Solvent Intermolecular Interactions Research Articles

Tutorial on Umbrella Sampling Simulation with a Combined QM/MM Potential: The Potential of Mean Force for an SN2 Reaction in Water.

We present a tutorial to carry out umbrella-sampling free-energy simulations with a combined quantum mechanical and molecular mechanical (QM/MM) potential, which may also be used in a computational or biophysical chemistry curriculum for first-year graduate and undergraduate students. In this article, we choose the Type II SN2 Menshutkin reaction between ammonia and chloromethane to construct the potential of mean force (PMF) for the reaction in aqueous solution. In this exercise, we wish to accomplish three tasks: (1) an understanding of the concept of PMF and the umbrella-sampling free-energy simulation method, (2) the use of a combined QM/MM potential in molecular dynamics simulation of chemical reactions, and (3) an understanding of solvent effects and intermolecular interactions on chemical reactions through comparison with gas-phase results. Analysis of the simulation results allows students to appreciate the difference between the transition state along a PMF from statistical simulations versus the optimized saddle point in the gas phase, the shift of transition state with respect to solvation, and the significance of electronic polarization. Through this tutorial, students will gain the necessary skills to carry out free energy simulations of chemical reactions in solution and in enzymes both in a classroom and in the laboratory.

On the Solute-Induced Structure-Making/Breaking Phenomena: Myths, Verities, and Misuses in Solvation Thermodynamics

We review the statistical mechanic foundations of the fundamental structure-making/breaking functions, leading to the rigorous description of the solute-induced perturbation of the solvent environment for the understanding of the solvation process of any species regardless of the type and nature of the solute–solvent interactions. Then, we highlight how these functions are linked to unambiguous thermodynamic responses resulting from changes in state conditions, composition, and solute–solvent intermolecular interaction asymmetries. Finally, we identify and illustrate the pitfalls behind the use of surrogate approaches to structure-making/breaking markers, including those based on Jones–Dole’s B-coefficient and Hepler’s isobaric-thermal expansivity, while highlighting their ambiguities and lack of consistency and the sources of misinterpretations.

Experimental and molecular simulation analysis of the dissolution behavior of Musk ambrette in organic solvents

The solubility of Musk ambrette in i-propanol (IPA), i-butanol (IBA), n-heptane (HPT), n-hexane (HX), cyclohexane (CYH), methyl acetate (MAC), ethyl acetate (EAC), acetone (ACE), IPA + ACE at 278.15 K to 318.15 K was determined. The mole fraction solubility of Musk ambrette in pure IPA at the temperature of 298.15 K were found to be 0.9492 × 10-2 mol·mol−1. The difference is that the solubility of Musk ambrette in ACE reaches 0.2257 mol·mol−1, which is much higher than the solvent mentioned above. The strong intermolecular hydrogen bonding formed by IPA resulted in its lowest solvation capacity for Musk ambrette. In addition, to further investigate the solubility pattern of Musk ambrette, we used 8 models (Van’t Hoff, modified Apelblat, Buchowski-Ksiazczak, Yaws, NRTL, Wilson, Jouyban-Acree and Sun model) to fit and obtain a general equation for solubility versus temperature. These results yielded a large amount of statistically significant data. Comparisons revealed that the modified Apelblat and Yaws equation showed the least deviation in forecasting solubility variations with temperature. Meanwhile, we proved that the dissolution of Musk ambrette is a heat-absorbing entropy increasing process by Van't Hoff equation calculation. ΔsolGo for the 12 solvents is in the following order: ACE < MAC < EAC < w = 0.2007 < w = 0.4025 < w = 0.6076 < CYH < w = 0.8070 < HPT < HX < IBA < IPA. ΔsolGo is smaller the easier it dissolves, which is consistent with the law of dissolution. Secondly, we performed thermal analysis and X-ray diffraction tests on Musk ambrette crystals prepared in different solvents, which showed that none of the several systems investigated led to the creation of new crystalline forms or solvatoids, further confirming the suitability of the solvents. Besides, we discuss the correspondence between solubility and the HSP, π, α, β, and CED of the solvents and thus tentatively confirm the significant influence of the solvent properties on solubility. The principle of similarity and compatibility is satisfied for most of the solvents. In particular, the CED values of the larger solvents were not favorable for the solubilization of Musk ambrette. We also analyzed the molecular surface electrostatic potential of Musk ambrette by visualization techniques. Finally, IPA and ACE and their binary solution systems were analyzed by molecular dynamics simulations. The effect of solvent intermolecular interactions on the solubilization pattern was discussed. It was further confirmed that weak interactions of solvent molecules contribute more to the dissolution of Musk ambrette. These findings suggest that the prediction of solvent solubility can be initially achieved by molecular simulation techniques. Undoubtedly, this study will furnish a valuable information for the purification of Musk ambrette.

