The heats of interaction between alanyl-phenylalanine and solutions of nitric acid and potassium hydroxide at 288.15 and 308.15 K and solution ionic strengths of 0.5, 0.75, and 1.0 are determined via calorimetry with KNO3. Standard thermodynamic characteristics (ΔrH°, ΔrG°, ΔrS°, Δ C_p^^∘ ) of the reactions of acid–base interaction in aqueous solutions of alanyl-phenylalanine. The effect temperature has on the heats of dissociation of alanyl-phenylalanine is considered along with the relationship between the thermodynamic characteristics of the dissociation of the dipeptide and the structure of this compound.

The publication reflects the experimental substantiation and fundamental development of some important ideas of the theory of the mutual influence of functional substitution in complex molecules of macrocyclic and chelating compounds on their coordination, solvation and redox properties, as well as the formation of algorithms for searching useful functions of these compounds. Researchers of the Analytical Chemistry Department of the Ivanovo State University of Chemistry and Technology have been studying the electrochemical and thermodynamic behavior of porphyrins, complexones, amino acids, peptides and the corresponding complexes with d- and f-metal ions, their influence on coordination, solvation and catalytic processes for a number of years. The results obtained together with the literature data are discussed in the review. For citation: Bazanov M.I., Berezina N.M., Gridchin S.N., Krutova O.N., Gorboletova G.G., Bychkova S.A., Lytkin A.I., Chernyavskaya N.V., Chernikov V.V., Volkov A.V. Theoretical and experimental approaches in the study of electrochemical and thermodynamic properties of polyfunctional organic compounds in liquid-phase and heterophase systems. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2023. V. 66. N 7. P. 98-110. DOI: 10.6060/ivkkt.20236607. 6839j.

Complexes are obtained of tetra-4-carboxyphthalocyanines with copper and zinc that are insoluble in water. Standard enthalpies of formation of the compounds are calculated according to additive groups based on group systematics with a Benson-type classification of fragments that considers the influence of the primary environment of atoms. Thermal effects of the dissolution of crystalline tetra-4-carboxymetallo-phthalocyanines in aqueous solutions at different concentrations of KOH (0.002 to 0.02 mol/L) at 298.15 K are determined via direct calorimetry. The standard enthalpies of formation are calculated for products of the dissociation of complexes of tetra-4-carboxyphthalocyanines with copper and zinc in aqueous solutions.

Potentiometry and calorimetry are used to study the Ce 3+ –pyridoxine system in aqueous solution at T = 298.15 K (KNO 3 ). The enthalpies of formation are determined calorimetrically for a complex of pyridoxine and cerium(III) ions at a temperature of 298.15 K and an ionic strength of 0.2 (supporting electrolyte, KNO 3 ). Thermodynamic characteristics ∆ r H , ∆ r G , and ∆ r S of reactions of the formation of pyridoxine complexes with Ce 3+ ions of compositions CеL 2+ , CеОHL + , CeHL 3+ , and Cе(ОH) 2 L are calculated at different [metal] : [ligand] molar ratios.

Calorimetry is used to determine the heats of interaction between D,L-alanil–D,L-phenylalanine and solutions of nitric acid and potassium hydroxide at 298.15 K and ionic strengths of 0.5, 0.75, and 1.0 in solutions with KNO 3 . Standard thermodynamic characteristics (Δ r H °, Δ r G °, Δ r S °) are calculated for acid–base interaction in aqueous solutions of D,L-alanil–D,L-phenylalanine. The effect the concentration of background electrolyte has on the heats of dissociation of D,L-alanil–D,L-phenylalanine is considered. A comparative analysis is performed of the standard thermodynamic characteristics of the stepwise dissociation of L-phenylalanine and D,L-alanil–D,L-phenylalanine in light of modern ideas about the structure and physicochemical properties of these compounds and solutions of them.

