The thermodynamic characteristics of complex formation of Cd<Superscript>2+</Superscript> with N,N-Bis(carboxymethyl)aspartic acid in aqueous solutions at 298.15 K

The equilibrium constants and heats of formation of complexes of N,N-bis(carboxymethyl)aspartic acid (H₄Y) with Cd²⁺ ions at 298.15 K and ionic strengths of 0.2, 0.5, and 1.0 (KNO₃) were determined by potentiometric titration and calorimetrically. The thermodynamic characteristics of formation of the CdY²⁻ complex at fixed and zero ionic strength values were calculated. The values obtained were interpreted.     

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.     

Hydrolytic Behavior of La<Superscript>3+</Superscript> and Sm<Superscript>3+</Superscript> at Various Temperatures

The hydrolytic species of lanthanide ions, La³⁺ and Sm³⁺, in water at I = 0.1 mol·dm^?3 KCl ionic strength and temperatures of 298.15, 310.15 and 318.15 K were investigated by potentiometry. The hydrolytic species were modeled by the HySS simulation program. From the results, the hydrolytic species of each metal ion at different temperatures were calculated using the program HYPERQUAD2013. The hydrolysis constants (log₁₀ β) of [La(OH)]²⁺ and La(OH)₃ were calculated as ?8.52 ± 0.46, ?26.84 ± 0.48, and log₁₀ β values of [Sm(OH)]²⁺, [Sm(OH)₂]⁺, Sm(OH)₃ were calculated as ?7.11 ± 0.21, ?15.84 ± 0.25 and ?23.44 ± 0.52 in aqueous media at 298.15 K, respectively. The dependence of the hydrolysis constants on the temperature allowed us to calculate the enthalpy, entropy, and Gibbs energy of hydrolysis values of each species.     

The thermodynamic characteristics of the formation of Al<Superscript>3+</Superscript> ion complexes with iminodisuccinic acid in aqueous solutions

Complex formation between Al³⁺ and iminodisuccinic acid (H₄L) was studied at 25°C against the background of 0.1, 0.4, 0.6, and 0.8 N solutions of KNO₃ by potentiometry and mathematical modeling. The extrapolation of concentration constants to zero ionic strength was used to calculate the thermodynamic constants of the formation of the AlL⁻, AlHL, and AlOHL²⁻ complexes using an equation with one individual parameter (logβ⁰ = 16.48 ± 0.08, 8.93 ± 0.14, and 22.88 ± 0.08, respectively).     

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.     

The thermodynamic characteristics of complex formation between Cd<Superscript>2+</Superscript> and iminodisuccinic acid in aqueous solution

The enthalpies of complex formation between iminodisuccinic acid (H₄L) and the Cd²⁺ ion were determined calorimetrically at 298.15 K and ionic strengths 0.5, 1.0, and 1.5 (KNO₃). The thermodynamic characteristics of formation of CdL²⁻ and CdHL⁻ complexes at fixed and zero ionic strength values were calculated.     

Thermochemical study of processes of complex formation of Cu<Superscript>2+</Superscript> ions with L-glutamine in aqueous solutions

Heats of the interaction of Cu(NO₃)₂ solutions with L-glutamine solutions were measured directly by calorimetry at a temperature of 298.15 K and ionic strength values of 0.5, 1.0, and 1.5 (KNO₃). Using RRSU universal software, the experimental data were subjected to rigorous mathematical treatment with allowances made for several concurrent processes in the system. The heats of formation of the CuL⁺ and CuL₂ complexes were calculated from the calorimetric measurements. The standard heats of the complex formation of Cu²⁺ with L-glutamine were obtained by extrapolation to zero ionic strength. The complete thermodynamic characteristic (Δ_r H ^o, Δ_r G ^o, Δ_r S ^o) of the complex formation processes in a Cu²⁺—L-glutamine system was obtained.     

Thermodynamics of Complex Formation of Ce<Superscript>3+</Superscript> and La<Superscript>3+</Superscript> Ions with Glycylglycine in Aqueous Solution

Enthalpy of the complex formation between diglycine (HL^±) and Ce³⁺ or La³⁺ at 308.15 K and ionic strength of 0.5 mol/L (KNO₃) has been determined by means of calorimetry. Thermodynamic parameters of the diglycine complexes formation with Ce³⁺ and La³⁺ at different metal to ligand molar ratios have been determined.     

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.     

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.     

Effects of La<Superscript>3+</Superscript> and Eu<Superscript>3+</Superscript> on outward potassium channels in Vicia guard cells

Effects of La³⁺ and Eu³⁺ on outward potassium channels (K_out⁺) in Vicia guard cells have been studied by patch clamping technique. Extracellular La³⁺ inhibited K_out⁺ currents with a half-inhibition concentration (IC₅₀) of 81 μmol·L⁻¹. Interestingly, intracellular La³⁺ activated K_out⁺ currents at a free concentration of 1.13 × 10⁻¹⁴ mol·L⁻¹, and inhibited K_out⁺ currents at a free concentration of 5.86 × 10⁻¹⁴ mol·L⁻¹. Extracellular Eu³⁺ also activated K_out⁺ currents at concentrations of 10 μmol·L⁻¹ and 50 μmol·L⁻¹, and inhibited K_out⁺ currents at concentrations of more than 1 mmol·L⁻¹. The effects of La³⁺ and Eu³⁺ on K_out⁺ currents may contribute to regulation of the plant water status, which may be one of the mechanisms of the biological effect of rare earth elements.     

