Hoff Equation Research Articles

Thermodynamic models for determination of solid–liquid equilibrium of para-tert-butylbenzoic acid in binary and ternary solvent system

Accurate solubility data is essential to make critical decisions from the earliest stage of drug discovery, through the entire process development, formulation, and up to process design. The present research work aims to evaluate the solid–liquid equilibrium data of para-tert-butylbenzoic acid (PTBBA) in binary systems such as acetonitrile + water, isopropyl alcohol + water, and isopropyl alcohol + acetonitrile at 288.15 to 328.15 K and a ternary solvent mixture of isopropyl alcohol + acetonitrile + water system in the temperature range of 298.15 to 323.15 K with varying mass fraction of the binary mixture (isopropyl alcohol + acetonitrile) for a constant mass fraction of water (0.1 and 0.3) using gravimetric and titrimetric methods. It is observed that the solubility of PTBBA increases with an increase in temperature for all the selected solvent systems. Moreover, the solubility of PTBBA in the binary and ternary system is affected by an increase in the mass fraction of water at a given temperature, which acts as an antisolvent. The measured data is correlated with various thermodynamic models such as Van’t Hoff equation, Modified Apelblat equation, Buchowski equation, and Wilson models. It is observed that there is a good agreement between measured and calculated values with an average relative deviation of 0.95 for isopropyl alcohol + acetonitrile system in the case of the modified Apelblat equation.

The potential of direct air capture using adsorbents in cold climates.

Global warming threatens the entire planet, and solutions such as direct air capture (DAC) can be used to meet net-zero goals and go beyond. This study investigates using DAC in a 5-step temperature vacuum swing adsorption (TVSA) cycle with adsorbents' Li-X and Na-X, readily available industrial zeolites, to capture and concentrate CO2 from air in cold climates. From this study, we report that Na-X in cold conditions has the highest known CO2 adsorption capacity in air of 2.54mmol/g. This combined with Na-X's low CO2 heat of adsorption, and fast uptake-rate in comparison to other benchmark materials, allowed for Na-X operating in cold conditions to have the lowest reported DAC operating energy of 1.1 MWh/tonCO2. These findings from this study show the promise of this process in cold climates of Canada, Alaska, Greenland, and Antarctica to be part of the solution to global warming.

Solubility measurement, correlation, and dissolution thermodynamics of 2,4,6,8,10,12-hexanitrohexaazaisowurtzitane · 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (2HNIW·HMX) co-crystal in two binary solvent mixtures

The solubility of 2HNIW·HMX co-crystal in two binary solvent mixtures (ethanol + methyl acetate, and 1,2-dichloroethane + methyl acetate) was measured by gravimetric method at various temperatures (283.15, 288.15, 293.15, 298.15, 303.15, 308.15, 313.15 and 318.15 K) under atmospheric pressure (0.1 MPa). The experimental results revealed that the solubility for co-crystal in binary solvent mixtures is a simple function of ethanol (or 1,2-dichloroethane) mass fraction and temperature, which decreased with increasing temperature and mass fraction of ethanol (or 1,2-dichloroethane) in the binary solvent mixtures. The solubility of 2HNIW·HMX co-crystal was correlated with the modified Apelblat equation, CNIBS/R-K model, Jouyban-Acree-van't Hoff model, and Jouyban-Acree-Apelblat model. The fitting results demonstrate that the modified Apelblat model and CNIBS/R-K model provided a better correlation with the experimental results than the other models. Furthermore, the van’t Hoff equation was used to study the thermodynamic properties of the 2HNIW·HMX co-crystal dissolution process, including the apparent molar enthalpy change (ΔdisH°), the apparent molar entropy change (ΔdisS°), and the apparent molar Gibbs free energy change (ΔdisG°). The results show that the dissolution of the co-crystal in the selected binary solvent mixture is an exothermic process. The experimental and calculated solubility data and thermodynamic properties of the 2HNIW·HMX co-crystal would be helpful for selecting the appropriate solvent system for the reaction, crystallization, and purification of the 2HNIW·HMX co-crystal.

