Standard Thermodynamic Characteristics Research Articles

THERMODYNAMICS OF STEPWISE DISSOCIATION OF GLYCYL-D-PHENYLALANINE IN AQUEOUS SOLUTION

Recently, more and more drugs that are derivatives of oligopeptides have been introduced to the pharmaceutical market. The structural elements of these compounds are amino acids and dipeptides. When stabilizing functional groups are introduced into the peptide structure, as well as through the use of special delivery systems, oligopeptide derivatives can be used as innovative medicines. The calorimetric method was used to determine the heat of interaction of glycyl-D-phenylalanine with solutions of nitric acid and potassium hydroxide at 298.15K and the values of the ionic strength of the solution 0.5, 0.75 and 1.0 in the presence of KNO3. Measurements were carried out on a calorimeter with an isothermal shell and automatic recording of the temperature-time curve. The unit was equipped with a reaction vessel with a volume of 60 cm3. Calibration was performed by current at T = (293.15–308.15) ± 0.01 K and P = 100.5± 0.7 kPa. A thermistor KMT-14 was used as a temperature sensor. The temperature of the calorimetric cell was controlled in a thermostat equipped with a PID controller with an accuracy of 0.002 K. The temperature sensor of the thermostat was a platinum resistance thermometer. The calorimeter was calibrated by current. The volume of the calorimetric liquid is 42.83 ml. The enthalpy of stepwise dissociation of glycyl-D-phenylalanine at zero ionic strength was found by an equation with one individual parameter. Standard thermodynamic characteristics (ΔrH°, ΔrG°, ΔrS°) of acid-base interaction reactions in aqueous solutions of glycyl-D-phenylalanine are calculated. The effect of the background electrolyte concentration on the dissociation heats of glycyl-D-phenylalanine is considered. Knowledge of the thermochemical characteristics of dipeptides is necessary for understanding and subsequent modeling of the process of protein biosynthesis occurring in biological systems. Data on the thermodynamic characteristics of dipeptide solutions are needed in various fields where these compounds are used: pharmacology, medicine, food and cosmetic industries, for the development, justification and optimization of technological processes involving these compounds and their complexes with metals.

Towards the MOCVD’s paradise: Thermodynamics of phase transitions of new scandium precursors

Scandium complexes with β-diketonate ligands are valuable precursors for the metal–organic chemical vapour deposition (MOCVD) of scandia based materials. The technology has been constantly developing and demanding novel precursors with accurately defined thermal properties, which could be used in MOCVD as well as related gas phase processes. Two new complexes with 1,1-difluoroacetylacetone (dfac) and 5,5,6,6,6-pentafluorohexane-2,4-dione (5Fac) have been synthesized, isolated, and characterized. The volatility and condensed phase behaviour including thermal stability and phase transitions of the obtained compounds have been studied; the saturated vapour pressures over crystalline Sc(dfac)3 and liquid Sc(5Fac)3 complexes have been measured. As a result, the standard molar thermodynamic characteristics of melting, sublimation, and vaporization processes have been calculated. Thermal properties of these compounds have been compared with literature data on scandium(III) β-diketonates already used as MOCVD precursor. These new compounds can be successfully used as precursors in the gas-phase deposition processes, and the set of obtained thermodynamic data can help in choosing the optimal deposition conditions.

Molecular and Electronic Structures of Macrocyclic Compounds Formed at Template Synthesis in the M(II)-Thiocarbohydrazide-Diacetyl Triple Systems: A Quantum-Chemical Analysis by DFT Methods.

Using density functional theory (DFT) B3PW91/TZVP, M06/TZVP, and OPBE/TZVP chemistry models and the Gaussian09 program, a quantum-chemical calculation of geometric and thermodynamic parameters of Ni(II), Cu(II), and Zn(II) macrotetracyclic chelates, with (NNNN)-coordination of ligand donor centers arising during template synthesis between the indicated ions of 3d elements, thiocarbohydrazide H2N-HN-C(=S)-NH-NH2 and diacetyl Me-C(=O)-C(=O)-Me, in gelatin-immobilized matrix implants was performed. The key bond lengths and bond angles in these coordination compounds are provided, and it is noted that in all these complexes the MN4 chelate sites, the grouping of N4 atoms bonded to the M atom, and the five-membered and six-membered metal chelate rings are practically coplanar. NBO analysis of these compounds was carried out, on the basis of which it was shown that all these complexes, in full accordance with theoretical expectations, are low-spin complexes. The standard thermodynamic characteristics of the template reactions for the formation of the above complexes are also presented. Good agreement between the data obtained using the above DFT levels is noted.

