Thermodynamics of complexation of lead(II) and cobalt(II) with N-(carboxymethyl)aspartic acid in aqueous solutions

The enthalpies of complexation of lead(II) and cobalt(II) with N-(carboxymethyl)aspartic acid (H₃Y) were determined calorimetrically at 298.15 K within a wide ionic strength range (KNO₃). The thermodynamic characteristics of formation of the CoY₂- and PbY_2? complexes were calculated at non-zero and zero ionic strengthes. The explanation of the obtained values is given.     

Thermodynamic parameters of complexation reactions between nickel(II) ion and L-serine in aqueous solutions

A thermochemical study of coordination equilibria in the nickel(II) ions-L-serine system was carried out. The heats of reaction between solutions of an amino acid and nickel(II) nitrate at 288.15, 298.15, and 308.15 K and ionic strength of 0.25, 0.50, and 0.75 (KNO₃) were measured. The heats of dilution of nickel nitrate solution in background electrolyte solutions were determined under identical conditions to make proper corrections. The results were processed with allowance for stepwise equilibria. The standard thermodynamic parameters of the complexation processes were calculated. The effect of temperature on heats of complexation reactions in the L-serine-nickel(II) ions was studied. The standard enthalpies of formation of NiSer⁺, NiSer₂, and NiSer ₃ ^? complexes in aqueous solutions were determined.     

Standard thermodynamic functions of complexation between copper(II) and glycine and L-histidine in aqueous solutions

The Cu²⁺–glycine–L-histidine system is studied calorimetrically at 298.15 K and an ionic strength of 0.2, 0.5, and 1.0 in aqueous solutions containing potassium nitrate. The standard thermodynamic parameters (Δ_rH°, Δ_rG°, Δ_rS°) of complexation processes are determined.     

Kinetics of complexation of nickel (II) and copper (II) with some azophenol derivatives in aqueous nonionic surfactant solution

The kinetics of formation of 11 complexes of nickel(II) and copper(II) ions with some azophenol derivatives in aqueous and micellar solution of a nonionic surfactant, Triton X-100, have been studied by a stopped-flow spectrophotometric method. Second order rate constants for the reactions were determined at 298 K and ionic strength 0.1 (NaClO₄) in aqueous solution. In the surfactant solution, the pseudo-first-order rate constants for the complexation reactions,k_obs, decreased with increasing the concentration of Triton X-100. This observation was explained by the assumption that the chelating reagents distribute between the micelle of the surfactant and bulk aqueous phase and rate-controlling reactions occur only in the bulk aqueous phase. On the basis of the relation betweenk_obs and the concentration of the surfactant, the partition constants of the reagents between micellar and aqueous phases were determined.     

Photophysical properties of a novel Ni(II)-diporphyrin in presence of fullerenes: insights from experimental and theoretical studies

The present paper highlights the photophysical aspects of the topologically new Ni(II)-diporphyrin (Ni(2)-1)/fullerene host-guest ensembles. Both absorption and fluorescence studies reveal that Ni(2)-1 undergoes efficient complexation with both C(60) and C(70) in toluene medium. In the fluorescence study, remarkable enhancement of the fluorescence intensity of Ni(2)-1 was observed by the addition of C(60), while normal quenching of fluorescence occurred in case of C(70). From the fluorescence and UV-vis studies, the binding constants of Ni(2)-1 with C(60) and C(70) were determined to be approximately 1.7 x 10(4) and approximately 2.7 x 10(4) dm(3) mol(-1), respectively. Ab initio theoretical calculations reveal that C(70)/Ni(2)-1 complex favor end-on orientation of C(70) rather than side-on approach.     

Potentiometric studies on homo and hetero chelates of copper(II) with some hydroxy acids

Summary Ternary complex-forming systems of the type Cu(A)L (A = 2,2-dipyridyl and L = 2,4-dihydroxybenzoic acid,o-cresotic acid and 2-hydroxy-3-naphthoic acid) have been examined potentiometrically in 50% v/v aqueous ethanol. Various stability constants have been measured.     

