Enthalpies of Iron(III) perchlorate and Fe3+ ion transfer from water into aqueous ethanol solvents

Thermal effects of the transfer of iron(III) perchlorate from water into aqueous ethanol solutions at 25.00 ± 0.01°C are determined calorimetrically. The enthalpies of Fe³⁺ ion transfer are calculated. An increase in the enthalpies of iron(III) ion transfer upon a rise in the ethanol content in the system is observed. The Gibbs energies of Fe³⁺ transfer are calculated using the linear correlation of solvation energy on the solvent and ion parameters.     

The thermochemistry of complexation of silver(I) with nicotinamide in water-ethanol solvents

The changes in the enthalpy of formation of complexes of nicotinamide with Ag⁺ ion at 25 ± 0.1^°C and ionic strength of 0.25 (NaClO₄) were obtained in the composition range of water-ethanol solvent from 0.1 to 0.9 mole fractions using precise calorimetry. We ascertained the stabilization of nicotinamide-silver(I) complexes in water-ethanol solvents and the maximum increase in exothermicity of the reaction in ethanol concentration range from 0 to 0.3 mole fractions. The enthalpy component of the change in the Gibbs energy of the complexation of Ag⁺ ions with NicNH₂ was shown to dominate over the entropy component; the changes in thermodynamic argue for the prevailing contribution of the solvation state of a ligand to the exothermicity of complexation process at low ethanol concentrations.     

Thermodynamics of the complex formation of copper(II) with L-phenylalanine in aqueous ethanol solutions

Constants of the acid dissociation and complexation of L-phenylalanine (HPhe) with copper(II) ions are determined by potentiometry in aqueous ethanol solutions containing 0 to 0.7 molar fraction of alcohol. Changes in the Gibbs energy for the transfer from water to a binary solvent of L-phenylalanine, Phe^? anion, and [CuPhe]⁺ complex are calculated. It is found that the weakening of solvation of the ligand donor groups in solvents with high ethanol contents is accompanied by an increase in the stability of [CuPhe]⁺ complex.     

Effect of water—ethanol solvent on the stability of copper(<Emphasis Type="SmallCaps">ii</Emphasis>) coordination compound with the nicotinate ion

The stability constants of copper(II) complexes with nicotinate ion in water—ethanol solvent were determined by the potentiometric method at 25.0±0.1 °C and ionic strength of 0.25 (NaClO₄) in the range X_EtOH = 0—0.7 mole fractions. The stability constant of copper(II) nicotinate complex considerably increases with increasing ethanol concentration in the solvent. The contributions of reactants to the Gibbs energy of the complex formation reaction on going from water to aqueous ethanol were analyzed. The results of thermodynamic analysis of solvation effects were used to evaluate the ratio of the ion and ligand transfer Gibbs energy contributions to the change in the reaction Gibbs energy in the water—ethanol system.     

Thermodynamics of Complexation of 18-Crown-6 with NH4+ Ion in Water-Dioxane Mixtures

The stability constants of 1 : 1 complexes of ammonium ion with 18-crown-6 in water and aqueous dioxane (dioxane weight fraction 0.2, 0.4, 0.6, and 0.8) in the range 283-318 K were determined electrometrically, and the thermodynamic parameters of the complexation were calculated. The stability of the complexes is determined by the enthalpy factor. The contributions from the Gibbs energy of solvation of NH₄ ⁺ ion, 18-crown-6·NH₄ ⁺ complex, and free 18-crown-6 to stabilization of the complex with increasing content of dioxane in the mixed solvent were estimated. The thermodynamics of complexation of ammonium, sodium, and potassium ions with 18-crown-6 in aqueous-organic solvents, such as water-2-propanol, water-acetone, and water-dioxane, were compared considering the effects of reactant solvation. The variations of the conformational component of the Gibbs energy of solvation of 18-crown-6 and the parameters of selective solvation of the reactants were evaluated. The influence of the dielectric permittivity and donor-acceptor properties of mixed aqueous-organic solvents on the Gibbs energy of complexation and solvation of the cations and 18-crown-6 was subjected to correlation analysis.     

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.     

The thermochemical characteristics of nicotinamide coordination by iron(III) and ligand protonation in aqueous-ethanolic mixtures

The heat effects of protonation of nicotinamide and formation of its complex with iron(III) were determined calorimetrically at 25.00 ± 0.01°C and ionic strength 0.25(NaClO₄) in water-ethanol solvent containing 0–0.75 ethanol mol fractions. The experimental and literature data were used to construct the dependences of the enthalpy, entropy, and Gibbs energy of the reaction on the composition of the water-ethanol solvent. The dependence of the enthalpies of both reactions passed an exothermic minimum at 0.1 ethanol mol fractions. The reagent solvation contributions to the thermodynamic characteristics of transfer were analyzed.     

