Preparative resolution of (±)-trans-1,2-diaminocyclohexane by means of preferential crystallization of its citrate monohydrate

Even if (±)-trans-1,2-diaminocyclohexane crystallizes as a conglomerate, its low melting point (?10 °C) and its sensitivity to light, CO₂, O₂, and moisture make this molecule difficult to resolve. It has been shown that the citrate monohydrate of this compound crystallizes as a stable conglomerate with a high thermal stability (up to 163 °C) with no drawbacks as to those listed above for the pure diamine. The crystal structure of this salt, resolved by single crystal X-ray diffraction, reveals structural features consistent with the thermal stability of this phase. Several preferential crystallization attempts (AS3PC) have been performed at a 100 ml scale and at a one liter scale in water with and without additives. Finally a productivity of 40 g per batch per liter of solvent per hour was achieved with a crude enantiomeric purity better than 90%. A simple recrystallization of the crude crops gives quantitatively the crystalline compound with an ee >99% proving the absence of partial solid solution at room temperature.     

Monolayers of an amphiphilic para-carboxy-calix[4]arene act as templates for the crystallization of acetaminophen

The title compound, 5,11,17,23-tetra-carboxy-25,26,27,28-tetradodecyloxy-calix[4]arene, 1, has been studied at the air–water interface, self-assembled as Langmuir monolayers, for its ability to interact with an active pharmaceutical ingredient (API), acetaminophen (APAP), and to initiate its crystallization. The Π/A isotherm study shows that there is a clear interaction between 1 and APAP causing an expansion of the monolayer. In addition to the known phase transition occurring at a surface tension of 38 mN m^?1, an additional kink is observed in the compression isotherm for concentrations of APAP above 40 mM suggesting that this API is causing an additional phase transition of the monolayer. Interface-initiated crystallization studies show that the presence of a monolayer spread on a supersaturated solution of APAP (26 g L^?1) triggers this API crystal growth from the interface. The transfer of 1-based monolayers on glass surfaces has been carried out using the Langmuir–Blodgett technique. The so-produced monolayers have been shown to template the crystallization of APAP. LB films of 1 have characterized using imaging and spectroscopic ellipsometry. The results suggest that each monolayer has an average thickness of 18 Å, which is consistent with the molecular structure of 1 self-organized parallel to the interface with the alkyl chains pointing out parallel to the axis of the macrocycle and without interdigitation of the alkyl chains. The presence of APAP in the subphase during the LB transfer causes a limited but relevant increase in the layer thickness. The study of the capabilities of the LB films to initiate crystallization of APAP is also demonstrated showing the influence of the monolayer packing on the quantity of formed crystals.     

Separability of diastereomer salt pairs of 1-phenylethylamine with enantiomeric 2-substituted phenylacetic acids by fractional crystallization,and its relation to physical and phase properties

The separations of three pairs of the title diastereomer salts by crystallization have been investigated, as examples of the ‘classical’ resolution of enantiomers via conversion to diastereomers. All three fractional crystallizations occurred relatively slowly, and appeared to be thermodynamically controlled with the outcomes corresponding with the key features of the phase diagrams. In one case, X = CH₃, the salts–solvent ternaries exhibited eutonic behaviour, and the direction of isomeric enrichment changed markedly on passing through the eutonic composition. These salts also formed solid solutions on crystallization, but high separation factors were nevertheless recorded. In another example, X = OH, the ternaries indicated near-ideal solubility behaviour of the salt mixtures, and the separations by crystallization again corresponded. The stability and solubility ordering of the diastereomer pair X = CH₃ in the crystallization temperature range 5–50 °C were determined by the temperature-dependent entropic contribution to the free energy. Our results show that the use of simple surrogate parameters, such as the difference in the enthalpies of formation of the two salts, cannot be used as a reliable guide to their separability by crystallization. More rapid crystallizations are likely to be additionally influenced by kinetic factors, and their investigation is planned in future work.     

