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.     

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.     

Solubility and Solution Thermodynamics of Some Sulfonamides in 1-Propanol + Water Mixtures

The solubilities of sulfadiazine (SD), sulfamerazine (SMR) and sulfamethazine (SMT) in some 1-propanol + water co-solvent mixtures were measured at five temperatures from 293.15 to 313.15 K over the polarity range provided by the aqueous solvent mixtures. The mole fraction solubility of all these sulfonamides was maximal in the 0.80 mass fraction of 1-propanol solvent mixture (δ _solv = 28.3 MPa^1/2) and minimal in water (δ = 47.8 MPa^1/2) at all temperatures studied. The apparent thermodynamic functions Gibbs energy, enthalpy, and entropy of solution were obtained from these solubility data by using the van’t Hoff and Gibbs equations. Apparent thermodynamic quantities of mixing were also calculated by using the ideal solubilities reported in the literature. Nonlinear enthalpy–entropy relationships were observed for these drugs in the plots of enthalpy versus Gibbs energy of mixing. The plot of ?_mix H° versus ?_mix G° shows different trends according to the slopes obtained when the mixture compositions change. Accordingly, the mechanism for the solution process of SD and SMT in water-rich mixtures is enthalpy driven, whereas it is entropy driven for SMR. In a different way, in 1-propanol-rich mixtures the mechanism is enthalpy driven for SD and SMR and entropy driven for SMT. Ultimately, in almost all of the intermediate compositions, the mechanism is enthalpy driven. Nevertheless, the molecular events involved in the solution processes remain unclear.     

Preferential Solvation of Boscalid in Ethanol/Isopropanol + Ethyl Acetate Mixtures from the Inverse Kirkwood–Buff Integrals Method

The preferential solvation parameters (δx _1,3) of Boscalid in solvent mixtures of ethanol (1) + ethyl acetate (2), and isopropanol (1) + ethyl acetate (2) were derived from their available solubility data by means of the inverse Kirkwood–Buff integrals method. The values of δx _1,3 vary non-linearly with the solvent (1) proportion in the two solvent mixtures. For the ethanol (1) + ethyl acetate (2) system, the values of δx _1,3 are negative in ethanol-rich and ethyl acetate-rich mixtures, but positive in intermediate compositions; for the isopropanol (1) + ethyl acetate (2) system, the values of δx _1,3 are positive in ethyl acetate-rich mixtures and in intermediate compositions, but negative in isopropanol-rich mixtures. The δx _1,3 values are positive indicating that Boscalid is preferentially solvated by ethyl acetate. The magnitude of the preferential solvation of Boscalid by ethyl acetate is higher in isopropanol (1) + ethyl acetate (2) mixtures than in ethanol (1) + ethyl acetate (2) mixtures at 298.15, 308.15 and 313.15 K. The ethyl acetate action may be related to the disordered structure of ethanol or isopropanol molecules around the polar moieties of Boscalid, which increases the solvation, with maximum values near x ₁ = 0.40–0.45 for the two solvent mixtures.     

The thermodynamic characteristics of formation of nickel(II) complexes with L-tyrosine in aqueous-ethanolic solvents

Acid dissociation constants of L-tyrosine (H₂Tyr) and the constants of complex formation between L-tyrosine and nickel(II) ions in water-ethanol mixtures were determined potentiometrically. The Gibbs energies of transfer of tyrosine, HTyr⁻ tyrosinate anion, and [NiHTyr]⁺ complex from water into binary solvents were calculated. An increase in the stability constants of the [NiHTyr]⁺ and [Ni(HTyr)₂] complexes in solvents with a high content of ethanol was caused by weakening of the solvation of amino ligand donor groups.     

