Self-diffusion of Co2+ ions in CoSO4 in agar gel medium: Concentration dependence of obstruction effect and activation energy

The obstruction effect and activation enerqy for the self-diffusion of Co²⁺ ions in CoSO₄ have been computed using the zone-diffusion technique in agar gel medium at five different concentrations of the electrolyte. Both parameters are found to decrease with an increase in electrolyte concentration. The decrease in obstruction effect expressed in terms of is attributed to the competitive hydration between ions and agar molecules in a diffusion system while the decrease in activation energy is explained by considering the changes in the physical properties of the solution with concentration at microscopic level.     

Application of NAA in diffusion studies

The diffusion of Mn₂+ ions in CoSO₄ , NiSO₄ and ZnSO₄ containing 1% agar gel as well as that of MnSO₄ in 1% agar gel was studied at 25 °C. The diffusion coefficientsat selected concentrations were determined by the zone diffusion techniqueand by measuring the concentration of diffusing ions using neutron activationanalysis.     

Diffusion studies of cobalt ions and their salts in agar gel medium: Obstruction effect and gel hydration

The obstruction effect in the electrolyte diffusion of cobalt halides and in tracer diffusion of Co²⁺ ions in the presence of different supporting electrolytes at various concentrations has been studied at 25 °C using the zone diffusion technique. It has been observed that obstruction effect expressed in terms of increases with concentration and is higher for electrolyte diffusion than in tracer diffusion. Further, for a given concentration it is found to decrease with increasing charge density of an anion. These observations are explained on the basis of competitive hydration between ions and agar molecules.     

Self-Diffusion of Co2+ Ions in CoBr2, CoI2 and Electrolyte-Diffusion of ZnSO4 in Agar Gel Medium

Self-diffusion of Co²⁺ ions in CoBr₂ and CoI₂ is reported in the concentration range of 10^–5 to 0.25M in 1% agar gel at 25 °C. The deviations observed between the experimental and theoretical values of diffusion coefficients are explained by considering different types of interactions occurring in the ion-gel water system. The applicability of the transition state theory to the diffusion of ZnSO₄ in agar gel medium is tested by varying the temperature as well as the gel concentration at high concentration of the electrolyte. The activation energy E and D ₀ value decrease with increasing gel concentration in agreement with the theory.     

Applications of Inorganic Ion Exchangers: II—Adsorption of Some Heavy Metal Ions from Their Aqueous Waste Solution Using Synthetic Iron(III) Titanate

Adsorption of Zn²⁺ and Cd²⁺ ions from aqueous waste solutions on iron(III) titanate as inorganic ion exchange material was investigated to determine the effect of contact time, pH of solution and the reaction temperatures. Batch kinetic studies were carried out and showed that the time of equilibrium for both Zn²⁺ and Cd²⁺ ions was attained within three hours, and the order of kinetic reaction is the first order reaction. Batch distribution coefficients of Zn²⁺ and Cd²⁺ ions on iron(III) titanate as a function of pH have been studied at 25, 40 and 60 ± 1°C. From the obtained results we found that the K _d values decreased with increasing reaction temperatures. Enthalpy change (H) values for Zn²⁺ and Cd²⁺ ions were found to be –8.19 and –22.49 kJ/mol, respectively. The data of adsorption of Zn²⁺ and Cd²⁺ ions at various concentrations were fitted with the Freundlich isotherm. Finally, separation of the above mentioned cations on iron(III) titanate in a column was performed.     

Cation distribution in MgxZn1 − x(HCOO)2·2H2O mixed crystals: X-ray diffraction and double matrix infrared spectroscopy

