Binary Mixed Solvents Research Articles

Solubility measurement, model evaluation and Hansen solubility parameter of ipriflavone in three binary solvents

Ipriflavone is a drug widely used in clinical treatment and prevention of osteoporosis, and it also has a certain protective effect on the nervous system. In this work, the laser dynamic method was used to measure the solubility data of IP in three binary solvents under normal pressure (temperature range: 278.15 K to 323.15 K). The results show that as both the mass fraction of positive solvents (NMP, DMF, DMAC) in the binary mixed solvents and the temperature increase, the solubility of IP increases. In addition, the Hansen solubility parameter (HSP) was used to analyze the order of solubility. The results indicated that the selected solubility parameters (Δδd, Δδp, Δδh, Δδt and Δδ) could explain the solubility trend well. Furthermore, the modified Apelblat equation, λH equation, NRTL model and UNIQUAC model were used to correlate the solubility data in binary mixed solvents. By calculating the deviation between the experimental data and the fitting data, it shows that the selected models have a good correlation with the solubility data of IP. Finally, the modified van’t Hoff equation was used to calculate the apparent thermodynamic properties of IP during the dissolution process. The results show that the dissolution process is always endothermic and entropy driven.

Solubility measurement, Hansen solubility parameter and thermodynamic modeling of etodolac in four binary solvents from 278.15 K to 323.15 K

In this study, the laser monitoring method was used to measure the solubility of etodolac in four binary mixtures ((n-propanol, methyl acetate, n-butyl acetate and acetone) + n-hexane) at 278.15 K–323.15 K. The results show that under a certain solvent composition, the solubility of etodolac increases with the increase of temperature. Except for the mixture of acetone + n-hexane, the solubility of etodolac in the other three mixing systems increases with the increase of the mass fraction of the co-solvent (n-propanol, methyl acetate and n-butyl acetate) at a certain temperature. For the acetone + n-hexane system, the order of solubility is: acetone > acetone (ω1 = 0.6000) + n-hexane > acetone (ω1 = 0.8000) + n-hexane > acetone (ω1 = 0.4000) + n-hexane > acetone (ω1 = 0.2001) + n-hexane, indicating that a co-dissolution phenomenon may occur when the mass fraction of acetone is 0.6000. The Hansen solubility parameter was used to explain the solubility order of etodolac in four binary mixed solvents. At the same time, five models (modified Apelblat model, Buchowski-Ksiazaczak λh model, Wilson model, Three-Suffix Margules model and Uniquac model) were used to correlate the solubility data, which shows that all the five models have a good correlation. Through the comparison of ARD and RMSD, it was found that the modified Apelblat model can get more satisfactory results.

Self-healing, stretchable, and freezing-resistant hydroxypropyl starch-based double-network hydrogels

Starch hydrogel is a biocompatible and biodegradable material. However, due to its poor mechanical properties and fragility, starch hydrogel has limited applications in the food and medicine industries. In this work, we prepared stretchable, compressible, and self-healing double-network (DN) hydrogels using hydroxypropyl starch (HPS) and sodium alginate (SA). By adjusting the amount of sodium alginate added, the DN hydrogels achieved adjustable mechanical properties. The storage modulus of the DN hydrogels with 1% SA increased by nearly 80 times compared with that of pure HPS hydrogels. When prepared in a water/glycerol binary mixed solvent, the DN hydrogels can maintain their gel properties at -30 ºC. These environmentally friendly and biocompatible hydrogels have broad application prospects in the fields of agriculture, food, and medicine.

