The kinetics of reduction of palladium (II) complexes with β-alanine at dropping mercury electrode and the complexes’ stability constants

By using dc and ac polarography, the kinetics of electroreduction of the palladium (II) complexes with β-alanine at a dropping mercury electrode was studied in solutions with the palladium (II) concentration from 2 × 10^?5 to 2 × 10^?4 M and variable β-alanine and sodium perchlorate concentrations (pH 6–12). One polarographic wave was observed in solutions with pH 9 and 10 at the β-alanine overall concentration of c _βala = 1 × 10^?3 to 5 × 10^?2 M; two waves, at lower pH or higher c _βala. It was concluded on the formation of different forms of palladium (II) complexes in the studied solutions; the complexes contained two to four β-alanine coordinated anions. Using the limiting diffusion currents for the two waves at pH 9–11 and c _βala = 0.1 and 0.5 M, the stepwise stability constant for the Pd(βala) ₄ ^2? complex was calculated. Using two ac peaks observed at pH 7–8 and c _βala = 1 × 10^?2 to 0.1 M, the stepwise stability constant for the Pd(βala) ₃ ^? . was calculated. The perchlorate ions adsorbed at the dropping mercury electrode, as well as βala^? anions at their higher concentrations, hamper the electroreduction of the palladium (II) complexes with β-alanine.     

Efficient electrocatalytic oxidation and selective determination of isoniazid by Fe(tmphen) 3 2+ -exchanged Nafion?-modified electrode

Cyclic voltammetry and electrochemical impedance studies of Fe(tmphen) ₃ ²⁺ (where tmphen?=?3,4,7,8-tetramethyl-1,10-phenanthroline)-immobilized Nafion?-modified glassy carbon electrode (GC/Nf/Fe(tmphen) ₃ ²⁺ ) are carried out in 0.1?M Na₂SO₄ solution. Nafion–Fe(tmphen) ₃ ²⁺ complex exhibits efficient electrocatalytic oxidation of isoniazid. The linear double reciprocal plot of current and concentration of isoniazid shows a Michaelis–Menten-type catalytic process. The catalytic oxidation currents are proportional to the concentration of isoniazid and show a wide linear calibration range for the quantitative determination of isoniazid. Detection limit and sensitivity are found to be 13?μM and 2.5?μA?mM^?1, respectively.     

Preconcentration and voltammetric determination of palladium (II) at sodium humate modified carbon paste electrodes

A chemically modified carbon paste electrode was prepared by incorporating appropriate amounts of sodium humate(NaA). Palladium(II) was selectively accumulated in a solution of Britton-Robinson(B-R) buffer (pH 2.8) onto the electrode surface in open circuit mode. The subsequent electrochemical measurement was carried out by cyclic voltammetry (CV) and linear sweep anodic stripping voltammetry (LSASV) in a supporting electrolyte of 1.0 M HCl. The obtained oxidation currents (I_pa1 and L_pa2) were proportional to the Pd(II) concentration in the range of 4.7 × 10^–6 - 9.4 × 10^–8 M. The developed method was applied to the quantitative determination of palladium in real samples.     

Spectrophotometric study of rare-earth element complexation in alkaline and near-neutral solutions

The hydrolytic behavior of La, Nd, Eu, Gd, Ho, and Tm in KOH solutions was studied at 25°C and a saturated vapor pressure using spectrophotometry with m-cresol purple and 2-naphthol as pH indicators. It was found that freshly prepared solutions of MCl₃ (M = La, Nd, Eu, Gd, Ho, and Tm) at pH 6.0–10.1 contain the ions M³⁺, M(OH)²⁺, M(OH) ₂ ⁺ , and M(OH) ₃ ⁰ , for Ho and Tm, the complex anions M(OH) ₄ ^? . were also detected. The formation constants of the hydroxide complexes a ionic strengths I = 0 were obtained as the parameters of linear regression equations that characterize the spectra of the indicators in the solutions under study.     