Solvation peculiarities of nicotinamide in aqueous ethanol

The solvation state of biologically active provitamin PP, viz., 3-pyridinecarboxamide, was studied in a water-ethanol solvent by ¹H and ¹³C NMR and IR spectroscopy. The resolvation of the N heteroatom was found to occur at an EtOH content of 0.05?C0.25 molar fraction. The degree of conjugation of the carbamide group with the heterocycle changes with an increase in the ethanol concentration. The structures of aqueous and ethanol nicotinamide solvates were optimized by the B3LYP/6-311G(d,p) method. The ¹³C chemical shifts (GIAO) and the IR spectra were calculated.     

Thermodynamic studies of binary methanol and ethanol solutions of 1-dodecanol and 1-tetradecanol at 25°C

The osmotic coefficients of binary methanol and ethanol solutions of 1-dodecanol and 1-tetradecanol wer measured at 25°C up to 8 mol-kg^–1 in methanol and 5.5 mol-kg^–1 in ethanol. The activity coefficients of the solute were calculated from Bjerrum's relation. From the osmotic and activity coeficients the excess Gibbs energies of solution as well as the respective partial molar functions of solute and solvent and the virial pair interaction coefficients for the excess Gibbs energies were calculated. In addition, the difference in the Gibbs energy of solvation for the solvent in solution relative to the pure solvent was calculated, as well as the partial molar volumes and excess partial molar volumes of solutes at infinite dilution, and the coefficients of pairwise contributions to the excess volume were determined. The thermodynamic parameters obtained are discussed on the basis of solute-solvent and solute-solute interactions.     

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.     

Complexation of nickel (II) ion with B3 vitamin in aqueous dimethyl sulfoxide

The stability change of nickel(II) ion complexes including one and two nicotinamide (B₃ vitamin) molecules in aqueous dimethyl sulfoxide (X_DMSO = 0–0.85 m.f.) was studied at 298.2±0.1 K and 0.25 ionic strength value (NaClO₄) using the potentiometric method. The first stage constant of complexation increased until organic solvent concentration was 0.5 m.f. and reduced at higher DMSO content. The difference between complex and central ions solvation is a dominating contribution into the Gibbs energy change of mononicotinamide complex formation reaction. When the second ligand molecule was bonded into the coordination compound, the nicotinamide contribution to Δ_trG_r rose and became prevailing at X_DMSO = 0.7–0.85. The ligand was found to replace a water molecule in the coordination sphere of the cation according to spectrophotometric study results.      

Stability constants of nickel(II)-nicotinamide complexes in aqueous-ethanol solutions

The change in stability of 1: 1 and 1: 2 nicotinamide nickel(II) complexes in an aqueous ethanol with ethanol contents of 0 to 0.85 molar fractions is studied via potentiometry at 298.2 ± 0.1 K and a ionic strength of 0.25 (NaClO₄). The constant of complex formation for the first step increases at concentrations of organic solvent lower than 0.5 molar fractions and decreases at a higher content of ethanol. The weakening of the solvation of the donor center in nicotinamide corresponds to the observed change in the stability of the complex. A linear interrelation between the change in the coordination equilibrium constant and the difference between the effect of solvent composition on the solvation of the complex ions and complexing agent is revealed.     

Adsorption and solvation of ethanol at the water liquid-vapor interface: a molecular dynamics study

The free energy profiles of methanol and ethanol at the water liquid-vapor interface at 310K were calculated using molecular dynamics computer simulations. Both alcohols exhibit a pronounced free energy minimum at the interface and, therefore, have positive adsorption at this interface. The surface excess was computed from the Gibbs adsorption isotherm and was found to be in good agreement with experimental results. Neither compound exhibits a free energy barrier between the bulk and the surface adsorbed state. Scattering calculations of ethanol molecules from a gas phase thermal distribution indicate that the mass accommodation coefficient is 0.98, and the molecules become thermalized within 10 ps of striking the interface. It was determined that the formation of the solvation structure around the ethanol molecule at the interface is not the rate-determining step in its uptake into water droplets. The motion of an ethanol molecule in a water lamella was followed for 30 ns. The time evolution of the probability distribution of finding an ethanol molecule that was initially located at the interface is very well described by the diffusion equation on the free energy surface.     

Solvation of reagents in a silver(I)-nicotinamide coordination equilibrium in water-ethanol solutions, according to NMR data

The solvation state of nicotinamide in water-ethanol solvent is investigated by means of ¹H and ¹³C NMR spectroscopy. It is found that the nitrogen heteroatom is resolvated at x _EtOH = 0.05–0.25. The resolvation boundary of the silver(I) ion is determined by nuclear magnetic relaxation. The relationship between the structural and thermodynamic characteristics of the solvation of nicotinamide and the silver(I) ion is demonstrated.     