Enthalpies of triglycine complexation are determined calorimetrically (HL ± ) with ions of neodymium(III), europium(III), gadolinium(III), and ytterbium(III) at a temperature of 298.15 K and an ionic strength of 0.1, using KNO 3 as the background electrolyte. The thermodynamic characteristics of the formation of complexes of the tripeptide and ions are calculated. Nd 3+ , Eu 3+ , Gd 3+ , and Yb 3+ composition LnL 2+ at different [metal] : [ligand] molar ratios in the 1.8–7.6 range of pH. Analysis of the resulting enthalpies of complexation confirms the preferred coordination of the central lanthanide ion through the carboxylic oxygen atom of triglycine, known from the literature.

Heats of dissolution of crystalline L-glutathione in water and solutions of potassium hydroxide at 298.15 K are measured via direct calorimetry. Numerical values of the standard enthalpies of formation of glutathione in the crystalline state are calculated by additive groups method, based on group systematics with Benson-type classification of fragments that considers the effect of the primary environment on atoms. Standard enthalpies of formation of the tripeptide and the products of its dissociation in aqueous solutions are calculated.

Pyridoxine, as well as its derivatives, are the main forms of vitamin B6, which plays extremely important biological roles in living organisms. In our work, the enthalpies of dissolution of crystalline pyridoxine and pyridoxal-5'-phosphate in water and in aqueous solutions of KOH at 298.15 K were measured by a direct calorimetric method in a wide concentration range. The measurements were carried out on a calorimeter with an isothermal shell and automatic recording of the temperature-time curve. The values of the standard enthalpies of combustion and formation of pyridoxine and pyridoxal-5'-phosphate were calculated using the additive group method based on the group systematics with the classification of fragments like the Benson classification, which takes into account the effect of the primary environment for atoms. The standard enthalpies of formation of pyridoxine and pyridoxal-5'-phosphate and the products of their dissociation in an aqueous solution were calculated. (C) 2021 Elsevier B.V. All rights reserved.

The enthalpies of interaction between β-aminobutyric acid and HNO3 and KОН solutions are measured calometrically in different pH ranges, a temperature of 298.15 K and ionic strengths of 0.25, 0.5, and 0.75 (KNO3). The enthalpies of the stepwise dissociation of amino acid are determined. The standard thermodynamic characteristics (ΔrH°, ΔrG°, ΔrS°) of reactions of acid–base interaction in aqueous solutions of β-aminobutyric acid are calculated. The correlation between the thermodynamic characteristics of amino acid dissociation and the structure of this compound is examined.

Interactions of proteins with various biologically active substances (hormones, drugs, enzymes, etc.) underlie many biochemical processes in the body. As part of the long-term task to studying various aspects of the interaction between model protein compounds and heterocyclic compounds that are into the structure of many enzymes and drugs, the thermochemical study of aqueous solutions containing aspartic acid amide (L-asparagine) and peridoxal-5¢-phosphate was carried out. Calorimetric measurements of the enthalpy of L-asparagine dissolution in an aqueous solution with pyridoxal-5¢-phosphate additives were performed on an ampoule-type isoperibolic dissolution calorimeter at 298.15 K. The error of measuring single heat effects was below 0.2%. The relative combined uncertainty in the measurements of the enthalpies of dissolution was not more than 0.7%. Based on the obtained experimental data and the using the HEAT computer program, the binding constants and thermodynamic parameters (lgK, ΔcG, ΔcH, ΔcS) of the complex formation between the reagents under study were calculated. A comparison of the affinity of amino acids to interaction with pyridoxal-5¢-phosphate and pyridoxine was carried out. The features of their behavior in an aqueous solution are revealed. It is shown that the interaction of L-asparagine with pyridoxine leads to the formation of a more stable complex than with peridoxal-5¢-phosphate. This fact may be explained in terms of a bulky phosphate group that hinders apparently the interaction of POP with aspartic acid amide. In addition, the peridoxal-5¢-phosphate molecule contains intramolecular hydrogen bonds between aldehyde CHO and phenolic OH groups, which must be destroyed by the interaction of peridoxal-5' - phosphate with an amino acid, which requires additional energy expenses. Thus, the selectivity of the interaction and the stability of the formed complexes are mainly regulated by the factors of structural and energy complementarity.