A Thermodynamic Study of Complex Formation Between 18-Crown-6 with T1 + , Hg 2+ and Ag + Metal Cations in Some Binary Mixed Non-aqueous Solvents Using the Conductometric Method

The complexation reactions betweenT1⁺, Hg²⁺ andAg⁺ metal cations with 18-Crown-6 (18C6)were studied in acetonitrile (AN)-methanol (MeOH) andbenzonitrile (BN)-methanol (MeOH) binary mixtures at differenttemperatures using the conductometric method. The conductance datashow that the stoichiometry of the complexes in most cases is1 : 1 (ML), but in the case of theTl⁺ cation, in addition to a1 : 1 complex, a 1 : 2 (ML₂)complex is formed in solutions. A non-linear behaviourwas observed for the variation of log K_fof the complexes vs the composition of the binary mixed solvents. The stability of 18C6 complexes with T1⁺, Hg²⁺ and Ag⁺ cations is sensitive to solvent composition and in some cases, the stability order is changed with changingthe composition of the mixed solvents. The values of the thermodynamic parameters (Δ H_c°, Δ S_c°) for formation of 18C6-T1⁺, 18C6-Hg⁺² and the 18C6-Ag⁺ complexes were obtained from the temperature dependence of the stability constants and the results show that the thermodynamics of the complexationreactions is affected by the nature and composition of the mixed solvents and in most cases, the complexes are enthalpy destabilized but entropy stabilized.     

Thermochemical study of complexation and solvation in the β-alanine-Cu(NO3)2-water-ethanol system: 2. Enthalpies of solvation of sodium alaninate and copper(II) nitrate in mixed solvents

The heats of mixing of aqueous copper(II) nitrate and sodium β-alaninate with water-ethanol solvents were measured thermochemically at 298.15 K. The enthalpies of transfer of the Ala⁻ alaninate anion and Cu²⁺ ion in binary water-ethanol mixtures were calculated. The effect of the composition of the binary solvent on the enthalpy of formation of [CuAla]⁺ and the enthalpies of solvation of the ligand, central ion, and complex ion was studied.     

A conductometric study of complexation reaction between dibenzo-24-crown-8 with yttrium cation in some binary mixed non-aqueous solvents

The complexation reaction of macrocyclic ligand, dibenzo-24-crown-8 (DB24C8) with Y⁺³ cation was studied in some binary mixtures of methanol (MeOH), ethanol (EtOH), acetonitrile (AN) and tetrahydrofuran (THF) with dimethylformamide (DMF) at different temperatures using the conductometric method. The conductance data show that in all solvent systems, the stoichiometry of the complex formed between DB24C8 and Y⁺³ cation is 1:1 (ML). The stability order of (DB24C8.Y)⁺³ complex in pure non-aqueous solvents was found to be: AN > EtOH > MeOH > DMF. A non-linear behaviour was observed for changes of log K_f of (DB24C8.Y)⁺³ complex versus the composition of the binary mixed solvents, which was explained in terms of solvent–solvent interactions and also the heteroselective solvation of the species involved in the complexation reaction. The obtained results show that the stability of (DB24C8.Y)⁺³ complex is sensitive to the mixed solvents composition. The values of thermodynamic parameters (?H°_c and ?S°_c) for formation of (DB24C8.Y)⁺³ complex were obtained from temperature dependence of the stability constant using the van’t Hoff plots. The results show that in most cases, the (DB24C8.Y)⁺³ complex is enthalpy destabilized but entropy stabilized and the values and also the sign of thermodynamic parameters are influenced by the nature and composition of the mixed solvents.     

Solution thermodynamics and preferential solvation of triclocarban in {1,4-dioxane (1) + water (2)} mixtures at 298.15 K

The equilibrium solubility and preferential solvation of triclocarban in {1,4-dioxane (1) + water (2)} mixtures at 298.15 K was reported. Mole fraction solubility varies continuously from 2.85 × 10^–9 in neat water to 2.39 × 10^–3 in neat 1,4-dioxane. Solubility behaviour was adequately correlated by means of the Jouyban-Acree model. Based on the inverse Kirkwood-Buff integrals, preferential solvation parameters were calculated. Triclocarban is preferentially solvated by water in water-rich mixtures (0.00 < x₁ < 0.18) and also in 1,4-dioxane-rich mixtures (0.78 < x₁ < 1.00) but preferentially solvated by 1,4-dioxane in mixtures with similar solvent compositions.     

