Thermodynamics of citrate complexation with Mn<Superscript>2+</Superscript>, Co<Superscript>2+</Superscript>, Ni<Superscript>2+</Superscript> and Zn<Superscript>2+</Superscript> ions

Isothermal titration calorimetry has been used to determine the stoichiometry, formation constants and thermodynamic parameters (ΔG ^o, ΔH, ΔS) for the formation of the citrate complexes with the Mn²⁺, Co²⁺, Ni²⁺ and Zn²⁺ ions. The measurements were run in Cacodylate, Pipes and Mes buffer solutions with a pH of 6, at 298.15 K. A constant ionic strength of 100 mM was maintained with NaClO₄. The influence of a metal ion on its interaction energy with the citrate ions and the stability of the resulting complexes have been discussed.     

Incorporation of Mg<Superscript>2+</Superscript>, Sr<Superscript>2+</Superscript>, Ba<Superscript>2+</Superscript> and Zn<Superscript>2+</Superscript> into aragonite and comparison with calcite

We have investigated the presence of foreign ions into the bulk structure and the external surfaces of aragonite using periodic ab-initio methods. Four cations isovalent to Ca²⁺ were studied: Mg²⁺, Sr²⁺, Ba²⁺ and Zn²⁺. The calculations were performed at structures (bulk, surface) that contain four and eight CaCO₃ units. Our results, at the Hartree-Fock level, show that the incorporation of those ions into aragonite depends strongly on their size. Mg²⁺ and Zn²⁺, due to their smaller size, can substitute Ca²⁺ ions in the crystal lattice while the incorporation of Sr²⁺ and Ba²⁺ into aragonite is energetically less favoured. Examination of the [011], [110] and [001] surfaces of aragonite revealed that the surface incorporation reduces the energetic cost for the larger ions. These systems provide challenging examples for most shape analysis methods applied in Mathematical Chemistry.     

Complex formation of maleic acid with the Zn<Superscript>2+</Superscript>, Ni<Superscript>2+</Superscript>, Co<Superscript>2+</Superscript>, Cu<Superscript>2+</Superscript> in aqueous solution

The process of complex formation of maleic acid (H₂L) with the ions Zn²⁺, Ni²⁺, Co²⁺, Cu²⁺ was studied by potentiometric titration in a wide range of concentration ratios at 298 K and I = 0.1 mol/l (NaNO₃). The moieties ZnL, CoL, NiL, NiL ₂ ^2? , CuL, and CuL ₂ ^2? were detected and their stability constants were determined.     

Sorption of Cu<Superscript>2+</Superscript> and Zn<Superscript>2+</Superscript> by Natural Biomaterial: Duck Feather

Feather fibers were modified by treatment with 5% tannic acid (TA) solution. Kinetics of the modification was investigated as a function of the reaction time. The maximum loading of TA on feather reached 8.3% after being treated by TA for 9 h. The adsorption of metal cations (Cu²⁺, Zn²⁺) by unmodified and TA-modified feather fibers was investigated as a function of fiber weight gain, temperature, and pH of the metal solution. The adsorption was enhanced at alkaline pH and ambient temperature and increased with the weight gain of TA. The maximum uptake of metal cations (Cu²⁺, 0.77 mmol/g; Zn²⁺, 0.95 mmol/g) was obtained by TA-modified feather at weight gain: 8.3%, pH 11, while at the acidic pH, the adsorption of metal cations by either unmodified or TA-modified feather was negligible. The influence of anions on the adsorption of metal cations was also studied. The uptake of Cu²⁺ from chloride was higher and faster than that from nitrate. Desorption of the metals was performed at acidic pH 2.5 for 48 h. The feather–TA–metal complexes exhibited higher stability for metal cations than the feather–metal complexes. All these experiments reveal that TA-modified feather fibers have good adsorption to metal cations and can be used as metal adsorbent in wastewater treatment.     