Soil Moisture and Temperature Effects on Granule Dissolution and Urease Activity of Urea with and without Inhibitors—An Incubation Study

Urea granule dissolution in soil and soil urease activity are essential parameters for the accurate prediction of nitrogen dynamics after urea application, but both are scarcely studied. The response of urease activity to temperature is unclear under the addition of urease or nitrification inhibitors. In this study, we conducted laboratory incubation trials using glass jars with 100 g soil to quantify urea granule dissolution. Urease activity after urease and nitrification inhibitor addition were investigated in plastic bottles (5 g soil) under different temperatures. Inhibitor N-(2-nitrophenyl) phosphoric triamide (2-NPT), and a mixture of dicyandiamide and 1 H-1,2,4-triazol (DCD/HZ) were tested as urease and nitrification inhibitors separately and in combination. The dynamics of urease activity was fitted with Michaelis–Menten kinetics combined with the Van’t Hoff equation. At low soil moisture contents close to air-dry conditions (4–8% w/w water content), soil moisture was the dominant factor, but at higher soil moisture contents (28% and 48% w/w), temperature controlled the dissolution process. Dissolution could take several days or even longer at very dry soil conditions, while it was completed between a few hours and 24 h at high soil moisture levels. Urea with urease inhibitor formulation dissolved significantly slower at a moisture level of 28% (w/w). In the studied soil, urease activity varied between 2.9 and 54.4 mg NH4+-N kg−1 h−1. Across all urea concentrations, the addition of urease inhibitor 2-NPT significantly reduced urease activity. The relationship between urease activity and urea addition rate could be accurately described with Michaelis–Menten kinetics, and urease inhibitor addition reduced the temperature sensitivity of urease activity by 7%, while the nitrification inhibitor increased it by 4%. Parameter estimates and process characterization for urea granule dissolution and urea hydrolysis in this study are meaningful for and helpful in agricultural practice and the model simulation of soil nitrogen dynamics.

Solubility study and thermodynamic modelling of succinic acid and fumaric acid in bio-based solvents

The solubility and involved energies of organic acids in green solvents are relevant to the design of sustainable biorefinery downstream processes. In this work, the solubility of two important bio-based organic acids such as succinic acid and fumaric acid, in water and four bio-based solvents (i.e., ethyl acetate, 1,8-cineole, cyclopentyl methyl ether, and 2-methyl tetrahydrofuran) were measured within a temperature range of [283 – 313] K. A gravimetric methodology was adopted, previously validated using the organic acid aqueous solubilities available in the literature. The reported data present an average estimated uncertainty of measurement, with a level of confidence of 95%, of 5.2·10-4 mol·mol−1. Experimental results were correlated with the van’t Hoff equation, and the Buchowski–Ksiazaczak λh model, where the root mean squared deviations were <3.9·10-4 for all systems. From the experimental data and the COSMO-RS molecular simulation method, the solid–liquid equilibria were modelled to estimate the excess energies and the solute activity coefficients of the saturated solutions. Excess enthalpy contribution analysis shows that attractive hydrogen-bonding interactions between the organic acids and the green solvents drive the dissolution phenomena. The magnitude of the hydrogen-bonding interactions increases with temperature for all systems, agreeing with the observed solubility trends. The organic acid energies of solution were estimated from the van’t Hoff equation, demonstrating an enthalpy–entropy compensation effect. The energetic analysis shows that the dissolution phenomenon is an enthalpy-driven process for fumaric acid, whereas no predominant effect is observed for succinic acid.

Efficient separation of CO2 from methane at high pressures by modified microporous titanosilicates; design and breakthrough studies

