Nature of polarographic catalytic current in the indium-acetylsalicylic acid system

The dependence of the limiting catalytic current in the system of In(III)-acetylsalycilic acid on the concentration of indium ions and the ligand anions was described theoretically. Dissociation and protonation constants of acetylsalycilic acid molecular form and kinetic parameter connected with the rate constant of formation of polarographically active complex {K _a = 3.59×10^?3, mol dm^?3; K _H = 0.12 mol dm^?3; k = 4.0×10², A (mol/dm^?3)²} were calculated.     

Complexation Equilibria of Indium in Aqueous Chloride,Sulfate and Nitrate Solutions: An Electrochemical Investigation

Electrochemical methods have been used to determine the speciation and stability constants of various aqueous indium complexes. Qualitative behavior is observed using UV–Vis spectroscopy and cyclic voltammetry. Equilibrium constants are determined using differential pulse voltammetry. In a titration where the titrant and sample contain equal concentrations of acid and In³⁺ ions and equivalent concentrations of ligand and supporting electrolyte anions, respectively, small changes in ligand concentration can be made quickly and accurately while maintaining the overall ionic strength. From the change in the half-wave reduction potential as a function of ligand concentration, the coordination number and the stability constants of sulfate, chloride and nitrate complexes were determined. We also highlight the difficulties finding a supporting electrolyte that does not interact with the In³⁺ ion. On the one hand, it was not possible to prevent the slow formation of chloride in perchlorate electrolytes containing indium. On the other hand, we show that, at concentrations of nitrate anions commonly used in such experiments, nitrate complexes form. In the light of these new findings, previously published stability constants of indium using nitrate-based supporting electrolytes should be used cautiously.     

Kinetics and mechanism of the Cu(I)/Cu(Hg) electrode reactions in DMSO solutions of halide ions

The electrode reaction Cu(I)/Cu(Hg) in complex chloride, bromide and iodide solutions with DMSO as solvent has been studied at the equilibrium potential by the faradiac impedance method and a cyclic current-step method. The kinetic data refer to the ionic strength 1 M with ammonium perchlorate as supporting electrolyte and to the temperature 25°C. Double-layer data have been obtained from electrocapillary measurements. From the results for the chloride system at [Cl^?]>15 mM it is concluded that the charge transfer is catalysed by ligand bridging at the amalgam and the following parallel reactions predominate: Cl_ads^?-Cu⁺+e^?(am)Cl_ads^?+Cu(am) Cl_ads^?-Cu₂Cl_j^2?j+e^?(am)Cl_ads^?+Cu(am)+CuCl_j^1?j At lower [Cl^?] and in the whole ligand concentration range available in the bromide and iodide systems the impedance measurements indicate a rate-controlling adsorption step. It is suggested that uncharged complex CuL (L^?=halide ion) then forms an adsorbed two-dimensional network on the amalgam surface.     

Admittance measurements of kinetic and adsorption parameters of anodic mercury complex formation with macrobicyclic (222) ligand in propylenecarbonate and dimethylformamide

Admittance measurements were applied to investigation of the charge-transfer rate and mechanism of anodic complex formation between mercury and macrobicyclic ligand (222) as well as to the cathodic reduction of Hg²⁺-(222) complex formed in the bulk. From measurements in PC and DMF using adsorbable and non-adsorbable base electrolyte anions it was shown that the reactant adsorption effects are observable only if adsorption of ClO₄^? and (222) takes place at the same time. Corresponding charge-transfer rates were evaluated and potential dependence of the adsorption capacity for two ligand concentrations was given. At the half-wave potential apparent rate constants k_1/2 listed below were found (data from Fig. 9).     

