The enthalpies of formation of copper(II) complexes with nicotinamide in aqueous ethanol and DMSO

The enthalpies of complex formation between nicotinamide and copper(II) perchlorate in aqueous ethanol and dimethylsulfoxide (DMSO) were determined calorimetrically. The maximum exothermic effect was observed in a solvent with ～0.1 mole fractions of DMSO. The exothermic effect of complex formation increased as the concentration of ethanol grew. The role played by solvation in the thermodynamic characteristics of monoligand complex formation was considered. The influence of solvent composition on Δ_r H ^o was largely related to the resolvation of the ligand donor atom.     

Effect of hydrogen bonding of solvent on the thermodynamic stability of cadmium ethylenediamine complexes

Changes in the stability of the cadmium(ii) ethylenediamine complexes in mixed water—DMSO solvents were studied by pH-metry and calorimetry. Complex cations [Cd(en)]²⁺, [Cd(en)₂]²⁺, and [Cd(en)₃]²⁺ are formed in aqueous solutions, and the [Cd(en)₄]²⁺ complex with a partially dentate ligand is stable in DMSO. An increase in the DMSO content in a solvent increases the stability of the complexes. The maximum increase in logK is observed for coordinatively saturated compounds. The thermodynamics of complexation is discussed from the viewpoint of solvation approach. Principal differences in the influence of aqueous-alcohol and aqueous-aprotic solvents on the stability of the metal amino complexes were revealed. Protolytic solvents exert a destabilizing effect on the multiligand complexes, because the coordination sphere is involved in H bonding.     

Complexation of nicotinamide with Ag+ ions in water-organic solvents

The effect of the water-ethanol and water-DMSO solvent composition on the stability of nicotinamide (NicNH₂) complexes with Ag⁺ ions at an ionic strength of 0.25 (NaClO₄) and a temperature of 25 ± 0.1°C is studied by potentiometric titration. An increase in the EtOH concentration in the mixed solvent is found to result in a higher stability of the nicotinamide complex with silver(I) ions; as the DMSO concentration increases, the complex becomes less stable. The results of the study are analyzed in terms of the solvation thermodynamic approach taking into account the electronic structure of the ligand and the solvation contributions of the fragments of the molecule.     

Reactivities of heterocyclic compounds in nitration. 5. Kinetics of nitration of 5-substituted 2-picrylaminopyridines

The kinetics of nitration of 5-bromo-, 5-chloro-, and 5-nitro-2-picrylaminopyridines in 80–96% sulfuric acid were studied by a spectrophotometric method. The kinetic parameters of nitration were calculated. The UV spectra of the neutral and protonated forms in aqueous sulfuric acid solutions were identified. It was established that the indicated compounds are nitrated in the protonated form. The relative (as compared with benzene) rates of nitration were calculated.See [1] for communication 4.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1632–1636, December, 1980.     

The thermodynamic parameters of complex formation between silver (I) ions and 2,2′-dipyridyl in water-dimethylsulfoxide solvents

The thermodynamic characteristics of complex formation between Ag(I) and 2,2′-dipyridyl (Dipy) in H₂O-DMSO solvents were studied. The calorimetric data obtained were used to calculate the enthalpies of formation of [AgDipy]⁺ and [AgDipy₂]⁺ in water-dimethylsulfoxide solvents containing from 0.0 to 0.8 mole fractions of DMSO. The solvation contributions of all reagents to changes in the stability of the [AgDipy]⁺ and [AgDipy₂]⁺ complexes were analyzed. An increase in the concentration of dimethylsulfoxide in solvents was found to have opposite effects on the energy characteristics of formation of mono-and biligand complexes between Ag⁺ and Dipy.     

Enthalpies of glycylglycinate ion transfer from water to water-dimethyl sulfoxide solvent

The thermal effects of sodium glycylglycinate dissolution are determined calorimetrically at 298.15 K, and the enthalpies of glycylglycinate ion transfer from water to water-dimethyl sulfoxide solvent are calculated for compositions between 0.00 and 0.99 mole fractions of dimethyl sulfoxide. It is shown that when the concentration of the nonaqueous component is increased, the endothermicity of glycylglycinate ion transfer in the solution is considerably enhanced, weakening the solvation of anions.     

Effect of medium acidity on the thermodynamics and kinetics of the reaction of pyridoxal 5′-phosphate with isoniazid in an aqueous solution

Thermodynamic characteristics of the formation of the Schiff base between isoniazid and pyridoxal 5'-phosphate in an aqueous solution at different pH values of a medium are determined by means of spectrophotometry and calorimetric titration. The process kinetics is studied spectrophotometrically, and the reaction rate constants for the formation of the imine at different acidities of a medium are determined. Biochemical aspects of the binding of pyridoxal 5'-phosphate into stable compounds are discussed.     

Pyrazine-2-carbohydrazone of Pyridoxal 5′-Phosphate: Synthesis,Stability, Formation Kinetics,and Interaction with DNA

Russian Journal of General Chemistry - (5-Hydroxy-6-methyl-4-{(E)-[2-oxo-2-(pyrazin-2-yl)ethyl]hydrazinylidenemethyl}pyridin-3-yl)- methyl phosphate has been synthesized via the interaction of...     

A thermodynamic study of reactions of amino acids with crown ethers in nonaqueous media as examples of guest—host molecular complex formation

Our findings and the literature data on the effect of binary aqueous organic solvents on the enthalpy and entropy of molecular complexation reactions of 18-crown-6 with glycine, D, L-alanine, and L-phenylalanine and on the stability of the resulting complexes were reviewed. The relationships between the thermodynamic parameters of the complexation reactions and the reactant solvation were analyzed to reveal the key factors that are crucial for the stability of the complexes and the increasing exothermicity of the processes under study in water—ethanol, water—DMSO, and water—acetone. The changes in the stability of 18-crown-6 complexes with amino acids were assumed to be predicted from the Gibbs energy changes in the transsolvation of the amino acids. This criterion was proposed as a basic thermodynamic parameter for estimating the changes in the stability of 18-crown-6 complexes with peptides and ammoniumtype cations (structurally related to amino acids) when the composition of the binary aqueous organic solvent is varied.     

Maleic acid solvation in mixed water-ethanol solvents

Heat effects of maleic acid dissolution in mixed water-ethanol solvents at 298.15 K are determined by means of calorimetry. A rise in exothermicity of maleic acid solvation is observed upon changes in the solvent copmosition in the direction of H₂O → EtOH, the minimum being at ∼0.2 mol fraction of EtOH.