In this work, type-4 titanosilicate (TS-4) having a micro-pore size of 3–4 Å, was synthesized from inexpensive source materials, such as commercial silicon dioxide, with the template-free hydrothermal method. The XRD analysis confirmed formation of the TS-4 crystalline phase. Then, strontium cation modification was performed using SrCl2 solution to adjust the pore structure and increase the basicity of the surface to improve CO2 selectivity versus methane. In this study, the adsorption isotherms of methane and CO2 were measured in the range of 0 to 50 bars, at two different temperatures of 298 K and 308 K, then the ideal selectivities of CO2/CH4 were calculated at different pressures. The ideal CO2/CH4 selectivity was determined at 19.04 and 38.49 for TS-4 and Sr-TS-4, respectively, at the pressure of 50 bar and the temperature of 298 K. The isosteric heat of adsorption of CO2 was calculated by Van’t Hoff equation as −29.63 kJ/mol and −26.22 kJ/mol, respectively. Low CO2 heat of adsorption of Sr-TS-4 and high selectivity of CO2/CH4 at high pressures, against zeolites, offer Sr-TS-4 as an economic and efficient adsorbent for cyclic adsorption processes. To study the dynamic selectivity of CO2/CH4, dynamic adsorption experiments were conducted at the temperature of 298 K, pressures of 7 and 15 bars, flow rates of 10 and 20 Nml/min in a bed of 2.7 gr adsorbent, with the inlet molar fraction of 5–95 % CO2-CH4 mixture. Comparison of the breakthrough curves indicated that Sr-TS-4 had a longer breakpoint and a larger used ratio of the length at any feed flow rate. The maximum relative dynamic selectivity of CO2/CH4 at 15 bar, by the Sr-TS-4, was obtained 95.29 at CO2 breakpoint of 40 min, whereas maximum relative dynamic selectivity, by the TS-4, was obtained 63.54 at CO2 breakpoint of 30 min. It is concluded that Sr-TS-4 would be an efficient adsorbent for separation of CO2 from natural gas in commercial scales at high pressures with high methane recovery.

Disagreements Between Calorimetric and Van't Hoff Enthalpies of Adsorption II: Effect of pH and pH Buffers on Phenobarbital Adsorption to Activated Carbon

The reported inconsistencies between the van't Hoff equation and calorimetry hinder the utility of thermodynamics in biochemical and pharmaceutical research. A novel thermodynamic approach is developed herein for ligand adsorption with a focus on the interpretation of calorimetric data in the presence of concurrent proton exchange reactions. Such exchange reactions typically result in a pH-dependence of calorimetric measurements that obscures intrinsic binding enthalpies. It is shown that for the adsorption of phenobarbital to activated carbon, the measured calorimetric enthalpy is a result of three linked acid/base equilibria. A model was established to predict the intrinsic binding enthalpy using 1) the adsorbate's pKa and 2) the adsorbate's enthalpy of protonation. The observed calorimetric enthalpy of binding exhibited both pH and buffer-dependence and was between -5 and -42 kJ/mol. Meanwhile, the predicted intrinsic enthalpy (-25.1 kJ/mol) of binding was in excellent agreement with the measured intrinsic enthalpy (-25.6 kJ/mol). Corrections to the observed calorimetric enthalpies allowed comparisons with enthalpies obtained from the van't Hoff method. It is shown that the predicted intrinsic calorimetric enthalpy agrees well with the van't Hoff enthalpies in instances where observed enthalpies significantly deviated. This treatment is general and is not specific to phenobarbital or activated carbon.

Revisiting the calculation of thermodynamic parameters of adsorption processes from the modified equilibrium constant of the Redlich–Peterson model

AbstractBACKGROUNDThe adsorption equilibrium constant of the Langmuir model (KL; L mol−1) has been applied as the standard thermodynamic equilibrium constant, , for calculating the thermodynamic parameters (∆G°, ∆S°, and ∆H°) of an adsorption processes by using the van't Hoff equation. Some authors have (directly and indirectly) applied the constant KRP (L kg−1) of the Redlich–Peterson model for such calculations. However, this is an incorrect application because the unit of KRP is not suitable (it is not an equilibrium constant). Its new adsorption equilibrium constant, Ke(RP) (L mol−1), was revisited based on aRP (L mol−1)g. In the literature, there is still uncertainty regarding the application of aRP as for calculating the thermodynamic parameters. Therefore, the present study aimed to evaluate the feasibility of applying Ke(RP) to calculate thermodynamic parameters using available literature data. The thermodynamic parameters obtained from Ke(RP) were compared to those from KL. A case study using a biosorbent for adsorbing methylene blue dye at different temperatures was carried out to re‐verify the feasibility.RESULTSThe Redlich–Peterson model is only valid when its exponent is in a strict range (0 ≤ g ≤ 1). The Redlich–Peterson model (68%; 227 observations collected from 52 published papers) describes adsorption equilibrium datasets better than the Langmuir model. The negative ΔG° values obtained based on Ke(RP) (11.7–47.6 kJ mol−1) were significantly different (p = 2.98 × 10−12) from those on KL (12.2–40.8 kJ mol−1). The magnitudes of ΔH° obtained based on Ke(RP) were significantly different (P &lt; 0.05) to those on KL; however, such differences did not affect conclusions drawn on dominant mechanism adsorption (physical or chemical). The magnitude of ΔH° for chemisorption (involved in covalent bonds) is higher than 200 kJ mol−1. For the case study, the ∆H° (kJ mol−1) and ∆S° [J mol−1 × K−1] values calculated based on Ke(RP) (11.65 and 111.5) were like those on KL (11.34 and 110.4, respectively).CONCLUSIONA new equilibrium constant, Ke(RP) (L mol−1), of the Redlich–Peterson model can be applied as for calculating the thermodynamic parameters (∆G°, ∆S°, and ∆H°) of an adsorption processes under specific cases (i.e., F, H, and L‐shaped adsorption isotherms). Most of the adsorption processes (98%) involve physical adsorption. © 2022 Society of Chemical Industry (SCI).