Addition of triphenylphosphine to electron-deficient alkenes in mixed binary solvents: Overcoming the problem of preferential solvation to determine the reaction order with respect to protic solvent

Kinetics of addition of PPh3 to electron-deficient alkenes has been studied in aprotic solvent+carboxylic acid binary mixtures as a function of the alkene and carboxylic acid concentrations. For ethyl acetate+acetic acid, ethyl acetate+propionic acid, butyl acetate+acetic acid, butyl acetate+propionic acid mixtures, the reactions of PPh3 with acrylic acid and methyl acrylate show no preferential solvation and follow third-order kinetics, first order in the phosphine, the activated alkene, and acetic (propionic) acid. Other alkene/solvent combinations tested also displayed acceleration in the presence of carboxylic acid, but the total effect of the acidic solvent concentration on the reaction rate was nonlinear due to occurrence of preferential solvation. The acid dependence gives the direct evidence for the rate-determining protonation of intermediate phosphonium enolate zwitterion under acidic solvent condition. Since proton transfers from protic solvents are typically fast, the kinetic data obtained give a new mechanistic insight into chemistry of phosphonium enolates: their decomposition to the reactants proceeds much faster than proton transfer step in acidic media. This unexpected finding emphasizes very short lifetime of phosphonium enolates, key intermediates of synthetically useful phosphine-catalyzed reactions.

Preferential solvation of pomalidomide, an anticancer compound, in some binary mixed solvents at 298.15 K

Abstract Preferential solvation of pomalidomide (PMD) was explored in dimethyl sulfoxide (DMSO)-dimethylformamide (DMF), DMSO-tetrahydrofuran (THF), DMSO-methanol (MeOH), DMSO-isopropanol, DMSO-water, water-DMF, water-THF, water-MeOH, and water–isopropanol binary mixed solvents at 298.15 K. Bosch-Rose model was utilized to determine the electronic transition energies (ET) and other preferential solvation parameters, describing solute-solute and solute-solvent interactions. We found that λmax situation shifted with dielectric constant of the pure solvents meaningfully. According to the obtained results, ET enhanced and λmax shifted to the lower wavelengths as the percentage of DMSO decreased in the binary mixtures, remarking the important role of DMSO for stabilizing the excited state (π⁎) of PMD chromophore via efficient intermolecular solute-solvent interactions. In addition, the aqueous binary systems showed an optimum point for the ET values as the percentage of water changed in the solutions. The local mole fraction of the solvents in the cybotactic region was also estimated to describe the specific and non-specific interactions in the systems.

Determination and correlation of solubility of 4,4′-difluorobenzophenone in pure and binary mixed solvents and thermodynamic properties of solution

The target of this study was to determine and correlate the solubility of 4,4′-difluorobenzophenone in various solvents from 293.15 K to 333.15 K by gravimetric method at 0.1 MPa, and at the same time got the thermodynamic parameters. In this work, methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, ethyl acetate, methyl acetate, acetone, acetonitrile pure solvents and ethanol + n-propanol mixed solvents were selected as the experimental solvents. The results showed that the solubility of 4,4′-difluorobenzophenone in selected solvents increased with increasing temperature within the investigated temperature range. The effect of solvent properties on 4,4′-difluorobenzophenone solubility behaviors was discussed by solvent polarity, hydrogen bonding donor and acceptor propensity, and cohesive energy density. Furthermore, the dissolution behavior was explained using the Hansen solubility parameter (HSP). In pure solvents, the modified Apelblat equation, van't Hoff equation, λh equation, nonrandom two-liquid (NRTL) equation, Wilson equation and universal quasichemical (UNIQUAC) equation were used to correlate the experimental solubility of 4,4′-difluorobenzophenone. While the solubility in ethanol + n-propanol mixed solvents was correlated by the modified Apelblat equation, van't Hoff equation, λh equation, NRTL model, Wilson model, Jouyban-Acree and the modified Jouyban-Acree model. The results indicated that the calculated values of all selected equations were in good agreement with the experimental data. Furthermore, the thermodynamic properties (∆H°sol, ∆S°sol, ∆G°sol, %ξH and %ξTS) were measured by Van't Hoff analysis. In a word, the physicochemical data of 4,4′-difluorobenzophenone obtained in this work will be helpful for the purification, crystallization, recrystallization and designing a new synthetic route of 4,4′-difluorobenzophenone.