Low-temperature adiabatic calorimetry of salol and benzophenone and microscopic observation of their crystallization: finding of homogeneous-nucleation-based crystallization

An adiabatic calorimetric and direct microscopic observation of crystallization at low temperatures was performed for salol and benzophenone. Both of the materials in the supercooled-liquid phase exhibited a low-temperature crystallization proceeding in the glass-transition temperature ( T_g) region. The crystallization was observed to proceed as the advance of the crystal front into the liquid phase, and stopped suddenly atT =  227 K and T ≈  215 K for salol and benzophenone, respectively. This anomalous temperature dependence of the crystal-growth rate is a characteristic feature of the homogeneous-nucleation-based (HNB) crystallization, which has been reported for o -terphenyl and triphenylethylene, and the presently observed low-temperature crystallization in salol and benzophenone was concluded to be the HNB crystallization, in which the crystal growth is brought about by the coalescence of crystal nuclei to the crystalline phase on the liquid-crystal interface. The substances exhibiting the HNB crystallization were revealed to have almost the same characteristics with respect to configurational entropy, and undergo the HNB crystallization in the same range of temperature normalized by T_g. These results indicate that the HNB crystallization is potentially a universal phenomenon in fragile liquids, and imply that the process is closely related to the liquid structure changing with temperature.     

Enantiomeric resolution of albuterol sulfate by preferential crystallization

Albuterol is a β₂-adrenoceptor agonist prescribed for the treatment of bronchial asthma; it exists as a racemate and its bronchodilator activity resides in the (R)-isomer or levalbuterol. The aim of this study was to determine a methodology that would separate the enantiomers of albuterol by preferential crystallization after a conglomerate is identified within its derivatives. We found that albuterol sulfate behaves as a conglomerate showing the characteristic α_x-value = 2 (mole fraction solubility ratio of racemate vs enantiomer), the V-shaped ternary phase diagram and the preferential crystallization by seeding with the pure enantiomer. On the basis of these characteristics, we separated the enantiomers by entrainment, and crystallizing out a saturated methanolic solution of albuterol sulfate at 15 °C.     

A new solid electrolyte to fill the gap between low temperatures and high temperatures SOFC materials?

According to TG/DTA analysis, the new pyrochlore-type compound K_0.88H_1.12Nb₂O₆·1.58H₂O (Fd-3 m, a = 10.645(4) Å at 300 K) loses crystallization water on heating up to 773 K, but retains –OH hydrogen. Impedance spectroscopy in non-humidified air suggests the material is promising for SOFC applications at intermediate temperatures because the bulk conductivity values reach 10⁻² S/cm at 623 K.     

Morphosynthesis of poly(ether ketone) by reaction-induced crystallization during polymerization

Morphology control of poly(ether ketone) (PEK) was examined by using the crystallization during the nucleophilic aromatic substitution reaction of potassium salt of 4-fluoro-4′-hydroxybenzophenone. Polymerizations were carried out at 290 °C. The PEK was obtained as precipitates and its morphology was highly influenced by the polymerization condition such as the solvent, the concentration and the polymerization time. High crystalline spindle-like crystals were obtained by the polymerization in diphenyl sulfone (DPS) at a concentration of 5.0% for 2 h with the yield of 86%. The average length and width were 1.4 μm and 300 nm respectively, and the maximum thickness was 130 nm. The surface was not smooth and it was hilly. The spindle-like crystal was likely consisted of multilayered lamellae comprised of the microcrystallites. The molecules were oriented perpendicular to the lamella. The polymerization in DPS at a higher concentration of 10.0% afforded the networks of nanofibres, of which the diameter was 100–250 nm. The obtained PEK precipitates possessed excellent thermal properties.     

The Influences of Elastomer toward Crystallization of Poly(lactic acid)

Poly (lactic acid)/elastomer blends were prepared via direct injection molding. In non-isothermal crystallization scan, the crystallinity of PLA increased with a decrease in the heating and cooling rate. The melt crystallization of PLA appeared in the low cooling rate (1, 5 and 7.5°C/min). The presence of elastomer tended also to increase the crystallinity of PLA. However, it started to decrease in 30% of elastomer. It was also showed by the decreasing of cold crystallization activation energy. Elastomer also gave plasticization effect in PLA properties. Thermal treatment through annealing completed after 1 h at 80 °C. In isothermal crystallization scan, the cold crystallization rate increased with increasing crystallization temperature in the blends. The Avrami analysis showed that at low temperatures, the cold crystallization had two regime processes whereas at high temperature only one stage was observed.     