Electrode kinetics of the metal complexes with aminopolycarboxylic acids: Part II. Cadmium-ethylenediamine-N,N,N′,N′-tetraacetate (EDTA) complexes

The d.c. polarographic current-potential curves of Cd(II)-EDTA complexes were examined in the pH range 0.5–10.0, to elucidate the mechanism of their electrode processes and to determine the relevant electrochemical kinetic parameters. It was shown that the first wave observed below pH 3 at ?0.58 to ?0.65 V vs. SCE is the reversible reduction wave of Cd(II) aquo-ion with kinetically-controlled limiting current, and the second wave observed above pH 1.5 at ?0.75 to ?1.21 V vs. SCE corresponds to the simultaneous irreversible reduction of four complex species, CdH₃L⁺, CdH₂L, CdHL^? and CdL^2?, where CdH_pL^(p?2)+ and L^4? denote the protonated complex species with p protons and the unprotonated EDTA ion, respectively. Analysis of the dependence of limiting current on the hydrogen ion concentration led to the conclusion that the preceding reaction determining the behaviour of limiting current is CdH₃L⁺?Cd²⁺+H₃L^? with k₃^d=6.3×10² s^?1 and k₃^f=3.3×10⁶ s^?1M^?1, where k₃^d and k₃^f are the dissociation and formation rate constants, respectively. On the other hand, from analysis of the dependence of half-wave potentials of the second wave on the hydrogen ion concentration, the kinetic parameters of the four complex species were evaluated, and are given in Table 1. Further, it was shown that the cathodic rate constants of these four charge transfer processes at some reference potential together with those of Cd(II)-HEDTA complexes fulfil the linear free energy relationship.     

Polarographic studies on the electrode kinetics of the nickel(II) complexes with glycine and some of its derivatives: I. glycine complexes

D.C. polarograms of the Ni(II)-glycine complexes were measured with varying pH values at constant total glycine concentration (0.05 M) and conversely with varying total glycine concentration at constant pH values (3.5, 4.5, 7.5 and 9.5). The current—voltage curves obtained were analysed to determine the limiting currents, the transfer coefficients, and the half-wave potentials, by using the non-linear least squares method. From the dependence of the half-wave potentials on the free glycine concentration, the mechanism of the electrode processes was elucidated. It was shown that the first wave corresponded to the reduction of the Ni²⁺ aquo-complex, the second to the NiG⁺ complex, the third to the NiG₂ complex and the fourth to the NiG^?₃ complex. The kinetic parameters for the four charge transfer processes were determined.The second and third waves were kinetic in character and the rate constants of the dissociation and association reactions between NiG⁺ and NiG₂ and between NiG₂ and NiG^?₃ were determined by analysing the dependence of the kinetic limiting currents on the free glycine concentration.     

Crystal structure,DFT study,antimicrobial properties and DNA cleavage potential and thermal behavior of some new mercury complexes

In this study, a new bidentate Schiff base ligand (L) entitled as N,N’-bis(dimethylaminocinnamaldehyde)-2,2-dimethyl-1,3-propanediamine and its mercury complexes were synthesized. The Schiff base ligand and its complexes were characterized using FT-IR, ¹H-, ¹³C-NMR spectroscopy, molar conductivity and electronic spectral study. Regarding physical and spectral data, the general formula for the complexes was suggested as HgLX₂ (L = Schiff base ligand and X = Cl^?, Br^?, I^?, SCN^?, N₃ ^?). For structural identification of these complexes, crystal structure of mercury iodide complex was analyzed as typical one. In the structure of this complex, Hg ion is surrounded by 2 iodide ions and 2 N atoms from the Schiff base ligand to form a four-coordinated mercury complex in triclinic system with space group of P ₁. Angular index (τ ₄) value was evaluated equal to 0.85, so the geometry around the mercury ion in this complex can be described as trigonal pyramid. A layered supramolecular structure for HgLI₂ complex is stabilized by C–H···I and C–H···π interactions in solid state. DFT study on the ligand and its complexes was also carried out, and then some calculated and experimental structural parameters of HgLI₂ were compared. Thermal behaviors of the titled compounds were investigated by thermogravimetric analyses. Furthermore, biological properties of the ligand and its complexes were examined against some Gram-negative and Gram-positive bacteria and also against 2 fungi. Finally, the interaction of the ligand and its complexes with DNA was investigated by electrophoresis method.     