Specific features of absorption of Cu<Superscript>2+</Superscript>, Zn<Superscript>2+</Superscript>, Co<Superscript>2+</Superscript>, and Pb<Superscript>2+</Superscript> cations from aqueous solutions by calcium phosphates

Kinetic characteristics of the interaction of trisubstituted calcium phosphate Ca₃(PO₄)₂ · xH₂O with Cu²⁺, Zn²⁺, Co²⁺, and Pb²⁺ ions in aqueous solutions were studied.     

Extraction of metal ions (Fe<Superscript>3+</Superscript>, Co<Superscript>2+</Superscript>, Ni<Superscript>2+</Superscript>, Cu<Superscript>2+</Superscript> and Zn<Superscript>2+</Superscript>) using immobilized-polysiloxane iminobis(n-2-aminophenylacetamide) ligand system

A new insoluble solid functionalized ligand system bearing chelating ligand group of the general formula P-(CH₂)₃-N[CH₂CONH(C₆H₄)NH₂]₂, where P represents [Si–O] _n polysiloxane network, was prepared by the reaction of the immobilized diethyliminodiacetate polysiloxane ligand system, P-(CH₂)₃N(CH₂CO₂Et)₂ with 1,2-diaminobenzene in toluene. ¹³C CP-MAS NMR, XPS and FTIR results showed that most ethylacetate groups (–COOEt) were converted into the amide groups (–N–C=O). The new functionalized ligand system exhibits high capacity for extraction and removal of the metal ions (Fe³⁺, Co²⁺, Ni²⁺, Cu²⁺ and Zn²⁺) with efficiency of 95–97% after recovery from its primary metal complexes. This functionalized ligand system formed 1:1 metal to ligand complexes.     

Extraction of Cu<Superscript>2+</Superscript>, Zn<Superscript>2+</Superscript>, and Co<Superscript>2+</Superscript> ions from aqueous solutions with calcium and magnesium phosphates

The efficiency of calcium and magnesium phosphates of different compositions in the extraction of Cu²⁺, Zn², and Co²⁺ ions from aqueous solutions was studied.     

Thermodynamic behavior of complexation of 18-crown-6 with Tl<Superscript>+</Superscript>, Pb<Superscript>2+</Superscript>, Hg<Superscript>2+</Superscript>, and Zn<Superscript>2+</Superscript> metal cations in methanol-water binary media

The equilibrium constants and thermodynamic parameters for complex formation of 18-Crown-6 (18C6) with Tl⁺, Pb²⁺, Hg²⁺, and Zn²⁺ metal cations have been determined by conductivity measurements in methanol (MeOH)-water (H₂O) binary solutions. 18-Crown-6 forms 1:1 complexes with Hg²⁺ and Zn²⁺ cations, but in the case of Tl⁺ and Pb²⁺ cations, in addition to 1:1 stoichiometry, 1:2 (ML₂) complexes are formed in some binary solvents. The thermodynamic parameters (ΔH _c⁰ and ΔS _c⁰), which were obtained from the temperature dependences of equilibrium constants, show that in most cases the complexes are enthalpy destabilized but entropy stabilized. Non-linear behavior is observed between the equilibrium constants (log K _f ) of complexes and the composition of the mixed solvent. The selectivity of the ligand for these metal cations is sensitive to the solvent composition, and, in some cases, the selectivity order is reversed in certain compositions of the mixed solvent. The results also show that the mechanism of complexation reactions and the stoichiometry of complexes of some metal cations change with the nature and even with the composition of the mixed solvent. The article was submitted by the authors in English.     

Thermodynamic characteristics of formation reactions of Zn<Superscript>2+</Superscript> and Ni<Superscript>2+</Superscript> complexes with succinic acid in aqueous solutions

The heat effects of complex formation between zinc(II) and nickel(II) ions and succinic acid were determined calorimetrically at 298.15 K and several ionic strength values against the background of NaNO₃. The standard thermodynamic characteristics of complex formation in aqueous solution were calculated.     