Conductance of the hydroxide ion intert-butyl alcohol-water and 1,4-dioxane-water mixtures

Limiting molar conductances λ_o of potassium hydroxide in 2 to 25 mol%tert-butyl alcohol (TBA)-water mixtures were determined at 25°C as a function of pressure up to 196 MPa. λ_o’s of KOH in (2.5 to 15 mol%) 1,4-dioxane-water mixtures at 25°C and 1 atm were also determined. The excess conductance λ _o ^e of the OH^- ion estimated as [λ _o ^e (OH^-) = λ_o(KOH) - λ_o(KCl)] decreased with an increase in the TBA or dioxane content, as did the excess proton conductance λ _o ^e (H⁺) [λ _o ^e (H⁺) = λ_O(HC1) - λ_o(KCl)]. Although λ _o ^e (OH^-) is smaller than λ _o ^e (H⁺) at all solvent compositions studied, the rate of decrease in λ _o ^e with organic content is larger for the OH^- ion than for the H₃O⁺ ion in both solvent mixtures except in the water-rich region of TBA-water mixtures. λ _o ^e (OH^-) increases with pressure more strongly in TBA-water mixtures than in pure water, and the rate of increase in λ _o ^e (OH^-) with pressure has a maximum at 5 mol% of TBA. These results are discussed in terms of the difference in stability of hydrogen bonds between the OH^- or the H₃O⁺ ion and water molecules and the increase in repulsive forces due to the orientation [H-O O-H] of water molecules in the mixtures.     

Study of solvent effects on the stability constant and ionic mobility of the dibenzo‐18‐crown‐6 complex with potassium ion by affinity capillary electrophoresis

The effect of solvent on the strength of noncovalent interactions and ionic mobility of the dibenzo‐18‐crown‐6 complex with K⁺ in water/organic solvents was investigated by using affinity capillary electrophoresis. The proportion of organic solvent (methanol, ethanol, propan‐2‐ol, and acetonitrile) in the mixtures ranged from 0 to 100 vol.%. The stability constant, K_KL, and actual ionic mobility of the dibenzo‐18‐crown‐6‐K⁺ complex were determined by the nonlinear regression analysis of the dependence of the effective electrophoretic mobility of dibenzo‐18‐crown‐6 on the concentration of K⁺ (added as KCl) in the background electrolyte (25 mM lithium acetate, pH 5.5, in the above mixed hydro–organic solvents). Competitive interaction of the dibenzo‐18‐crown‐6 with Li⁺ was observed and quantified in mixtures containing more than 60 vol.% of the organic solvent. However, the stability constant of the dibenzo‐18‐crown‐6‐Li⁺ complex was in all cases lower than 0.5 % of K_KL. The log K_KL increased approximately linearly in the range 1.62–4.98 with the increasing molar fraction of organic solvent in the above mixed solvents and with similar slopes for all four organic solvents used in this study. The ionic mobilities of the dibenzo‐18‐crown‐6‐K⁺ complex were in the range (6.1–43.4) × 10^?9 m² V^?1 s^?1.     

