Recrystallization Solvent Research Articles

The propensity of recrystallization solvents to form solvates

Using statistical analysis of Cambridge Structural Database (CSD) to investigate propensity of solvent towards solvate formation.

Evaporative Drying Induced Self-Assembly of Epicuticular Wax: A Biomimetic Approach in Tuning Surface Roughness.

Epicuticular wax is an example of a naturally created functional material that forms a layer on the outermost surface of plants with the objective to protect them from adverse environmental conditions, such as UV-solar radiation, uncontrolled water loss, microbial attacks, and so forth. Their functionalities are often attributed to the chemical composition of the wax as well as the physical structuration formed by the wax crystals on the surface. With this work, we present a simple, one-step biomimetic approach to replicate similar surface structures, on model substrate, using wax extracted from Euphorbia Cerifera (Candelilla wax). First, we describe formation of structured wax due to self-assembly induced by evaporative drying on quartz plates. Subsequently, we highlight the fundamental physical parameters required to tune the surface morphology. Our experiments reveal that it is possible to achieve considerably diverse surface morphologies depending on the solvent properties and deposition temperature. This diversity is due to the kinetics of recrystallization of wax during evaporation of solvent which, in turn, is primarily driven by the solubility of wax as well as evaporation rate of the solvent. Thus, the final morphology that we obtain is an interplay between recrystallization kinetics and solvent evaporation. Additionally, the degree of crystallinity of the structured films could also be tuned by solvent polarity. Surprisingly, X-ray diffraction indicates that the crystalline structure at the molecular level remains similar to that of bulk Candelilla wax. Our results provide fundamental insights into the replication of epicuticular wax films and identification of tuning parameters to obtain different surface morphologies with the same wax material for potential bioinspired multifunctional coatings in cosmetic applications.

Synthesis of L-Lactide from Lactic Acid and Production of PLA Pellets: Full-Cycle Laboratory-Scale Technology.

Lactide is one of the most popular and promising monomers for the synthesis of biocompatible and biodegradable polylactide and its copolymers. The goal of this work was to carry out a full cycle of polylactide production from lactic acid. Process conditions and ratios of reagents were optimized, and the key properties of the synthesized polymers were investigated. The influence of synthesis conditions and the molecular weight of lactic acid oligomers on the yield of lactide was studied. Lactide polymerization was first carried out in a 500 mL flask and then scaled up and carried out in a 2000 mL laboratory reactor setup with a combined extruder. Initially, the lactic acid solution was concentrated to remove free water; then, the oligomerization and synthesis of lactide were carried out in one flask in the presence of various concentrations of tin octoate catalyst at temperatures from 150 to 210 °C. The yield of lactide was 67-69%. The resulting raw lactide was purified by recrystallization in solvents. The yield of lactide after recrystallization in butyl acetate (selected as the optimal solvent for laboratory purification) was 41.4%. Further, the polymerization of lactide was carried out in a reactor unit at a tin octoate catalyst concentration of 500 ppm. Conversion was 95%; Mw = 228 kDa; and PDI = 1.94. The resulting products were studied by differential scanning calorimetry, NMR spectroscopy and gel permeation chromatography. The resulting polylactide in the form of pellets was obtained using an extruder and a pelletizer.

Ellagic Acid from Hull Blackberries: Extraction, Purification, and Potential Anticancer Activity.

Ellagic acid (EA) is present at relatively high concentrations in many berries and has many beneficial health effects, including anticancer properties. To improve the development and utilization of blackberry fruit nutrients, we divided Hull blackberry fruits into five growth periods according to color and determined the EA content in the fruits in each period. The EA content in the green fruit stage was the highest at 5.67 mg/g FW. Single-factor tests and response surface methodology were used to optimize the extraction process, while macroporous resin adsorption and alkali dissolution, acid precipitation, and solvent recrystallization were used for purification. The highest purity of the final EA powder was 90%. The anticancer assessment results determined by MTT assay showed that EA inhibited HeLa cells with an IC50 of 35 μg/mL, and the apoptosis rate of the cells increased in a dose-dependent manner, with the highest rate of about 67%. We evaluated the changes in the mRNA levels of genes related to the EA-mediated inhibition of cancer cell growth and initially verified the PI3K/PTEN/AKT/mTOR pathway as the pathway by which EA inhibits HeLa cell growth. We hope to provide a theoretical basis for the deep exploration and utilization of this functional food.