The effect of sodium cation concentration on the electrochemical reduction of copper(I) thiosulfate complexes

The electrochemical behavior of copper(I) thiosulfate complexes from aqueous solutions containing different amounts of sodium perchlorate NaClO₄ is studied by the methods of hydrodynamic voltammetry and potentiometry with a Na⁺-selective electrode. The electrochemical reaction orders p with respect to Na⁺ cations are determined from the dependences of exchange currents and direct reaction currents at fixed potential on the equilibrium concentration of Na⁺ cations. The reaction order p is close to 1 in the Na⁺ concentration range of 0.06–0.12 M and drops to zero for $c_{Na^ + } $ > 0.12 M. The ion pair (IP) {Na[Cu(S₂O₃)₂]}_2? the formation of which precedes the electron transfer reaction is the electrochemically active species for the reduction of copper(I) thiosulfate complexes. The stability constant of IP is determined (K = 27.0 ± 2.4) as well as the rate constants of IP formation and decomposition.     

Transfer of the chelating ligands in the systems [LAuCl2]+-[PdCl4]2−: Synthesis and structure of the salt (NH4)0.20[(Bipy)AuCl2]1.04[(Bipy)PdCl2]0.96[AuCl4]0.76[PdCl4]0.24

The formation of binary complex salts containing gold(III) in the cation and palladium(II) in the anion in the systems [(Bipy)AuCl₂]⁺-[PdCl₄]^2? occurs by transfer of the N,N-electron-donating chelating ligand bipyridine and the chloride ligands between the gold-containing cation and the palladium-containing anion. The resulting neutral salt [(Bipy)PdCl₂] crystallizes together with the anion [AuCl₄]^? from acetonitrile-water (1 : 1-1 : 2, v/v) to give the complex salt (NH ₄ ⁺ )_0.20[(Bipy)AuCl ₂ ⁺ ]_1.04[(Bipy)PdCl₂]_0.96[AuCl ₄ ^? ]_0.76PdCl ₄ ^2? ]_0.24 with a total Au : Pd ratio of 3 : 2. The ammonium cation is formed from acetonitrile upon its hydrolysis most likely catalyzed by Pd complexes. Quantum-chemical calculations were performed to study the transfer of the chelating ligand theoretically.     

Extraction of nitric acid,technetium and palladium by bidentate carbamoylphosphonates

The extraction of HNO₃, TcO ₄ ^? , and Pd by solutions of dibutyl N,N-diethylcarbamoylmethylenephosphonate (DBDECMP) and dibutyl N,N-diethylcarbamoylphosphonate (DBDECP) in CCl₄ has been studied. At low aqueous acidities, HNO₃ is extracted by both extractants (S) as HNO₃·S and HNO₃·S₂, at >1M HNO₃ only HNO₃·S is formed. The distribution of TcO ₄ ^? and Pd(II) is nearly independent of HNO₃ concentration. A second power dependence on extractant concentration was found for the extraction of Pd(II) by DBDECMP and TcO ₄ ^? by DBDECP, and a 4th power dependence for TcO ₄ ^? -DBDECMP.     

Complexation and ligand exchange in aqueous of Cu(II) and Ni(II) with hydrazides of some aromatic acids

Solvation and complexation of Cu(II) and Ni(II) with benzoic (L′), p-methoxybenzoic (L″), and isonicotinic (L) acid hydrazides in aqueous-ethanol solutions (ethanol mole fraction 0.07–0.68) were studied by pH-metry, spectrophotometry, and nuclear magnetic relaxation. The formation constants of the species M(L′)²⁺, M(L′) ₂ ²⁺ , M(L″)²⁺, M(L″) ₂ ²⁺ , M(LH)³⁺, M(L)²⁺, M(L)(LH)³⁺, and M(L) ₂ ²⁺ , where M = Cu²⁺ and Ni²⁺, were determined. With isonicotinic acid hydrazide, a change in the coordination mode was observed in an isomer of Cu(L) ₂ ²⁺ , with one of the ligands coordinating in the bidentate fashion, and the other, in the monodentate fashion via the pyridine nitrogen atom. The suggested structures were confirmed by analysis of the parameters of the ESR and electronic absorption spectra of the complexes. The rate constants of ligand exchange and formation of the complexes Cu(L′)²⁺, Cu(L′) ₂ ²⁺ , Cu(L″)²⁺, and Cu(L″) ₂ ²⁺ in aqueous solutions were determined from nuclear magnetic relaxation measurements; the reactions occur by the associative mechanism. A cyclic process of reduction of Cu(II) to colloidal copper in the presence of L″ and atmospheric oxygen is described.     

