Dissociation constants of protolytic dissociation of glutamyl-glutamic and glycyl-glutamic acids in aqueous solution at 298 K

Protolytic dissociation constants of stepwise dissociation of glutamyl-glutamic and glycyl-glutamic acids in aqueous solutions at 298.15 K at ionic strengths of 0.1, 0.5, and 1.0 M on the NaCl background were measured by potentiometric titration. The thermodynamic dissociation constants were calculated. Using the obtained and published data, we discuss the effect of additional carboxy groups in the side chains of the molecule on the protolytic dissociation constants of peptides.     

Photometric Determination of Zirconium with Semimethylthymol Blue

The complexation of zirconium(IV) with Semimethylthymol Blue (H₄L) was studied by spectrophotometry. The formation of the (ZrOH)₂(H₂L)²⁺ ₂ complex with log = 20.68 ± 0.12 and ₅₆₅ = (7.26 ± 0.02) × 10⁴ was revealed by the isomolar series and molar ratio methods. A simple, reliable, and sensitive method was developed for the photometric determination of zirconium. The calibration plot is linear in the concentration range of 10^–6–10^–5 M zirconium. In a sample of frit 24–70 containing 5.7% ZrO₂, 5.44 ± 0.15% ZrO₂ was found.     

The potentiometric study of maleic acid complexation with the alkaline-earth metal ions in aqueous solutions

The potentiometric titration was used to study the process of complex formation of maleic acid (H₂L) with the alkaline-earth metal ions at the ionic strength 0.1 and T = 298 K. The following logarithmic stability constants of maleic acid complexes were obtained: logβ_MgL = 1.79 ± 0.11, logβ_CaL = 1.91 ± 0.05, logβ_SrL = 1.89 ± 0.09, logβ_BaL = 1.94 ± 0.10.     

Thermodynamical characteristics of acid-base equilibria in glycyl-glycyl-glycine aqueous solutions at 298 K

The constants and enthalpies of acid dissociation of glycyl-glycyl-glycine peptide in aqueous solutions at 298.15 K and ionic strength values of 0.1, 0.5, and 1.0 M containing NaCl as a background electrolyte, were determined by potentiometry and calorimetry. The standard values of pK ₁^° and pK ₂^° constants, the change of Gibbs energy, enthalpy, and entropy for the dissociation processes were calculated. It was found that the acidic properties of the carboxylic group in aqueous solution subside upon the transition from α-amino acids to peptides due to the lower entropy effect of dissociation. It was concluded that the increase of dissociation constant of a protonated peptide amino group upon an increase in the length of its molecule is determined by entropy factor associated with the attenuation of amino group solvation.     

Heat effects of complex formation between maleic acid and zinc(II) and nickel(II) ions

The heat effects of formation of zinc(II) and nickel(II) complexes with maleic acid were determined by the direct calorimetric method 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.     

The heat effects of formation of Co2+ ion complexes with carboxylic acids

The heat effects of complex formation between cobalt(II) ions and malonic, maleic, and succinic acids were measured on an isothermic-shell calorimeter 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.     

Enthalpy of Solution of Glycine at Various pHs

A new approach to determination of the enthalpies of solution of amino acids in multicomponent solutions at various pHs is proposed. The approach allows correct estimation of the contribution of acid-base processes occurring in the system and, therefore, correct interpretation of experimental data with regard to interactions between components of the investigated systems. The approach is checked for consistency with an example of glycine.     

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.     

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.     

The thermodynamic characteristics of formation of copper(II) ion complexes with carboxylic acids in aqueous solutions

The heat effects of complex formation between copper(II) ions and malonic, maleic, and succinic acids were measured in an isothermic-shell calorimeter at 298.15 K and several ionic strength values against the background of NaNO₃. The standard thermodynamic characteristics of complex formation in aqueous solutions were calculated.