Solubility measurement and correlation of 2-aminoterephthalic acid in eight alcoholic solvents at different temperatures

This research experimentally measured the solubility of 2-aminoterephthalic acid in eight pure alcoholic solvents – methanol, ethanol, 1-propanol, 1-butanol, 2-propanol, 2-butanol, 2-methyl-2-propanol, and 3-methyl-1-butanol – from 303.15 to 338.15 K at normal pressure p = 0.1 MPa by the excess solid method. The measured solubility of 2-aminoterephthalic acid in these pure organic solvents was found to increase with the rise of temperature in the following order: 3-methyl-1-butanol (lowest solubility) < 1-butanol < 2-butanol < 1-propanol < 2-methyl-2-propanol ≈ 2-propanol < ethanol < methanol (highest solubility). The experimental solubility was correlated by the Van’t Hoff equation and the λh (Buchowski) equation. The apparent thermodynamic properties (Δ0Gsol, Δ0Hsol and Δ0Ssol) were calculated by the Van’t Hoff equation, from which it was concluded that the dissolution process is entropy-motivated and endothermal. In addition, the solvent effects on 2-aminoterephthalic acid solubility were studied by the KAT-LSER model, where the results showed that the polarizability accounts for 47.9 ± 4.2 % of the total solvent effect.A volcano-type relation between the dissolution entropy and enthalpy versus the solvent boiling point is reported, showing maximal values of 55.3 J mol−1 K−1 and 29.2 kJ mol−1, respectively, for intermediate molecular interactions of solute and solvent.

Effect of La Doping on Kinetic and Thermodynamic Performances of Ti1.2CrMn Alloy upon De/Hydrogenation.

Development of efficient hydrogen storage materials is one of the great challenges in the area of hydrogen energy and fuel cells. Herein, a La-doped Ti1.2CrMn alloy with high hydriding capacity (2.1 wt % H) and dehydriding capacity (1.8 wt % H) was successfully developed. The crystallographic characteristics, microstructural evolution, and hydrogen storage mechanisms of the alloy were investigated systematically. It was found that the introduction of La increased the cell volume of alloy and thus improved the hydrogenation kinetic, practical hydrogenation capacity, and cyclic property. The hydrogenation kinetic results of the La-doped alloy indicate that it exhibited a higher hydrogenation rate than that of the La-free alloy. It is ascribed to the formation of LaH3, which provides a fast diffusion channel for hydrogen atoms to enter the alloy matrix. The dehydrogenation enthalpy (ΔH) of the La-doped alloy was calculated by the van't Hoff equation and PCT curves to be ∼18.2 kJ/mol. The cycle test proves that the La-doped Ti1.2CrMn alloy, due to La addition, reduces the lattice expansion and lattice stress and exhibits excellent durability.

Effect of choline chloride based deep eutectic solvents on the aqueous solubility of 4-hydroxycoumarin drug: Measurement and correlation

