most stable copper(II) complexes are formed with the tetrabasic podand.

Determination of the Stability Constants of the Acetate Complexes of the Actinides Am(III), Th(IV), Np(V), and U(VI) Using Capillary Electrophoresis-Inductively Coupled Plasma Mass Spectrometry.

Capillary electrophoresis-inductively coupled plasma mass spectrometry (CE-ICP-MS) was used to determine the stability constants of the actinides Am(III), Th(IV), Np(V), and U(VI) at an ionic strength of I = 0.3 M. The obtained stability constants were extrapolated to zero ionic strength by means of the Davies equation. For both U(VI) and Am(III), three consecutive acetate complexes with log(β10) = 3.01 ± 0.12, log(β20) = 5.27 ± 0.07, log(β30) = 6.82 ± 0.09, and log(β10) = 3.70 ± 0.09, log(β20) = 5.35 ± 0.08, log(β30) = 6.45 ± 0.09, respectively, could be identified. For Np(V), there was just one acetate complex, with log(β10) = 1.56 ± 0.03. In the case of Th(IV), five different complex species could be determined: log(β10) = 4.73 ± 0.16, log(β20) = 8.92 ± 0.09, log(β30) = 12.16 ± 0.11, log(β40) = 12.96 ± 0.87, and log(β50) = 14.39 ± 0.16. The actinides were selected with regard to their most stable oxidation state in aqueous solution so that four different oxidation states from +III to +VI could be investigated. A great benefit of CE-ICP-MS is the opportunity to measure at significantly lower concentrations compared to the available literature, allowing the study of actinide complexation in environmentally relevant concentration ranges. Furthermore, it is possible to analyze all four actinides simultaneously in one and the same sample.

A detailed spectrophotometric investigation of the stability constants of [PdCln(OH)4-n]2− and [PdBrn(OH)4-n]2− (n = 0–4)

Complex formation of mixed palladium (II) chloro-hydroxo and palladium(II) bromo-hydroxo complexes have been investigated employing spectrophotometry at 25 °C and an ionic strength of 1.0 M. Hyperquad Simulation and Speciation (HySS) was employed to determine the ideal titration conditions and an autotitrator (equipped with a flow-through cell) was used to accurately vary the pH over 80 and 90 intervals respectively. The stability constants (log βn) for the mixed chloro-hydroxo complexes [PdCl4-n(OH)n]2− (n = 0–4), are: log β1 = 18.36, log β2 = 23.21, log β3 = 26.91 and log β4 = 29.68. These newly obtained values represent a more accurate representation for the stability constants of the mixed palladium(II) chloro-hydroxo speciation. The same experimental procedure was employed to calculate, for the first time, the stepwise stability constants of the palladium(II) bromo-hydroxo system, [PdBr4-n(OH)n]2− (n = 0–4), i.e. log β1 = 18.73, log β2 = 22.25, log β3 = 25.58 and log β4 = 28.47. Molar absorption spectra for all the complexes in question have been obtained. For both systems, complete Pourbaix diagrams were constructed from the new speciation data showing the predominant species for each system.