Deep analysis of the solubility behaviour mechanism of alpha-(trichloromethyl) benzyl acetate in three binary aqueous solvents

The solubility of alpha-(Trichloromethyl) benzyl acetate (ATMBA) in three water-organic binary solvent mixtures at atmospheric pressure from 288.15 K to328.15 K was investigated by the gravimetric method and molecular simulations. The experimental solubility data were well correlated by the modified Apelblat model Van’t Hoff equation and the NRTL model. In addition calculations of the mixed thermodynamic properties indicate that the mixing process of ATMBA in the solvent systems studied is exothermic and spontaneous. Further to reveal the solubility behaviour of ATMBA thermodynamic analysis crystallographic structure analysis and σ-profile analysis were applied. After comprehensive analysis we found that the reason of the abnormal solubility of ATMBA in acetic acid is that in the binary solvent of acetic acid and water the solute (ATMBA) forms a strong halogen bond with the ionized acetic acid (acetate ion). Finally we validate the rationality of the above analysis process by dynamics simulation (MS). And the Radial distribution function (RDF) shows that it is indeed possible to form a halogen bond between the solute and the acetate ion. Subsequently under the guidance of this theory the binary mixed solvents of formic acid and water were used for experimental verification and the results showed an excellent solubility tendency which proved that the theory is indeed credible. The experimental data can be used as basic data in the industrial production and scientific research of ATMBA a high value-added product. Thermodynamic analysis crystallographic structure analysis σ-profile analysis MD simulations and correlation models herein are helpful to a further understandingof solid–liquid equilibrium of compounds in binary solvent systems.

Fluorescence anisotropy studies on the Hoechst 33258-DNA interaction: the solvent effect

Fluorescence anisotropy method was applied to characterize the interactions of DNA minor groove binder Hoechst 33258 with different solvents without and in the presence of DNA. It is important to study the interaction of small molecules with DNA for the purpose of better understanding the mechanism of their action, as well as to design novel and more effective compounds. Spectroscopic study of the ligand in different binary mixed solvents containing DMSO, alcohols and buffer was carried out. Studies were performed without and in the presence of DNA. Fluorescence anisotropy studies reveal the characteristics of Hoechst 33258 in different mixed solvents. The results show the strong dependence of the anisotropy of Hoechst 33258 on solvent content, viscosity and intermolecular interactions. Communicated by Ramaswamy H. Sarma

Correlation and prediction of small to large sized pharmaceuticals solubility, and crystallization in binary and ternary mixed solvents using the UNIQUAC-SAC model

The recently reported UNIversal QUAsiChemical Segment Activity coefficient (UNIQUAC-SAC) model [developed by Haghtalab and Yousefi Seyf Ind. Eng. Chem. Res. 2015, 54, 8611] provides a practical thermodynamic framework to be used in VLE, LLE, and SLE calculations. The UNIQUAC-SAC model has the advantage of being independent of area (q) and volume (r) structural parameters used in the combinatorial part. While the UNIFAC or UNIFAC-DMD could not apply to the 47% (44 of 94) of the studied molecules because of the undefined groups. Here, the numbers of solvents with identified segment numbers were extended from 82 to 130 with a slight refinement to the previous values. The model parameters obtained via a large consistent set of VLE (isobaric and isothermal), and LLE experimental data. Also, the model was tested with pharmaceutical solubility experimental data in pure (94 solutes with 6210 solubility data), binary, and ternary solvents. The model provides a robust correlation of pharmaceuticals solubility in a mono-solvent and robust prediction of pharmaceuticals solubility in mixed solvents. The UNIQUAC-SAC model was successfully evaluated in solvent screening in cooling crystallization of ibuprofen and valsartan in both pure and binary solvents mixture (combined cooling and anti-solvent crystallization). The model with 130 solvents as a robust database provides a useful and practical thermodynamic tool in the conceptual design of pharmaceutical processes. A MATLAB based graphical user interface (GUI), finally, was developed to be used in the conceptual segment numbers regression procedure.