This work aims to improve the aqueous solubility of 4-hydroxycoumarin (4H-coumarin) as one of the lowest soluble derivatives of coumarin, by using deep eutectic solvents (DESs). The applied DESs are composed of choline chloride (ChCl) as a hydrogen bond acceptor (HBA) and ethylene glycol (EG), urea (U), or glycerol (GLY) as hydrogen bond donors (HBD). The shake-flask method was used to determine the experimental solubility of 4H-coumarin at T = (298.15 to 313.15) K. The results demonstrate that 4H-coumarin solubility was increased noticebly at higher DES concentration and temperature. Moreover, in the presence of ChCl/EG, the 4H-coumarin solubility was more than 250 times higher than that in pure water. The experimental solubility data were fitted to the Wilson, electrolyte Non-Random Two-Liquid (e-NRTL), and UNIQUAC activity coefficient models, which shows that the Wilson model has the best correlation performance for aqueous solutions containing ChCl/EG, ChCl/GLY and ChCl/U with 0.05, 0.07 and 0.22 of ARD%, respectively. The Gibbs and van't Hoff equations to estimate the dissolution apparent thermodynamic quantities including enthalpy, Gibbs free energy, and entropy. The results indicate that 4H-coumarin dissolution processes in the investigated systems are endothermic. Quantum mechanical Density functional theory (DFT) method has also been implemented to discover the nature of the interactions in the studied DES/4H-coumarin complexes at the B3LYP-D3(BJ)/6-311g(d,p) level of theory. The DFT calculations confirm that the formations of the DESs and DES/4H-coumarin complexes are spontaneous, and the most dominant interactions are hydrogen-bonding of Cl from ChCl as electron donor and H of the other components as electron acceptor.

Correlation of Surface Tension of Mono-Solvents at Various Temperatures

Surface tension is among the most important factors in chemical and pharmaceutical processes. Modeling the surface tension of solvents at different temperatures helps to optimize the type of solvent and temperature. The surface tension of solvents at different temperatures with their solvation parameters was used in this study to develop a model based on the van’t Hoff equation by multiple linear regression. Abraham solvation parameters, Hansen solubility parameters, and Catalan parameters are among the most discriminating descriptors. The overall MPD of the model was 3.48%, with a minimum and maximum MPD of 0.04% and 11.62%, respectively. The model proposed in this study could be useful for predicting the surface tension of mono-solvents at different temperatures.

Experimental determination of dissociation constants (pKa) for N‐(2‐aminoethyl)‐1,3‐propanediamine, 2‐methylpentamethylene diamine, N,N‐dimethyldipropylenetriamine, 3,3′‐diamino‐N‐methyldipropyl‐amine, Bis[2‐(N,N‐dimethylamino)ethyl]ether, 2‐[2‐(dimethyl‐amino) ethoxy] ethanol, 2‐(dibutylamino) ethanol, and N‐propylethanol‐amine and modeling with artificial neural network

AbstractThe dissociation constants (pKa) of the eight amines, namely, N‐(2‐aminoethyl)‐1,3‐propanediamine, 2‐methylpentamethylene diamine, N,N‐dimethyldipropylene‐triamine, 3,3′‐diamino‐N‐methyl‐dipropylamine, Bis[2‐(N,N‐dimethylamino) ethyl]ether, 2‐[2‐(dimethyl‐amino)ethoxy] ethanol, 2‐(dibutylamino) ethanol, and N‐propylethanolamine were measured between 298.15 and 313.15 K with 5 K increment. Based on the experimental values and using the van't Hoff equation, thermodynamic properties such as the standard state changes of enthalpy, entropy, and Gibbs free energy were calculated. Using computational chemistry calculations, the amine that is protonated first was predicted. Furthermore, computer‐free group contribution methods such as the original Perrin–Dempsey–Serjeant (PDS), the modified PDS, and the Qian–Sun–Sun–Gao (QSSG) model were used to estimate the dissociation constants of the studied amines at 298.15 K. The QSSG provided the most accurate results. Finally, this work utilized an artificial neural network for estimating the pKa values, which were in excellent agreement with the experimental data.

Study on the interaction of the bromodomain inhibitor JQ1 with human serum albumin by spectroscopic and molecular docking studies

