16 research outputs found

    Correlation of Solubility and Prediction of the Mixing Properties of Capsaicin in Different Pure Solvents

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    Using a static analytical model, experimental solubility data were obtained for capsaicin in <i>n</i>-hexane, cyclohexane, carbon disulfide, butyl ether, and isopropyl ether at temperatures ranging from 278.15 to 323.15 K. The melting temperature and fusion enthalpy of capsaicin were measured using differential scanning calorimetry. The measured solubility data were well correlated by the van’t Hoff, modified Apelblat, λ<i>h</i> (Buchowski), Wilson, and NRTL models, with the Wilson model showing the best agreement. The activity coefficients of capsaicin and the mixing Gibbs free energies, enthalpies, and entropies of the resulting solutions were predicted on the basis of the Wilson model parameters at measured solubility points. In addition, the infinite-dilution activity coefficients and excess enthalpies of capsaicin were estimated. Finally, the effects of solute–solvent intermolecular repulsive interactions on the solubility behavior and the values of mixing Gibbs free energy were discussed

    Solid–Liquid Phase Equilibrium and Mixing Properties of Cloxacillin Benzathine in Pure and Mixed Solvents

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    Experimental solubility data of cloxacillin benzathine in pure solvents and binary solvent mixtures from 278.15 to 313.15 K were measured using a multiple reactor setup. The measured data in pure solvents were correlated by the van’t Hoff equation, modified Apelblat equation, <i>λh</i> equation, Wilson model, and NRTL model, and the Wilson model showed the best agreement. Thus, the activity coefficients of cloxacillin benzathine as well as the mixing Gibbs free energies, enthalpies, and entropies of the solutions were predicted with the correlation of experimental data based on the Wilson model. Some other properties were also estimated, including the infinite-dilution activity coefficients and excess enthalpies in pure solvents. The solubility data in binary solvent mixtures as a function of solvent composition were correlated by the Wilson model. The negative values of the calculated partial molar Gibbs free energies indicated the variation trend of the solubility

    Research Progress and Model Development of Crystal Layer Growth and Impurity Distribution in Layer Melt Crystallization: A Review

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    Layer melt crystallization has been widely utilized in numerous chemical industries because of its high selectivity for pure products, low energy consumption, and the convenience to industrialization. This review will lay out the research progress and process model development of the key processes (crystal layer growth and impurity distribution) involved in layer melt crystallization. First, the nucleation mechanism, the preparation approaches of the initial crystal layer, and classic experimental configurations are illustrated. Second, modeling approaches are outlined to release the progress of separation effect evaluation, parameter optimization, and sweating process simulation in layer melt crystallization. Novel theories (fractal, porous media, and so on) and technologies (gradient freezing, sonocrystallization, and so forth) with suitable interpretation are potential solutions for the shortcomings of the current process research. Consequently, application areas related to layer melt crystallization are highlighted. Finally, the key issue for further research, challenges, and perspectives will be concluded

    Interplay between Kinetics and Thermodynamics on the Probability Nucleation Rate of a Urea–Water Crystallization System

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    In this contribution, by employing the Poisson distribution combined with the regular solution theory in the classical nucleation theory (CNT) framework, we construct a new model to uncover the relationship between induction time (<i>t</i><sub>ind</sub>) and supercooling (Δ<i>T</i>) and saturation temperature (<i>T</i><sub>0</sub>) at different specific probabilities. By choosing the urea aqueous solution as a benchmark system, we show that the value of ln­(1/<i>t</i><sub>ind</sub>) follows a reasonable linear relationship with (<i>T</i><sub>0</sub>/Δ<i>T</i>)<sup>2</sup>/(<i>T</i><sub>0</sub> – Δ<i>T</i>), except the probability value tends to be 0 or 1. Furthermore, we also shed new light on the role of chemical potential difference and nucleation temperature in determining the nucleation rate; namely, although the chemical potential difference is the driving force for the crystallization process, it does not always favor the nucleation process. We demonstrated that when the chemical potential difference increases as the nucleation temperature decreases (Δ<i>T</i> gradually increases), in this case, the kinetic factor overwhelms the thermodynamic factor thus leading to a faster nucleation rate by employing the CNT theory. However, when the chemical potential difference decreases as the nucleation temperature increases, we found that increasing the nucleation temperature favors the nucleation process both in kinetic and thermodynamic aspects

    Determination of the Solubility, Dissolution Enthalpy, and Entropy of Pioglitazone Hydrochloride (Form II) in Different Pure Solvents

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    The solubility of pioglitazone hydrochloride (Form II) in <i>N,N</i>-dimethylacetamide, methanol, dimethyl sulfoxide, and acetic acid was determined at temperatures ranging from 283.15 to 323.15 K. The experimental data were correlated with the modified Apelblat equation, <i>λh</i> equation, van’t Hoff equation, ideal model, Wilson model, and nonrandom two-liquid model. Calculation results show that the <i>λh</i> equation, van’t Hoff equation, and the ideal model are more suitable in determining the solubility of pioglitazone hydrochloride (Form II) compared with the other three models. By using the van’t Hoff equation, the dissolution enthalpy, entropy, and molar Gibbs free energy of pioglitazone hydrochloride (Form II) are predicted in different solvents