The gibbs energies of transfer of nicotinamide from water to water-ethanol mixtures and formation of the nicotinamide-silver(I) complex

The distribution coefficients of nicotinamide (NicNH₂) and solubility products of nicotinamide-silver perchlorate were determined by the distribution and solubility methods over a wide range of water-ethanol (EtOH) solvent compositions. The Gibbs energies of transfer of NicNH₂ and the AgNicNH ₂ ⁺ complex cation from water into water-ethanol mixtures were calculated. The influence of H₂O-EtOH solvent compositions on the stability of the nicotinamide-Ag⁺ complex was studied potentiometrically at a 0.25 ionic strength of the medium (NaClO₄) and 25.0 ± 0.1°C. The stability of complexes increased as the concentration of ethanol in mixtures grew. Reagent solvation contributions to complex formation equilibrium shifts were analyzed.     

One-dimensional model for water and aqueous solutions. III. Solvation of hard rods in aqueous mixtures

A simple one-dimensional model for aqueous solution is applied to study the solvation thermodynamics of a simple solute (here, a hard-rod particle) in mixtures of waterlike particles and a cosolvent. Two kinds of cosolvents are considered, one that stabilizes and one that destabilizes the "structure of water." The results obtained for the Gibbs energy, entropy, enthalpy, and heat capacity of solvation are in qualitative agreement with experimental data on the solvation of argon and methane in mixtures of water and ethanol and of water and p-dioxane.     

The influence of composition of acetonitrile-dimethyl sulfoxide solvent on stability of silver(I)-ethylenediamine complexes

The influence of the composition of acetonitrile-dimethyl sulfoxide solvent on shifting complexation equilibrium between silver(I) and ethylenediamine was studied potentiometrically at 298.15 K. The stability of the monoethylenediamine complex with silver(I) was found to increase with increasing acetonitrile content in the mixed solution, while the stability of bis-complexes changes only insignificantly. A decrease in the Gibbs energy of formation of [AgEn]⁺ ion was found to be caused by resolvation of the monoligand ion and a reduced stability of the solvation complex of silver(I). The Gibbs energy for the second coordination step remained constant due to the mutual compensation for the solvation contributions from all reagents.     

Thermodynamic cycle for the calculation of ab initio pKa values for hydroxamic acids

A thermodynamic cycle to calculate pK_a values (Minus log of acid dissociation constants) of hydroxamic acids is presented. Hydroxamic acids exist mainly as amide isomers in the aqueous medium. The amide form of hydroxamic acids has two deprotonation sites and may yield either an N-ion or an O-ion upon deprotonation. The thermodynamic cycle proposed includes the gas-phase N–H deprotonation of the hydroxamic acid, the solvent phase transformation of the N-ion to the O-ion and the solvation of the hydroxamic acid molecule and the O-ion in water. The CBS-QB3 method was employed to obtain gas-phase free energy differences between 12 hydroxamic acids and their respective anions. The aqueous solvation Gibbs free energy changes were calculated at the HF/6-31G(d)/CPCM and HF/6-31+G(d)/CPCM levels of theory using HF/6-31+G(d)/CPCM geometries. For the proton, literature values of the gas-phase free energy of formation and the solvation free energy change were used. The free energy change for the transformation of the N-ion to O-ion in the aqueous medium was calculated by employing CBS-QB3/CPCM in the aqueous medium. For this, the hydroxamic acids were divided in two classes according to the substituent at the carbonyl carbon. A common transformation free energy difference for aliphatic substituted hydroxamic acids and a separate common transformation free energy difference for aromatic substituted hydroxamic acids were obtained. The pK_a calculation yielded a root mean square error of 0.32 pK_a units.     

Solubility of minoxidil in binary mixture of ethanol + water at various temperatures

ABSTRACT

The solubility of minoxidil in the aqueous binary mixtures of ethanol at different temperature are investigated and the obtained solubility data are fitted by using some cosolvency models including van’t Hoff equation, Yalkowsky model, Jouyban–Acree model and Jouyban–Acree–van’t Hoff model. The mean relative deviations (MRD%) are used to illustrate the models performance. Moreover, the apparent entropy, enthalpy, and Gibbs free energy of minoxidil dissolution process in the investigated solvent mixtures are computed using van’t Hoff and Gibbs equations. Finally, by means of the inverse Kirkwood–Buff integrals preferential solvation of minoxidil by water is observed in water-rich and ethanol-rich mixtures.