Facilitated Transfer of Alkali Metal Ions by a Tetraester Derivative of Thiacalix[4]arene at the Liquid–Liquid Interface

The facilitated transfer of alkali metal ions (Na⁺, K⁺, Rb⁺, and Cs⁺) by 25,26,27,28‐tetraethoxycarbonylmethoxy‐thiacalix[4]arene across the water/1,2‐dichloroethane interface was investigated by cyclic voltammetry. The dependence of the half‐wave transfer potential on the metal and ligand concentrations was used to formulate the stoichiometric ratio and to evaluate the association constants of the complexes formed between ionophore and metal ions. While the facilitated transfer of Li⁺ ion was not observed across the water/1,2‐dichloroethane interface, the facilitated transfers were observed by formation of 1 : 1 (metal:ionophore) complex for Na⁺, K⁺, and Rb⁺ ions except for Cs⁺ ion. In the case of Cs⁺ a 1 : 2 (metal:ionophore) complex was obtained from its special electrochemical response to the variation of ligand concentrations in the organic phase. The logarithms of the complex association constants, for facilitated transfer of Na⁺, K⁺, Rb⁺, and Cs⁺, were estimated as 6.52, 7.75, 7.91 (log β₁°), and 8.36 (log β₂°), respectively.     

Collisional de-excitation of the metastableD-states of Ba+ by He,Ne, N2 and H2

The rate constants 〈σ · υ〉 for collisional de-excitation of the metastable 5D states of Ba⁺ ions have been determined in an ion trap experiment. TheD-states are selectively populated by pulsed laser excitation of the 6P _1/2 or 6P _3/2 state and the decay at different background pressures is monitored by the change in fluorescence intensity of the excited ions. From the pressure dependence of the decay constants we calculate the de-excitation rate constants for different collision partners, averaged over the velocity distribution of the trapped ion cloud. For He, Ne, H₂ and N₂ we obtain in the c.m. energy range of 0.1–0.5 eV: 〈σ·υ〉 (He)=3.0±0.2·10^?13cm³/s, 〈σ·υ〉 (Ne)=5.1±0.4·10^?13cm³/s, 〈σ·υ〉 (H₂)=3.7±0.3·10^?11cm³/s, 〈σ·υ〉 (N₂)=4.4±0.3·10^?11cm³/s. The results can be understood qualitatively by a consideration of the ion-atom and ion-molecules interaction potential.     

Reactivity of base catalysed hydrolysis of 2-pyridinylmethylene-8-quinolinyl-Schiff base iron(II) iodide complexes: solvent effects

Three ligands of 2-pyridinylmethylene-8-quinolinyl (L1), methyl-2-pyridinylmethylene-8-quinolinyl (L2), and phenyl-2-pyridinylmethylene-8-quinolinyl (L3), Schiff bases were synthesised by direct condensation of 8-aminoquinoline with 2-pyridinecarboxaldehyde, 2-acetylpyridine, or 2-benzoylpyridine. They coordinated to Fe(II) ion in a 1: 2 mole ratio followed by treatment with iodide ions affording complexes with a general formula [Fe(L)₂]I₂·2H₂O, (L = L1, L2, or L3). Spectrophotometric evaluation of the kinetics of base catalysed hydrolysis of these complex cations was carried out with an aqueous solution of NaOH in different ratios of water/methanol binary mixtures. Kinetics of the hydrolysis followed the rate law (k ₂[OH^?] + k ₃[OH^?]²)[complex]. Reactivity trends and their rate constants were compared and discussed in terms of ligand structure and solvation parameters. The methanol ratio affects the hydrolysis as a co-solvent which was analysed into initial and transition state components. The increase in the rate constant of the base hydrolysis of Fe(II) complexes, as the ratio of methanol increases, is predominantly caused by the strong effect of the organic co-solvent on the transition states.     

Quartz crystal microbalance measurements of kinetic parameters of anodic dissolution of gold in thiocarbamide electrolytes in the presence of sulfide ions