Solubility and thermodynamic properties of musk xylene in binary mixed solvents from t = (278.15 to 313.15) K

In this study, the solubility of musk xylene in four binary solvents (ethyl acetate + methanol, ethyl acetate + ethanol, ethyl acetate + isopropanol, and ethyl acetate + n-butanol) was measured by the isothermal saturation method at temperatures ranging from 278.15 K to 313.15 K under atmospheric pressure. The results indicate that the solubility of musk xylene increases with increasing temperature and ethyl acetate mass fraction. The experimental solubility data of musk xylene were correlated by five thermodynamic models, including modified Apelbla equation, λh equation, Van't Hoff equation, Sun model and Jouyban–Acree model. All models can be well correlated with the experimental data of solubility. The Jouyban–Acree model provides the best correlation in this study. The thermodynamic properties of the standard dissolution enthalpy (ΔsolH○), the standard dissolution Gibbs (ΔsolG○), the standard dissolution entropy (ΔsolS○), %ξH and %ξTS of musk xylene in the selected binary solvent were calculated based on the van't Hoff equation. Results show that the dissolution of musk xylene in the selected binary solvent is endothermic and entropy-driven. This study can provide basic physical property data for crystallization and industrial separation of musk xylene.

Physically Cross-Linked Silk Fibroin-Based Tough Hydrogel Electrolyte with Exceptional Water Retention and Freezing Tolerance.

Flexible ionic conductive hydrogel is attracting significant interest as it could be one of the crucial components for multifunctional ionotronic devices. However, their features of inevitably drying out without package and freezing at subzero temperatures may greatly limit the applications of conventional hydrogels in specific situations. Here, we present an ionic conductive hydrogel with water retention and freezing tolerance that consists of silk fibroin, ionic liquid, water, and inorganic salt. It is discovered that the ionic liquid serves multiple purposes to prevent water evaporation, decrease the freezing point, provide the essential conductivity of the hydrogel, etc. As a binary mixed solvent, the ionic liquid/water mixture enhances both water retention and freezing tolerance of the hydrogel electrolyte. Based on the silk fibroin (SF)/1-ethyl-3-methylimidazolium acetate (EMImAc)/H2O/KCl hydrogel electrolyte, the flexible fiberlike supercapacitor could still function well at a temperature as low as -50 °C and after being stored in the open air for a long time. It is anticipated that this hydrogel will prove useful in developing new applications operating under harsh environments.

Thermodynamic studies of thiamethoxam in nine pure solvents and one mixed solvent, solubility and correlation ranged from 278.15 to 323.15 K

The solubility of thiamethoxam in nine single solvents (acetic acid, methanol, acetonitrile, 2-methoxyethanol, 2-ethoxyethanol, propionic acid, DMSO, 1,4-dioxane, DMA) and binary mixed solvents (methanol + acetonitrile) was measured by dynamic laser method from 278.15 K to 323.15 K under pressure of 101.2 kPa. Modified Apelblat equation, λh equation, NRTL model, and Wilson model were used to fit the experimental data of pure solvents; for mixed solvents, Modified Apelblat equation, λh equation, Jouyban-acree model and Wilson model were used for solubility data correlation. The results showed that the fitting value is in good agreement with the experimental value, the solubility of thiamethoxam in selected solvents increased with the increase of temperature. It was found that the solubility of thiamethoxam in mixtures with different proportions of methanol and acetonitrile was higher than that of two single solvent, which might be related to the bipolarity/polarizability of the solvent. What’s more, the mixing enthalpy, entropy, and Gibbs free energy in pure and mixed solvents were obtained according to the Wilson model, the value of ΔmixG is negative in the dissolution, the value of ΔmixS is positive, indicating that the mixing process in selected solvents was entropy-driven. When thiamethoxam dissolved in methanol, acetic acid, propionic acid, the value of ΔmixH is positive, which showed that thiamethoxam was endothermic during dissolution, When thiamethoxam dissolved in acetonitrile, 2-methoxyethanol, 2-ethoxyethanol, DMSO, 1, 4-dioxane, DMA and mixed solvents the value of ΔmixH is negative, which showed that thiamethoxam was exothermic during dissolution. The solubility data, solubility model and thermodynamic parameters of thiamethoxam are of great significance to the application of thiamethoxam industrial production and crystallization.