The present study examined the interaction of the bromodomain inhibitor/anti-cancer drug JQ1 with human serum albumin (HSA) by spectroscopic and molecular docking methods. Spectroscopic analysis of the fluorescence emission quenching at different temperatures and UV-vis spectroscopy revealed that the quenching mechanism of human serum albumin by JQ1 was static in nature. The quenching data was analyzed using Stern-Volmer equation. JQ1 was bound to HSA at only one site with a binding constant of 3.5 × 104 mol L−1 at 293 K. The binding site of JQ1 in HSA was identified as subdomain IIA in site I, predominantly interacting with Trp-214 residue present at the site I revealed by the site binding experiment. van't Hoff equation was applied to calculate thermodynamic parameters like enthalpy change (∆H°) -29.9 kJ/mol and entropy change (∆S°) +0.09 J/mol K at a temperature of 293 K. The negative value of ∆H° and positive ∆S° suggest the involvement of hydrogen bond and hydrophobic interactions as the predominant binding forces. Circular dichroism spectroscopy revealed that JQ1 induced a slight change in the secondary structure of HSA by reducing the percentage of α-helical content from 56.34% to 56.12%. Molecular docking studies showed that JQ1 majorly interacts with the amino acid residues present in the active site of site I through different types of interactions, including polar, hydrogen bond, electrostatic and hydrophobic interactions.

Effect of temperature and propylene glycol as a cosolvent on dissolution of clotrimazole

Herein, the solubility study of clotrimazole was performed in a propylene glycol+water system. The solubility values were fitted to various cosolvency equations. The model accuracies were studied with the computation of the mean relative deviations. The thermodynamic behavior was investigated according to the van't Hoff and Gibbs equations for clotrimazole in the propylene glycol+water system. Furthermore, the density data for clotrimazole were determined in mixtures of propylene glycol+water and fitted to the Jouyban-Acree equation.

Effect of N-Methyl-pyrrolidone (NMP) on the Equilibrium Solubility of Meloxicam in Aqueous Media: Correlation, Dissolution Thermodynamics, and Preferential Solvation.

Meloxicam is an analgesic and anti-inflammatory drug widely prescribed in current therapeutics that exhibits very low solubility in water. Thus, this physicochemical property has been studied in N-methyl-pyrrolidone (NMP)–aqueous mixtures at several temperatures to expand the solubility database about pharmaceutical compounds in aqueous–mixed solvents. The flask-shake method and UV–vis spectrophotometry were used for meloxicam solubility determination as a function of temperature and mixture composition. Several cosolvency models, including the Jouyban–Acree model, were challenged for equilibrium solubility correlation and/or prediction. The van’t Hoff and Gibbs equations were employed here to calculate the apparent standard thermodynamic quantities for the dissolution and mixing processes of this drug in these aqueous mixtures. Inverse Kirkwood–Buff integrals were employed to calculate the preferential solvation parameters of meloxicam by NMP in all mixtures. Meloxicam equilibrium solubility increased with increasing temperature, and maximal solubilities were observed in neat NMP at all temperatures. The mole fraction solubility of meloxicam increased from 1.137 × 10–6 in neat water to 3.639 × 10–3 in neat NMP at 298.15 K. The Jouyban–Acree model correlated the meloxicam solubility in these mixtures very well. Dissolution processes were endothermic and entropy-driven in all cases, except in neat water, where nonenthalpy- nor entropy-driven was observed. Apparent Gibbs energies of dissolution varied from 34.35 kJ·mol–1 in pure water to 7.99 kJ·mol–1 in pure NMP at a mean harmonic temperature of 303.0 K. A nonlinear enthalpy–entropy relationship was observed in the plot of dissolution enthalpy vs dissolution Gibbs energy. Meloxicam is preferentially hydrated in water-rich mixtures but preferentially solvated by NMP in the composition interval of 0.16 < x1 < 1.00.

Equilibrium Solubility of Triclocarban in (Cyclohexane + 1,4-Dioxane) Mixtures: Determination, Correlation, Thermodynamics and Preferential Solvation

Equilibrium solubility of triclocarban (TCC) expressed in mole fraction in 1,4-dioxane and cyclohexane, as well, as in 19 {cyclohexane (1) + 1,4-dioxane (2)} mixtures, was determined at seven temperatures from T = (288.15 to 318.15) K. Logarithmic TCC solubility in these cosolvent mixtures was adequately correlated with a lineal bivariate equation as function of both the mixtures composition and temperature. Apparent thermodynamic quantities for the dissolution and mixing processes were computed by means of the van’t Hoff and Gibbs equations observing endothermal and entropy-driven dissolution processes in all cases. The enthalpy–entropy compensation plot of apparent enthalpy vs. apparent Gibbs energy was linear exhibiting positive slope implying enthalpy-driving for TCC transfer from cyclohexane to 1,4-dioxane. Ultimately, by using the inverse Kirkwood–Buff integrals it is observed that TCC is preferentially solvated by cyclohexane molecules in 1,4-dioxane-rich mixtures but preferentially solvated by 1,4-dioxane molecules in cyclohexane-rich mixtures.

