Study on complex formation equilibria of tervalent lanthanons with fluorinated β-ketoesters in aqueous dioxane medium

Summary The thermodynamic stepwise formation constants (log ^T K _n) of nine tervalent lanthanons (La³⁺, Pr³⁺, Nd³⁺, Sm³⁺, Eu³⁺, Gd³⁺, Dy³⁺, Er³⁺ and Lu³⁺) with three fluorinated -ketoesters (methyltrifluroacetoacetate, ethyltrifluoroacetoacetate, and ethylpentafluoropropionylacetate) have been evaluated potentiometrically in a 50% dioxane-water mixture at 25 and 35 ± 0.01 °C. The values of log ^T K _n do not follow a linearity when plotted againstZ/r and invariably obey the sequence: La³⁺ < Nd³⁺ < Pr³⁺ < Sm³⁺ < Gd³⁺ < Eu³⁺ < Dy³⁺ Er³⁺ Lu³⁺ in all instances. The standard thermodynamic parameters (G ₁ ⁰ , H ₁ ⁰ , S ₁ ⁰ ) associated with log ^T K _n have also been calculated. The validity of the chosen equilibrium model was examined by an error analysis usingS _min values (sum of the squared residuals), scatter plots, and slopes and intercepts of Abrahams-Kave type normal probability plots.

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Komplexbildungsgleichgewichte von dreiwertigen Lanthanoiden mit fluorierten -Ketoestern in wäßrigem Dioxanmedium

Zusammenfassung Es wurden die thermodynamischen stufenweisen Komplexbildungskonstanten (log ^T K _n) von 9 dreiwertigen Lanthanoiden (La³⁺, Pr³⁺, Nd³⁺, Sm³⁺, Eu³⁺, Gd³⁺, Dy³⁺, Er³⁺ und Lu³⁺) mit drei fluorierten -Ketoestern (Methyltrifluoracetoacetat, Ethyltrifluoracetoacetat und Ethylpentafluopropionylacetat) in 50% Dioxan-Wasser bei 25 und 35±0.01 °C potentiometrisch bestimmt. Die Werte für log ^T K _n ergeben keine lineare Abhängigkeit gegenüberZ/r, sie gehorchen stets der Reihenfolge: La³⁺ < Nd³⁺ < Pr³⁺ < Sm³⁺ < Gd³⁺ < Eu³⁺ < Dy³⁺ Er³⁺ Lu³⁺. Die thermodynamischen Standardparameter G ₁ ⁰ , H ₁ ⁰ und S ₁ ⁰ wurden ebenfalls berechnet. Die Gültigkeit des gewählten Gleichgewichtsmodells wurde unter Verwendung der Summe der Quadratreste (S _min), von Streukurven und Steigung/Ordinatenabschnitt der Normalwahrscheinlichkeitsdarstellung nach Abrahams-Kave untersucht.

     

Spectrophotometry and Luminescence Spectroscopy of Acetohydroxamate Complexes of Trivalent Lanthanide and Actinide Ions

The complexation chemistries of acetohydroxamic acid (HA) with the trivalent Eu, Tb and Cm ions have been probed by combinations of Optical Absorbance Spectroscopy (OAS), Time Resolved Laser Induced Fluorescence Spectroscopy (TRLIFS) and emission spectroscopy, with some rather unexpected trends being observed. The formation of four complexed species was established for all three metal cations by OAS. The magnitudes of the formation constants of the respective M(A) _n ³⁻ⁿ complexes suggested a much stronger binding efficiency of HA for the first two complexation steps than the third and fourth steps. Tb(III) and Eu(III) TRLIFS data both suggested a final octadentate tetrakis-hydroxamato complex in which the metal ion is close to being fully dehydrated. Step-wise dehydration of Tb(III) by successive ligands did not appear to proceed as expected for a bidentate ligand. Of the EuA _n complexes, only the tetrakis species was found to luminesce, with HA causing an unusually strong quenching effect for all other Eu species. Cm(III) complexation appeared similar to the lanthanide analogs.     