Thermodynamic Studies of Complexes of Amlodipine Besylate with Ni2+, Mg2+, Co2+ and Ca2+ cations in pure and in mixed binary solvent systems at 303.15, 313.15 and 323.15 K by Conductometric Method

The present work relates to the complexation reaction between Amlodipine Besylate[AML] with Ni2+, Mg2+, Co2+ and Ca2+ cation in dimethylsulfoxide (DMSO), pure methanol (MeOH) and their binary mixtures(DMSO-MeOH and DMSO-Water) by conductometric method. The conductance data show that the stoichiometry of the complexes formed between AML with Ni2+, Mg2+, Co2+ and Ca2+ cation in pure DMSO, pure MeOHas well as in the binary solvent mixtures was 1:1. The stability of AML complexes with Ni2+ , Mg2+, Co2+ and Ca2+ metal ion was observed to be sensitive to the nature of the solvent system. In case of DMSO-Water binary solvent systems there was a linear change in LogKf values but in case of DMSO-MeOH binary solvent systems non linear change in LogKf values observed.The negative values of ΔG0 show that the reaction is spontaneous and ability of the AML ligand to form stable complexes. However, the result shows positive value of ΔH0 which indicates that enthalpy is not driving force for the formation of the complexes. Furthermore, the positive value of ΔS0 indicates that entropy is a driving force for the complexation. The values of ΔH0 and ΔS0 for formation of the complexes were obtained from temperature dependence of the stability constants.

Cosolvent action of promethazine hydrochloride in (ethyl acetate + alcohols) and thermodynamic property analysis

This study presents the solubility profiles of promethazine hydrochloride in pure and mixed solvents. The effects of temperature and composition of mixed solvents on solubility were investigated. Maximum solubility value was obtained in n-propanol in pure solvents, and in ethyl acetate, it is the lowest. While in two mixtures of ethyl acetate (1 − w) + ethanol (w, mass fraction) and ethyl acetate (1 − w) + isopropanol (w), the values increased monotonically with the increasing temperature, and increased with increasing co-solvent (alcohols) mass fraction (w) to a maximum value at w = 0.4 and then decreased. The interaction between promethazine hydrochloride molecule and solvent molecules was discussed. The function of temperature and solvent composition in pure and binary mixed solvents was evaluated by some thermodynamic models. The dissolution thermodynamic properties, including enthalpy, entropy and Gibbs energy of promethazine hydrochloride in the dissolution process were evaluated using the van't Hoff equation. The results indicate that in all selected solvents the dissolution behavior were endothermic and entropy-driven.

Solubility and isoelectric point of cefradine in different solvent systems

The solubility data of cefradine in different solvent systems as a function of pH were determined by dynamic method. The effect of pH and solvent compositions on the solubility data and the isoelectric points were evaluated and discussed. It was found that the solubility data of cefradine are consistent with the dissolution property of ampholyte, whether in mono-solvent or binary mixed solvent, which has a large solubility at large pH and small pH values and the solubility curves exhibit U shapes. The isoelectric points of cefradine in different solvent systems were also determined and discussed. Two theoretical models were used to correlate the experimental solubility data. It was found that model I can give better correlation results.