Zn<Superscript>2+</Superscript> cation triggers self-assembly of cyclen into a stable metallogel

A novel type of ligands contained 1,4,7,10-tetrazacyclododecane and functionalized by two azobenzene moieties grafted with two alkyl chains was designed and synthesized. The ligands with long alkyl chains can form metallogels in the presence of Zn²⁺ cations. The formation of metallogel was followed by NMR and electronic spectral detection. The morphology of the xerogels is varied with the equivalent of Zn²⁺ cations and the concentration of the gel. Spectral and structural analysis indicated that the driving forces of the gel formation were attributed to intermolecular hydrophobic interactions between alkyl chains and π-π interaction between azobenzenes.     

Vinylimidazole copolymers: coordination chemistry,solubility, and cross-linking as function of Cu<Superscript>2+</Superscript> and Zn<Superscript>2+</Superscript> complexation

P(1-VIm-co-MMA) copolymers with 4 or 44 wt.% 1-VIm (abbreviated PVM-4 and PVM-44) where polymerized from 1-VIm (1-vinylimidazole) and methylmethacrylate with azobisisobutyronitrile as initiator and reacted with either Cu²⁺ or Zn²⁺. The resulting coordinated polymer complexes were studied using ICP-AES, CP/MAS ¹³C NMR, conductivity measurements, vibrational spectroscopy (mid-FTIR and far-FTIR), DSC, and EPR. It was established by ICP-AES, CP/MAS ¹³C NMR, conductivity, mid-FTIR and EPR measurements that the transition metal ions in the complexes were exclusively coordinated by the imidazole ligand. The coordination geometry is square planar with regard to Cu(II) complexes. The strong interaction between the polymeric imidazole ligand and the transition metal ion cross-links the system, resulting in augmentation of T _g (the glass transition temperature), especially for copolymers with high relative amount of 1-VIm. The effect of changing metal ion is more complicated and depends on both the strength of the coordinate interaction as well as the coordination number. The solubility of the coordinate polymer complex in conventional solvents is low due to the coordinate cross-links. However, the coordinate polymer complexes are soluble in strongly coordinating solvents such as acetonitrile and dimethylsulfoxide.     

Difference of Electron Capture and Transfer Dissociation Mass Spectrometry on Ni<Superscript>2+</Superscript>-, Cu<Superscript>2+</Superscript>-, and Zn<Superscript>2+</Superscript>-Polyhistidine Complexes in the Absence of Remote Protons

Electron capture dissociation (ECD) and electron transfer dissociation (ETD) in metal-peptide complexes are dependent on the metal cation in the complex. The divalent transition metals Ni²⁺, Cu²⁺, and Zn²⁺ were used as charge carriers to produce metal-polyhistidine complexes in the absence of remote protons, since these metal cations strongly bind to neutral histidine residues in peptides. In the case of the ECD and ETD of Cu²⁺-polyhistidine complexes, the metal cation in the complex was reduced and the recombination energy was redistributed throughout the peptide to lead a zwitterionic peptide form having a protonated histidine residue and a deprotonated amide nitrogen. The zwitterion then underwent peptide bond cleavage, producing a and b fragment ions. In contrast, ECD and ETD induced different fragmentation processes in Zn²⁺-polyhistidine complexes. Although the N–C_α bond in the Zn²⁺-polyhistidine complex was cleaved by ETD, ECD of Zn²⁺-polyhistidine induced peptide bond cleavage accompanied with hydrogen atom release. The different fragmentation modes by ECD and ETD originated from the different electronic states of the charge-reduced complexes resulting from these processes. The details of the fragmentation processes were investigated by density functional theory.