Study of dabigatran etexilate polymorphs for improved manufacturing processability

In the present work on anhydrous form-I and tetrahydrate form of Dabigatran etexilate a comparative study was done to seek a polymorph which will perform better in downstream processing and dissolution. Anhydrous form I of Dabigatran etexilate used in this study is having a needle shape. Tetrahydrate form was recrystallized from the anhydrous form I by solvent recrystallization using a slow evaporation method with acetone at NMT 25 °C, 2–8 °C, and −20 °C. The crystal shape of recrystallized tetrahydrate form was tabular. Scanning electron microscopy (SEM) was used to confirm the shape of crystals. Powder X-ray Diffraction (PXRD), Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TGA), and Fourier Transform Infrared Spectroscopy (FTIR) analysis confirmed polymorphic change. Flow characterization indicates that tetrahydrate has better bulk density, tapped density, Hausner ratio, and Cars index than anhydrous form I. Kawakita analysis shows that tetrahydrate has better compactibility and lesser cohesive nature than anhydrous form I. Heckel plots indicates tendency of tetrahydrate form to undergo plastic deformation linearly as pressure increases compared to anhydrous form I. The tensile strength of tetrahydrate is better than anhydrous form I and it also have a lesser tendency for capping and lamination at higher compression pressure. A dissolution study in USP dissolution media for dabigatran etexilate showed that tetrahydrate has a higher dissolution rate than anhydrous form I which is also backed by higher solubility. Overall, the tetrahydrate form can be preferred over the anhydrous form I during polymorph selection.

Crystal Structure, Hirshfeld Analysis, and DFT Calculations of Three Trinuclear Cu(II) Polymorphs

The crystal structure of the ferromagnetically-coupled CuII3−pyrazolato complex, (Bu4N)2[Cu3(μ3-Cl)2(μ-4-NO2-pz)3Cl3] (1a, pz = pyrazolato anion), was originally determined in the triclinic P-1 space group. By varying the recrystallization solvent and temperature, two additional true polymorphs were crystallized in the monoclinic P21/n (1b) and orthorhombic Pbca (1c) space groups. Comparison of the metric parameters of the three polymorphs revealed only minor variations in their bond lengths and angles but clearly distinguishable packing patterns. The DFT calculations showed that, in vacuum, 1a had the lowest energetic minimum (also the densest of three polymorphs), whereas 1b and 1c lay at 6.9 kcal/mol and 7.8 kcal/mol higher energies. The existence of isolable 1b and 1c is, therefore, attributed to the intermolecular interactions analyzed by the Hirshfeld methods.

Selected Tricyclic Fused Systems: Host Behavior in the Presence of Mixed Xylenes and Ethylbenzene

Two tricyclic fused host systems, namely, N,N′-bis(5-phenyl-5-dibenzo[a,d]cycloheptenyl)ethylenediamine H1 and N,N′-bis(5-phenyl-10,11-dihydro-5-dibenzo[a,d]cycloheptenyl)ethylenediamine H2, were investigated for their selectivity behavior in xylene isomer (o-Xy, m-Xy, p-Xy) and ethylbenzene (EB) mixtures. H1 only formed a complex with p-Xy, and H2 only with o-Xy, in single solvent recrystallization experiments. When H1 and H2 were recrystallized from equimolar mixtures of every combination of the four organic solvents, contrasting host selectivities were observed: H1 favored p-Xy and H2 favored o-Xy. High selectivities for p-Xy (87.2–88.7%) were noted in equimolar binary experiments with H1, while H2 furnished crystals with 91.3% o-Xy from an o-Xy/p-Xy mixture. Remarkably, only the apohost was recovered when p-Xy or o-Xy (for H1 or H2) was absent from the mixtures. Constructed selectivity profiles affirmed observations from these equimolar experiments. Thermal analyses demonstrated that H1·p-Xy was significantly less stable than H2·o-Xy, and SCXRD analyses explained these observations: p-Xy, in its complex with H1, was accommodated in wide open channels and did not experience any noncovalent interactions with the host molecule; on the other hand, o-Xy in H2 was bound tightly in near-discrete cages and, furthermore, interacted with H2. Both host compounds demonstrated the ability to separate various of the mixtures reported in this work.