The thioantimonate anion [Sb4S8]4− acting as a tetradentate ligand: Solvothermal synthesis,crystal structure and properties of {[In(C6H14N2)2]2Sb4S8}Cl2 exhibiting unusual uniaxial negative and biaxial positive thermal expansion

The new compound {[In(C₆H₁₄N₂)₂]₂Sb₄S₈}Cl₂ was prepared under solvothermal conditions reacting InCl₃, Sb and S using 1,2-trans-diaminocyclohexane as solvent and structure directing molecule. The compound crystallizes in the monoclinic space group C2/c with a = 29.0259(12), b = 6.7896(2), c = 24.2023(12) Å, β = 99.524(4)°, V = 4703.9(3) ų. The central structural motif is the thioantimonate(III) anion [Sb₄S₈]^4? acting as a tetradentate ligand thus joining two symmetry related In³⁺ centered complexes. This binding mode was never observed before for the [Sb₄S₈]^4? anion. The optical band gap was determined as 2.03 eV in agreement with the red color of the compound. The thermal decomposition was monitored with in-situ X-ray diffraction experiments. After the emission of the amine molecules an amorphous intermediate is formed followed by the crystallization of InSbS₃ which is stable up to about 590 °C. On further heating, InSbS₃ is destroyed and reflections of γ-In₂S₃ appear being contaminated with some elemental Sb. Temperature dependent in-situ X-ray powder diffractometry performed between 30 and 220 °C reveals an unusual reversible negative and positive thermal expansion. The decrease of the a-axis in the temperature range is about 0.74 Å and the increase of the c-axis ca. 0.54 Å. Interestingly, the b-axis exhibits also a thermal expansion, i.e., a biaxial positive and an uniaxial negative thermal expansion coexist which is very unusual. The relative negative expansion coefficients for the a-axis of ?194 × 10^?6K^?1 (30–120 °C) and ?82 × 10^?6K^?1 (120–220 °C) are in the region of so-called colossal thermal expansion.     

Magneto-structural correlation and low temperature heat capacity of a Mn (III) quadridentate Schiff-base coordination compound

A new Mn (III) Schiff-base coordination compound, [Mn(L)(NCS)]₂ (H₂L = N,N′-bis(5-chlorosalicylidene)-1,2-diaminoethane), has been synthesized and characterized structurally and magnetically. The target compound is a phenoxo-bridged dimeric compound with the isothiocyanate coordinating in a usual bent mode. A magnetic susceptibility study reveals that the target compound exhibits antiferromagnetic intra-dimer coupling between Mn (III) ions. The low temperature heat capacity of the compound over the temperature range (2 to 300) K has been measured using the heat capacity option of a Quantum Design Physical Property Measurement System (PPMS). The thermodynamic functions in the experimental temperature range have been determined by curve fitting. The standard entropy and enthalpy of the as-prepared compound at T = 298.15 K have been calculated to be (924.52 ± 10.17) J · K⁻¹ · mol⁻¹ and (133.47 ± 1.47) kJ · mol⁻¹, respectively.     

Enhancing Stability and Purity of Crude Chitinase of Achatina fulica by Crystallization

A crystallization method was developed to enhance the purity and stability of hydrolase mixtures from the digestive gland of the snail Achatina fulica, as demonstrated by chitinase activity. Crude chitinase was concentrated by freeze drying and then crystallized at 10 °C. Crystal formation was observed under the microscope. The best concentration for crystallization was obtained with 1.5-fold concentrated crude chitinase. Crystallization enhanced the chitinase specific activity from 0.87 U mg^-1 to 0.95 U mg^-1. The loss of chitinase activity from liquid and crystals of crude chitinase on four days storage at 10 °C was 83.0% and 17.7%, respectively. It was concluded that the crude chitinase crystals showed a significant increase in stability and purity.     

Preferential crystallization in an unusual case of conglomerate with partial solid solutions

Ethanolamine mandelate (E.M.) crystallizes as a stable conglomerate and has been found to form partial solid solutions. The crystal structure of the pure enantiomer has been solved from single-crystal X-ray diffraction. In order to determine the extreme compositions of the partial solid solutions in equilibrium (87% ee), the isothermal ternary section in the system [(+)-E.M.–(−)-E.M.–(ethanol–water azeotropic mixture)] was established at 25 °C. Several consecutive preferential crystallization attempts (AS3PC method) were undertaken between T_B = 41 °C (starting temperature) and T_F = 25 °C (final temperature) on a 2-L scale.We initially expected to obtain crude crops whose enantiomeric purities would be close to that defined by the isothermal ternary phase diagram (T_F). In fact, the filtered solid phases are of lower enantiomeric excesses: ca. 62% ee. The monitoring of the mother liquor composition over the course of the entrainment shows that the enantiomeric composition of the filtered solid is related to the metastable equilibria involved in the preferential crystallization.     