The metal ion distributions at the two metal sites (hexaformate-coordinated Me1 sites and mixed-coordinated Me2 sites) in the title mixed crystals as determined by single crystal X-ray diffraction and double matrix infrared spectroscopic methods are presented and discussed. The mixed formates are isostructural with the end compounds (space group P2₁/c). The local metal ion concentrations as a function of the total metal ion concentrations exhibit a clear preference of Zn²⁺ ions to Me1 sites and the Mg²⁺ ions to Me2 sites.The analysis of the infrared spectra reveals that the spectral regions 2300–2500 cm⁻¹ (ν_OD of matrix-isolated HDO molecules) and 1300–1400 cm⁻¹ (symmetric COO stretching (ν₂) and bending CH (ν₅) modes) are mostly sensitive to the metal ion environment. The inclusion of Mg²⁺ and Zn²⁺ in the structures of Zn(HCOO)₂·2H₂O and Mg(HCOO)₂·2H₂O, respectively, leads to an appearance of new infrared bands corresponding to ν_OD of HDO molecules bonded to the incorporated ions (i.e. new hydrogen bonding systems MgOH₂⋯OCHOZn and ZnOH₂⋯OCHOMg are formed in the mixed formates). The respective new bands are observed at small concentrations of included Mg²⁺ ions (about 5 mol%, x = 0.05) and at considerably higher concentrations of included Zn²⁺ ions (about 30 mol%, x = 0.7). Contrarily, the ν₂ and ν₅ modes caused by the incorporated cations bonded to formate ions occur at x ≥ 0.3 and x ≤ 0.85 (Mg²⁺ ions in Zn(HCOO)₂·2H₂O and Zn²⁺ ions in Mg(HCOO)₂·2H₂O, respectively). Thus, the infrared spectroscopy experiments confirm the single crystal X-ray measurements that the Mg²⁺ ions are localized predominantly at Me2 sites and the Zn²⁺ ions at Me1 sites in the title mixed crystals. The pronounced preference of the Mg²⁺ ions to Me2 sites is owing to the strong affinity of these ions to water molecules.     

Selective turn-on fluorescence for Zn and Zn + Cd metal ions by single Schiff base chemosensor

Chemosensor based on Schiff base molecules (1, 2) were synthesized and demonstrated the selective fluoro/colorimetric sensing of multiple metal ions (Mn²⁺, Zn²⁺ and Cd²⁺) in acetonitrile–aqueous solution. Both 1 and 2 showed a highly selective naked-eye detectable colorimetric change for Mn²⁺ ions at 10⁻⁷ M. Fluorescence sensing studies of 1 and 2 exhibited a strong fluorescence enhancement (36 fold) selectively upon addition of Zn²⁺ (10⁻⁷ M, λ_max = 488 nm). Fluorescence titration and single crystal X-ray analysis confirmed the formation of 1:1 molecular coordination complex between 1 and Zn²⁺. Interestingly, a rare phenomenon of strong second turn-on fluorescence (190 fold, λ_max = 466 nm) was observed by the addition of Cd²⁺ (10⁻⁷ M) into 1 + Zn²⁺ or Zn²⁺ (10⁻⁷ M) into 1 + Cd²⁺. Importantly both 1 and 2 exhibited different fluorescence λ_max with clearly distinguishable color for both Zn²⁺ and Cd²⁺.     

Adsorption of zinc(II) on hydrous iron oxides

The adsorption of Zn²⁺ ions on amorphous Fe(OH)₃ and -Fe₂O₃, as a function of pH, has been investigated. In the pH region corresponding to the formation of positively charged Zn-hydroxy complexes, an abrupt increase in adsorption was observed. The influence of EDTA and glycine on the adsorption of Zn²⁺ by -Fe₂O₃ has also been investigated. Strong suppression of the adsorption of Zn²⁺ was observed for high [EDTA or Gly]/[Zn²⁺] concentration ratios. The results of the adsorption of Zn²⁺ in the presence of an organic ligand were explained by the formation of Zn-EDTA or Zn-glycine complexes and also by the occupation of adsorption sites by the free organic ligand.     

Zinc(II)cysteine and zinc(II)cystine systems: Selection of species from potentiometric data

Summary The formation constants of species formed in the systems H⁺-Zn²⁺-cysteine and H⁺-Zn²⁺-cystine have been determined in aqueous solution at 37° and I = 0.15 mot dm^–3 (NaClO₄), using the pH-metric method. The existence of the following species [ZnL], [ZnL₂], [ZnL₂H] and [Zn₂L₃] (2.3 pH 7.7) was proved for the Zn²⁺-cysteine system, whereas for the Zn²⁺-cystine [Zn₂L] (5.3 pH 6.4) was the only species found. In the Zn²⁺-cystine system the pH range was severely restricted because of precipitation occurring at pH > 6.4. A new experimental and numerical approach was employed in order to implement the possibility of rigorously selecting the species present in each system. The results have been compared with data previously reported on the same systems, considering in particular the different sets of species found in the various works.     

