Selective solvation of copper(I) thiocyanate in acetonitrile-water mixtures at 30°C

The selective solvation of copper(I) thiocyanate has been studied in water-acetonitrile (AN) mixtures at 30°C by solubility and EMF measurements. The solubility of the salt increases continuously and changes only slightly beyond X _AN =0.7 mole fraction. The Gibbs energy of transfer of copper(I) ion from water to mixtures with acetonitrile (determined on the basis of the ferrocene reference method) decreases continuously, while that of the thiocyanate ion increases with the addition of acetonitrile. The solvent transport number of acetonitrile passes through a maximum (=6.4) at X _AN =0.25. These results were interpreted as arising due to a heteroselective solvation of the salt, the copper(I) ion being preferentially solvated by acetonitrile and the thiocyanate ion by water in these mixtures.     

Selective solvation effects in phase separation in aqueous mixtures

Selective solvation can be crucial in phase separation in polar binary mixtures (water–oil) with a small amount of hydrophilic ions or hydrophobic particles. They are preferentially attracted to one of the solvent components, leading to a number of intriguing effects coupled to phase separation. For example, if cations and anions interact differently with the two components, an electric double layer emerges at a liquid–liquid interface. The main aim of this paper is to show that a strongly hydrophilic (hydrophobic) solute induces precipitation of water-rich (oil-rich) domains above a critical solute density n_p outside the solvent coexistence curve.     

Preferential solvation of some antiepileptic drugs in {cosolvent (1) + water (2)} mixtures at 298.15 K

The solubility of lamotrigine (LTG), clonazepam (CZP) and diazepam (DZP) in some {cosolvent (1) + water (2)} mixtures expressed in mole fraction at 298.15 K was calculated from reported solubility values expressed in molarity by using the densities of the saturated solutions. Aqueous binary mixtures of ethanol, propylene glycol and N-methyl-2-pyrrolidone were considered. From mole fraction solubilities and some thermodynamic properties of the solvent mixtures, the preferential solvation of these drugs by both solvents in the mixtures was analysed by using the inverse Kirkwood–Buff integrals. It is observed that LTG, CZP and DZP are preferentially solvated by water in water-rich mixtures in all the three binary systems analysed. In {ethanol (1) + water (2)} mixtures, preferential solvation by water is also observed in ethanol-rich mixtures. Nevertheless, in {propylene glycol (1) + water (2)} and {N-methyl-2-pyrrolidone (1) + water (2)} mixtures preferential solvation by the cosolvent was observed in cosolvent-rich mixtures.     

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.     

Solubility of phenobarbital in aqueous cosolvent mixtures revisited: IKBI preferential solvation analysis

The preferential solvation parameters of phenobarbital in aqueous binary mixtures of 1,4-dioxane, t-butanol, n-propanol, ethanol, propylene glycol and glycerol were derived from solution thermodynamic properties by using the IKBI method. This drug is sensitive to preferential solvation effects in all these mixtures. The preferential solvation parameter by the cosolvent (δx_1,3) is negative in almost all the water-rich mixtures but positive in mixtures with similar proportions of solvents and cosolvent-rich mixtures, except in 1-propanol + water mixtures, where negative values are also found in mixtures with x₁ ≥ 0.70. Hydrophobic hydration around the non-polar ethyl and phenyl groups of this drug in water-rich mixtures could play a relevant role in drug solvation. Otherwise, in mixtures of similar solvent compositions and in cosolvent-rich mixtures the preferential solvation by cosolvent could be due to the acidic behaviour of the drug.     

Studies on silver(I) solvation in binary solvent mixtures containing dimethylsulfoxide. IV determination of solvent transference numbers for AgSCN and ionic coordination numbers of Ag+ in methanol-dimethylsulfoxide mixtures at 25°C

Solvent transport by AgSCN in the methanol (M)+dimethylsulfoxide (DMSO) system has been studied at 25°C by e.m.f. measurements. The solvent transference number of DMSO is positive as its concentration increases in the cathode compartment during electrolysis. The solubility of AgSCN has been determined in methanol, in DMSO and in methanol-DMSO mixtures. Using the known Gibbs free energy of solvation for the Ag⁺ ion, the corresponding energy for SCN, was found to be independent of the mole fraction. The experimental solvent transference numbers therefore only represent the contribution of Ag⁺, this is because it is preferentially solvated by DMSO. A coordination model has been applied to the Gibbs free energy of transfer of Ag⁺ in order to obtain coordination numbers thereby allowing calculation of solvent transference numbers. The experimental and the calculated solvent transference numbers are in good agreement at mole fractions of DMSO greater than 0.5. In highly methanolic solutions the assumption that the solvation of Ag⁺ in the solvent system studied is adequately represented by a total coordination number of four, proves to be too simple.     

