Thermodynamics of L-valine complex formation with Cu<Superscript>2+</Superscript> ions in an aqueous solution

Heat effects of mixing of aqueous solutions of Cu(NO₃)₂ and L-valine were measured by the calorimetric method at 298.15 K and a ionic strength of 0.5–1.5 (KNO₃). The standard heat effects of formation of the Cu(II) complexes with L-valine in an aqueous solution were obtained by the extrapolation to the zero ionic strength using the equation with one individual parameter. The standard thermodynamic characteristics of complex formation in the Cu²⁺-L-valine system were calculated.     

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.     

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.     

Thermochemical study of equilibria in the Cu<Superscript>2+</Superscript>-D,L-threonine system in an aqueous solution

The heats of interaction of Cu²⁺ ions with D,L-threonine in an aqueous solution were determined by direct calorimetry at ionic strengths of 0.50, 0.75, 1.00 (KNO₃) and temperatures of 288.15, 298.15, and 308.15 K and the corresponding heats of dilution were found. In calculation of the equilibrium composition of the system, side protolytic processes were taken into account along with the complexation reactions. The standard heats of formation of the CuThr⁺ and CuThr₂ species were found. The results were analyzed on the basis of Gurney views. The standard enthalpies of formation of complex species in the hypothetical undissociated state in an aqueous solution were calculated.     

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.     

Thermodynamic characteristics of Cu<Superscript>2+</Superscript> complexation processes with L-phenylalanine in an aqueous solution

The heats of interaction of Cu²⁺ ions with L-phenylalanine in aqueous solution were determined by calorimetry at ionic strengths of 0.50, 0.75, 1.00 (KNO₃) and a temperature of 298.15 K. The results of thermochemical study were interpreted taken into account complexation reactions, protolytic processes, and complexation with the competing ligand (OH^?) taking place in parallel. The effect of supporting electrolyte concentration on the heats of Cu²⁺ complexation with the amino acid was considered. The standard enthalpies of complexation were found by extrapolation to zero ionic strength. The standard enthalpies of formation of complex species in an aqueous solution were calculated.     

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.     

Structural parameters of Cu<Superscript>2+</Superscript> aqua complexes in aqueous solutions of its salts

Published data of various research techniques and own experimental results obtained by the X-ray structural analysis concerning structural characteristics of copper(II) aqua complexes in aqueous solutions of its salts under standard conditions have been generalized. Structural parameters of the nearest environment of this ion, such as coordination number, interparticle distances, and ionic association types, were considered. The possibility of the Jahn-Teller effect realization in aqueous solutions of Cu²⁺ salts was examined.     

Effect of background electrolyte concentration on the heat effects in the processes of formation of L-asparagine complexes with Cu<Superscript>2+</Superscript> ions in aqueous solution

A direct calorimetric method was used to measure the heat effects in the reactions of formation of Cu(II) complexes with L-asparagine in aqueous solutions at 298.15 K and ionic strength 0.5, 1.0, 1.5 (KNO₃). The standard thermodynamic characteristics (Δ_r H ⁰, Δ_r G ⁰, Δ_r S ⁰) of the processes of complex formation in the system under study were calculated.     

Allopurinol and its interactions with Cu<Superscript>2+</Superscript> ions: radical reactions and complex structure

Allopurinol (ALP), an inhibitor of the xanthine oxidase enzime, is reported to provide protection against free-radical mediated damage by various mechanisms, including free-radical scavenging and metal chelation (i.e. Cu(II)). To obtain a wider insight into the molecular aspects of the beneficial action of ALP, free ALP and the Cu(II)- ALP system were investigated by radiation chemical and spectroscopic studies. Pulse radiolysis experiments show that ALP is a good · OH scavenger (1.8 × 10⁹ and 5.4 × 10⁹ M^-1 s^-1 at pH 6.0 and 11.0, respectively), leading to · OH-adducts and transient semi-oxidized species, such as phenoxyl radicals. The latter are also formed by the reaction of ALP with some specific one-electron oxidizing radicals (i.e. N₃ and SO₄ ^-). The semi-oxidized species are stabilized by their resonance properties and scarcely react with oxygen. In addition, the chelation of Cu(II) by ALP does not significantly affect the reactivity of the drug towards ·OH (2.5×0⁹ M^-1 s^-1). Raman and the IR spectra support the good chelating ability of ALP, indicating the formation of two Cu(II)- ALP complexes with a slightly different structure. Depending on the metal/ligand ratio, pyrimidine nitrogens may take part to the Cu(II) co-ordination in addition to the N pyrazolic atoms and the C O groups of some ALP molecules. These results suggest that ALP may inhibit oxidative damage both through the direct radical scavenging and the copper-chelation mechanism. In fact, both the conversion of a harmful radical, such as ·OH, into a less reactive transient species, and the capture of copper ions, which play a relevant role in metal-catalysed generation of reactive oxygen species, will prove beneficial for the cell protection.     