Diffusion of Manganese Ions in Agar Gel Containing Alkali Metal Chlorides

The obstruction effect for tracer-diffusion of Mn²⁺ ions in the presence of different supporting electrolytes (LiCl, NaCl, KCl, CsCl) at various concentrations has been studied at 25 °C using the zone diffusion technique. It has been observed that the obstruction effect determined in terms of increases with concentration of the electrolyte. Further, for a given concentration it is found to decrease with increasing charge density of the cation. We also report here on the effect of temperature on obstruction and found that is constant over the temperature range studied (25–45 °C). These observations are explained on the basis of competitive hydration between ions and agar macromolecules.     

Diffusion of zinc sulphate in agar gel medium

The activation energy for the diffusion of ZnSO₄ as a function of electrolyte concentration is computed by least squares fitting of the diffusion coefficient data obtained at various temperatures in the Arrhenius equation. It is observed that the activation energy decreases with increasing concentration of the electrolyte. This observation is accounted for on the basis of Wang's model. Further, the obstruction effect caused by the agar macromolecules in the diffusion path of ZnSO₄ uis also determined at these concentrations by varying the gel concentration at 25°C., The obstruction effect expressed in terms of a found to decrease with ZnSO₄ concentration and explained on the basis of competitive hydration of diffusing ions and agar molecules.     

Electrolyte diffusion of ZnCl2 and self-diffusion of Cd2+ ions in agar gel medium at different temperatures

The values of activation energy required for the diffusion of ZnCl₂ and for Cd²⁺ ions in Cd/Ac/₂ are reported in agar gel medium at 5×10^–5 and 0.001M concentration, respectively. These values are compared with the previously reported values in the same systems at different concentrations. The decrease in activation energy with concentration of electrolyte is in agreement with the Wang's model.     

Selectivity of mixed zirconium-titanium phosphates toward transition metals

Mixed zirconium-titanium phosphates were synthesized by various methods and under various conditions. The effect of these conditions on the selectivity of synthetized samples toward the transition metal ions was investigated. It was found that the k_d values are independent of the metal concentration and they give the selectivity order Zn²⁺>Cu²⁺ Co²⁺, Ni²⁺>Mn²⁺.     

Tracer-diffusion of Zn2+ ions in some transition metal sulphates

Tracer-diffusion of Zn²⁺ ions is studied in zinc, manganese and copper sulphates over a concentration range of 10^–4 to 0.25M using 1% agar gel medium at 25 °C. A comparison of the experimental and theoretical values of tracer-diffusion coefficients shows a deviation from the theory. This is explained in the light of different types of interactions occurring in the ion-gel-water system. The effect of supporting electrolytes and its concentration on the obstruction effect in the tracer-diffusion of zinc ions is also examined. The obstruction effect decreases with increasing charge density of the cation of the electrolytes at a given concentration and for a particular elecrolyte it decreases with its concentration. These observations are accounted on the basis of competitive hydration between ions and agar macromolecules.     

A chemosensor showing discriminating fluorescent response for highly selective and nanomolar detection of Cu and Zn and its application in molecular logic gate

A fluorescent based receptor (4Z)-4-(4-diethylamino)-2-hydroxybenzylidene amino)-1,2dihydro-1,5-dimethyl-2-phenylpyrazol-3-one (receptor 3) was developed for the highly selective and sensitive detection of Cu²⁺ and Zn²⁺ in semi-aqueous system. The fluorescence of receptor 3 was enhanced and quenched, respectively, with the addition of Zn²⁺ and Cu²⁺ ions over other surveyed cations. The receptor formed host-guest complexes in 1:1 stoichiometry with the detection limit of 5 nM and 15 nM for Cu²⁺ and Zn²⁺ ions, respectively. Further, we have effectively utilized the two metal ions (Cu²⁺ and Zn²⁺) as chemical inputs for the manufacture of INHIBIT type logic gate at molecular level using the fluorescence responses of receptor 3 at 450 nm.     