Structural correlations of complexation of apple pectin with imidazole and L-histidine methyl ester

The thermodynamic and structural study of the complex formation of apple pectin with structural analogs of histidine (imidazole and its methyl ester) was carried out using spectral methods. The composition, stability constants of the complexes, and standard thermodynamic characteristics (Δ G° , Δ H° , Δ S° ) of the complex formation process were determined. The decisive contribution of the imidazole fragment of the amino acid to the stability of the pectin-histidine complex is shown. The esterification of the carboxyl group of histidine, its conversion into methyl ester, has an insignificant effect on the efficiency of complex formation with pectin, leading only to a slight increase in binding.

Dicopper(II) complexes with N3,N4-bridging 1-alkyltetrazoles: Synthesis, crystal structure, magnetic and thermodynamic properties

1-R-Tetrazoles (R ​= ​Et, i-Pr, t-Bu) were found to react with copper(II) tetrafluoroborate hexahydrate and copper(II) nitrate tetrahydrate giving the complexes [Cu2L8(H2O)2]X4, where L ​= ​1-R-tetrazole, X ​= ​BF4− or NO3−. Single crystal X-ray analysis showed that the complexes comprised dinuclear cations [Cu2L8(H2O)2]4+, with six tetrazole ligands showing monodentate N4-coordination, and two ones providing N3,N4 bridges between the copper(II) cations; water molecules complete the distorted octahedral coordination of metal ions. Magnetic susceptibility measurements revealed that the copper(II) ions were very weakly antiferromagnetically coupled. Сomplex [Сu2L8(H2O)2](BF4)4 (L ​= ​1-isopropyltetrazole) was found to exhibit a temperature induced reversible single-crystal to single-crystal polymorphic phase transition. For this complex, adiabatic calorimetry was used to find the standard thermodynamic characteristics of this transition as well as the standard thermodynamic functions of the compound in the temperature range of 80–370 ​K. Additionally, mononuclear complex of the composition [CuL6](BF4)2 (L ​= ​1-ethyltetrazole) was obtained during the investigation and structurally characterized.

Heat capacity and thermodynamic functions of poly(1-(hydroxyimino)trimethylene)

In the present work, the temperature dependence of the molar heat capacity of a partially crystalline poly(1-(hydroxyimino)trimethylene) has been measured over the range of T = (6–500) K using a precise automated adiabatic calorimeter and a heat-flux differential scanning calorimeter. In the above temperature interval, the glass transition has been detected, and the standard thermodynamic characteristics of polyoxime have been determined and analysed. The standard thermodynamic functions of the studied polyoxime, namely, the heat capacity Cpo(T), the enthalpy [H°(T) − H°(0)], the entropy [S°(T) − S°(0)], and the potential Φ°(T) have been calculated for the range from T → (0 to 400) K based on the experimental data. The standard thermodynamic properties of poly(1-(hydroxyimino)trimethylene) have been discussed and compared with the previously studied alternating polyketone (copolymer of ethylene C2H4 and carbon monoxide CO).

Thermodynamic Characteristics of Protolytic Equilibria of L-Alanayl-L-isoleucine in Aqueous Solutions

Potentiometry and calorimetry are used to study protolytic equilibria in aqueous solutions of L‑alanyl-L-isoleucine. The equilibrium constants and heat effects of the dipeptide dissociation reactions are determined. The standard thermodynamic characteristics of the investigated equilibria are calculated. The obtained results are compared to the corresponding data for related compounds.