Heat-induced solid-state polymorphic transition of 4,4′,5,5′- tetranitro-1H,1′H-[2,2′-biimidazole]-1,1′-diamine (DATNBI)

Polymorphs of energetic materials generally exhibit distinct features, such as density, thermal stability, sensitivity, and detonation performance. These features are important in determining the appropriate applications of a given polymorph. To understand the thermal stability of new high explosive 4,4′,5,5′-tetranitro-1H,1′H- [2,2′-biimidazole]-1,1′-diamine (DATNBI), we systematically investigated its polymorphic transition (PT) under thermal stimulation and discovered a novel stable γ form of DATNBI. The results showed that the solid-solid PT path was β→α→γ. In this study, the three polymorphs of DATNBI were prepared through solvent recrystallization, and their PT processes in solution were explored. Crystal structure analysis of γ-DATNBI suggested that its special cross-cross grid crystal packing may be the main reason for its stable existence at room temperature and its lack of PT process before chemical decomposition, which starts at 240 ​°C. To further explore the PT process of DATNBI, the solid phase transition mechanism of DATNBI was analyzed using non-isothermal kinetics. The results demonstrated that the two high-temperature PT processes—β→α and α→γ—were not single-step reactions but complex multi-step reactions. The PT activation energy of the β→α process was slightly higher than that of the α→γ process. In addition, the influences of different polymorphs on the performance of DATNBI were explored. The results revealed that safety and detonation performance should decrease as a result of the incorporation of γ-DATNBI. This study contributes to understanding the PT behavior and the crystal structure evolutionary mechanism of DATNBI. This study provides practical support for formula design, process condition selection, and thermal stability evaluation of DATNBI explosives.

Mechano-responsive D–A luminogen based on bisarylic methanone derivative with brightly tricolored mechanochromic luminescence

A new luminogen PTZ-BZ-DBF bearing an electron donor phenothiazine unit and an electron acceptor carbonyl group is designed and synthesized. This molecule adopts highly twisted molecular conformation and exhibits intramolecular charge transfer (ICT), effective solid-state luminescence, and high contrast mechanofluorochromic (MFC) properties. The as-prepared powders show bright yellow-green fluorescence. Under conditions of external mechanical stimulation, the color changes to bright orange-red, and a red shift of 87 nm is observed in the emission spectral profile. Meanwhile, the solid-state luminescence efficiency increases from 20.5% to 28.5%. It is different from general MFC materials, when fumed using DCM vapor or annealed at 150 °C, the fluorescence peaks blue shift to approximately 560 nm, and the yellowish-emitting Y-powders are obtained. The ground solids and Y-powders can be converted to the as-prepared solid powders following the process of solvent recrystallization. Thus, tricolor switching is realized. The results obtained using the PXRD and DSC techniques indicate that the MFC phenomenon can be attributed to the process of crystalline-to-amorphous transition. The red shift of the PL spectra is attributed to the planar intramolecular charge transfer (PICT) process induced by conformational planarization in response to external forces.

