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.     

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.     

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.     

Preparation of graphene oxide and its application in Ni<Superscript>2+</Superscript> removal

Graphene oxide (GO) has been prepared by the modified Hummers method using graphite as starting material. The product was studied by the X-ray diffraction (XRD), Raman spectroscopic, transmission electron microscopic (TEM), and scanning electron microscopic (SEM) analyses. Adsorption capacity of GO for heavy metal ions was studied for the example of the Ni²⁺ ions and the adsorption kinetics and adsorption isotherm were determined. It was shown that the adsorption equilibrium curves are adequately described by the Langmuir equation.     

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.     

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.     

Thermochemistry of complex formation of Ni<Superscript>2+</Superscript> with glycyl-L-asparagine in aqueous solutions

The heats of formation of complexes in the glycyl-L-asparagine—Ni²⁺ system were determined by calorimetry in an aqueous solution at ionic strengths of 0.5, 1.0, and 1.5 (KNO₃) and a temperature of 298.15 K. The thermodynamic characteristics of the formation of nickel complexes with dipeptide were determined. The influence of the ligand structure on the complexation thermodynamics in solutions was discussed.Translated from Koordinatsionnaya Khimiya, Vol. 31, No. 2, 2005, pp. 143–148.Original Russian Text Copyright © 2005 by Zelenin, Kochergina.     

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.     

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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Interaction of the Ni<Superscript>2+</Superscript> ion with citric acid in an aqueous solution

The formation of nickel citrate complexes was studied at ionic strength values of 0.1 and 0.3 mol/l (Et₄NCl) and 298.15 K by potentiometric titration. The NiCit^?, NiHCit, and NiH₂Cit⁺ complexes were formed in a Ni²⁺ ion-citric acid (H₃Cit) system. The thermodynamic formation constants of the nickel(II) citrate complexes were calculated in an aqueous solution at \(I = 0:\log \beta _{NiCit^ - }^0 \) = 6.86 ± 0.12 (Ni²⁺ + Cit^3? ai NiCit^?), logK ₁ ⁰ = 4.18 ± 0.10 (Ni²⁺ + HCit^2? ai NiHCit), and logK ₂ ⁰ = 2.24 ± 0.11 (Ni²⁺ + H₂Cit^? ai NiH₂Cit⁺). The spectral properties of the Ni²⁺-H₃Cit system were studied by spectrometry. The conditions of calorimetric determination of the thermal effects of formation of the nickel citrate complexes in an aqueous solution were optimized on the basis of the calculated stability constants of the Ni(II) complexes with H₃Cit.     

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.     

Studies of surface properties of pure and modified by Mn<Superscript>2+</Superscript> and Ni<Superscript>2+</Superscript> ions of aluminium oxide samples using complex methods

Complex studies of physicochemical properties of pure and modified of aluminia oxides samples are presented. The presence of Mn²⁺ and Ni²⁺ modifiers on the aluminium oxide surface causes increase in water adsorption capacity and decrease in benzene and n-octane adsorption. This is due to decrease of specific surface area, volume and radius of pores as a result of surface impregnation and microcrystal formation during modification with manganese and nickel chlorides. Microcrystal formation on the surface and porosity decrease as confirmed by AFM, EDX and powder diffraction studies using automated diffractometer by step scanning. From the Q-TG and Q-DTG data, the energies of liquid desorption from the surface of the samples and the functions of desorption, energy distribution were calculated. High degree of nonlinearity of the functions resulting from great heterogeneity of the studied surface was found. Adsorption of cations creates more homogeneous surface in aluminium oxide, and it is responsible for the change in adsorbate molecule interaction energy and changes mechanism of adsorption and desorption as well as thickness and structure of the adsorbed film. From the experimental data some parameters characterizing adsorption properties and porosity of the studied samples were determined using the complex measuring methods (thermal analysis, sorptometry, porosimetry, AFM and EDX).     

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⁺.     