On the molecular-based thermodynamics of dilute solutions along orthobaric conditions: Concise review of the fundamental microscopic constraints, rigorous formal results, and macroscopic modeling implications

We review the fundamentals underlying a rigorous and general molecular-based formalism for the microscopic interpretation of the solvation phenomena involving dilute solutes along the vapor–liquid envelope of a pure solvent up to its critical point. This approach bridges the path between the microstructure of the system, described in terms of correlation function integrals, and the macroscopic solvation properties resulting from the solute–solvent intermolecular interaction asymmetries. We focus on the solvation phenomena associated with the behavior of the Henry’s law constant, vapor–liquid solute distribution coefficient, and the corresponding Ostwald constant whose proper description in the compressible regime of a solvent becomes crucial to the determination of the solute’s Krichevskii parameter. Toward that end, we aim at the widespread use of linear orthobaric-density representations for the behavior of the thermodynamic quantities of infinitely dilute species in near-critical pure solvents. Then, we (i) confront their behavior against that from model systems for which we have full and accurate knowledge of the outcome, such as those for the solvation of an ideal gas solute in a real solvent, and that of a self-solvated species representing thermodynamically the Lewis-Randall solution ideality, (ii) identify the non-monotonic orthobaric-density slope of the vapor–liquid solute distribution coefficient involving the ideal gas solute in either light- or heavy-aqueous solutions, a condition that disallows the central hypothesis underpinning the conventional linear regression approach and the accuracy of the defining Krichevskii parameters, (iii) present a novel path leading to the calculation of the Krichevskii parameter of any solute according to a universal thermodynamic expression connecting rigorously the solute–solvent intermolecular asymmetry, as described by the Henry’s law constant of a solute at infinite dilution in a pure solvent, to the desired Krichevskii parameter, and (iv) establish a direct route leading to the accurate determination of the solvent effect on the Krichevskii parameter of a solute, based solely on the contrasting standard solvation Gibbs free energies of the solute at normal conditions and the corresponding Krichevskii parameters of an ideal gas solute in the desired pair of solvents. Finally, we discuss the assessment of the reliability of current modeling approximations, their internal consistency, and the conformity of limiting behaviors as fundamental constraints in the accurate description of solvation phenomena involving infinitely dilute solutions over wide ranges of state conditions and solute–solvent intermolecular interaction asymmetries.

Thermodynamic analysis of nifedipine sublimation, dissolution and solvation

The saturated vapour pressure of the cardiovascular drug nifedipine is measured within the temperature range (390.15–404.15) K by the inert gas-carrier method. The thermodynamic functions of sublimation of the compounds are calculated at a reference temperature. The standard molar enthalpy of nifedipine sublimation is found to be equal to 144.8 kJ∙mol−1. The drug solubility in solvents modeling various media of the human body is determined in the temperature range (293.15–313.15) K. In the ascending order of solubility values of the studied compound, the solvents can be arranged as follows: buffer pH 7.4, buffer pH 2.0, n-hexane, 1-octanol. The solute–solvent intermolecular interactions are discussed based on the thermodynamic functions of solubility, solvation and transfer.