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Crystal structures of a family of layered coordination polymers containing divalent metal ions (Mn<Superscript>2+</Superscript>, Co<Superscript>2+</Superscript>, Ni<Superscript>2+</Superscript> and Zn<Superscript>2+</Superscript>) and the 3-amino 4-methyl benzoate ion

The syntheses and crystal structures of the layered coordination polymers M(C₈H₈NO₂)₂ [M = Mn (1), Co (2), Ni (3) and Zn (4)] are described. These isostructural compounds contain centrosymmetric trans-MN₂O₄ octahedra as parts of infinite sheets; the ligand bonds to three adjacent metal ions in μ³-N,O,O′ mode from both its carboxylate O atoms and its amine N atom. In each case, weak intra-sheet N–H?O and C–H?O hydrogen bonds may help to consolidate the structure. Crystal data: 1, C₁₆H₁₆MnN₂O₄, M _r = 355.25, monoclinic, P2₁/c (No. 14), a = 10.6534(2) Å, b = 4.3990(1) Å, c = 15.5733(5) Å, β = 95.1827(10)°, V = 726.85(3) ų, Z = 2, R(F) = 0.026, wR(F ²) = 0.067. 2, C₁₆H₁₆CoN₂O₄, M _r = 359.24, monoclinic, P2₁/c (No. 14), a = 10.6131(10) Å, b = 4.3374(4) Å, c = 15.3556(17) Å, β = 95.473(4)°, V = 703.65(12) ų, Z = 2, R(F) = 0.041, wR(F ²) = 0.091. 3, C₁₆H₁₆N₂NiO₄, M _r = 359.02, monoclinic, P2₁/c (No. 14), a = 10.6374(4) Å, b = 4.2964(2) Å, c = 15.2827(8) Å, β = 95.9744(14)°, V = 694.66(6) ų, Z = 2, R(F) = 0.028, wR(F ²) = 0.070. 4, C₁₆H₁₆N₂O₄Zn, M _r = 365.68, monoclinic, P2₁/c (No. 14), a = 10.6385(5) Å, b = 4.2967(3) Å, c = 15.2844(8) Å, β = 95.941(3)°, V = 694.89(7) ų, Z = 2, R(F) = 0.038, wR(F ²) = 0.107.     

Competitive binding of Na<Superscript>+</Superscript> and Ca<Superscript>2+</Superscript> ions to teichoic acid analogues

The competitive binding of monovalent and divalent counterions to poly(alkylene phosphate) related to bacterial teichoic acids and poly(styrenesulfonate) was studied experimentally by potentiometry with ion-selective electrodes. The binding of calcium ions and the release of sodium ions accompanying calcium ions binding in aqueous solutions of the polyelectrolytes was analysed and the mean exchange ratio Na⁺/Ca²⁺ was estimated. It was found that in the process of addition of calcium ions to sodium poly(alkylene phosphate) and sodium poly(styrenesulfonate) solutions all the Ca²⁺ ions added are bound to polyions and the initially condensed Na⁺ ions are released proportionally to the concentration of the added Ca²⁺ ions up to the critical concentration of the Ca²⁺ ions added. For a molar concentration ratio of calcium counterions to charged groups on the polyion up to 0.20 the exchange ratio was approximately equal to 1 or 2 for the sodium poly(alkylene phosphate)/CaCl₂ and sodium poly(styrenesulfonate)/CaCl₂ systems, respectively.     

Effect of Ca<Superscript>2+</Superscript>, Mg<Superscript>2+</Superscript>, Fe<Superscript>3+</Superscript>, and Al<Superscript>3+</Superscript> Ions on the Deposition of Electrolytic Manganese Dioxide from Chloride Solutions

The effect of Ca²⁺, Mg²⁺, Fe³⁺, and Al³⁺ ions on the deposition of electrolytic manganese dioxide from chloride solutions was studied.__________Translated from Zhurnal Prikladnoi Khimii, Vol. 78, No. 5, 2005, pp. 751–754.Original Russian Text Copyright © 2005 by Kolosnitsyn, Minnikhanova, Karaseva, Dmitriev, Muratov.     