As shown by quartz-crystal microbalance measurements, in the potential range from 0.0 to 0.55 V (NHE), sulfide ions adsorbed on the gold electrode surface accelerate the electrode reaction of anodic dissolution of gold in acidic thiocarbamide solutions. The microbalance determination of kinetic parameters at a constant electrode surface coverage with sulfide ions includes a special procedure developed for the determination of the gold dissolution rate. The conditions (the potential range and the potential scan rate) of independence of the dissolution rate from the diffusion limitations associated with the ligand delivery is determined. Under these conditions, the polarization curve is shown to be linear on semilogarithmic coordinates and correspond to the Tafel equation. In this potential range, the transfer coefficient α and the reaction order with respect to the ligand p are determined at a constant electrode surface coverage θ with adsorbed sulfide ions. It is shown that with the transition from the surface coverage with sulfide ions θ = 0.1 to θ = 0.8, the transfer coefficient α changes from 0.25 to 0.55, the exchange current (i ₀) changes from 10^?5 to 5 × 10^?5 A/cm², and the effective reaction order p with respect to the ligand changes from 0.2 to 1.3. The mentioned changes are associated not only with the acceleration of gold dissolution in the presence of chemisorbed sulfide ions but also with the changeover in the mechanism of this process. Quartz-crystal microbalance data on the gold dissolution rate qualitatively agree with the results of voltammetric measurements of a renewable gold electrode. A possible version of explanation of the catalytic effect of sulfide ion adsorption on the gold dissolution is put forward.     

Formation and Stability of Binary Complexes of Divalent Ecotoxic Ions (Ni, Cu, Zn, Cd, Pb) with Biodegradable Aminopolycarboxylate Chelants (dl-2-(2-Carboxymethyl)Nitrilotriacetic Acid, GLDA, and 3-Hydroxy-2,2′-Iminodisuccinic Acid, HIDS) in Aqueous Solutions

The protonation and complex formation equilibria of two biodegradable aminopolycarboxylate chelants {dl-2-(2-carboxymethyl)nitrilotriacetic acid (GLDA) and 3-hydroxy-2,2??-iminodisuccinic acid (HIDS)} with Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺ and Pb²⁺ ions were investigated using the potentiometric method at a constant ionic strength of I?=?0.10?mol·dm^?3 (KCl) in aqueous solutions at 25?±?0.1?°C. The stability constants of the proton?Cchelant and metal?Cchelant species for each metal ion were determined, and the concentration distributions of various complex species in solution were evaluated for each ion. The stability constants (log₁₀ K _ML) of the complexes containing Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺ and Pb²⁺ ions followed the identical order of log₁₀ K _CuL?>?log₁₀ K _NiL?>?log₁₀ K _PbL?>?log₁₀ K _ZnL?>?log₁₀ K _CdL for either GLDA (13.03?>?12.74?>?11.60?>?11.52?>?10.31) or HIDS (12.63?>?11.30?>?10.21?>?9.76?>?7.58). In each case, the constants obtained for metal?CGLDA complexes were larger than the corresponding constants for metal?CHIDS complexes. The conditional stability constants (log₁₀ $ K_{\text{ML}}^{'} $ ) of the metal?Cchelant complexes containing GLDA and HIDS were calculated in terms of pH, and compared with the stability constants for EDTA and other biodegradable chelants.     

Radiotracers in kinetics of ion-isotopic exchange reactions using anion exchange resins indion-103 and indion-870

The kinetics of iodide and bromide ion-isotopic exchange reactions was studied by radio analytical technique using ¹³¹I and ⁸²Br as tracer isotopes. The parameters like specific reaction rate (min^?1), amount of ions exchanged (mmol), initial rate of ion exchange (mmol/min) and logK _d were studied to evaluate the performance of nuclear and non-nuclear grade anion exchange resins Indion-103 and Indion-870. For iodide ion-isotopic exchange reactions under experimental conditions of 35.0°C, 1.000 g of ion exchange resins and 0.002 M labeled iodide ion solution, the parameters were 0.223 min^?1, 0.300 mmol, 0.067 mmol/min and 18.7, respectively, for Indion-103, and those of 0.165 min^?1, 0.251 mmol, 0.041 /min and 16.2, respectively, for Indion-870. The similar tendency was observed during bromide ion-isotopic exchange reactions. The results suggest that Indion-103 shows greater performance than Indion-870 resin under similar experimental conditions.     