Interpretable Machine Learning Model for Predicting Interaction Energies between Dimethyl Sulfide and Potential Absorbing Solvents

Non-bonding intermolecular interactions largely dominate the selective dissolution of trace species into physical solvents and, therefore, are fundamentally important to solvent development for the capture of environment-undesired compounds or purification of chemicals. However, acquirement of the interaction energy requires costly quantum chemical computation and still encounters a practical challenge to build a chemically interpretable machine learning (ML) prediction model using documented molecular descriptors. Herein, we report an ML model for predicting the interaction energies (Eint) between dimethyl sulfide and potential absorbing solvents. Applying the reduced density gradient and quantum theory of atoms in molecules analyses, the non-bonding intermolecular interactions of dimethyl sulfide with solvent compounds were elucidated through focusing on the molecular fragments containing the main center (MC) and secondary center (SC) rather than the whole molecule. The training data set was obtained using a molecular generation strategy, and 21 molecular descriptors were defined to describe the electronic states of the central atoms in each solvent molecule and its nearby hydrogen-bond donors. Model analysis reveals that Eint is mainly determined by the charge state of the crucial fragments and the hydrogen-bond donors of the solvent molecule. The custom-defined descriptors not only improve the regression and prediction performance but also enable the interpretability of the ML model. Additionally, the absorption equilibrium measurements of solubilities of dimethyl sulfide in several commercial solvents verified the strong correlation between the dissolving affinity and solute–solvent intermolecular interaction energy. The present study provides an approach to building practical and interpretable intelligent algorithms to aid the development of sustainable chemicals or processes.

Solubility Data, Modeling, and Solvent Effect of 8-Isoquinolinamine in Four Mixed Solvents and Ten Monosolvents from 278.15 to 323.15 K

The equilibrium solubility of 8-isoquinolinamine in methanol, ethanol, n-propanol, isopropanol, N,N-dimethylformamide (DMF), acetonitrile, acetone, propylene glycol (PG), ethylene glycol (EG), and water, and aqueous mixtures of methanol/ethanol/n-propanol/isopropanol plus water was experimentally measured by the isothermal saturation method at 278.15–323.15 K under 101.2 kPa. The mole fractions of 8-isoquinolinamine in monosolvents were obtained to be maximum in neat DMF. For the four binary mixed solvent systems, the amount of 8-isoquinolinamine dissolved in n-propanol + water is more than that in the other three systems. The mole fractions of 8-isoquinolinamine in pure solvents were correlated using the Apelblat model, van’t Hoff model, and Wilson model, and the calculated value of the Apelblat model was the closest to the experimental value. The Jouyban–Acree model, modified Apelblat–Jouyban–Acree model, and van’t Hoff–Jouyban–Acree model were applied to calculate the solubility of 8-isoquinolinamine in the four solvent mixtures. The feedback obtained by comparing the experimental data with the calculated data is that the calculated data from the Jouyban–Acree model was relatively close to the experimental results. Solvent effects as a powerful tool can be used to estimate interactions at the molecular level, and the results showed that solvent–solvent intermolecular interactions contribute to dissolution. van’t Hoff plots are adopted as a method to show the relationship between ln(x) and 1/T.

Solubility Determination and Thermodynamic Properties of 5-Bromo-2-pyridinecarboxylic Acid in 10 Monosolvents and 3 Binary Solvents at T = (278.15–323.15) K

The static equilibrium method combined with high-performance liquid chromatography was used to determine the solubility of 5-bromo-2-pyridinecarboxylic acid at T = 278.15–323.15 K in 10 monosolvents (methanol, ethyl alcohol, acetonitrile, methyl acetate, ethyl acetate, n-propanol, isopropanol, n-butanol, tetrahydrofuran, and 1,4-dioxane) and 3 kinds of binary solvents (ethyl acetate + tetrahydrofuran, ethyl acetate + methanol, and ethyl acetate + 1,4-dioxane). The results show that 5-bromo-2-pyridinecarboxylic acid is positively related to temperature, and the solubility of 5-bromo-2-pyridinecarboxylic acid in tetrahydrofuran was the highest. In monosolvents, the modified Apelblat model and λh model were used to fit the solubility data of 5-bromo-2-pyridinecarboxylic acid. The solubility data of binary solvents were obtained by combining the nearly ideal binary solvent/Redlich–Kister model and Jouyban–Acree model, which showed that the experimental data were in good agreement with the fitting data. Furthermore, we chose the Kamlet, Abboud, and Taft linear solvation energy relationship model to analyze the relationship between the solute–solvent intermolecular interaction and the solubility of 5-bromo-2-pyridinecarboxylic acid. The results show that the increase of solvent–solvent interaction is beneficial to the dissolution of 5-bromo-2-pyridinecarboxylic acid.