The enthalpies of complexation of L-glutamine with Gd3+ and Ho3+ are determined calorimetrically at 298.15 K and ionic strength of 0.5 (KNO3). The thermodynamic characteristics of the formation of complexes of amino acids with lanthanide ions are calculated. The stability constants of gadolinium and holmium complexes with glutamine ion are determined potentiometrically at 298.15 K and an ionic strength of 0.5 (KNO3). The thermodynamic characteristics of the formation of complexes of an amino acid with Gd3+ and Ho3+ of composition LnL are calculated at [metal] : [ligand] molar ratios of 1 : 4.

Values of the standard enthalpies of formation D,L-alanyl-D,L-serine are calculated using additive groups approach based on group systematics with such classifications of fragments as the Benson classification, which considers the effect of the primary environment of atoms. The heat effects of the dissolution of crystalline D,L-alanyl-D,L-serine in water and in solutions of potassium hydroxide at 298.15 K are determined via direct calorimetry in a wide range of concentrations. The standard enthalpies of formation of the peptide and products of its dissociation in an aqueous solution are calculated.

The enthalpies of l-carnosine interaction with solutions of hydrochloric acid have been measured by calorimetric method in the presence of NaCl at 298.15 K and ionic strength as high as 0.25, 0.50 and 0.75 mol dm−3. The enthalpies of acid dissociation have been determined from the obtained data. The effect of a background electrolyte concentration on the dissociation enthalpy of peptide has been considered. Standard thermodynamic quantities (ΔdisH°, ΔdisG°, ΔdisS°) of the acid dissociation of the dipeptide in aqueous solutions have been determined on the basis of the obtained thermochemical results and available data on the acid dissociation constants corrected for the zero-order ionic strength. Ability to acid dissociation of amino acids in a free state is compared with those for amino acid residues involved in the dipeptide linkage. The alteration of acidity has been connected with variation in hydration of reactivity centers.

Витамин В6 один из самых важных витаминов, необходимых для жизнедеятельности живых организмов. Витамин В6 в организме представлен коферментными формами  пиридоксальфосфатом и пиридоксаминфосфатом, входит в состав более чем 100 ферментов. В качестве объекта исследования мы выбрали пиридоксин. Прямым калориметрическим методом измеряли тепловые эффекты взаимодействия раствора пиридоксина с растворами азотной кислоты и гидроксида калия при 298,15 К и значениях ионной силы 0,25; 0,5 и 0,75, фоновый электролит нитрата калия. Измерения проводились в калориметре с изотермической оболочкой, оснащенной реакционным сосудом объемом 60 см 3 и электрической калибровкой, при T = 298,15 ± 0,01 К и Р = 100,5± 0,7 кПа, а также автоматической записью кривой темпера-время. Относительная погрешность измерения для теплоты растворения стандартного вещества составляла 0,1-0,3%. Расчет равновесного состава системы с учетом процессов ступенчатой диссоциации и диссоциации воды проводился по программе KEV. Тепловые эффекты диссоциации пиридоксина в стандартном растворе были обнаружены путем экстраполяции теплоты ступенчатой диссоциации при фиксированных значениях ионной силы на нулевое значение ионной силы раствора. Поскольку тепловые эффекты разбавления измерялись в трех диапазонах концентраций KNO3, то число экспериментов в каждой серии было не менее трех. Для расчета доверительного интервала среднее значение критерия Стьюдента ΔH было взято при доверительном интервале 0,95. Рассчитаны стандартные термодинамические характеристики (ΔrH°, ΔrG°, ΔrS°) реакций кислотно-основного взаимодействия в водных растворах пиридоксина. С увеличением концентрации фоновой концентрации электролита увеличивается эндотермичность процессов ступенчатой ионизации пиридоксина.