Polarographic waves of tri-n-butyl phosphate and polarographic determination of uranium in the presence of tri-n-butyl phosphate

The results of a study on the polarographic behaviour of TBP and its influence on the determination of uranyl ions is presented. The half-wave potential of the adsorption wave of TBP depends on the concentration of TBP, type of supporting elec trolyte and its concentration. In the presence of TBP the polarographic wave of U(VI) ion is changed. Below 7·10^?5 M TBP the polarographic wave of U(VI) is not affected, between 7·10^?5 and 2·10^?4 M TBP the shape, height and half-wave potential of U(VI) waves are changed and above 2·10^?4 M, up to saturated solution of TBP, the waves of U(VI) do, not change further. The bes supporting electrolytes for the determination of U(VI) are KNO₃ or NaClO₄ in concentrations of 0.1 to 0.5 M, pH 1–2 and TBP concentrations from 3·10^?4 to 1.2·10^?3 M.     

Polarographic determination of the stability constants of metal complexes based on the shifts in half-wave or peak potentials of the anodic oxidation of mercury: methylthioacetato- and 2,2′-thiobisacetato complexes

The stability constants of metal-ion complexes, other than those of mercury ions, can be determined from the shifts, caused by an excess of that metal ion, in the anodic waves of mercury oxidation in the presence of the ligand.Let a solution contain L, a ligand that can react with mercury ion from the anodic oxidation of mercury to form the complexes HgL_p. The half-wave potential of the anodic wave will be shifted by the presence of an excess of a metal ion M, which can also react with L forming the complexes M_jL (where j = 1, $\text{1}\text{2}$,…1/N). A general expression is derived relating the half-wave potential shift ΔE_{$\text{1}\text{2}$} to the overall stability constants. If the excess of metal ion M is great enough for the 1:1 complex to predominate in solution (and if HgL₂ is the predominating mercury complex), for reversible, diffusion-controlled processes the general equation can be simplified to:

where c_M is the total concentration of metal ion M.This equation provides an easy and fast method for β₁ determination. The simplified equation is best suited for experimental data obtained from techniques such as DP, AC₁ and AC₂ polarography, whose increased precision in ΔE measurement enables poorly-developed dc-polarographic anodic waves to be used for β₁ determination. Since the metal-to-ligand concentration ratio must be large in order to apply the simplified equation, the determination can be carried out at very small ligand concentrations. This fact renders the new method especially useful when the ligand solubility does not allow the high ligand concentrations needed in the DeFord—Hume method to be reached. The adequacy of the deduced equations when applied to polarographic processes which are irreversible or not controlled by diffusion is discussed.The simplified equation is tested using several metal complexes of methylthioacetate and 2,2′-thiobisacetate ligands and comparing some of the values obtained from experimentally measured ΔE's with known β₁ values taken from the literature. Good agreement is found. For the U(VI)—methylthioacetate complex, which has not been previously reported in the literature, log β₁ = 1.75 ± 0.1.     

Ion-Molecule reactions in methylamine and dimethylamine and trimethylamine systems

Fourier transform ion cyclotron resonance mass spectrometry has been used to measure the reaction rates for ions derived from methylamine with dimethylamine or trimethylamine. The use of the selective ion ejection technique greatly simplifies the elucidation of the ion-molecule reaction channels. The rate constants for proton transfer from protonated metwlamine, CH₃NH ₃ ⁺ (m/z 32), to dimethylamine and trimethylamine are 16.1 ± 1.6 × 10^?10 and 9.3 ± 0.9 × 10^?10 cm³ molec^?1s^?1, respectively. The rate constants for charge transfer from methylamine molecular ion, CH₃NH ₂ ⁺ (m/z 31), to dimethylamine and trimethylamine are 9.3 ± 1.8 x 10^?10 and 15.0 ± 5 × 10^?10 cm³molec^?1s^?1, respectively.     

Voltammetry of Dissolved Iron(III)–Nitrilotriacetate–Hydroxide System in Water Solution