Preferential solvation of methocarbamol in aqueous binary co-solvent mixtures at 298.15 K

The preferential solvation parameters of methocarbamol in dioxane + water, ethanol + water, methanol + water and propylene glycol + water mixtures are derived from their thermodynamic properties by using the inverse Kirkwood–Buff integrals (IKBI) method. This drug is sensitive to solvation effects, being the preferential solvation parameter δx_1,3, negative in water-rich and co-solvent-rich mixtures, but positive in mixtures with similar proportions of solvents, except in methanol + water mixtures, where positive values are found in all the methanol-rich mixtures. It is conjecturable that the hydrophobic hydration around the non-polar groups in water-rich mixtures plays a relevant role. Otherwise, in mixtures of similar solvent compositions, the drug is mainly solvated by co-solvent, probably due to the basic behaviour of the co-solvents; whereas, in co-solvent-rich mixtures, the preferential solvation by water could be due to the acidic behaviour of water. Nevertheless, the specific solute–solvent interactions present in the different binary systems remain unclear.     

Solubility and preferential solvation of benzocaine in {methanol (1) + water (2)} mixtures at 298.15 K

The equilibrium solubility of benzocaine (BZC) in several {methanol (1) + water (2)} mixtures at 298.15 K was determined. Solubility values are expressed in mole fraction and molarity and were calculated with the Jouyban–Acree model. Preferential solvation parameters of BZC by methanol (δx_1,3) were derived from their thermodynamic solution properties using the inverse Kirkwood–Buff integrals method. δx_1,3 values are negative in water-rich mixtures (0.00 < x₁ < 0.32) but positive in the other mixtures (0.32 < x₁ < 1.00). To explain the preferential solvation by water in the former case, it is conjecturable that the hydrophobic hydration around non-polar groups of BZC plays a relevant role in the solvation. Moreover, the higher solvation by methanol in mixtures of similar cosolvent compositions and methanol-rich mixtures could be explained in terms of the higher basic behaviour of methanol regarding water.     

Thallium(I) iodate solubility product and iodic acid dissociation constant from 2 to 75°C

Using methods of potentiostatic coulometry, the solubility of thallium(I) iodate in 0.1m sodium perchlorate and in 0.1m perchloric acid was determined over the temperature range 2–75°C. Thermodynamic functions were calculated for the dissociation of thallium(I) iodate into its aqueous ions. From the solubilities in the acid solutions the dissociation constant of iodic acid was calculated over the temperature range, along with the value of –1.83±0.07 kcal-mol^–1 for the standard enthalpy change for the dissociation.     

X-ray structural studies on microscopic mixing in binary mixtures of dimethyl sulphoxide with acetonitrile and N,N-dimethylformamide

The liquid structures of binary acetonitrile (AN)–dimethyl sulphoxide (DMSO) and N,N-dimethylformamide (DMF)–DMSO mixtures were investigated by the X-ray scattering method. Comparison of the X-ray scattering data of AN–DMSO liquid mixtures with those of neat AN and DMSO revealed that the intermolecular AN–DMSO interactions are practically not detected; that is, the X-ray scattering data of the liquid mixtures are well reproduced by summing up those of neat AN and DMSO weighted by their mole fractions. The same applies for DMF–DMSO mixtures. Thus, each component solvent molecule independently forms self-assembled clusters in the liquid mixtures, the structures of which are the same as those in the neat liquids. The clusters are mixed to form macroscopically homogeneous liquid mixtures. The thermodynamic quantities on mixing process for the AN–DMSO, DMF–DMSO and AN–DMF systems in the literature are well elucidated on the basis of the microscopic structure of the liquid mixtures.     

Solubility and preferential solvation of acetaminophen in methanol + water mixtures at 298.15 K

The equilibrium solubility of acetaminophen in methanol + water binary mixtures at 298.15 K was determined and correlated with the Jouyban–Acree model. Preferential solvation parameters by methanol (δx_1,3) were derived from their thermodynamic solution properties by means of the inverse Kirkwood–Buff integrals method. δx_1,3 values are negative in water-rich mixtures but positive in compositions from 0.32 in mole fraction of methanol to pure methanol. It is conjecturable that in the former case, the hydrophobic hydration around non-polar groups plays a relevant role in the solvation. The higher solvation by methanol in mixtures of similar cosolvent compositions and methanol-rich mixtures could be explained in terms of the higher basic behavior of this cosolvent.     