Chromotropic acid,a fluorogenic chelating agent for aluminium(III)

Complexation of aluminium(III) with the fluorogenic ligand chromotropic acid (4,5-dihydroxynaphthalene-2,7-disulfonic acid) has been revisited with the aim of using enhancement of the fluorescence intensity as an analytical tool. Complexation at the optimum pH4 was shown to lead to a 1:1 complex with a stability constant log ₁₁₀=18.4±0.7. The fluorogenic effect was thoroughly investigated. Nearly selective excitation of the chelate rather than the ligand could be achieved at wavelengths longer than 360 nm. For analytical purposes the main interfering ion was Ga³⁺. The strongest competing ligand was shown to be citric acid. Competitive complexation by acetate or formate ions can also make their use in a buffer at the usual concentration, 0.2 mol L^–1, questionable, whereas a 10^–2 mol L^–1 formic acid buffer was shown to be a good alternative. The calibration plot showed that the dependence of response on Al(III) concentration was linear up to 500 g L^–1; the detection limit was 0.65 g L^–1 (3SD _blank, n=10, SD=±1.4% at 10 g L^–1 and ±0.8% at 100 g L^–1). The analytical procedure was successfully applied to several samples of tap water and the results were in good agreement with those from AAS determination.     

A new fluorescent metal sensor with two binding moieties

A new fluorescent chelator Oxa, having two metal-binding sites, was designed and synthesized in six steps. Oxa exhibited two distinctive dissociation constants for Zn²⁺ ( μM and  μM), with considerable fluorescence increase in aqueous buffer at pH 7.2. Affinities of Oxa for the other biologically important ions such as Ca²⁺ ( μM and  mM) and Mg²⁺ ( μM and could not be determined) in the same conditions were also obtained.     

Enantiomer separation of 2-halocarboxylic acid esters by chiral complexation gas chromatography

The enantiomer separation of 2-halocarboxylic acid esters on two chiral nickel(II) bis-((perfluoroacyl)terpeneketonates) by complexation gas chromatography is described. The quantitative entiomer separation of branched 2-halocarboxylic acid esters is achieved with nickel (II) bis (3-(heptafluorobutanoyl)(1R, 2S)-pinan-4-onate) 1 while unbranched 2-halocarboxylic acid esters are preferably separated on nickel(II) bis(3-(heptafluorobutanoyl)-(1S)-10-methylenecamphorate) 2. The metal chelates 1 and 2 are accessible in both enantiomeric forms allowing the determination of the enantiomeric excess (ee) effective and reliable.     

Nanoparticles prepared by self-assembly of Chitosan and poly-γ-glutamic acid

The present paper describes the preparation and characterization of novel biodegradable nanoparticles based on self-assembly of poly-gamma-glutamic acid (γ-PGA) and chitosan (CH). The nanosystems were stable in aqueous media at low pH conditions. Solubility of the systems was determined by turbidity measurements. Surface charge and mobility were measured electrophoretically. The particle size and the size distribution of the polyelectrolyte complexes were identified by dynamic light scattering and transmission electron microscopy (TEM). It was found that the size and size distribution of the nanosystems depends on the concentrations of γ-PGA and CH solutions and their ratio as well as on the pH of the mixture and the order of addition. The diameter of individual particles was in the range of 20–285 nm measured by TEM, and the average hydrodynamic diameters were between 150 and 330 nm. These biodegradable, self-assembling stable nanocomplexes might be useful for several biomedical applications.     

Controlled complexation of plasmid DNA with cationic polymers: effect of surfactant on the complexation and stability of the complexes

The aggregation of the cationic polymer-plasmid DNA complexes of two commonly used polymers, polyethyleneimine (PEI) and poly-l-lysine (PLL) were systematically compared. The complexation was studied in 5% glucose solution at 25 degrees C using dynamic light scattering and isothermal titration calorimetry. The aggregation of the complexes was controlled by addition of the surfactant polyoxyethylene stearate (POES). The stability of the complexes was evaluated using dextran sulphate (DS) as relaxing agent. The relaxation of the complexes in the presence of DS was studied using agarose gel electrophoresis. This study elucidates the role of surfactant in controlling the size of the PEI/pDNA complex and reveals the differences of the two polymers as complexing agents.     