Investigation of solid–liquid equilibrium of stevioside in different pure and binary mix solvents at various temperatures

The solubility of stevioside (a natural sweetener) in 12 pure solvents (methanol, 1-propanol, 2-propanol, 1-buthanol, 2-buthanol, 1-pentanol, 2-pentanol, 2-ethoxyethanol, 2-propoxyethanol, 2-buthoxyethanol, water, and acetone) and in binary mixed solvents (2-ethoxyethanol + water) have been determined using high performance liquid chromatography (HPLC) method at temperatures ranging from 288.15 to 328.15 K and atmospheric pressure. From the experimental data, it was found that the solubility increased with the rising temperature in all selected solvents. The experimental data for the solubility of stevioside were correlated with Apelblat and non-random two-liquid (NRTL) models. It was found that the Apelblat model has the better quality in fitting the solubility data. Also, thermodynamic functions of dissolution, mixing and transfer process were calculated by the van’t Hoff equation. Furthermore, the crystal habits of stevioside in selected solvents were studied.

Measurement and correlation of solubility of flunarizine hydrochloride in ten pure and ethanol + n-propanol mixed solvents at temperatures within 293.15–333.15 K

The objective of this work is to obtain the solubility data for flunarizine hydrochloride, the parameters of its correlation equations,and the thermodynamic parameters involved in its dissolution process. The solubility was determined in ten pure solvents, includ-ing methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol,ethyl acetate, methyl acetate, acetone and acetonitrile, and binary mixed solvents of ethanol and n-propanol at 293.15–333.15 K using the gravimetric method under atmospheric pressure. The results revealed that the solubility increased with increasing temperature forall the selected solvents. In addition, Hansen solubility parameters (HSP) were used to explain and predict the solubility behavior. The experimental solubility in the mono solvents was correlated by the modified Apelblat equation，van't Hoff equation, λh equation, nonrandom two-liquid (NRTL) equation and Wilson model, respectively.While the solubility in the binary mixed solvents was correlated with the above methods as well as the Jouyban-Acree model and modified Jouyban-Acree model. The results showed that the solubility is in good agreement with the fitted values. In addition, the thermodynamic parameters including the enthalpy of dissolution (∆H°sol), entropy of dissolution (∆S°sol), Gibbs free energy (ΔG°sol) and the respective contributions of enthalpy and entropy were calculated. Consequently, the experimental solubility and correlation equations can be used as the essential data and simulation models in the purification and separation of flunarizine hydrochloride.

An investigation on the feasibility of using mixed Reversible ionic liquids for extraction of Kerogen from oil shale

Numerous of the separation issue usually accompanying with traditional ionic liquids can solve with Reversible ionic liquids. It can be forth and reversed back between ionic and molecular forms empowering superficial separations by means of considerable changes in situ property. This leads to actually sustainable processes. A comprehension of the systems phase behavior gives frameworks into the ability of separation.To our knowledge, the experimental information available in the literature for mixtures containing the pair Kerogen-Reversible Ionic Liquids (RevIL) is limited. Thus the objective of the current investigation is to produce data for Kerogen with different Reversible Ionic Liquids RevIL solvents to aid the extraction efficiency.The samples of Oil Shale collected from real Iraqi sedimentary rock deposits. Four Reversible Ionic Liquids solvents 3-(triethoxysilyl)-propylammonium 3-(triethoxysilyl)-propyl carbamate (TESAC), (3-(tripropylsilyl)-propylammonium 3-(tripropylsilyl)-propyl carbamate (TPSAC), 3-(trimethoxysilyl)-propylammonium 3-(trimethoxysilyl)-propyl carbamate (TMSAC), 3-(triethylsilyl)-propylammonium 3-(triethylsilyl)-propyl carbamate (TEtSAC)) are derived from carbon dioxide which reacts reversibly with silylated amine molecular liquids to produce ionic liquids.The efficiency of four Reversible Ionic Liquids (TEtSAC, TMSAC, TPSAC, and TESAC) and for mixed Reversible ionic liquid (Binary mixtures) as a selective solvent in the kerogen extraction from oil shale was investigated.The extraction efficiency was found to be more dependent on the basicity strength of hydrogen bond of the RevIL. It was found that higher extraction efficiencies are accompanied with higher hydrogen bond basicity.Four single RevILs and three binary mixtures (RevIL) to extract the Kerogen from oil shale is used. The study shows that the highest Kerogen extraction efficiency of 90.2% and 97.9% respectively, can be achieved by TESAC and (TESAC + TMSAC) respectively. One mixed binary solvent (TESAC + TMSAC) has the highest distribution coefficient, extraction efficiency and selectivity and greatest variation between its density and boiling point and those of Kerogen is selected. Therefore it can be considered as an excellent extracting solvent for Kerogen from oil shale.