    Transformations among the New Solid-State Forms of Clindamycin Phosphate

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    An experimental study is undertaken to establish a transformation screen for the solid-state forms of clindamycin phosphate. The experimental study results in six novel crystalline forms: two solvates (with ethanol/water, methanol/water), one hydrate (Form III), and three polymorph forms. Further, all solid-state forms are characterized by various analytical techniques such as X-ray diffraction, differential scanning calorimetry, etc. Two polymorph forms (IV and VI) are selectively prepared by desolvation of the solvates (I and V). The solid-state desolvation results in the appearance of delamination of the 2D layers. Moreover, polymorph IV shows a clear polymorphic transition to a new polymorph form (polymorph II) above 165 °C. Phase transformations of the solid-state forms were also established by slurry conversions at 25 °C. These experiments suggest the reversible relationship between solvate I/V and hydrate Form III at different solvent mixtures. Through the aqueous dissolution test, it is also judged that polymorph II, IV, VI can transform to Form III in water at 25 °C. The conversion relationships among the six solid forms are illustrated

    Higher-Order Self-Assembly of Benzoic Acid in Solution

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    Benzoic acid forms hydrogen-bonded dimers in solution that further stack into tetramers by aromatic interactions. Both dimers and higher-order packing motifs are preserved in the resultant crystal structure. The finding hints at the significance in the hierarchy of intermolecular interactions in driving the self-association process in solution

    Glycine’s pH-Dependent Polymorphism: A Perspective from Self-Association in Solution

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    As a simple amino acid, glycine (Gly)’s polymorphism is pH-dependent. The α form is typically obtained from aqueous solution between pH of 4 and 9, while the γ is produced at either lower or higher pH. Formation of cyclic, hydrogen-bonded dimer in water is debated as a possible cause for the formation of the α form. To further understand the pH-dependent polymorphism, our current study examined the self-association of Gly in aqueous solutions under a wide range of pH, utilizing NMR, FTIR, and electronic calculation. The results indicate that glycine molecules form open, not cyclic, hydrogen-bonded dimers in water. It is revealed that the dimerization becomes significant between pH of 4 and 8 but remains trivial at the two pH extremes. The apparent connection between the pH-dependent polymorphism and self-association in solution implies that formation of the α form is driven by the dimerization, and moreover, charged molecular species at the extreme pH facilitate stabilization of γ nuclei

    Ultrasonic Irradiation and Seeding To Prevent Metastable Liquid–Liquid Phase Separation and Intensify Crystallization

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    During the crystallization of complex pharmaceutical molecules, a liquid–liquid phase (LLP) separation phenomenon may occur that could hinder crystallization processes and adversely affect the crystal quality and process robustness. In this study, the LLP separation behavior of a vanillin and water mixture was investigated using a hot-stage microscope and a cooling crystallization process. Thermodynamic stability of phases and the crystallization phase diagram including the metastable zone width, nucleation, and LLP separation were developed. The impact of ultrasound and seeding on LLP separation was investigated and used to optimize the crystallization process. Our results show that the LLP separation may exist in both the stable and metastable zones of the crystallization phase diagram. Ultrasound can effectively promote nucleation, narrow the metastable zone of LLP separation, and inhibit LLP separation within the concentration range of 3.8–4.8 g/100 g water. Moreover, ultrasonic crystallization was optimized to produce small, uniformly sized crystals in a reproducible manner, whereas seeding crystallization was able to grow larger crystals without obvious agglomeration. In the case of a vanillin aqueous solution, both the ultrasonic induced and seeding crystallization strategies were able to prevent LLP separation and improve process performance. These results would be of significant use in the crystallization of other pharmaceutical molecules in which LLP separation occurs

    Solubility and Thermodynamic Stability of the Enantiotropic Polymorphs of 2,3,5-Trimethyl-1,4-diacetoxybenzene

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    The solubility data of two polymorphs of 2,3,5-trimethyl-1,4-diacetoxybenzene (TMHQ-DA) in ethanol, 1-propanol, 2-propanol, and 1-butanol at various temperatures were experimentally measured using gravimetrical method and correlated by the modified Apelblat model and the van’t Hoff equation, respectively. Differential scanning calorimetry (DSC) and thermogravimetry (TG) analyses were performed to investigate the thermodynamic stability and the transition of the two forms of TMHQ-DA. An enantiotropic relationship was found between TMHQ-DA Form A and TMHQ-DA Form B, and the transition point between them was experimentally determined to be 314.50 ± 1 K. A thermodynamic model for estimation of the transition point was also derived, and the estimated results are satisfactorily consistent with the experimental values. Finally, the accuracy of the transition point obtained in this research was validated by the polymorphic transformation experiments monitored using Raman spectroscopy
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