Molecular mechanism of liquid–liquid phase separation in preparation process of crystalline materials

Molecular mechanism of liquid–liquid phase separation (LLPS) before nucleation in the preparation of crystalline materials is not well understood. In this work, the evolutions of solute–solvent intermolecular interactions and molecular self-assembly before and after LLPS were investigated by using citicoline sodium as model compound. Raman spectroscopy and molecular dynamics simulation (MD) were applied to reveal different interactions. It was found that the solute–solvent intermolecular interactions were firstly enhanced and then weakened before and after LLPS, indicating that LLPS was caused by the enhanced solute–solvent intermolecular interactions. Solute molecules will self-assemble to form clusters in binary mixed solvents, according to the 2D 1H–1H NOESY measurements and small angle X-ray scattering (SAXS). The clusters will further self-assemble to form a dense liquid phase with the process proceeding. Based on these results, the molecular mechanism of LLPS was proposed and discussed.

Solubility determination and correlation for spirotetramat in different solvent systems at T = 278.15–318.15 K

The solubility of spirotetramatin four binary solvents (methanol + water, ethanol + water, isopropanol + water, acetone + water) were studied by laser monitoring observation technique. The solubility data of spirotetramat in binary mixed solvents were subsequently fitted by the modified Apelblat model, λh model, Van't Hoff model, Jouyban-Acree model and NRTL model. The results showed that Apelblat model and Van't Hoff model were more suitable for fitting the solubility data. Furthermore, the effects of the solute–solvent intermolecular interactions on the solubility were analyzed using the KAT-LSER model. The results showed that the dipolar/polarizability of the solvent had the greatest influence on the solubility of spirotetramat.

Small-molecule catalyzed H2O2 production via a phase-transfer photocatalytic process

Hydrogen peroxide (H2O2) production has long been one of the key technologies in modern chemical industries. Conventional methods for large-scale H2O2 production are challenged by either high-energy-consumption or harsh reaction conditions. Here, we demonstrate a strategy to produce H2O2 with high yield catalyzed by organophotocatalyst using only H2O and O2 as the raw material without the assistance of additional scavengers. Our strategy features the design principle of the organophotocatalyst and a phase-transfer photocatalytic process under ambient condition. We show that both photocatalytic reduction of O2 and photocatalytic oxidation of H2O are responsible for H2O2 production in this phase-transfer photocatalytic process, and the solvent permittivity and intermolecular interaction between O2 and organophotocatalyst are the keys to achieve high efficiency. The photocatalytic H2O2 production rate in the system reaches 9000 μmol g−1 h−1 in the initial stage under ambient condition，and the apparent quantum efficiency (AQE) was ca. 8.2% based on the 595 nm wavelength. This work brings new insight to H2O2 production in a distinct mechanism that may inspire the development of low-energy consumption and cost-effective H2O2 production through photocatalysis.

Application of the Solute-Solvent Intermolecular Interactions as Indicator of Caffeine Solubility in Aqueous Binary Aprotic and Proton Acceptor Solvents: Measurements and Quantum Chemistry Computations.

The solubility of caffeine in aqueous binary mixtures was measured in five aprotic proton acceptor solvents (APAS) including dimethyl sulfoxide, dimethylformamide, 1,4-dioxane, acetonitrile, and acetone. The whole range of concentrations was studied in four temperatures between 25 °C and 40 °C. All systems exhibit a strong cosolvency effect resulting in non-monotonous solubility trends with changes of the mixture composition and showing the highest solubility at unimolar proportions of organic solvent and water. The observed solubility trends were interpreted based on the values of caffeine affinities toward homo- and hetero-molecular pairs formation, determined on an advanced quantum chemistry level including electron correlation and correction for vibrational zero-point energy. It was found that caffeine can act as a donor in pairs formation with all considered aprotic solvents using the hydrogen atom attached to the carbon in the imidazole ring. The computed values of Gibbs free energies of intermolecular pairs formation were further utilized for exploring the possibility of using them as potential solubility prognostics. A semi-quantitative relationship (R2 = 0.78) between caffeine affinities and the measured solubility values was found, which was used for screening for new greener solvents. Based on the values of the environmental index (EI), four morpholine analogs were considered and corresponding caffeine affinities were computed. It was found that the same solute–solvent structural motif stabilizes hetero-molecular pairs suggesting their potential applicability as greener replacers of traditional aprotic proton acceptor solvents. This hypothesis was confirmed by additional caffeine solubility measurements in 4-formylmorpholine. This solvent happened to be even more efficient compared to DMSO and the obtained solubility profile follows the cosolvency pattern observed for other aprotic proton acceptor solvents.