The stability and solubility of cadmium(II)-8-oxyquinoline complexes in water and micellar solutions of sodium dodecyl sulfate

The formation of cadmium 8-oxyquinoline (HOx) complexes in water and a 0.01 M aqueous solution of sodium dodecyl sulfate (293 K, 0.01) was studied by pH-metric titration. Mathematical simulation of the most probable equilibria gave complex formation constants logβ₁ = 6.17 ± 0.32 (CdOx⁺) and logβ₂ = 14.60 ± 0.14 (CdOx₂) in aqueous solution and apparent stability constants logβ₁ = 8.64 (CdOx⁺) and logβ₂ = 17.59 (CdOx₂) in a solution of dodecyl sulfate. The solubility of cadmium dioxyquinolate in water at pH from 3 to 6 and a micellar sodium dodecyl sulfate medium was determined by the method of saturated solutions. The solubility product pL _p = 21.3 ± 0.9 (H₂O, 293 K) was calculated by modeling the solution of CdOx₂ with taking into account all acid-base interactions and complex formation reactions.     

Stability constants of cesium complexes with 18-crown-6 in ionic liquids

The stability constants of the complex[Cs(18C6)]⁺ (18C6 is 18-crown-6 (L)) in N-butylpyridinium methyl sulfate (I) and of the complex [Cs(18C6)₂]⁺ in 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide (II) were measured by using ¹³³Cs NMR spectroscopy at 23°C. It was found that logK(Cs + L) in solvent I is 1.20±0.13 and logK(CsL + L) in solvent IIis 1.18±0.05. For the complex [Cs(18C6)₂]⁺, the dependence of its stability constant on the temperature in the 23–50°C range was obtained and the enthalpy change in the complexation was determined: ΔH(CsL + L)= ?47 kJ/mol. It was demonstrated that the enthalpy change is favorable for the formation of [Cs(18C6)₂]⁺, while the entropy change hinders the complexation.     

Molecular complexation of some amino acids and triglycine with 18-crown-6 ether in H2O-EtOH solvents at 298.15 K

The influence of composition of H₂O-EtOH solvent on the reaction of formation of a molecular complex of 18-crown-6 ether (18C6) with triglycine (3Gly) has been studied at 298.15 K by a thermochemical method. The standard thermodynamic parameters (Δ_r G°, Δ_r H°, and TΔ_r S°) of the reaction of [3Gly18C6] complex formation in water-ethanol (H₂O-EtOH) solvents having an EtOH mole fraction of 0.0, 0.1, 0.15, 0.2, 0.25, 0.30, and 0.50 have been calculated from the data of calorimetric measurements performed on a TAM III titration microcalorimeter. It has been found that an increase in EtOH concentration in the mixed solvent results in an increase in stability of [3Gly18C6] and in an enhancement in exothermicity of its formation reaction. The water-ethanol solvent has an analogous effect on the stability and energetics of the reactions of formation of molecular complexes of 18C6 with glycine, D,L-alanine, and L-phenylalanine.     

Effect of a water-ethanol solvent on the stability of copper(II) complexes with L-tyrosine

Stability constants of copper(II) mono- and bis-complexes with L-tyrosine were determined by the potentiometric titration method. Gibbs energies of the transfer (Δ_tr G ⁰) of a ligand and a complex ion from water into water-ethanol solvents were calculated. Stability of the complexes [CuHTyr]⁺ and [Cu(HTyr)₂] increases as the ethanol concentration in solutions increases. Increasing stability of the complexes is promoted by weakening solvation of ligand donor groups entering into coordination.     

Micellization and Thermodynamic Parameters of Butanediyl-1,4-bis(tetradecyldimethylammonium Bromide) Gemini Surfactant at Different Temperatures: Effect of the Addition of 2-Methoxyethanol

The effect of the addition of 2-methoxyethanol on the critical micelle concentration (cmc) and on the degree of counterion dissociation (??) of butanediyl-1,4-bis(tetradecyldimethylammonium bromide) gemini surfactant, [C₁₄H₂₉N⁺(CH₃)₂?C(CH₂)₄?CN⁺(CH₃)₂C₁₄H₂₉,2Br^?] (referred as 14?C4?C14,2Br^?), has been studied by varying the compositions of the 2-methoxyethanol + water mixed solvent media (0 to 50?%). To determine various thermodynamic parameters of micellization, on the basis of the mass?Caction model for micelle formation, the experiments were performed at selected compositions of the mixed solvent at four temperatures ranging between 25?°C and 50?°C. Furthermore, the air/bulk surface tensions of the pure and mixed media were determined, and a successful attempt was made to correlate the cohesive energy density described through the Gordon parameter with the values of Gibbs energy of micellization.     