Synthesis,spectroscopic, structural and thermal characterizations of [(C7H6NO4)2TeBr6·4H2O]

Tellurium (IV) complexes with pyridine-2,6-dicarboxylate ligand were synthesized by slow evaporation from aqueous solutions yielding a new compound: [(C₇H₆NO₄)₂TeBr₆·4H₂O]. The structure of this compound was solved and refined by single-crystal X-ray diffraction. The compound is centrosymmetric P2₁/c (N°: 14) with the parameters a = 8.875(5) Å, b = 15.174(5) Å, c = 10.199(5) Å, β = 94.271° (5) and Z = 2. The structure consists of isolated H₂O, isolated [TeBr₆]^2? octahedral anions and (pyridine-2,6-dicarboxylate) [C₇H₆NO₄]⁺ cations. The stability of the structure was ensured by ionic and hydrogen bonding contacts (N–H?Br and O–H?Br) and Van-Der Walls interaction. The thermal decomposition of the compound was studied by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The FTIR and Raman spectroscopy at different temperatures confirm the existence of vibrational modes that correspond to the organic, inorganic and water molecular groups. Additionally, the UV–Vis diffuse reflectance spectrum was recorded in order to investigate the band gap nature. The measurements show that this compound exhibits a semiconducting behavior with an optical band gap of 2.66 eV.     

Synthesis,structure and thermochemical study of a cobalt energetic coordination compound incorporating 3,5-diamino-1,2,4-triazole and pyridine-2,6-dicarboxylic acid

An energetic coordination compound [Co₂(C₂H₅N₅)₂(C₇H₃NO₄)₂(H₂O)₂]·2H₂O (Hdatrz(C₂H₅N₅) = 3,5-diamino-1,2,4-triazole, H₂pda(C₇H₅NO₄) = pyridine-2,6-dicarboxylic acid) has been synthesized and characterized by elemental analysis, chemical analysis, IR spectroscopy, single-crystal X-ray diffraction and thermal analysis. X-ray diffraction analysis confirmed that the compound possessed a di-nuclear unit and featured a 3D super-molecular structure. Furthermore, a reasonable thermochemical cycle was designed based on the preparation reaction of the compound and the standard molar enthalpy of dissolution of reactants and products was measured by the RD496-2000 calorimeter. Finally, the standard molar enthalpy of formation of the compound was determined to be −(2475.0 ± 3.1) kJ · mol⁻¹ in accordance with Hess’s law. In addition, the specific heat capacity of the compound at T = 298.15 K was determined to be (1.13 ± 0.02) J · K⁻¹ · g⁻¹ by RD496-2000 calorimeter.     

Crystallization kinetics of polypropylene/ethylene–octene copolymer blends

Blends of polypropylene and ethylene–octene copolymers (EOC) were investigated by transmission electron microscopy, optical microscopy and differential scanning calorimetry (DSC). The main focus was on phase morphology and crystallization for blends containing EOC with different octene content (28, 37 and 52 wt.%). Also, for a given octene content (37 wt.%), the effect of molecular weight (115, 180, 229k) of EOC on morphology was observed. The largest particles were found in the blend with EOC-28 and the smallest with EOC-52. This blend with the smallest particles exhibits the fastest crystallization kinetics by two independent methods, optical microscopy and DSC. This behavior was explained by a model. Crystallizing polypropylene lamellae have to travel a longer distance going around large particles, which slows down overall crystallization growth rate. In the case of smaller particles, the obstacles are smaller and the crystallization is faster.     

Structural evolution of poly(lactic acid) upon uniaxial stretching investigated by in situ infrared spectroscopy

Structural evolution of poly(lactic acid) (PLA) upon uniaxial stretching was studied with in-situ polarized infrared spectroscopy measurements, and its structural change affected by annealing was also investigated. Band shifting was used to reflect the structural ordering process. It was found that the band at 1302 cm⁻¹ always moves to low wavenumbers before crystallization, indicating the occurrence of intermolecular packing ordering. However, the band at 869 cm⁻¹ shifts to high wavenumbers, which is related to the transition from the amorphous phase to the ordered phase. Interestingly, during stretching, the shifting for the band at 1302 cm⁻¹ always occurs before that for the lower wavenumber band, whereas these two band shifts take place simultaneously under annealing. Based on the different characteristics of the structural evolution under stretching and annealing processes, a critical temperature was found at around 63 °C, which influences the effect weight of kinetic and thermodynamic factors to the crystallization behavior. The effect of the drawing temperature on crystallization and mechanical property of PLA films was also analyzed.     