Kinetics of Ca2+ complexation with some carbohydrates in aqueous solutions

For solutions of four saccharides in water with alkaline-earth chlorides added ultrasonic attenuation spectra between 100 kHz and 2 GHz are reported and compared to those for carbohydrate solutions without salt. Calcium chloride does not alter the relaxation times in the spectra of D-glucose and D+-maltose solutions, reflecting the exocyclic hydroxymethyl group rotation, a saccharide-saccharide association, and, with the disaccharide, also motions of both rings of a molecule relative to one another. The spectra of D-xylose and D-fructose solutions are substantially changed by the salts. With both saccharides an additional term with relaxation time around some nanoseconds exists which is assigned to a rearrangement of a carbohydrate-cation complex. Other relaxation terms of these saccharide solutions are also subject to noticeable changes by the salt, indicating specific carbohydrate-cation interactions. The ultrasonic spectra show that such interactions may exist also with carbohydrates which do not display the particular hydroxyl group sequences that are considered to promote complexation with cations.     

Experimental and theoretical study of Zn(II) complexation with ceftriaxone

Complexation of Zn²⁺ cations with antibiotic ceftriaxone anions (Ctx^2–) has been studies by pH-metric titration at 25°С and a ionic strength of 0.1 (KNO₃). The formation of the ZnCtx complex has been revealed, and logβ(ZnCtx) = 4.45 ± 0.09 has been calculated. The computer model of the complex has been calculated by the DFT method with the use of the B3LYP hybrid functional and the LACV3P**+ basis set. According to these calculations, Zn(II) in the complex has the coordination number 4 and a nearly tetrahedral coordination sphere and is coordinated to Ctx^2– through carboxylate, β-lactam, and hydroxytriazinone oxygen atoms and the thiazole nitrogen atom. Formation of the chelate structure accounts for the high stability of the complex.     

Oxidation of aqueous solutions of cobalt(II) in the presence of some aminoacids

Summary The complexes between cobalt(III) and aminoacids such as glutamine, asparagine, glutamic acid, aspartic acid and proline were studied.Cobalt(III)-aminoacid systems were investigated by spectrophotometry after oxidizing the cobalt(II) complexes by sodium peroxide. The variation of the absorption spectra shows the pH dependence of the process and it is clear that the formation of the complexes occurs through oxo-intermediates.Complexation ratios, molar absorptivity values and the concentration quotients at equilibrium were determined at pH 2.2 to avoid the formation of binuclear dioxygen-cobalt complexes.     

Spectrophotometric and theoretical studies on complexation of a newly synthesized vic-dioxime derivative with nickel(II) in dimethylformamide

The complexation of a recently synthesized vic-dioxime derivative, 1-({2-[(2-aminoethyl) amino]ethyl}amino)-6-methyl-9H-xanthen-9-one with Ni(II) in N,N-dimethylformamide, was investigated by spectrophotometric and conductometric methods. The possible molecular geometries, binding, and spectroscopic properties for the formed complexes were theoretically studied in detail by the Hyperchem program. The stoichiometry of the complex species was determined from spectrophotometric molar ratio methods at 25°C. The spectral data were further treated by KINFIT to calculate the formation constants of the 1?:?1 and 1?:?2 complexes and their molar absorptivities. Program DATAN was used to calculate the spectral behavior of the complexes in the wavelength range ～380–～550?nm for different mole ratio solutions.     

The kinetics of complexation of nickel(II) and cobalt(II) with cinchomeronate in aqueous solution

The pressure-jump method has been used to determine the rate constants for the formation and dissociation of nickel(II) and cobalt(II) complexes with cinchomeronate in aqueous solution at zero ionic strength. The forward and reverse rate constants obtained are k_f = 2.27 × 10⁶ M^?1 s^?1 and k_r = 3.81 × 10¹ s^?1 for the nickel(II) complex and k_f = 1.23 × 10⁷ M^?1 s^?1 and k_r = 2.66 × 10² s^?1 for the cobalt(II) complex at 25°C. The activation parameters of the reactions have also been obtained from the temperature variation study. The results indicate that the rate determining step of the reaction is a loss of a water molecule from the inner coordination sphere of the cation for the nickel(II) complex and the chelate ring closure for the cobalt(II) complex. The influence of the pyridine ring nitrogen atom of the cinchomeronate ligand on the complexation of cobalt(II) ion is also discussed.     