Characterization of extraframework Zn<Superscript>2+</Superscript> cationic sites in silicalite-2: a computational study

Siting and coordination of Zn²⁺ ions at six plausible positions in all-silicate ZSM-11 material known as silicalite-2 have been investigated via hybrid density functional theory method at the B3LYP level employing molecular cluster models to represent the active site. The symmetrical trapping of Zn²⁺ ions in six-membered ring (6MR) sites of the main channels with a fivefold coordination to the framework oxygens was associated with the most stable binding among the investigated sites. On the contrary, the cation was found to be most weakly bound in sites at the intersections where it was twofold coordinated with slightly shorter Zn–O distances. A basket-like position for Zn doping was also recognized that exhibited no clear trends in the electronic and structural properties investigated.     

Effect of temperature on the sorption behavior of sodium potassium fluorophlogopite with respect to the heavy metal ions Cd<Superscript>2+</Superscript>, Hg<Superscript>2+</Superscript>, and Pb<Superscript>2+</Superscript>

The effect of temperature on the sorption behavior of a synthesized gel structurally close to the fluorine mica mineral, sodium potassium fluorophologopite, was studied for the heavy metal ions Cd²⁺, Hg²⁺, and Pb²⁺. The synthesized gel was characterized by X-ray powder pattern, energy dispersive spectrometry, infrared spectroscopy, and thermogravimetric analysis and was found to have the composition Na_0.5K_0.5Mg(AlSi₃O₁₀)F₂·6H₂O. The effect of temperature on sorption was studied with respect to varying concentrations of metal ions. The overall sorption capacity of the synthesized gel was found to depend on the number of ion active groups per unit weight of the material. The data were expressed in terms of distribution coefficients (K _d). Sorption data followed Freundlich adsorption isotherms. Studies showed that sorption decreased as the concentration of metal ions increased and increased as the temperature grew, which was evidence that the process was endothermic. The text was submitted by the authors in English.     

New metal organic framework structures based on 2,5-pyridinedicarboxylate ligands and Zn<Superscript>2+</Superscript> ions

Structural characteristics and adsorption properties of new heteroaromatic framework structures based on Zn²⁺ ions and 2,5-pyridinedicarboxylate ligands are investigated. A comparative study of the aromatic framework structure MOF-5 based on Zn₄O clusters and 1,4-benzenedicarboxylate ligands is also performed in order to reveal the effect of the nature of the organic fragment.     

Aminopeptidase B,a glucagon-processing enzyme: site directed mutagenesis of the Zn<Superscript>2+</Superscript>-binding motif and molecular modelling

Background  

Aminopeptidase B (Ap-B; EC 3.4.11.6) catalyzes the cleavage of basic residues at the N-terminus of peptides and processes glucagon into miniglucagon. The enzyme exhibits, in vitro, a residual ability to hydrolyze leukotriene A₄ into the pro-inflammatory lipid mediator leukotriene B₄. The potential bi-functional nature of Ap-B is supported by close structural relationships with LTA₄ hydrolase (LTA₄H ; EC 3.3.2.6). A structure-function analysis is necessary for the detailed understanding of the enzymatic mechanisms of Ap-B and to design inhibitors, which could be used to determine the complete in vivo functions of the enzyme.     

Thermodynamics of resolvation of Mg<Superscript>2+</Superscript>, Ca<Superscript>2+</Superscript>, Cd<Superscript>2+</Superscript>, and Cu<Superscript>2+</Superscript> ions in aqueous-ethanol mixtures on the basis of volta potential difference method

The volta potential difference method at 298.15 K was used to determine the real primary medium effect for magnesium, calcium, cadmium, and copper ions, and also the real Gibbs transfer energy of these ions from water into a mixed water ethanol (EtOH) solution. The surface potential value at the nonaqueous solution/gas phase interface $ \Delta \chi _{H_2 O}^{EtOH} $ \Delta \chi _{H_2 O}^{EtOH} was obtained. With account for this value, chemical thermodynamic characteristics of the studied ions in the water-ethanol solvent were calculated and the effect of composition and nature of the mixed solvent on the values obtained was analyzed. The dependence of variation in the thermodynamic characteristics of cation resolvation was established on their crystallographic radius that corresponds to the following sequence: Ca²⁺ < Cd²⁺ < Cu²⁺ < Mg²⁺.