Equilibrium solubility,preferential solvation and apparent specific volume of sucrose in some {cosolvent (1) + water (2)} mixtures at 298.2 K

Sucrose is the most widely used sweetener in food and pharmaceuticals. Solubility data of this excipient in aqueous cosolvent mixtures is not abundant. Thus, the main objective of this research was to determine and correlate the equilibrium solubility of sucrose in some {cosolvent (1) + water (2)} mixtures at 298.2 K. Cosolvents were ethanol, propylene glycol and glycerol. Shaken flask method was used to determine isothermal solubility. Concentration measurements were performed by means of density determinations. Solubility of sucrose decreases non-linearly with the addition of cosolvent to water. By means of the inverse Kirkwood–Buff method it is shown that sucrose is preferentially solvated by cosolvent in water-rich mixtures but preferentially solvated by water in cosolvent-rich mixtures. Jouyban–Acree model correlates solubility values with the mixtures composition for all cosolvent systems. Moreover, apparent specific volume of sucrose was also calculated from density and compositions.     

Preferential solvation of Fe(phen)2(CN)2 in binary aqueous acetone and 2-methoxyethanol mixtures

Summary Preferential solvation ofbis-1,10-phenanthroline-bis-cyanoiron(II) was investigated in aqueous acetone and 2-methoxyethanol binary mixtures. The solvatochromic behaviour is discussed in terms of donor and acceptor numbers. The thermodynamic model ofFrankel was used to treat preferential solvation in the binary aqueous 2-methoxyethanol mixtures and reveals that preferential solvation by the organic solvent occurs. The preferential solvation constant at 298.15K was found to be equal to 3.30±0.039, and the free energy of preferential solvation amounts to 2.96kJ·mole^–1.

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Bevorzugte Solvatation von Fe(phen)₂(CN)₂ in binären Mischungen aus Wasser und Aceton bzw. 2-Methoxyethanol

Zusammenfassung Die bevorzugte Solvatation vonbis-1,10-Phenanthrolin-bis-cyanoeisen(II) wurde in binären wäßrigen Mischungen mit Aceton bzw. 2-Methoxyethanol als organischer Komponente untersucht. Das solvatochrome Verhalten wird in Zusammenhang mit Donor- und Akzeptorzahlen diskutiert. Die theoretische Behandlung erfolgte mit Hilfe des thermodynamischen Modells vonFrankel und zeigt, daß das organische Lösungsmittel bevorzugt solvatisiert. Die entsprechende Konstante bei 298.15K wurde zu 3.30±0.039 ermmittelt. Die freie Energie der bevorzugten Solvatation beträgt 2.96kJ·mol^–1.

     

Preferential solvation effects in the electrochemistry and charge-transfer spectra of cyanoiron(II) complexes

The energies of the charge-transfer bands and the redox potentials of substituted cyanoiron complexes are strongly influenced by preferential solvation effects in water-acetonitrile mixed solvents, exhibiting a linear dependence with respect to the acceptor number scale. The dependence increases with the number of cyanide ligands in the complexes.     

Solubility and preferential solvation of some non-steroidal anti-inflammatory drugs in methanol + water mixtures at 298.15 K

The equilibrium solubilities of naproxen (NAP), ketoprofen (KTP), and ibuprofen (IBP) in methanol + water binary mixtures at 298.15 K were determined and the preferential solvation parameters were derived by means of the inverse Kirkwood–Buff integrals (IKBI) method. These drugs are very sensitive to specific solvation effects. The preferential solvation parameters by methanol δx_1,3 are negative in water-rich mixtures but positive in compositions from 0.32 in mole fraction of methanol to pure methanol. It is conjecturable that in the former case the hydrophobic hydration around aromatic rings and/or methyl groups plays a relevant role in the solvation. The higher solvation by methanol in mixtures of similar co-solvent compositions and in methanol-rich mixtures could be explained in terms of the higher basic behaviour of this co-solvent interacting with the hydroxyl group of the drugs. Moreover, drug solubilities were correlated by using the modified nearly ideal binary solvent/Redlich–Kister model obtaining average percentage deviations (APDs) lower than 9.0%.     

Ion-solvent interactions of silver(I)-18-crown-6 perchlorate complex in methanol-acetonitrile mixtures

The standard Gibbs transfer energies of the silver(I)-18-crown-6 perchlorate complex salt from methanol to various compositions of methanol-acetonitrile mixtures were determined from solubility measurements at 30°C and these data were separated into the corresponding ionic contributions by employing the negligible liquid junction potential method of Parkeret al. The solvent transport numbers _AN, for the salt were also determined at various solvent compositions using a concentration cell with transference.The Gibbs transfer energy of the silver(I)-18-crown-6 complex cation is negative and decreases with the addition of acetonitrile but the transfer energy of the anion is positive and increases under the same conditions. The solvent transport number, _AN, increases and passes through a maximum value of 5.48 at _AN=0.55. These results indicate that the complex salt is heteroselectively solvated in these mixtures with the cation being preferentially solvated by acetonitrile and the anion by methanol molecules.     