ТЕХНОЛОГИЯ ПОЛУЧЕНИЯ НОВЫХ БИОЛОГИЧЕСКИ АКТИВНЫХ ПЕКТИНОВЫХ МАТЕРИАЛОВ, МОДИФИЦИРОВАННЫХ L - ТРИПТОФАНОМ

New polymer complexes of copper (II) were obtained on the basis of apple pectin modified with the amino acid L-tryptophan. The stoichiometry of the complexes formed was determined by spectrophotometric methods, and the stability constants and standard thermodynamic characteristics of the complexation process (Hº; Gº; Sº) were calculated. It was found that the interaction of pectin modified with an amino acid with Cu (II) cations leads to the formation of enthalpy - entropy stabilized metal complex compounds. The IR spectral method showed that the coordination interaction of copper (II) cations with tryptophan-modified pectin involves not only carboxyl groups, but also the hydroxyl functions of the polymer matrix. The obtained polymer metal complexes in the future can be proposed for the production of new generation drugs, which, in addition to the specific properties of the amino acid introduced into the polysaccharide, also have membranotropic, immunomolulatory properties and prolonged action.

Calorimetric Study of Bis(η6-Diphenyl)chromium Fulleride [(η6-Ph2)2Cr]$$^{{ \bullet + }}$$[C70]$$^{{ \bullet - }}$$

The molar heat capacity of the crystalline bis(η6-diphenyl)chromium fulleride [(η6-Ph2)2Cr] $$^{{ \bullet + }}$$ [C70] $$^{{ \bullet - }}$$ was determined by precise adiabatic calorimetry over the temperature range T = (6–350) K for the first time. The reversible glass-like transformation was detected on the heat capacity curve of [(η6-Ph2)2Cr] $$^{{ \bullet + }}$$ [C70] $$^{{ \bullet - }}$$ in the interval of T = (12–30) K, and its thermodynamic characteristics were estimated and analyzed. The fundamental thermodynamic functions, namely the enthalpy [H°(T) − H°(0)], the entropy [S°(T)−S°(0)], and the potential Φ° were calculated for the range from T → 0 to 350 K based on the experimentally determined molar heat capacity of [(η6-Ph2)2Cr] $$^{{ \bullet + }}$$ [C70] $$^{{ \bullet - }}$$ . The standard entropy of formation ΔfS° of the investigated fulleride was evaluated at T = 298.15 K. The standard thermodynamic characteristics of [(η6-Ph2)2Cr] $$^{{ \bullet + }}$$ [C70] $$^{{ \bullet - }}$$ were compared with the previously reported data for the studied bis(η6-diphenyl)chromium fulleride [(η6‑Ph2)2Cr] $$^{{ \bullet + }}$$ [C60] $$^{{ \bullet - }}$$ .

Thermodynamic Parameters of the Mixed-Ligand Complexation of Cobalt(II) with Triglycine and L-Histidine in an Aqueous Solution

The Co2+–triglycine–L-histidine system is studied in an aqueous solution at Т = 298.15 K (KNO3) via potentiometry and calorimetry. The formation of mixed-ligand CoL2Y− complex is established, and the standard thermodynamic characteristics (ΔrH°, ΔrG°, ΔrS°) of the complexation reaction are determined. A structure is proposed for this complex.

Thermodynamics of Complexation of Triglycine with Cobalt(II) in Aqueous Solutions

The thermal effects of the reactions of Co(II) complex formation with triglycine in aqueous solution at a temperature of 298.15 K and ionic strengths of 0.2, 0.5, and 1.0 (KNO3) were determined by direct calorimetry. The standard thermodynamic characteristics (ΔrH°, ΔrG°, ΔrS°) of complexation reactions in the system were calculated.