Reduction kinetics of glycinate complexes of palladium(II) on a dropping-mercury electrode in acid perchlorate solutions

Polarograms for the reduction of glycinate complexes of palladium(II) (5 × 10^?5 M) are obtained in equilibrium solutions of pH 0.8–3.0 with different protonated-glycine concentrations c _Hgly (supporting electrolyte, 0.5 M NaClO₄). It is established that the irreversible wave of reduction of complexes Pd(gly)₂ corresponds to the diffusion limiting current I _d ⁽²⁾ . A similar wave at pH 1.5 and c _Hgly = 0.005 M, as well as at pH 1.0 and c _Hgly = 0.05–0.5 M is preceded by the diffusion limiting current I _d ⁽¹⁾ . Values of the I _d ⁽²⁾ /I _d ⁽¹⁾ ratio are close to the ratio between equilibrium concentrations of Pd(gly)₂] and [Pdgly⁺], calculated using the step stability constant for Pd(gly)₂. This fact testifies to the reduction of complexes Pdgly⁺ in the vicinity of I _d ⁽¹⁾ and complexes Pd(gly)₂, in the vicinity of I _d ⁽²⁾ . At pH 0.8–1.2 and [H₂gly⁺] = 1 × 10^?4 to 5 × 10^?3 there is observed the diffusion-kinetic limiting current of the first wave I ₁ ⁽¹⁾ , which increases with increasing [H⁺] and decreasing [H₂gly⁺]. The nature of the slow preceding chemical stage that occurs during the reduction of complexes Pdgly⁺ is discussed.     

Kinetics and Mechanism of Palladium Electrodeposition from Alkaline Solutions of Palladium(II) Bisethylenediamine Complexes

The electroreduction kinetics of Pd(en)²⁺ ₂ complexes (0.01 M) is studied on a rotating disk electrode of Pd by recording CVA at 25, 50, and 70°C in solutions of pH 12–13 at ethylenediamine concentrations of 0.03–1.0 M. Established is a diffusion nature of limiting currents, from which diffusion coefficients for Pd(en)²⁺ ₂ complexes are calculated. The Pd electrode capacitance, determined by a pulsed galvanostatic method, is used for taking into account the true surface areas of electrolytic Pd deposits. Parameters of the slow electrochemical stage, which involves Pd(en)²⁺ ₂ complexes, are determined. The temperature dependence of the rate constant of cathodic reduction of Pd(en)²⁺ ₂ complexes is used for calculating an apparent activation energy. An electroreduction mechanism of Pd(en)²⁺ ₂ complexes on a Pd electrode is discussed.     

Photosensitized formation of peroxyl radicals in aqueous solutions of adenine at 77 K

Conditions for the formation of peroxyl radicals photosensitized by near-UV irradiation in frozen aqueous solutions of adenine containing 0.1 M NaCl (pH 4–7) are studied. Analysis of the EPR spectra shows that the systems under study contain two types of peroxyl radicals presumably classified earlier as O ₂ ^?· and HO _2· ^· . The effect of freezing methods on the production of the radicals is shown. The signal from O ₂ ^?· predominates in the spectra of samples with open surfaces and is likely due to the reduction of adsorbed O₂ molecules with photoejected electrons. The signal from HO ₂ ^· could be due to photoinduced interaction between the sensitizer and solvent. Possible mechanisms of these processes are considered.     

Mixed complexes of palladium(II) with 1-aminoethylidene-1,1-diphosphonic acid and glycine

The complexing of palladium(II) with two biological active reagents: glycine (Gly, HA) and 1-aminoethylidene-1,1-diphosphonic acid (AEDP, H₄L) at concentrations of chloride ions (0.15 mol/L) corresponding to physiological levels is studied by means of spectrophotometry, pH potentiometry, and ³¹P NMR spectroscopy. The formation constants for mixed complexes with compositions of [PdH₂LA]^? (log?? = 43.7) and [PdHLA]^2? (log?? = 39.05) are determined. The both ligands are found to be coordinated to palladium(II) in a bidentant-cyclic manner: through amine nitrogen and the oxygen atom of the carboxyl group (in the case of Gly), or through the phosphonic group (in the case of AEDP). A diagram of the distribution of equilibrium concentrations of the complexes depending on pH is calculated for the system K₂[PdCl₄]: Gly: AEDP = 1: 1: 1. It is demonstrated that there are complexes with compositions of [PdHLA]^2?, [PdA₂], and [Pd(HL)₂]^4? in solutions with $C_{Cl^ - } = 0.15 mol/L$ and pH 6?C7.     