Twisted phenothiazine-terminated bisarylic methanone π-architecture exhibiting high-contrast mechanofluorochromism

Bisarylic methanone π-architecture PTZ-BZ-DBT with carbonyl group as the acceptor and phenothiazine as the donor was synthesized. Theoretical calculations and photophysical properties in solution demonstrated that the obtained donor-acceptor (D-A) type molecule PTZ-BZ-DBT adopts a molecular conformation of high distortion and significant intramolecular charge transfer (ICT) behavior, which endows it not only with intense solid-state luminescence but also with a high-contrast mechanofluorochromic (MFC) feature. The original as-prepared samples of PTZ-BZ-DBT display bright yellow-green fluorescence. When the as-prepared samples are ground, the ground solid powders exhibit orange-red fluorescence are obtained. Accordingly, during the grinding process, the emission wavelength of the solid powders red shifts from 518 nm of the as-prepared samples to 617 nm of the ground samples, and thus a spectral shift of 99 nm is observed. Different from general MFC materials, if the ground solid powders are fumed by DCM vapor or annealed at 150 °C, the fluorescence peaks blue shift to about 564 nm, and the yellow-emitting Y-powders are gained. However, the ground samples can be converted into the as-prepared solid powders through solvent recrystallization; thus tri-color switching is obtained. The PXRD, fluorescence lifetimes, DSC and the spectral analysis demonstrate that the remarkable MFC nature of PTZ-BZ-DBT is attributed to crystalline-to-amorphous transition. Further, the red shift of the fluorescence band after grinding can be ascribed to the extension of conjugate length and subsequent planar intramolecular charge transfer (PICT) induced by conformational planarization under external forces.

Recrystallization solvent-dependent elastic/plastic flexibility of an n-dodecyl-substituted tetrachlorophthalimide.

A long alkyl-chained organic molecule, 4,5,6,7-tetrachloro-2-dodecylisoindoline-1,3-dione (1), was crystallized into needle-like crystals in dichloromethane (1DCM) or plate-like ones in tetrahydrofuran (1THF) depending on the recrystallisation solvent. X-ray crystallography analyses revealed the alkyl chains of the molecules, in which they were assembled differently, with the former responding flexibly bendable and elastic deformation, and the later being a permanent plastic one by external mechanical stress. The elastic modulus (E) and hardness (H) indicating both compliant and soft nature, reflecting their weak interaction in crystals, were quantified from the nano-indentation test.

A novel heterometallic platinum(ii)–silver(i) alkynyl complex [PtAg(dppm)2(CCC6H4COOCH3-4)2Cl] with two crystal morphologies exhibiting morphology-dependent photoluminescence

A novel complex [PtAg(dppm)2(CCC6H4COOCH3-4)2Cl] with two crystal morphologies as rod-like and prism was separately obtained by manipulating the recrystallization solvents. They exhibit glamorous morphology-dependent photoluminescence.

Solvent Recrystallization‐Enabled Green Amplified Spontaneous Emissions with an Ultra‐Low Threshold from Pinhole‐Free Perovskite Films

AbstractGreen and amplified spontaneous emissions with low thresholds are crucial for the development of solution‐processable perovskite light sources. Although mixed‐cation CsPbBr3 perovskites are highly promising, pinholes are inevitably formed during the spin‐coating process, which results in considerable optical losses. This study proposes a solvent recrystallization strategy to reduce the number of pinholes and enhance the crystallinity of (Cs, FA, MA)PbBr3/NMA (FA = CH(NH2)2, MA = CH3NH3, and NMA = C11H9NH3) films in a dimethyl sulfoxide gas environment. Amplified spontaneous green emissions are produced with a low threshold of 1.44 μJ cm−2 and a high net modal gain of 1176 cm−1. The reduced threshold is attributed to the relatively low propagation loss and suppressed Auger recombination, which results from the formation of a pinhole‐free surface and enlarged grain size. These results can be utilized in the development of high‐performance perovskite laser devices.