The investigation of the dissolved iron(III)–nitrilotriacetate–hydroxide system in the water solution (I=0.1 mol L^?1 in NaClO₄; pH 8.0±0.1) using differential pulse cathodic voltammetry, cyclic voltammetry, and sampled direct current (DC) polarography, was carried out on a static mercury drop electrode (SMDE). The dissolved iron(III) ion concentrations varied from 2.68×10^?6 to 6×10^?4 mol L^?1 and nitrilotriacetate concentrations were 1×10^?4 and 5×10^?4 mol L^?1. By deconvoluting of the overlapped reduction voltammetric peaks using Fourier transformation, four relatively stable, dissolved iron(III) complex species were characterized, as follows: [Fe(NTA)₂]^3?, mixed ligand complexes [FeOHNTA]^? and [Fe(OH)₂NTA]^2?, showing a one‐electron quasireversible reduction, and binuclear diiron(III) complex [NTAFeOFeNTA]^2?, detected above 4×10^?4 mol L^?1 of the added iron(III) ions, showing a one‐electron irreversible reduction character. The calculations with the constants from the literature were done and compared with the potential shifts of the voltammetric peaks. Fitting was obtained by changing the following literature constants: log β₂([Fe(NTA)₂]^3?) from 24 to 27.2, log β₁([FeNTA]^?) from 8.9 to 9.2, log β₂([Fe(NTA)₂]^4?) from 11.89 to 15.7 and log β₂([Fe(OH)₂NTA]^3?) from 15.63 to 19. The determination of the electrochemical parameters of the mixed ligand complex [FeOHNTA]^?, such as: transfer coefficient (α), rate constant (k_s) and formal potential (E°') was done using a sampled DC polarography, and found to be 0.46±0.05, 1.0±0.3×10^?3 cm s^?1, and ?0.154±0.010 V, respectively. Although known previously in the literature, these four species have now for the first time been recorded simultaneously, i.e. proved to exist simultaneously under the given conditions.     

Polarography of complex compounds in the absence of large excess of the complexing agent

A general expression for the current—voltage characteristic was derived which is valid for all degrees of reversibilities and ligand concentrations, taking into account quantitatively the effect of complex formation on the polarographic curves. When the reaction is reversible the current—voltage characteristic and half-wave potential are independent of the reaction mechanism. For quasi-reversible electron-transfer reactions both the reaction mechanism and the stability constants may be established. When the reaction is irreversible, quantitative investigation of the changes of (E_1/2^′)_irr with concentrations of complexing ligands leads to the composition of the activated complex. However, except in special cases independent information is necessary to determine stability constants. The theory of the polarographic reduction of metal ions in the absence of large excess of the complexing agent was tested experimentally. In the case of the Bi-NTA complex reduction, the electrode reaction was found to be quasi-reversible and the equations of the theoretical section to be applicable.     

A Spectrophotometric Investigation of the Interaction of Iodine with Dibenzyldiaza‐18‐crown‐6, Aza‐15‐crown‐5 and N‐phenylaza‐15‐crown‐5 in Chloroform Solution

The complex formation reactions between iodine and DBzDA18C6, A15C5 and N‐phenylA15C5 have been studied spectrophotometrically in chloroform solution. In the case of DBzDA18C6 is the resulting 1:2 (ligand…I⁺)I₃^?, while, in the case of A15C5 and N‐phenylA15C5 a 2:2 molecular complex of [(ligand)₂…I⁺]I₃^? type was formed. The spectrophotometric results indicate that gradual release of triiodide ion from its contact ion paired form in the molecular complex into the solution is the rate‐determining step of the reaction. The kinetic rate constants for the complexation reactions were determined at different temperatures, and activation parameters were calculated from Arrhenius and Eyring equations.     

Reactions of indium phosphide cluster cations with ammonia and trimethylamine

Chemistry of indium phosphide clusters is studied using the powerful trapped ion cell techniques of Fourier transform ion cyclotron resonance (FTICR) mass spectrometry in conjunction with an external cluster source and ion guide. The external source is capable of generating a wide range of cluster ions which the ion guide loads with high efficiency into the FTICR cell. The differential pumping of the ion guide allows for operation of the FTICR at requisite low pressure conditions while extracting clusters generated in a high pressure environment. Highly selective reactions of indium phosphide clusters are observed with ammonia and trimethylamine. Of all the In_xP⁺_y cluster sizes and stoichiometries studied, only the indium dimer ion reacts exothermically with ammonia. Thermalized In⁺₂ reacts by indium ion transfer to ammonia. Owing to its much higher basicity, trimethylamine is much more reactive. The smaller indium phosphide clusters react by indium ion transfer to trimethylamine. As the clusters become larger, however, the reaction probability decreases to zero.