Photocatalysis enhancement of CaAl<Subscript>2</Subscript>O<Subscript>4</Subscript>:Eu<Superscript>2+</Superscript>, Nd<Superscript>3+</Superscript>@TiO<Subscript>2</Subscript> composite powders

CaAl₂O₄:Eu²⁺, Nd³⁺@TiO₂ composite powders were synthesized by a sol–gel method under mild conditions (i.e. low temperature and ambient pressure). The as-prepared powders were characterized by transmission electron microscopy (TEM) and analyzed by X-ray diffraction (XRD). The photocatalytic behavior of the TiO₂-base surfaces was evaluated by the degradation of nitrogen monoxide gas. It suggested that CaAl₂O₄:Eu²⁺, Nd³⁺@TiO₂ composite powders were composed of anatase titania and that CaAl₂O₄:Eu²⁺, Nd³⁺. TiO₂ particles were deposited on the surface of CaAl₂O₄:Eu²⁺, Nd³⁺ to form uniform film. CaAl₂O₄:Eu²⁺, Nd³⁺@TiO₂ composite powders exhibited higher photocatalytic activity compared with pure TiO₂ under visible light. And the result also clearly indicated that the long afterglow phosphor absorbed and stored lights for the TiO₂ to remain photocatalytic activity in the dark.     

Synthesis,crystal structure of a new tetranuclear Ni<Stack><Subscript>2</Subscript><Superscript>II</Superscript></Stack>Cu<Stack><Subscript>2</Subscript><Superscript>II</Superscript></Stack> complex containing a macrocyclic ligand

The first inorg/organic hybrid complex incorporating the macrocyclic oxamide, of formula [(NiL)₂Cu₂(μ-NSC)₂(NSC)₂] (1), (NiL, H₂L = 2, 3-dioxo-5,6,14,15-dibenzo-1,4,8,12-tetraazacyclo-pentadeca-7,13-dien), have been synthesized and structurally characterized. The crystals crystallize in the triclinic system, space group P-1, for (1) a = 8.319(3) Å, b = 10.434(4) Å, c = 14.166(5) Å, a = 107.030(5)°, β  =  91.257(5)°, γ = 107.623(5)°. The complex involved both bridging N, S-ligand, and oxamide ligand, C–H?S interactions and NCS → Ni weak coordination interactions making the complex superamolecular.     

Interaction energies of histidine with cations (H<Superscript>+</Superscript>, Li<Superscript>+</Superscript>, Na<Superscript>+</Superscript>, K<Superscript>+</Superscript>, Mg<Superscript>2+</Superscript>, Ca<Superscript>2+</Superscript>)

The imidazol side group of histidine has two nitrogen atoms capable of being protonated or participating in metal binding. Hence, histidine can take on various metal-bound and protonated forms in proteins. Because of its variable structural state, histidine often functions as a key amino acid residue in enzymatic reactions. Ab initio (HF and MP2) calculations were done in modeling the cation (H⁺, Li⁺, Na⁺, K⁺, Mg²⁺, Ca²⁺) interaction with side chain of histidine. The region selectivity of metal ion complexation is controlled by the affinity of the side of attack. In the imidazol unite of histidine the ring nitrogen has much higher metal ion (as well as proton) affinity. The complexation energies with the model systems decrease in the following order: Mg²⁺ > Ca²⁺ > Li⁺ > Na⁺ > K⁺. The variation of the bond lengths and the extent of charge transfer upon complexation correlate well with the computed interaction energies.     

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.     

Macro-kinetics of styrene oxidation catalyzed by Co<Superscript>2+</Superscript>-exchanged X

The macro-kinetics and pathway of styrene oxidation catalyzed by Co²⁺-exchanged X, using O₂ as oxidant, were investigated. The effects of external diffusion, internal diffusion, the styrene concentration, O₂ pressure, the catalyst concentration and the reaction temperature on the styrene oxidation reaction rate were examined. The results showed that the reaction rate of styrene oxidation was 0.19 order with respect to the styrene concentration, 0.64 order with respect to O₂ pressure, and zero to first order with respect to the different catalyst concentration. The calculated activation energy for this reaction was 13.79 kJ/mol. On the other hand, the three products in the styrene oxidation reaction were, respectively, used as the reactant to examine the reaction pathway of styrene oxidation. The results revealed that styrene oxidation reaction occurred as two parallel reactions. One was the production of styrene oxide and the other was the production of benzaldehyde and formaldehyde with former partially oxidized to benzoic acid and the latter mostly oxidized to O₂ and H₂O. Published in Russian in Kinetika i Kataliz, 2009, vol. 50, No. 2, pp. 212–217. The article is published in the original.     

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.