Study of Solvation Behavior Thermodynamics and FT-IR Spectroscopic Analysis of N-Butylethanolammonium Based Ionic Liquids with Polar Solvents

The effect of anion geometry on aggregation behavior of surfactant with aqueous solutions was investigated by the systematic measurements of concentration, temperature dependent density and derived thermodynamic properties. In this work, N-Butylethanolammonium trifluoroacetate [BEATFA] and N-Butylethanolammonium nitrate [BEAN] ionic liquids (ILs) were synthesized and characterized by 1H NMR. The binary systems IL+water/ethanol were prepared for the concentration ranges from 0.0264 to 0.4621 mol·kg−1 and the temperature ranges from 298.15 K to 318.15 K. Further, the apparent molar volume (Vɸ), partial molar volume (Vɸ∞), thermal expansion coefficient (α) and apparent molar expansivity (Eɸ) were derived from the experimentally measured density data. The critical aggregation concentration (cac), apparent molar volume at critical aggregation concentration (Vɸ,CAC), apparent molar volume in aggregation phase (Vɸ,mic), change in apparent molar volume due to aggregation (∆Vɸ,m) and degree of ionization (α′) were derived from the plot of apparent molar volume versus inverse of ILs concentration. The thermodynamic aggregation properties such as standard Gibb's free energy of micellization (∆Gom), standard enthalpy of micellization (∆Hom) and standard entropy of micellization (∆Som) were calculated from experimental measurements. The sign and magnitude of apparent molar volume at infinity dilution reveals about IL+solvent or IL-IL interactions between the component molecules. The system [BEAN]+water showed lowest positive magnitude in both Vɸ∞ and cac than compare to [BEATFA]+water due to the formation of stronger IL+solvent intermolecular interactions through the H-bonding. The variance in observed Vɸ∞ and cac data with different solvents due to the solvophobic effect and hydrogen bonding tendency was explained by FT-IR spectroscopy and DFT computational study. Among the all binary systems, [BEAN]+water showed highest intermolecular interaction tendency than other systems, the obtained results were compared with available literature data and analyzed in terms of intra and intermolecular interactions, polarity of solvents, hydrophobicity, nature anion, size and shape of the anion.

Rationalizing the Formation of Belinostat Solvates with Experimental Screening and Computational Predictions

Belinostat is a histone deacetylase inhibitor for the treatment of refractory T-cell lymphoma. Our study found that the tendency to form solvates of belinostat with hydrogen-bond acceptor type solvents was obvious based on the COSMO-RS model. Motivated by the prediction results, we investigated eight novel solvates, with 1,4-dioxane, tetrahydrofuran, furan, 3-picoline, cyclopentanone, 1-methyl-2-pyrrolidinone, and dimethyl sulfoxide/water as guest molecules, obtained by different crystallization methods. The obtained solid forms were thoroughly characterized with various analytical techniques, namely, powder X-ray diffraction, Fourier transform infrared spectroscopy, and thermal analysis. The thermal stability order of solvates was S3PC > S′Diox > SNMP > SCP > SFuran > STHF > SDiox > SDMSO/H2O, and a strong correlation between the boiling points of solvents and the crystal lattice energy with the thermal stability of solvates was observed. Additionally, six crystal structures of five solvates and the reported Form I were successfully determined from single-crystal X-ray diffraction data. The results revealed that the belinostat molecule adopted flexible conformations in different crystal structures; meanwhile, the formation of belinostat solvate was mainly driven by the belinostat–solvent intermolecular interactions and the improved packing efficiency due to the introduction of solvent molecules.