The effect of properties of water-organic solvent mixtures on the solvation enthalpy of 12-crown-4, 15-crown-5, 18-crown-6 and benzo-15-crown-5 ethers at 298.15 K

Crown ethers are preferential solvated by organic solvents in the mixtures of water with formamide, N-methylformamide, acetonitrile, acetone and propan-1-ol. In these mixed solvents the energetic effect of the preferential solvation depends quantitatively on the structural and energetic properties of mixtures. The energetic properties of the mixtures of water with hydrophobic solvents (N,N-dimethylformamide, dimethylsulfoxide, N,N-dimethylacetamide, hexamethylphosphortriamide) counteract the preferential solvation of the crown ether molecules. The effect of the hydrophobic and acid-base properties of the mixture of water with organic solvent on the solvation of 12-crown-4, 15-crown-5, 18-crown-6 and benzo-15-crown-5 ethers was discussed. The solvation enthalpy of one -CH₂CH₂O- group in water, N,N-dimethylformamide and hexamethylphosphortriamide is equal to −24.21, −16.04 and −15.91 kJ/mol, respectively. The condensed benzene ring with 15-crown-5 ether molecule brings about an increase in the exothermic effect of solvation of the crown ether in the mixtures of water with organic solvent.     

Solution thermodynamics and preferential solvation of hesperidin in aqueous cosolvent mixtures of ethanol,isopropanol, propylene glycol,and n-propanol

The solubility of hesperidin in some {cosolvent (1) + water (2)} mixtures expressed in mole fraction at temperatures from 293.15 K to 333.15 K reported by Xu et al. has been used to calculate the apparent thermodynamic functions, Gibbs energy, enthalpy, and entropy, of the dissolution processes by means of the van’t Hoff and Gibbs equations. Non-linear enthalpy–entropy relationships were observed for this drug in the plots of enthalpy vs. Gibbs energy of dissolution with positive or negative slopes regarding mixtures composition and/or cosolvent. Moreover, the preferential solvation of hesperidin by the cosolvents was analysed by using the inverse Kirkwood–Buff integrals observing that this drug is preferentially solvated by water in water-rich but preferentially solvated by cosolvents in mixtures 0.20 (or 0.24) ≤ x₁° ≤ 1.00. Furthermore, a new mathematical model was proposed for correlating/predicting the solubility of hesperidin in binary solvent mixtures at various temperatures.     

Preferential solvation of nifedipine in some aqueous co-solvent mixtures

Preferential solvation parameters of nifedipine (NIF) in ethanol (EtOH) + water and propylene glycol (PG) + water mixtures were obtained from their thermodynamic properties in solution using the inverse Kirkwood–Buff integrals. Preferential solvation parameter (δx_1,3) by both co-solvents is negative in the water-rich mixtures but positive in almost all the other compositions at 293.2, 303.2 and 313.2 K. Nevertheless, in EtOH-rich mixtures the values of δx_1,3 are also negative. It can be assumed that in water-rich mixtures the hydrophobic hydration around the non-polar groups of NIF plays a relevant role in the solvation. The higher drug solvation by co-solvent in mixtures of similar solvent proportions and in co-solvent-rich mixtures could be due mainly to polarity effects. Moreover, in these mixtures the drug could be acting as a Lewis acid with the co-solvents molecules. Finally, in EtOH-rich mixtures the drug could be acting as a Lewis base with water molecules.     

Polarographic behaviour of some organotin(IV) compounds in dimethyl sulphoxide

The differential pulse polarographic behaviour in dimethyl sulphoxide (DMSO) of 14 organotin(IV) compounds having the general formula R₃SnX (R = Me, Ph; X^? = NCS^?, N₃^?, N₃^?, NO₃^?, OH^?, NCO^? and OAc^?) and ⁿBu₃SnCl and ⁿBu₂SnCl₂ has been studied. The peak potential was found to depend markedly on the organic group and to a lesser extent on the nature of the anion X. The phenyltin compounds were reduced at lower potentials than the corresponding methyltin compounds. The data obtained could be used for trace determination of these compounds. Linear calibration curves were obtained over the concentration range of 2.8 × 10^?4 to 1.9 × 10^?6 mol dm^?3.