Influence of the Lewis basicity hardness of recrystallization solvents on the coordination sphere of the complex [Co(3,5-dinitrobenzoate-O,O′)2

Influence of the Lewis basicity hardness of recrystallization solvents on the coordination sphere of the complex [Co(3,5-dinitrobenzoate-<i>O</i>,<i>O</i>′)₂

Prior Likelihoods and Space-Group Preferences of Solvates

For a range of organic solvents, the likelihood of the solvent forming solvates has been estimated using the recrystallization solvent (RS) data in the Cambridge Structural Database (CSD). Although RS data are viewed with caution by some crystallographers, most of the likelihood estimates are shown to have good precision. Strong trends are apparent in the results. For example, high likelihoods are found for aromatic solvents with electron-withdrawing substituents and low likelihoods for acyclic aliphatic hydrocarbons. Results for different CSD subsets, such as organic and metalloorganic, are highly correlated. The likelihood that a solvent will form solvates is almost always higher when the solvent is part of a mixture than when it is pure. The likelihood of two solvents forming a heterosolvate (i.e., both solvents in the structure) can be well estimated by the product of the likelihoods of the solvents forming normal solvates (i.e., only one solvent in the structure). The space-group preferences of solvates vary significantly with the nature of the cocrystallized solvent. Those of nonsolvates vary significantly with the solvent(s) from which they were crystallized. Solvents with inversion centers favor solvate crystallization in centrosymmetric space groups, and solvents with 2-fold rotational symmetry promote crystallization in space groups with 2-fold proper rotational axes. The inclusion of cyclohexane and carbon tetrachloride in a lattice can facilitate crystallization in trigonal and tetragonal space groups, respectively. Our results can: (a) guide solvent selection when solvates are undesired; (b) assist in predicting solvate formation, e.g., using Bayesian algorithms; (c) assist in the choice of space groups for solvate crystal structure prediction; and (d) suggest ways in which solvent incorporation can be used to influence space groups.

Use of Bis(pyrrolidone)-Based Dicarboxylic Acids in Poly(ester–amide)-Based Thermosets: Synthesis, Characterization, and Potential Route for Their Chemical Recycling

In this study, we report on the synthesis and characterization of thermosets based on the renewable N,N′-octamethylene-bis(pyrrolidone-4-carboxylic acid) (BP-C8) and 1,3-bis(4,5-dihydro-2-oxazolyl)benzene (IAox). The BP-C8, having two pyrrolidone rings, is obtained via a bulk aza-Michael addition reaction of 1,8-diaminooctane with 2 equiv of itaconic acid using water as catalyst. Thermosets are prepared by mixing the desired ratio of BP-C8 with IAox, followed by thermal curing at 180 °C. The cross-link density of the thermosets is controlled by the usage of an excess of bis(2-oxazoline), and achievement of full conversion is confirmed by Fourier transform infrared spectroscopy. As anticipated, the glass transition temperature of the thermosets increases with increasing cross-linking density to values up to 100 °C. All thermosets are found to absorb water upon storage, resulting in a strong plasticizing effect and thus a suppression of the glass transition temperature. To assess the role of water on the thermo-mechanical properties, all thermosets are exposed to various relative humidities and their mechanical performance is evaluated. In general, we observe that the suppression in Tg under the influence of water facilitates a brittle-to-ductile transition as the Tg of the thermosets approaches room temperature. Additionally, in this study we demonstrate that hydrolysis of the ester bonds in the thermosets can be enforced at elevated temperatures in the presence of water, resulting in the liberation and migration of BP-C8 monomer. Interestingly, BP-C8 can readily be isolated by filtration as it crystallizes from water during cooling, thereby providing a promising route for its chemical recycling. Overall, these findings indicate that water plays a pivotal role in these poly(ester–amide)s as it functions as a catalyst in the BP-C8 synthesis, governs the thermal and mechanical properties of the thermosets, and opens up routes for chemical recycling of BP-C8 after hydrolysis as it acts as a recrystallization (co)solvent.