The central ion effect on the complex formation process in aqueous organic solvents. The Jahn-Teller effect in the Cu<Superscript>2+</Superscript> solutions

The complex formation of the Ni²⁺ and Cu²⁺ ions in aqueous solutions of 16 organic solvents of different nature (hydrophilic, hydrophobic, and neutral according to the dielectric data) was studied by the electronic spectroscopy. It was shown that in the case of nickel, the solvents under study behaved similarly (except for acetonitrile), i.e., were coordinated to the metal ion through oxygen, and turned weaker than water as regards the spectrochemical series. In the case of copper, the organic solvents exhibited their pronounced hydrophilic and hydrophobic nature. This is explained by nonequivalence of the equatorial and axial positions in the coordination polyhedron of copper due to the Jahn-Teller effect.     

Structural parameters of hydration of Be<Superscript>2+</Superscript> and Mg<Superscript>2+</Superscript> ions in aqueous solutions of their salts

Published data on structural characteristics of hydration of beryllium and magnesium ions in aqueous solutions of their salts under standard conditions, obtained by various methods, as well as authors’ X-ray data are reviewed. Structural parameters of the immediate environment of Be²⁺ and Mg²⁺, specifically coordination numbers, interparticle distances, and types of ionic association, are discussed. It is noted that Be²⁺ coordinates four water molecules at an average distance of 0.167 nm and Mg²⁺ coordinates six water molecules at an average distance of 0.210 nm. In aqueous solutions of their salts, both Be²⁺ and Mg²⁺ form the second coordination spheres.     

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.     

Thermodynamics of reactions of complex formation for Ce<Superscript>3+</Superscript> and Er<Superscript>3+</Superscript> ions with glycine in an aqueous solution

Enthalpies of complex formation for glycine (HL^±) with Ce³⁺ and Er³⁺ ions at 298.15 K and the value of the ionic strength of 0.5 (KNO₃) are determined by calorimetric means using two independent procedures. Thermodynamic characteristics of the reactions of formation for complexes of glycine with Ce³⁺ and Er³⁺ ions at various [metal]: [ligand] molar ratios are calculated.     

Adsorption of the Cu<Superscript>2+</Superscript> ions from aqueous solutions on the active carbon oxidized with hydrogen peroxide and impregnated with nitrogen-containing compounds

Adsorption of the copper ions from aqueous solutions, benzene, and water on the active carbon obtained by chemical activation from walnut shells was studied. The active carbon was additionally oxidized with hydrogen peroxide and then impregnated with nitrogen-containing compounds. As a result of impregnation with melamine, a secondary porosity is formed within the oxidized active carbon, leading to an increase in the specific surface of the sorbent. A modified carbon surface is heterogeneous, and the carbons themselves exhibit catalytic activity in the oxidation of luminol and decomposition of hydrogen peroxide.     

Molecular dynamic studies of amyloid-beta interactions with curcumin and Cu<Superscript>2+</Superscript> ions

Amyloid-beta (Aβ) peptide readily forms aggregates that are associated with Alzheimer’s disease. Transition metals play a key role in this process. Recently, it has been shown that curcumin (CUA), a polyphenolic phytochemical, inhibits the aggregation of Aβ peptide. However, interactions of Aβ peptide with metal ions or CUA are not entirely clear. In this work, molecular dynamics (MD) simulations were carried out to clear the nature of interactions between the 42-residue Aβ peptide (Aβ-42) and Cu²⁺ ions and CUA. Altogether nine different models were investigated, and more than 2 µs of the simulation data were analyzed. The models represent the possible modes of arrangement between Aβ-42 and Cu²⁺ ions and CUA, respectively, and were used to shed light on the Aβ-42 conformational behavior in the presence of Cu²⁺ ions and CUA molecules. Obtained data clearly showed that the presence of a CUA molecule or a higher concentration of copper ions significantly affect the conformational behavior of Aβ-42. Calculations showed that the change of the His13 protonation state (Aβ(H13δ)-Cu²⁺, Aβ(H13δ)-Cu²⁺ -CUA models) leads to higher occurrence of the Asp23-Lys28 salt bridge. Analyzes of trajectories revealed that C-terminal β-sheet structures occurred significantly less frequently, and CUA promoted the stabilization of the α-helical structure. Further, calculations of the Aβ-42 complex with CUA and Cu²⁺ ions showed that CUA can chelate the Cu²⁺ ion and directly interact with Aβ, which may explain why CUA acts as an inhibitor of Aβ aggregation.     

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.     

The thermodynamic characteristics of complex formation between Ni<Superscript>2+</Superscript> ions and D,L-threonine in aqueous solution

The heat effects of interaction between solutions of D,L-threonine and Ni(NO₃)₂ were measured by direct calorimetry at 298.15 K and ionic strength values of from 0.5 to 1.5 (KNO₃). The heat effects of formation of the NiL⁺, NiL₂, and NiL ₃ ^? complexes were calculated. The influence of background electrolyte concentration on the heats of complex formation in the Ni²⁺-D,L-threonine system was studied. The standard heat effects of formation of Ni²⁺ complexes with D,L-threonine were obtained by extrapolation to zero ionic strength. The standard enthalpies of formation of NiL⁺, NiL₂, and NiL ₃ ^? in aqueous solution were calculated.     

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⁺.