Extraction of beryllium(II) from iodide solutions by tributyl phosphate

The distribution of beryllium between aqueous sulfuric acid/potassium iodide solutions and organic phases of tributyl phosphate is described. The dependence of extraction on the pH of the aqueous phase, metal and extractant concentration, diluent type and organic additive, has been investigated. Extraction mechanism is discussed on the basis of results obtained. A method for the separation and determination of beryllium, in a mixture of beryllium and aluminium (with other contaminants) is outlined.     

Electro-surface properties of nickel(II) and iron(III) oxides in aqueous solutions of 1,2,4-triazole

It was studied in systems constituted by aqueous solutions of 1,2,4-triazole, and NiO and Fe₂O₃ adsorbents how the electrokinetic potential of the surface of the oxides, amount of adsorbed triazole, and its concentration in solution vary during a long time.     

The kinetics of cobalt(II) complexation with o-phthalate in aqueous solution

The rate constants for the formation and dissociation of cobalt(II) complexes with o-phthalate in aqueous solution have been determined by a pressure-jump technique. The forward and reverse rate constants obtained are k_f = 1.1 x 10⁶ M⁻¹ s⁻¹ and k_r = 1.6 x 1O³ s⁻ at 25°C, respectively. The activation parameters of the reaction were also obtained from the temperature variation study. The results indicate that chelate ring closure and rupture are affected by the rigidity of the benzene ring of the ligand, and thus the rate determining step of the reaction is the chelate ring closure process.     

Behavior of cadmium(II) in irradiated aqueous solutions

Behavior of cadmium(II) in aqueous solutions irradiated by accelerated electrons was studied. A concentration of 8.8 × 10⁻⁴ mol L⁻¹ of cadmium dissolved from Cd(NO₃)₂ requires dose of 15 kGy to be effectively removed from the system containing 1 × 10⁻² mol L⁻¹ of HCOOK as a scavenger of OH radicals. The positive effect of deaeration with N₂O or N₂ was observed in the range of lower doses. The addition of solid modifiers (bentonite, active carbon, zeolite, Cu₂O, NiO, TiO₂ and CuO) reduced the effectivity of radiation removal of cadmium. Product of irradiation is CdCO₃. On the contrary, in the system with cadmium dissolved from CdCl₂ radiation reduction takes place. Systems contained organic complexants (ethylene diamine tetraacetic acid–EDTA, citric acid) were also studied. The solutions of Cd(NO₃)₂ containing initial concentration 2.37 × 10⁻⁴ mol L⁻¹ of Cd^II were mixed with 3 × 10⁻⁴ mol L⁻¹ EDTA. In this system the efficient degradation proceeds up to 90% at a dose of 45 kGy with addition of 5 × 10⁻³ mol L⁻¹ carbonate (pH 10.5). The product of irradiation is CdCO₃. The presence of 1 × 10⁻² mol L⁻¹ of HCOOK in the solution is necessary for radiation removal of cadmium complexed with citric acid (1 × 10⁻³ mol L⁻¹) at pH 8. With increasing concentration of HCOOK (up to 5 × 10⁻² mol L⁻¹) decreases the pH value necessary for the radiation induced precipitation of cadmium. The best result was obtained in the system containing zeolite as a solid modifier.     

Synthesis and characterization of palladium(II) complexes of some tellurium heterocycles

Summary A series of square planar complexes of the type [PdX₂L₂] where X=Cl, Br, I; L=telluracyclopentane (tcp), telluracyclohexane (tch) or benzotelluracyclopentane (btp) have been synthesised. The complexes were characterised by far-i.r., n.m.r. and u.v.-vis. spectroscopy. The data implytrans-geometries except for the complex [PdCl₂(tch)₂] where a mixture ofcis- andtrans-isomers is obtained.     

Distribution of Pb(II) species in aqueous solutions

Turbidity and zeta potential measurements were made on solid precipitates formed after raising the pH of a 10(-3) mol/l lead nitrate aqueous solutions containing 10(-2) mol/l KCl with KOH. Distribution diagrams of Pb(II) species in aqueous solutions at a total Pb(II) concentration of 10(-3) mol/l and 10(-2) mol/l KCl was constructed to explain the results. Several solubility products for solid Pb(OH)(2) were found from the literature and used to construct the diagrams. It was observed that distribution diagrams constructed using a solubility product of 1.43x10(-20) explained the experimental results better than those with other reported solubility products.