THERMOCHEMICAL STUDY OF ACID-BASE REACTIONS IN AQUEOUS SOLUTION OF PYRIDOXINE

Vitamin B6 is one of the most important vitamins necessary for the life of living organisms. Vitamin B6, which in the body is represented by coenzyme forms - pyridoxal phosphate and pyridoxamine phosphate, is a part of more than 100 enzymes. As the object of study, we chose pyridoxine. The thermal effects of interaction of the solution of pyridoxine with solutions of nitric acid and potassium hydroxide at 298.15K and ionic strength values of 0.25; 0.5 and 0.75 against the background of electrolyte-supporting potassium nitrate were measured with direct calorimetric method. The measurements were carried out in a calorimeter with an isothermal shell equipped with a 60 cm3 reaction vessel and electric calibration at T = 298.15 ± 0.01 К and P = 100.5 ± 0.7 kPa and automatic recording of the temperature-time curve. Relative measurement error for heats of dissolution of a standard substance was -0.1-0.3%. Calculation of the equilibrium composition of the system taking into account processes a step dissociation and water dissociation was carried out according to the KEV program. The thermal effects of dissociation of pyridoxine in a standard solution were found by extrapolating the heats of stepwise dissociation at fixed values of ionic strength to zero ionic strength. Since the thermal effects of dilution were measured in three concentration ranges of KNO3, the number of experiments in each series was at least three. To calculate the confidence interval of the average value of DН the Student's criterion was taken at a confidence interval of 0.95. Standard thermodynamic characteristics (DrH°, DrG°, DrS°) of reactions of acid-base interaction in aqueous solutions of pyridoxine were calculated. With an increase in the background electrolyte concentration, the endothermicity of stepwise pyridoxine ionization processes increases.

COMPLEXATION OF APPLE PECTIN, MODIFIED TO PHARMACOPHORE, WITH THE CATIONS MANGANESE (II) IN AQUEOUS SOLUTIONS

Complex formation in systems containing manganese (II), natural pectin and/or pectin modified by organic pharmacophores (nicotine, salicylic, 5-aminosalicylic, anthranilic acids) was studied by spectral (UV-, IR-, NMR 13C spectroscopy), potentiometric and viscometric methods. Method isomolar series and the molar relationship defined by the molar composition and the range of stability of metal complexes: pectin + nicotinic acid > pectin + acid 5-aminosalicylic > pectin + anthranilic acid > pectin + salicylic acid > native pectin. It is shown that the stability constant of metal complexes is significantly influenced by the reaction temperature and the structure of the pharmacophore. The presence of an amino group in the structure of an aromatic molecule increases the stability of metal complexes by 1.5–2 orders of magnitude. The standard thermodynamic characteristics (∆Hº; ∆Gº; ∆Sº) are calculated, which indicate that the processes of complexation in all cases are enthalpy-entropy favorable (∆Hº<0, ∆Sº>0) and proceed spontaneously (∆Gº<0). The influence of the structure of the drug compound in the polymer ligand on a number of physical and chemical properties of metal complexes was revealed. The data of NMR 13C and IR-spectra allow us to conclude that not only carboxyl groups but also hydroxyl functions of polymer matrices participate in the coordination interaction of pectin and/or pharmacophore-containing pectin with manganese (II) cations.

Thermochemistry of the Acid-Base Interactions in Aqueous Solutions of Isonicotinic and Picolinic Acids

The calorimetric method was employed to measure the heat effects of the interaction of isonicotinic and picolinic acids with HNO3in aqueous solutions over different pH ranges at 298.15 K and ionic strengths of 0.5, 1.0, and 1.5 against potassium nitrate. The heat effects of stepwise dissociation of the acids were determined. The standard thermodynamic characteristics (ΔrH°, ΔrG°, ΔrS°, ΔCp°) of the acid-base reactions in aqueous solutions of isonicotinic and picolinic acids were calculated.

Thermodynamics of bis-dioxolene cobalt complex with imino-pyridine functionalized by TEMPO moiety

Firstly in the present research, the heat capacity of bis-dioxolene cobalt complex with imino-pyridine functionalized by TEMPO moiety (TEMPO-Im-Py)Co(3,6-DBSQ)2 was measured over the range T = (6 and 347) K by the precise adiabatic vacuum calorimeter. In the temperature interval of T = (220 to 285) K, the phase transition in the crystalline state was observed, and its standard thermodynamic characteristics were determined. The standard thermodynamic functions (p° = 0.1 MPa) of (TEMPO-Im-Py)Co(3,6-DBSQ)2(cr), namely Cp,mo, Δ0THmo, Δ0TSmo and Δ0TGmo, were calculated using the obtained experimental data from T → 0 to 350 K. The low-temperature (T < 50 K) heat capacity dependence was analysed on the basis of the Debye heat capacity theory of solids and its multifractal model, so the characteristic temperature and the fractal dimension were determined, and chain-layered structure topology of the studied complex was established.