Covalent Bonding in Au(BO) 2 − and Au(BS) 2 −

We perform in this work a comprehensive first-principles investigation on the geometric and electronic structures of Au(BO) ₂ ^? and Au(BS) ₂ ^? which are valent isoelectronic to the well-known Au(CN) ₂ ^? monoanion. Au(BO) ₂ ^? and Au(BS) ₂ ^? complexes prove to possess linear ground-state structures similar to Au(CN) ₂ ^? and the BO^? and BS^? ligands in them are found to be coordinated terminally via boron atoms to gold centers which are weakly negatively charged. Au–B bonds in Au(BO) ₂ ^? and Au(BS) ₂ ^? appear to have higher Wiberg bond indices (0.79 and 0.80) and more covalent components (60 and 53 %) than the corresponding values of Au–C interaction in Au(CN) ₂ ^? (0.67 and 39 %, respectively) at the same theoretical levels. Their Au–B bifurcation values of the electronic localization function also turn out to be higher than Au–C. These results strongly suggest that the Au–B bonds in Au(BO) ₂ ^? and Au(BS) ₂ ^? with multiple-bond character possess stronger covalent characters than Au–C in Au(CN) ₂ ^? .     

Separation of trace amounts palladium by SiO2/TiO2/Ce nanoparticles prior to flame atomic absorption spectrometry determination in anodic slime and wastewater samples

In the present work, a new SiO₂/TiO₂/Ce, nanoparticle was synthesed using sol-gel method and evaluated as an adsorbent for preconcentration trace amounts of Pd(II) ions. The characterization of the nanoparticles has been studied by transmission electron microscope and X-ray diffraction. The preconcentration method is based on palladium adsorption onto the surface of nanoparticle at pH 8.5. The main factors affecting Pd(II) adsorption, such as pH of sample solution, concentration and volume of eluent, sample volume, interfering of the coexisting ions and flow rate of sample and eluent were investigated and optimized. At optimum conditions, linearity was maintained between 4.0 to 1000.0 ng mL^?1. Detection limit based on 3S_b/m was 2.3 ng mL^?1. Seven replicate determinations of a solution containing of 12.5 µg palladium gave a relative standard deviation ±1.7%. According to the Langmuir linear model, the maximum adsorption capacity of palladium was found to be 34.5 mg g^?1. Finally, the feasibility of the proposed method for Pd(II) determination was assessed by analysis of certified reference materials, anodic slime and wastewater samples and satisfactory results were obtained.      

Kinetics and Mechanism of Reduction of Palladium(II) Complexes with Ethanolamine on a Dropping Mercury Electrode

The kinetics of electroreduction of palladium(II) complexes with ethanolamine (mea) is studied by ac and dc polarography at pH 6.2–11.5 and different ethanolamine concentrations. At c _mea 0.3–1 M and pH 6.2, commensurate quantities of Pd(mea)²⁺ ₄ and Pd(mea)²⁺ ₃ complexes are present in solutions. The latter, as opposed to the former, contains one bidentate-coordinated ligand. The equilibrium constant for the reaction of mutual conversion of these two complexes at pH 6.2 is determined, along with the equilibrium constant for a similar reaction at pH 7.2. A diffusion nature of observed limiting currents is established. Kinetic parameters of the slow electrochemical stage are determined. The E _1/2 shift in the negative direction with pH adjusted from 9.5 to 11.5 is due to the preceding reversible chemical stage of protonation of the Pd(mea)₃(H_–1mea)⁺ complexes predominant in solution in the pH interval mentioned.     