The morphology and non-isothermal crystallization characteristics of poly(trimethylene terephthalate)/BaSO4 nanocomposites prepared by in situ polycondensation

A simple method was developed for preparing nano-BaSO₄ suspension by reacting H₂SO₄ with Ba(OH)₂ in 1,3-propanediol (PDO). The zymotechnics 1,3-propanediol and newly prepared nano-BaSO₄ suspension were used for fabricating PTT/BaSO₄ nanocomposites by in situ polymerization. The size distribution curves revealed that most of the nano-BaSO₄ particles in PDO have a diameter of 15–23 nm. Transmission electron microscopy (TEM) showed that BaSO₄ disperses uniformly in PTT matrix when BaSO₄ content was no more than 12 wt%. The non-isothermal crystallization behavior was studied quantitatively by modified Avrami equation and Ozawa theory. Both theories can successfully describe the non-isothermal crystallization of pure PTT and PTT/nano-BaSO₄ composites. The crystallinity and crystallization rate of nanocomposites was greatly increased by addition of BaSO₄. The maximum enhancement of crystallization rate for the nanocomposites was observed in nanocomposites containing about 12 wt% BaSO₄ with a range of 2–16 wt%, which was confirmed by both Avrami crystallization rate parameter (Z_c) and Ozawa crystallization rate parameter logK(T). The Avrami and Ozawa mechanism exponents, n and m of the nanocomposites, were higher than those of neat PTT, suggesting more complicated interaction between molecular chains and the nanoparticles that caused the changes of the nucleation mode and the crystal growth dimension. Effective activation energy calculated from the Friedman formula was reduced as nano-BaSO₄ content increased, suggesting that the nano-BaSO₄ made the molecular chains of PTT easier to crystallize during the non-isothermal crystallization process. The polarizing micrographs showed that much smaller or less perfect crystals formed in composites due to the interaction between molecular chains and nano-BaSO₄ particles.     

Design,synthesis, and fungicidal activity of novel 1,3,4-oxadiazole derivatives

Employing the intermediate derivatization method (IDM), a series of 1,3,4-oxadiazole derivatives containing arylpyrazoloxyl moiety were designed and synthesized. In vitro bioassays showed that these compounds have moderate to significant fungicidal activity against rice sheath blight and sorghum anthracnose. Furthermore, compound 20 is a promising fungicide for further development.     

An improved synthesis of 3-[3-(trifluoromethyl)-3H-1,2-diazirin-3-yl]aniline: A key intermediate in the synthesis of photoaffinity probes

An improved synthesis of 3-[3-(trifluoromethyl)-3H-1,2-diazirin-3-yl]aniline, achieving an overall yield of 38% over seven steps is reported. Only three chromatographic separations were needed and the preparation of ～0.7 g of the target compound was demonstrated. The stability of the diazirine in solution at room temperature while exposed to ambient light was studied. No significant degradation of the compound was observed over the course of five weeks in a 130 mM sample and only minor degradation was observed in weaker samples (10, 5, and 2.5 mM), as demonstrated by ¹H and ¹⁹F NMR.     

Carbon black as successful screen-printed electrode modifier for phenolic compound detection

We report a miniaturized and disposable electrochemical sensor for phenolic compound detection. The sensor was constructed by modifying the working electrode surface of screen-printed electrode (SPE) with carbon black (CB) dispersion. This new probe showed higher sensitivity and better resistance to fouling than the bare SPE, displaying the suitability of CB as an excellent nanomodifier of SPE for phenolic compound detection. Catechol, gallic acid, caffeic acid, and tyrosol were detected by square wave voltammetry with a detection limit of 0.1 μM, 1 μM, 0.8 μM, and 2 μM, respectively. The sensor was able to selectively discriminate the mono-phenols and ortho-diphenols with rapid and easy measurement, paving the way to use a cost-effective device for quality control of foods and beverages containing phenolic compounds.