The co-solvency and thermodynamic properties of camptothecin in mixtures of (ethyl acetate + methanol/ethanol)

The solubility profile, molecular interactions and apparent dissolution thermodynamic properties of camptothecin in mixtures of (ethyl acetate + methanol) and (ethyl acetate + ethanol) was studied at the temperature range from T = (273.15 to 318.15) K under 101.3 kPa. In two mixtures, the solubility profile increased firstly and then decreased with the increasing mass fraction of ethyl acetate. In mixture of (ethyl acetate + methanol) at 318.15 K, it reached a maximum (9.176 × 10-5) in mole fraction when the mass fraction of ethyl acetate (w) = 0.80, and 7.554 × 10-5 in mixture of (ethyl acetate + ethanol) at w = 0.60. The Jouyban-Acree model and CNIBS/R-K model were applied to evaluate the solubility profile. The relative average deviation (RAD) data of Jouyban-Acree model in mixture of (ethyl acetate + methanol) was 3.81%, and 5.50% in mixture of (ethyl acetate + ethanol). However, it was no more than 3.59% for CNIBS/R-K model. The CNIBS/R-K model was more consistent than Jouyban-Acree model. In addition, the KAT-LSER model was used to analyse the effect of the solute–solvent intermolecular interactions on solubility profile. Furthermore, apparent dissolution thermodynamic analysis of camptothecin in mixtures of (ethyl acetate + methanol) and (ethyl acetate + ethanol) at the mean harmonic temperature was also performed. The results indicated that the dissolution process was endothermic and entropy-increasing, and the enthalpy is the main contributor to standard free energy of solution process.

Measurement and correlation of the solubility of 3-methoxybenzoic acid in fourteen mono-solvents at temperatures from 278.15 K to 323.15 K

A gravimetric method was used to determine the equilibrium solubility of 3-methoxybenzoic acid (3MBA) in 14 kinds of organic mono-solvents (methanol, ethanol, n-propanol, iso-propanol, n-butanol, iso-butanol, sec-butanol, formic acid, acetic acid, ethyl formate, methyl acetate, ethyl acetate, iso-propyl acetate, butyl acetate) from 278.15 K to 323.15 K at 0.1 MPa. In all the solvent systems studied, the solubility increases monotonously with the increasing of temperature. In addition, the effect of solvent properties on solid–liquid equilibrium of 3MBA was investigated. The results show that dissolving process of 3MBA in solvent is a complex process, which is affected by the action of solvent properties; Correlation analysis found that the solvent properties containing hydrogen bond donation (α), hydrogen bond acceptance (β), polarity index (ET30), Hildebrand solubility parameter (δH), cohesive energy density and surface tension process great influence on the dissolving behavior of 3MBA. And then, topological index (H) which can reflect the molecular structure information of the solvents was calculated. It was found that the solubility of 3MBA decreased with the increasing of H values in alcohol and ester solvents, and increased with the increasing of H values in carboxylic acid solvents. Besides, the solubility of 3MBA were related to the modified Apelblat model, λh model, van’t Hoff model and NRTL model, and the modified Apelblat model gave the best correlation results, with the ARD% of 0.68%. In addition, COSMO-RS model was used to calculate the σ-profiles and solvation free energy of selected solute–solvent systems, σ-profiles analysis was qualitatively described the intermolecular interaction, it was found that the solubility of 3MBA in the selected solvents was correlated with the solute–solvent intermolecular interactions; Solvation free energy was calculated in the “Molar” framework and found that the solubility of 3MBA in alcohols, esters and carboxylic acids decreased with the decreasing of the absolute value of the solvation free energy.

The solubility profile and dissolution thermodynamic properties of minocycline hydrochloride in some pure and mixed solvents at several temperatures