Electron spin resonance of Mn2+ ions in matrices of polycrystalline samples of Zn4O[(CH3)2CHCOO]6 and Zn4O[(CH3)3CCOO]3

The ESR spectra of polycrystalline samples of Zn₄O[(CH₃)₂CHCOO]₆ and Zn₄O[(CH₃)₃CCOO]₆, activated by Mn²⁺ ions at various concentrations, were investigated. An analytical theory was developed for the contour of the hyperfine components of the permitted and various types of forbidden transitions. On the basis of the obtained magnetic-resonance parameters conclusions were reached about the local symmetry and coordination of the Mn²⁺ ion in the investigated compounds.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 21, No. 5, pp. 572–579, September–October, 1985.     

Metal binding and interdomain thermodynamics of mammalian metallothionein-3: enthalpically favoured Cu+ supplants entropically favoured Zn2+ to form Cu4+ clusters under physiological conditions

Metallothioneins (MTs) are a ubiquitous class of small metal-binding proteins involved in metal homeostasis and detoxification. While known for their high affinity for d¹⁰ metal ions, there is a surprising dearth of thermodynamic data on metals binding to MTs. In this study, Zn²⁺ and Cu⁺ binding to mammalian metallothionein-3 (MT-3) were quantified at pH 7.4 by isothermal titration calorimetry (ITC). Zn²⁺ binding was measured by chelation titrations of Zn₇MT-3, while Cu⁺ binding was measured by Zn²⁺ displacement from Zn₇MT-3 with competition from glutathione (GSH). Titrations in multiple buffers enabled a detailed analysis that yielded condition-independent values for the association constant (K) and the change in enthalpy (ΔH) and entropy (ΔS) for these metal ions binding to MT-3. Zn²⁺ was also chelated from the individual α and β domains of MT-3 to quantify the thermodynamics of inter-domain interactions in metal binding. Comparative titrations of Zn₇MT-2 with Cu⁺ revealed that both MT isoforms have similar Cu⁺ affinities and binding thermodynamics, indicating that ΔH and ΔS are determined primarily by the conserved Cys residues. Inductively coupled plasma mass spectrometry (ICP-MS) analysis and low temperature luminescence measurements of Cu-replete samples showed that both proteins form two Cu₄⁺–thiolate clusters when Cu⁺ displaces Zn²⁺ under physiological conditions. Comparison of the Zn²⁺ and Cu⁺ binding thermodynamics reveal that enthalpically-favoured Cu⁺, which forms Cu₄⁺–thiolate clusters, displaces the entropically-favoured Zn²⁺. These results provide a detailed thermodynamic analysis of d¹⁰ metal binding to these thiolate-rich proteins and quantitative support for, as well as molecular insight into, the role that MT-3 plays in the neuronal chemistry of copper.

Metallothioneins (MTs) are a ubiquitous class of small metal-binding proteins involved in metal homeostasis and detoxification.     

Hartley–Crank Equations for Coupled Diffusion in Concentrated Mixed Electrolyte Solutions. The CaCl2 + HCl + H2O System

Nernst—Planck equations and ionic conductivities are used to calculate accurate limiting interdiffusion coefficients D _ik ^o for mixed electrolyte solutions. The electrostatic mechanism for coupled electrolyte diffusion is investigated by calculating the electrostatic contribution to each D _ik ^o coefficient to give the flux of each electrolyte driven by the electric field, which is generated by the migration of ions of different mobilities. Ternary diffusion coefficients are measured for dilute aqueous K₂SO₄ + KOH and Li₂SO₄ + LiOH solutions. Because of the different mobilities of K⁺ and Li⁺ ions relative to SO ₄ ^2– ions, diffusing K₂SO₄ drives cocurrent flows of KOH, but diffusing Li₂SO₄ drives counterflows of LiOH. To describe coupled diffusion in concentrated mixed electrolyte solutions, the Hartley–Crank theory is used to correct the limiting D _ik ^o coefficients for nonideal solution behavior, viscosity changes, ionic hydration, and the zero-volume flow constraint. Diffusion coefficients predicted for concentrated aqueous CaCl₂ + HCl solutions are compared with recently reported data. The large amount of HCl cotransported by the diffusing CaCl₂ is attributed to the salting out of HCl by CaCl₂ and to the migration of H⁺ ions in the diffusion-induced electric field, which slows down the Cl^– ions and speeds up the less-mobile Ca²⁺ ions to maintain electroneutrality along the CaCl₂ gradient.     