A Conductometric Study of Complexation Reaction between Kryptofix 22DD with Yttrium(III) Cation in Some Binary Mixed Non-aqueous Solvents

The complexation process between Y3+ cation and kryptofix 22DD was studied in ethyl acetate–dimethylformamide (EtOAc–DMF), ethyl acetate–methanol (EtOAc–MeOH), ethyl acetate–nitromethane (EtOAc–NM) and ethyl acetate–dimethylsulfoxide (EtOAc–DMSO) binary mixtures at different temperatures by using conductometric method. The conductance data show that in most cases, the stoichiometry of the complex formed between the macrocyclic ligand and the Y3+ cation is 1 : 1 [ML]. But in some systems such as, in the case of EtOAc–DMSO (90 mol % DMSO) binary solvent solution, in addition to formation of a 1 : 1 (ML) complex, a 1 : 2 (ML2) complex is formed in solution, which shows that the stoichoimetry of complexes may be changed by the nature of the medium. The stability order of (kryptofix 22DD · Y)3+complex in the studied binary solvent solutions at 25°C was found to be: EtOAc–MeOH > EtOAc–DMF > EtOAc–DMSO and in the case of pure non-aqueous solvents at 25°C it was: EtOAc > MeOH > DMF ∼ NM. A density functional theory (DFT) study of the interaction of yttrium(III) cation with kryptofix 22DD in the liquid phase for the pure organic solvents was performed. The results are in reasonably good agreement with the experimental data. A non-linear behavior was observed for changes of log Kf of (kryptofix 22DD · Y)3+ complex versus the composition of the binary mixed solvents, which was explained in terms of solvent–solvent interactions and also the preferential solvation of the species involved in the complexation reaction.

Do the solvent properties affect the propensity for self-association of α-cyclodextrin? Insights from NMR self-diffusion

Whether cyclodextrins (CDs) self-aggregate or not in solution is an interesting and timely scientific question. Yet, we are far from a scientific consensus as regards the nature of the phenomenon. Those who are in favor of the formation of CD aggregates justify the phenomenon by the presence of H-bonds, occurring between the hydroxyl groups located at both rims of cyclodextrins. To gain further insight with regard to the importance of these intermolecular CD-CD interactions, a systematic study of 1H NMR self-diffusion of α-cyclodextrin in binary mixtures of deuterated DMSO and water, at different mole fractions, has been carried out. The choice of these solvents was made based on their different degree of polarity and the fact that they are miscible at any molar ratio. The experimental α-CD diffusion coefficients scale with the solution viscosity. Moreover, hydrodynamic radii of α-CD are independent of the solvent composition. No evidence of α-cyclodextrin aggregation at any DMSO mole fraction is found. Finally, experimental diffusion data are compared with those obtained from atomic level hydrodynamic calculations.In addition, diffusion coefficients of heavy water and DMSO in binary mixed solvents are also measured and analyzed. The obtained diffusion coefficients for DMSOd6 and D2O show a minimum at the eutectic composition and depend on the solution viscosity. The experimental results are compared with published molecular dynamic simulations.