Solubility measurement, thermodynamic modeling and solubility parameters of Clarithromycin（form ӀӀ）in aqueous ethanolic solution

ABSTRACT To develop and optimise the crystallisation process of clarithromycin, the solid–liquid equilibrium solubility and solvent effect of clarithromycin form ӀӀ in aqueous ethanol mixtures was experimentally determined at the temperature range from 273.15 K to 333.15 K under atmospheric pressure of 0.1 MPa. Experimental results confirmed that the crystal form did not change during the determination of solubility. The results indicated that the solubility of clarithromycin is dependent on the composition of the mixed solvent, and it reaches its maximum value when the mole fraction of ethanol in the mixture solvent is equal to 0.61. In addition, the solubility of clarithromycin was positively related to the temperature in the ethanol-water mixed solvent. Furthermore, solubility parameter was used to elucidate the relation between the solubility and the mixed solvent. The modified Apelblat equation, van’t Hoff equation, λh equation, CNIBS/R–K model and Jouyban–Acree model were employed to correlate the solubility data. The correlation results showed good agreement with the experimental data, the modified Apelblat equation provides the best correlation results. The NRTL equation was utilised to calculate the thermodynamic properties of the dissolution process of clarithromycin, and the dissolution process of clarithromycin was estimated to be endothermic and entropy-driven.

Solubility and thermodynamic properties of 2-naphthoxyacetic acid in twelve mono-solvents

The solubility of 2-naphthoxyacetic acid in methanol, ethanol, n-propanol, i-propanol, i-butanol, n-pentanol, methyl acetate, ethyl acetate, n-propyl acetate, i-propyl acetate, acetonitrile, and acetone was determined with the gravimetric method under the barometric pressure in the temperature range of 278.15 K to 323.15 K. The experimental results indicate that the solubility of 2-naphthoxyacetic acid in the twelve solvents was positively related to temperature over the whole range of temperature studied. Six mathematical models were used to fit the experimental results, including modified Apelblat equation, UNIQUAC model, λh equation, NRTL model, Two-Suffix Margules model and Jouyban model. The best correlation results were shown using the modified Apelblat model. The Hansen Solubility Parameter (HSP) was used to discuss the order of solubility of 2- naphthoxyacetic acid in the studied solvents. In addition, the thermodynamic properties during the dissolution of 2-naphthoxyacetic acid were analyzed and discussed according to the Van't Hoff equation.

Stress Relaxation Behavior of Poly(Methyl Methacrylate)/Graphene Composites: Ultraviolet Irradiation.

The graphene/poly (methyl methacrylate) (PMMA) composites are a promising candidate for electronic, optoelectrical, and environmental applications. Understanding the mechanical degradation of PMMA-based materials is of practical importance in improving the reliability and lifespan of the associated structures and systems. In this study, we investigate the effects of functionalized graphene (FG) and UV irradiation on the stress–relaxation of PMMA. Uniaxial tensile and stress –relaxation tests are performed to evaluate the mechanical properties of the composites. The mechanical strength and elongation at the break increase with the graphene concentration but decrease with the increase of the irradiation dose. Raman spectroscopy and intrinsic viscosity measurement are applied to examine the root cause of the degradation in the composites. UV irradiation leads to polymer chain scission and loss of molecular weight. The Kelvin representation of the standard linear solid model (SLSM) is used to describe the stress–relaxation curves of the composites. The value of the elastic modulus in the Kelvin element decreases with the increase in temperature. The viscosity follows the Arrhenius equation. The activation energy of viscosity increases with the increasing FGs concentration because the FGs hinder the chain motion of PMMA. However, UV irradiation makes chain scission of PMMA/FGs composite so that the polymer chain moves more easily and the activation energy of stress relaxation lowers. The steady-state stress follows the van ’t Hoff equation that stress relaxation is an exothermal deformation process. Although Maxwell’s representation of SLSM is mathematically identical to the Kelvin representation of SLSM, the former cannot interpret the stress–relaxation behavior of PMMA/FGs composite, which is against the concept of Young’s modulus as a decreasing temperature function.