Octadecylamine cobalt(III) dimethyl glyoximato complexes: synthesis,thermodynamics of micellization,steady-state photolysis and biological activities

A new class of surfactant–cobalt(III) complexes of the type trans-[Co(DH)₂(OA)X], where DH = dimethylglyoxime, OA = octadecylamine, X = Cl^?, Br^?, I^?, N₃ ^?, NO₂ ^?, SCN^? or OA, were synthesized and characterized by physicochemical and spectroscopic methods. The critical micelle concentration (CMC) values of these surfactant–cobalt(III) complexes in ethanol solution were obtained by measuring absorption at ~250 nm. Specific conductivity data (at 303–313 K) served for the evaluation of the temperature-dependent CMC and the thermodynamics of micellization (ΔG _m ⁰ , ΔH _m ⁰ and ΔS _m ⁰ ). Steady-state photolysis and cyclic voltammetry of the complexes were studied. The surfactant–cobalt(III) complexes were screened for their antibacterial and antifungal activities against various microorganisms.     

Composition, stability, and structure of Cu(II), Ni(II), and Co(II) complexes with adipic acid dihydrazide in aqueous and aqueous-ethanol solutions

Solvation and complexation of Cu(II), Ni(II), and Co(II) with adipic acid dihydrazide (L) in aqueous and aqueous-ethanol solutions (ethanol mole fraction 0.07–0.68) were studied by spectrophotometry. The formation constants of the species M(LH)³⁺, ML²⁺, M₂L⁴⁺ (μ = Cu²⁺, Ni²⁺, Co²⁺), and also M₂L ₂ ⁴⁺ and ML ₂ ²⁺ (μ = Cu²⁺, Ni²⁺) were determined. With Cu(II), the complexes Cu(LH) ₂ ⁴⁺ , CuL(LH)³⁺, and Cu₂L(LH)⁵⁺ were also detected and characterized. Evidence is given for the hydrazide coordination mode: tridentate in ML²⁺, bidentate in M(LH)³⁺ and ML ₂ ²⁺ , and tetradentate in M₂L⁴⁺ and M₂L ₂ ⁴⁺ . The ligand exchange reactions involving CuL²⁺, Cu(LH)³⁺, Cu(LH) ₂ ⁴⁺ , CuL(LH)³⁺, CuL ₂ ²⁺ , and Cu₂L(LH)⁵⁺ in aqueous solutions of Cu(II) were revealed and kinetically characterized by nuclear magnetic relaxation. The heretofore unknown rate constants of formation of these complexes were calculated from the thermodynamic and kinetic parameters. Factors controlling the rate constants of the complex formation and chemical exchange are discussed.     

Comparison of chemical effects of UV radiation from spark discharge in air and a low-pressure mercury lamp

The chemical effects of UV radiation from atmospheric-pressure spark discharge and a DBK-9 low-pressure mercury lamp in distilled water and aqueous solutions of hydrogen peroxide and tryptophan have been studied. Reactive species generated in water by the both radiation sources are HO ₂ ^· radicals, acid residue ions NO ₂ ^? and NO ₃ ^? , and ammonium ions. The yield of HO ₂ ^· radicals has appeared to be the same for both sources, (1.1–1.2) × 10^?6 mol L^?1 s^?1. This is confirmed by measurements of the degradation kinetics of tryptophan, which can be destroyed by HO ₂ ^· radicals. The pH of water monotonically decreases with time during the spark discharge treatment. In the case of the mercury lamp, the pH varies insignificantly because of the competition of NH ₄ ⁺ alkali ions with the acid residues. UV radiation plays the major role in the decomposition of hydrogen peroxide.     

Chemical and electrochemical syntheses of the binuclear zinc and cadmium chelates based on the sterically hindered Schiff bases

Chemical and electrochemical syntheses of a series of the zinc(II) and cadmium(II) complexes were carried out on the basis of sterically hindered Schiff bases, which are the condensation products of 4,6-di-tert-butyl-2-aminophenol with the salicylaldehyde derivatives (H₂L, H₂L¹). The structures and compositions of the synthesized binuclear complexes M₂L₂ and M₂L ₂ ¹ where M = Zn(II) and Cd(II), were proved by the data of elemental analysis, IR spectroscopy, and ¹H NMR spectroscopy. The structures of the Zn₂L₂ · 2Py and Zn₂L₂ · 2DMF dimers were proved by X-ray diffraction analysis. The electrochemical dissolution of zero-valence zinc and cadmium in methanol in the presence of equimolar amounts of H₂L and H₂L¹ made it possible to isolate dimeric complexes of the corresponding metals of the composition M₂L₂ and M_{2 2} ¹ .