Spontaneous chiral resolution of N,N′-diarylsquaramides: Formation of various types of one-handed helical networks during crystallization

N,N′-Bis(ortho-substituted phenyl)squaramides afforded chiral crystals, in which squaramide molecules are arranged in one-handed helical networks, upon simple recrystallization. Three types of crystals with different helices were obtained, depending on the substituents or recrystallization solvent. Folded-type intermolecular hydrogen-bonding interactions of squaramides play a key role in forming the helical networks.

A Novel and Simple Approach for Extraction and Isolation of Curcuminoids from Turmeric Rhizomes

Turmeric (Curcuma longa L. Family: Zingiberaceae) is a widely cultivated spice in India and other Asian countries. Curcumin is the main coloring substance in Curcuma longa and two related compounds, demethoxycurcumin and bisdemethoxycurcumin are altogether known as curcuminoids. Turmeric is rich in curcuminoids, and recognized for their broad spectrum of biological activities. During isolation and purification of curcuminoids from oleo resin, the volatile oil present turmeric solubilizes curcumin creating problem in recrystallization process. To eliminate the interference of volatile oil and resolve the problem recrystallization, the present research work was undertaken. Various organic solvents and their combinations were tried for selective recrystallization of curcuminoids. Mixture of hot isopropyl alcohol: hexane (1:1.5) was found to be the best recrystallization solvent for purification of curcuminoids. The identity of curcuminoids was further confirmed by thin layer chromatography (TLC) and Fourier Transform Infra-Red spectroscopy (FTIR). The total curcumin content of crude curcuminoid powder was found to be 76.82% W/W whereas in recrystallized powder the purity was increased to 99.45% W/W.

Conformational polymorphs of a novel TCNQ derivative carrying an acetylene group

TCNQ is one of the most important organic acceptors and lots of its derivatives have been prepared. However the reports on their crystal polymorphs are limited to their complexes, and simple polymorphs of TCNQ derivatives are uncommon. We succeeded in preparation of a novel TCNQ derivative, 2,2'-(2-(prop-2-yn-1-yloxy)cyclohexa-2,5-diene-1,4-diylidene)dimalononitrile, having a propynyloxy group on a substituent. This compound was found to have two crystal polymorphs depending on a solvent for recrystallization. In polymorph I, dimeric hydrogen bonds are formed between acetylenic hydrogens and cyano nitrogens with the molecule in an inversion symmetry. While, in polymorph II, the molecules make intermolecular hydrogen bonds between acetylenic hydrogens and cyano nitrogens with the molecule in 21 symmetry, forming a hydrogen bonded molecular helix along the b axis. Besides patterns of the intermolecular hydrogen bonds, difference was recognized in conformation of propynyloxy group. The molecule has an anti conformation in polymorph I and a gauche conformation in polymorph II. DFT calculation indicates that the anti conformer is less stable than the gauche one. But a solvation model suggests the anti conformer is estimated to be more stable in a toluene solution.

Preparation and Characterization of Cyclotrimethylenetrinitramine (RDX) with Reduced Sensitivity

The internal defects and shape of cyclotrimethylenetrinitramine (RDX) crystal are critical parameters for the preparation of reduced sensitivity RDX (RS-RDX). In the current study, RDX was re-crystallized and spheroidized to form the high-quality RDX that was further characterized by purity, apparent density, size distribution, specific surface area, impact sensitivity, and shock sensitivity. The effects of re-crystallization solvent on the growth morphology of RDX crystal were investigated by both theoretical simulation and experiment test, and consistent results were obtained. The high-quality RDX exhibited a high purity (≥99.90%), high apparent density (≥1.811 g/cm3), spherical shape, and relatively low impact sensitivity (6%). Its specific surface area was reduced more than 30%. Compared with conventional RDXs, the high-quality RDX reduced the shock sensitivities of PBXN-109 and PBXW-115 by more than 30%, indicating that it was a RS-RDX. The reduced sensitivity and good processability of the high-quality RDX would be significant in improving the performances of RDX-based PBXs.