The influence of isomerism on the self-assembly behavior and complexation property of 1,3-alternate tetraaminopyridyl-thiacalix[4]arene derivatives

A series of 1,3-alternate conformation thiacalix[4]arenes containing different isomeric aminopyridyl pendent arms have been synthesized. It was found that their self-assembly behaviors and complexation properties strongly depended on the structures of aminopyridyl pendent arms. The crystal structures demonstrate that tetra(meta-aminopyridyl)-thiacalix[4]arene motif is capable of forming intramolecular hydrogen bondings between the sp² nitrogen donors in the meta position of the aminopyridyl groups and the facing amide N-H of the adjacent aminopyridyl groups, and self-assembles via C-H?O weak hydrogen bondings and C-H?π interaction to generate a double stranded rectilineal networks. By contrast, in the case of tetra(para-aminopyridyl)-thiacalix[4]arene, the presence of para-aminopyridyl units enables the formation of N-H?N strong hydrogen bondings between the individual molecules leading to the solid-state structure with water-bridged double strands. Their complexation properties had been also studied by measurement of the stability constants for their complexation in a range of metal cations and investigation of their binding models via ¹H NMR titration and ESI-MS experiments. It was found that the three ligands exhibited high and selective extractability toward Ag⁺, and their stoichiometry of ligand to Ag⁺ was 1:1, while the meta-aminopyridyl derivative showed the best extraction capacity and possessed the most efficient binding sites.     

The Hydrolysis of Hydroxamic Acid Complexants in the Presence of Non-Oxidizing Metal Ions 2: Neptunium (IV) Ions

Hydroxamic acids are salt free, organic compounds with affinities for cations such as Fe³⁺, Np⁴⁺ and Pu⁴⁺, and have been identified as suitable reagents for the control of Pu and Np in advanced nuclear fuel reprocessing. The results of a UV-visible, near-IR spectrophotometric study of the 1:1 and 2:1 complexes formed between formo- and aceto-hydroxamic acids (FHA, AHA) and Np(IV) ions are interpreted using speciation diagrams for the identification of the species present at different pH and ligand to metal ratios. A kinetic model that describes the instability of the complex due to hydrolysis of the hydroxamate moiety, previously developed for the Fe(III)-AHA complexes (Andrieux et al. in J. Solution Chem. 36:1201–1217, [2007]), is tested here against experimental Np(IV)-FHA data. Consequently, the complexation constant for formation of the 1:1 Np(IV)-FHA complex in nitric acid is estimated at K ₁=2715 and indications are that complexation protects the ligand against hydrolysis at 0.1>pH>−0.1.     

Thermodynamic Model for the Solubility of TcO2⋅xH2O in Aqueous Oxalate Systems

The room temperature solubility of amorphous, hydrous technetium(IV) oxide (TcO₂⋅xH₂O) was studied across a broad range of pH values extending from 1.5 to 12 and in oxalate concentrations from dilute (10⁻⁶ mol⋅kg⁻¹) to complete saturation with respect to sodium bioxalate at lower pH values, and to saturation with respect to sodium oxalate at higher pH values. The solubility was measured to very long equilibration times (i.e., as long a 1000 days or longer). The thermodynamic modeling results show that the dominant species in solution must have at least one more hydroxyl moiety present in the complex than proposed by previous investigators (e.g., TcO(OH)Ox⁻ rather than TcO(Ox)(aq)). Inclusion of the single previously unidentified species TcO(OH)Ox⁻ in our aqueous thermodynamic model explains a wider range of observed solubility data for TcO₂⋅xH₂O(am) in the presence of oxalate and over a broad range of pH values. Inclusion of this species is also supported by the recently proposed thermodynamic data for the TcO(OH)⁺ hydrolysis species that indicates that this species is stable at pH values as low as one.