16 research outputs found
Correlation of Solubility and Prediction of the Mixing Properties of Capsaicin in Different Pure Solvents
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
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
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
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 lnÂ(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
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
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
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
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
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
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