Effects of La<Superscript>3+</Superscript> on inward K<Superscript>+</Superscript> channels at plasma membrane in guard cells

The effects of La³⁺ on inward K⁺ channels at plasma membrane in vicia guard cells are investigated using the whole-cell patch-clamp recording mode. It is shown that La³⁺ on both sides of plasma membrane blocks inward K⁺ currents in a concentration-dependent manner, indicating that La³⁺ binding sites may exist on both sides of plasma membrane in guard cells in vicia. The dose response is fitted by the Michaelis-Menten relation characterized by an inhibitor constant K _i of 2.56±0.25 μmol · L⁻¹ (outside membrane) and (1.18±0.11)×10⁻¹⁵ mol · L⁻¹ (inside membrane). Intracellular La³⁺ has much stronger inhibitory effect on inward K⁺ currents than extracellular La³⁺ does, suggesting there may exist stronger binding sites inside membrane than outside membrane. Since ion channel activities of guard cells directly affect plant stomatal movement and water status, our results imply that rare earth elements might have potential practical values in regulating plant water status and strengthening plant drought endurance.     

Recovery and separation of Ce<Superscript>3+</Superscript> and Y<Superscript>3+</Superscript> ions from aqueous solutions by ion flotation

Experimental dependences of the distribution coefficients of cerium(III) and yttrium(III) dodecyl sulfates on the pH value of the equilibrium aqueous phase in the course of ion flotation are reported. Conditions for separation of cerium(III) and yttrium(III) are discussed. A value of the dissociation constant found from experimental results of potentiometric titration of dodecylsulfuric acid with sodium hydroxide is presented.     

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.     

The study of Gd<Superscript>3+</Superscript> complexation with 4-dihydroxyboropenylalanine in aqueous solutions

The process of Gd³⁺ complexation with 4-dihydroxyborophenylalanine (DHBPA) in aqueous solutions was studied by the contact conductometry, IR, and X-ray photoelectronic spectroscopy methods. The complex formation reactions of Gd³⁺ with DHBPA were found to occur in steps, depending on the metal: ligand ratio. In the final reaction product, i.e., the chelate complex [Gd(DHBPA)₃], each molecule of a ligand occupies two coordination sites.     

Standard thermodynamic functions of complex formation between Cu2+ and glycine in aqueous solution

Heat effects of the interaction of copper(II) solutions with aminoacetic acid (glycine) are measured by the direct calorimetry at 298.15 K and ionic strengths of 0.5, 1.0, and 1.5 against a background of potassium nitrate. Standard enthalpy values for reactions of the formation of aminoacetic acid copper complexes in aqueous solutions are obtained using an equation with a single individual parameter by extrapolating it to zero ionic strength. The standard thermodynamic characteristics of complex formation in the Cu²⁺-glycine system are calculated. It is shown that glycine-like coordination is most likely in Cu(II) complexes with L-asparagine, L-glutamine, and L-valine.     

The thermodynamic characteristics of formation of Zn<Superscript>2+</Superscript> complexes with D,L-tryptophan in aqueous solution

The heat effects of formation of D,L-tryptophan complexes with doubly charged zinc ions were determined calorimetrically. The heat effects of interaction of amino acid solutions with a solution of Zn(II) were measured at 288.15, 298.15, and 308.15 K and ionic strengths of 0.25, 0.50, and 0.75 against the background of KNO₃. The heats of dilution of solutions of zinc nitrate with solutions of the background electrolyte were determined under the same conditions. The corresponding corrections were introduced. The thermochemical data were processed taking into account step equilibria. Along with complex formation, “side” protolytic processes were included. The standard thermodynamic characteristics of complex formation were calculated. The influence of temperature on the heat effects of complex formation in the β-alanine-zinc(II) ions system was considered.     

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.     

Effect of the Electrode Material on the Reduction of La<Superscript>3+</Superscript> and Ce<Superscript>3+</Superscript> in Fluoride-Conducting Solid Electrolytes

The reduction of immobile cations La³⁺ and Ce³⁺ in fluoride-conducting solid electrolytes (FSE) LaF₃ (Eu²⁺ 0.8 mol %), LaF₃ (Sr²⁺ 5 mol %), and CeF₃ (Sr²⁺ 5 mol %) in contact with Ag, Bi, Si, La, Ce, and Sm working electrodes is studied by chronoamperometry and voltammetry with linear potential scan. Discovered is linear dependence of initial segments of potentiostatic transients of cathodic current on t ^1/2 at FSE interfaces with Ag, Bi, La, Ce, and Sm. The dependence is due to diffusion-controlled instantaneous nucleation of Ln and Ce. The La³⁺ and Ce³⁺ reduction at the FSE/Ag interface is reversible in a narrow region. The reduction and oxidation of La³⁺ and Ce³⁺ (cations of the FSE rigid lattice) at the FSE/Me (Me = La, Ce and Sm, Bi, Si) interface is irreversible and involves a chemical reaction.__________Translated from Elektrokhimiya, Vol. 41, No. 5, 2005, pp. 662–672.Original Russian Text Copyright © 2005 by Turaeva, Kot, Urchukova, Murin.     

Synthesis of Y-type zeolites with high degree of Na<Superscript>+</Superscript> cation exchange for La<Superscript>3+</Superscript>

Effect of parameters of the ion exchange of Na⁺ cations for La³⁺ in Y zeolites with SiO₂/Al₂O₃ molar ratios of 5.1 and 6.0 on the degree of exchange and physicochemical properties of the resulting LaNaY samples was studied. The conditions in which deeply substituted La-forms of a Y zeolite with high degree of crystallinity can be obtained were determined.