Proton NMR probing of stoichiometry and thermodynamic data for the complexation of Na and Li ions with 15-Crown-5 in acetonitrile-nitrobenzene mixtures

Proton NMR was used to study the complexation reaction of Li⁺ and Na⁺ ions with 15-Crown-5 (15C5) in a number of binary acetonitrile (AN)-nitrobenzene (NB) mixtures at different temperatures. In all cases, the exchange between free and complexed 15C5 was fast on the NMR timescale and only a single population average ¹H signal was observed. The formation constants of the resulting 1:1 complexes in different solvent mixtures were determined by computer fitting of the chemical shift mole ratio data. There is an inverse relationship between the complex stability and the amount of AN in the solvent mixtures. The enthalpy and entropy values for the complexation reaction were evaluated from the temperature dependence of the formation constants. In all the solvent mixtures studied, the resulting complex is enthalpy stabilized but entropy destabilized. Finally, the experimental results were compared with theoretical ones that were obtained from molecular modeling methods. Based on our results, it is most probable that Li⁺-15C5 in solvent stays in a rather nesting complex form with greater LogK_f values, but Na⁺-15C5 forms a complete perching complex form with lower LogK_f values.     

Composition and stability of complexes of maleic and succinic acids with Cu2+ ions in water-ethanol solutions at 298 K

The composition and stability of coordination compounds of the anions of maleic (H₂L) and succinic (H₂Y) acids with copper(II) ions in water-ethanol solutions is studied by means of potentiometric titration at a sodium perchlorate ionic strength of 0.1 and a temperature of 298.15 K. The composition of the water-ethanol solvent was varied from 0 to 0.7 molar parts of ethanol for maleic acid and from 0 to 0.4 molar parts for succinic acid. The stability of monoligand complexes of copper ions with the anions of maleic and succinic acids grows with increase of ethanol concentration from 3.86 to 6.62 for logβ_CuL and from 2.98 to 6.01 for logβ_CuY. It is shown that a monotonic rise in stability upon an increase in the content of ethanol in solution is observed, while the values of logβ_CuL change more sharply. The succinic acid anion forms a stronger complex with copper ions than maleic acid anions do at an ethanol content of 0.4 molar parts. The possibility of the formation of a protonated CuHY⁺ particle is established.     

The thermodynamic characteristics of dissolution and solvation of cetyltrimethylammonium perchlorate in the water-propan-2-ol system

The solubility of cetyltrimethylammonium perchlorate (CTAP) in propan-2-ol and its mixtures with water was determined by the isothermal saturation method over the whole composition range at 278.15–308.15 K. The solubility products and total standard Gibbs energies of transfer of the n-C₁₆H₃₃N(CH₃) ₃ ⁺ and ClO ₄ ^? ions were calculated. The solubility of CTAP in the mixed solvent specified was substantially influenced by solvophilic effects and the heterosolvation of ions caused by them.     

Solubility diagrams of the potassium iodide-water-ethanol and iodine-water-ethanol ternary systems

The solubility of potassium iodide and iodine in water-methanol mixed solvents was studied by the method of sections at 25°C and atmospheric pressure. The solubility of potassium iodide was found to decrease as the content of ethanol in aqueous-alcoholic solutions increased. The solubility of crystalline iodine had a complex dependence on mixed solvent composition; it was maximum in mixtures containing 90 wt % alcohol. The compositions of the solid phases that crystallized in the KI-H₂O-C₂H₅OH and I₂-H₂O-C₂H₅OH systems were substantiated by X-ray measurements.