The dissolution process of α-minocycline hydrochloride in different solvent within the temperature range from 273.15 K to 313.15 K was studied by using “isothermal saturation method” under atmospheric pressure. It is found that the minocycline hydrochloride is insoluble in ethyl acetate and acetonitrile compared with alcohols. The maximum “mole fraction solubility” of minocycline hydrochloride in methanol is 2.88 × 10−3 at 313.15 K and followed by ethanol is 1.90 × 10−3 at 313.15 K, n-propanol is 1.23 × 10−3 at 313.15 K, isopropanol is 2.10 × 10−4 at 313.15 K, acetonitrile is 7.78 × 10−5 at 313.15 K and ethyl acetate is 2.63 × 10−5 at 313.15 K. The higher solubility of minocycline hydrochloride in alcohols could be due to their ability to form hydrogen bonds with solute molecule compared with ethyl acetate and acetonitrile. However, in mixtures of ethyl acetate (1-w) + methanol (w), the solubility values increased firstly, and then decreased with the mass fraction (w) of methanol, the maximum data is 6.07 × 10−3 at w = 0.60 at 313.15 K, an increase about 230 fold. In dissolution process of a solute in pure or mixed, solute - solvent interactions are more significant among other interactions and should be considered in any interpretation of the solubility behaviour. In order to obtain a rough evaluation of the solute - solvent intermolecular interactions, the solvatochromic parameters of pure and mixed solvents were discussed. Moreover, the experimental solubility are correlated by the modified Apelblat equation and Jouyban-Acree’s model, and the values of relative average deviation (RAD) are all less than 0.76% in pure organic solvents, and no more than 6.80% in mixtures. Besides, the results of apparent thermodynamic analysis indicates that the dissolution is an endothermic and entropy driven process. The solubility data and thermodynamic properties would be useful in the process of purification, recrystallization and dosage form design in pharmaceutical industries.

Gatifloxacin–Ionic Surfactant Interactions: Volumetric, Acoustic, Voltammetric, and Spectroscopic Studies

AbstractSurfactant systems have been frequently used as pseudomodels for investigating interactions of drugs with biological membranes because of their structural similarities with the latter. This helps to understand complicated yet very important biological processes like diffusion of bioactive moieties through biomembranes. The current study deals with voltammetric and spectroscopic studies to evaluate the interaction of a potential antibacterial drug, gatifloxacin (GTF), with a cationic surfactant, dodecyltrimethylammonium bromide (DTAB), and an anionic surfactant, sodium dodecyl sulfate (SDS), under physiological conditions (phosphate buffer, pH 7.4). For more detailed insight into the GTF–ionic surfactant interactions, density and acoustic data were also recorded and used to calculate several important parameters, namely, apparent molar volume (ɸV), isentropic compressibility (Ks), and apparent molar isentropic compressibility (ɸK) at T = 298.15, 303.15, 308.15, and 313.15 K. Values for partial molar volume (, partial molar expansivity , specific acoustic impedance (Z), relative association (RA), intermolecular free length (Lf), and sound velocity number (U) were also obtained. The interpretation of the concentration dependence of the above‐mentioned quantities using a cosphere overlap model led to a better apprehension of solute–solute and solute–solvent intermolecular interactions present in the investigated system, whereas cyclic voltammetry and ultra violet (UV)–visible spectroscopic studies assisted in predicting the location of adsorbed GTF molecules within the DTAB and SDS micelles.

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

The dissolution behaviour and thermodynamic properties calculation of praziquantel in pure and mixed organic solvents

The purpose is to study the dissolution behaviour for praziquantel in different solvent. The dissolution capacity within the temperature range from 273.15 K to 313.15 K was researched by using the isothermal equilibrium method and evaluated with the modified Apelblat equation, λh equation and Jouyban-Acree model. In pure solvents, the largest values were found in N-methyl pyrrolidone (NMP, 8.106 × 10−2 in mole fraction) at 313.15 K, and followed by cyclohexanone (5.964 × 10−2), toluene (3.842 × 10−2), acetonitrile (3.519 × 10−2), acetone (3.001 × 10−2), ethyl acetate (2.896 × 10−2), n-octanol (2.715 × 10−2), isopropanol (1.882 × 10−2) and n-hexane (4.379 × 10−2). While in mixtures of (NMP + isopropanol), the solubility capacity increased monotonically with the increase of temperature and NMP mass fraction. KAT-LSER method was applied to analyse the effect of solute–solvent intermolecular interactions on the solubility in pure solvents. More importantly, the selection of appropriate solvents for praziquantel dissolution is important to its application. Moreover, the effect of the solute–solvent intermolecular interactions on the solubility in pure and mixed solvents was discussed as well. In the following, the analysis of apparent thermodynamic analysis indicates that the dissolution is an endothermic, spontaneous and entropy driven process.