Calorimetric study of siloxane dendrimer of the third generation with trimethylsilyl terminal groups

The molar heat capacity of siloxane dendrimer of the third generation with trimethylsilyl terminal groups G3[OSi(CH3)3]24 was determined by precise adiabatic calorimetry and differential scanning calorimetry over the temperature range T = (6–570) K for the first time. The low-temperature structural anomaly and the glass transition were observed in the above temperature range, and the standard thermodynamic characteristics of the revealed transformations were determined and analyzed. The fundamental thermodynamic functions such as the enthalpy [H°(T) − H°(0)], the entropy [S°(T) − S°(0)], and the Gibbs energy [G°(T) − H°(0)] were calculated for the range from T → 0 to 570 K based on the experimentally determined molar heat capacity of the investigated compound. The standard entropy of formation ΔfS° of dendrimer G3[OSi(CH3)3]24 was evaluated at T = 298.15 K. The thermal stability of the studied compound was investigated by thermogravimetric analysis. The standard thermodynamic properties of siloxane dendrimer G3[OSi(CH3)3]24 were compared and discussed with the previously reported data for the studied G3 carbosilane dendrimers with different functional terminal groups on the surface layer.

Effect of Temperature on the Thermodynamic Characteristics of Acid–Basic Reactions in Aqueous Solutions of DL-Valyl-DL-leucine

Temperature effects of the reaction between a DL-valyl-DL-leucine solution and solutions of HNO3 and KOH are measured via calorimetry in different ranges of pH, at temperatures of 288.15 and 308.15 K and ionic strengths of 0.5, 1.0, and 1.5 (using KNO3 and LiNO3 as background electrolytes). The thermal effects of the stepwise dissociation of the dipeptide are determined. Standard thermodynamic characteristics (ΔrH°, ΔrG°, ΔrS°, $$\Delta {C}_{p}^{\circ }$$ ) are calculated for the acid–base reactions in aqueous solutions of DL-valyl-DL-leucine. The connection between the thermodynamic characteristics of dipeptide dissociation and the structure of this compound is considered.

Thermodynamics of Mixed-Ligand Complexation of Copper(II) with Triglycine and L-Histidine

The Cu2+–triglycine–L-histidine system was studied by potentiometry and calorimetry in an aqueous solution at T = 298.15 K (KNO3). Mixed-ligand CuLY and CuLHY+ complexes formed in the system. The standard thermodynamic characteristics (ΔrH°, ΔrG°, ΔrS°) of their formation reactions were determined. The possible structures of the mixed-ligand complexes were given.

Features of Cobalt(II) Complexes Formation with Pharmacophore-Modified Apple Pectin

Complexation of cobalt(II) chloride with apple pectin modified with organic pharmacophores (nicotinic, salicylic, 5-aminosalicylic, or anthranilic acid) has been studied by spectral methods. Molar composition, stability constants of the complexes, and pH range of their existence have been determined; standard thermodynamic characteristics (ΔH°, ΔG°, ΔS°) of the complexes formation have been calculated. it has been shown that cobalt(II) ions form complexes of different stability with pharmacophore-containing pectins, which may be due to the unequal affinity of the metal ions to the donor groups of the monomer unit of the polysaccharide matrices.

Determining the Potential of a Silver/Silver Chloride Electrode at Different Temperatures

A simple and reliable way of determining the potential of a laboratory silver/silver chloride electrode (SSCE) is proposed, based on measuring the emf of a galvanic cell composed of silver/silver chloride and copper/copper sulfate (copper in a saturated aqueous solution of copper sulfate) electrodes. The standard thermodynamic characteristics of the reduction of a hexacyanoferrate(III) ion to hexacyanoferrate(II) in an aqueous solution are determined using the determined values of the SSCE potential.