Structure and magnetic properties of diaqua(4,4′-bipyridine) terbium(III) and the zinc(II) carboxylate dimer [Tb2Zn2(CH2C(CH3)COO)10(bipy)(H2O)2]2

A novel heteronuclear complex, [Tb₂Zn₂L₁₀(bipy)(H₂O)₂]₂ (HL = -methylacrylic acid, bipy = 4,4-bipyridine), was synthesized and characterized by elemental analysis and i.r. absorption spectra. Its structure, determined by X-ray diffraction, is a discrete octanuclear molecule, in which two Zn^II ions are linked by a bipy molecule and between Tb^III ions, or Tb^III and Zn^II ions are bridged by bidentate -methylacrylato groups. The temperature dependence of the magnetic susceptibility of the complex shows strong ferromagnetic interaction between the terbium atoms.     

Three different fluorescent responses to transition metal ions using receptors based on 1,2-bis- and 1,2,4,5-tetrakis-(8-hydroxyquinolinoxymethyl)benzene

The dipod 1,2-bis(8-hydroxyquinolinoxymethyl)benzene (3) and tetrapod 1,2,4,5-tetrakis(8-hydroxyquinolinoxymethyl)benzene (5) have been synthesized through nucleophilic substitution of respective 1,2-bis(bromomethyl)benzene (2) and 1,2,4,5-tetra(bromomethyl)benzene (4) with 8-hydroxyquinoline (1). For comparison, 1,3,5-tris(8-hydroxyquinolinoxymethyl)benzene derivatives (7a and 7b) have been obtained. The complexation behavior of these podands towards Ag⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, and Cd²⁺ metal ions has been investigated in acetonitrile by fluorescence spectroscopy. The sterically crowded 1,2,4,5-tetrapod 5 displays unique fluorescence ‘ON-OFF-ON’ switching through fluorescence quenching (λ_max 395 nm, switch OFF) with <1.0 equiv of Ag⁺ and fluorescence enhancement (λ_max 495 nm, switch ON) with >3 equiv Ag⁺ and can be used for estimation of two different concentrations of Ag⁺ at two different wavelengths. The addition of Cu²⁺, Ni²⁺, and Co²⁺ metal ions to tetrapod 5 causes fluorescence quenching, i.e., ‘ON-OFF’ phenomena at λ_max 395 nm for <10 μM (1 equiv) of these ions but addition of Zn²⁺ and Cd²⁺ to tetrapod 5 results in fluorescence enhancement with a gradual shift of λ_em from 395 to 432 and 418 nm, respectively. Similarly, dipod 3 behaves as an ‘ON-OFF-ON’ switch with Ag⁺, an ‘ON-OFF’ switch with Cu²⁺, and an ‘OFF-ON’ switch with Zn²⁺. The placement of quinolinoxymethyl groups at the 1,3,5-positions of benzene ring in tripod 7a-b leads to simultaneous fluorescence quenching at λ_max 380 nm and enhancement at λ_max 490 nm with both Ag⁺ and Cu²⁺. This behavior is in parallel with 8-methoxyquinoline 8. The rationalization of these results in terms of metal ion coordination and protonation of podands shows that 1,2 placement of quinoline units in tetrapod 5 and dipod 3 causes three different fluorescent responses, i.e., ‘ON-OFF-ON’, ‘ON-OFF’, and ‘OFF-ON’ due to metal ion coordination of different transition metal ions and 1, 3, and 5 placement of three quinolines in tripod 7, the protonation of quinolines is preferred over metal ion coordination. In general, the greater number of quinoline units coordinated per metal ion in 5 compared with the other podands points to organization of the four quinoline moieties around metal ions in the case of 5.