Showing papers on "Crystallization published in 2013"

Synthesis Modulation as a Tool To Increase the Catalytic Activity of Metal–Organic Frameworks: The Unique Case of UiO-66(Zr)

Abstract: The catalytic activity of the zirconium terephthalate UiO-66(Zr) can be drastically increased by using a modulation approach. The combined use of trifluoroacetic acid and HCl during the synthesis results in a highly crystalline material, with partial substitution of terephthalates by trifluoroacetate. Thermal activation of the material leads not only to dehydroxylation of the hexanuclear Zr cluster but also to post-synthetic removal of the trifluoroacetate groups, resulting in a more open framework with a large number of open sites. Consequently, the material is a highly active catalyst for several Lewis acid catalyzed reactions.

X-ray analysis on the nanogram to microgram scale using porous complexes

Abstract: X-ray single-crystal diffraction (SCD) analysis has the intrinsic limitation that the target molecules must be obtained as single crystals. Here we report a protocol for SCD analysis that does not require the crystallization of the sample. In our method, tiny crystals of porous complexes are soaked in a solution of the target, such that the complexes can absorb the target molecules. Crystallographic analysis clearly determines the absorbed guest structures along with the host frameworks. Because the SCD analysis is carried out on only one tiny crystal of the complex, the required sample mass is of the nanogram–microgram order. We demonstrate that as little as about 80 nanograms of a sample is enough for the SCD analysis. In combination with high-performance liquid chromatography, our protocol allows the direct characterization of multiple fractions, establishing a prototypical means of liquid chromatography SCD analysis. Furthermore, we unambiguously determined the structure of a scarce marine natural product using only 5 micrograms of the compound. Chemists need reliable methods to analyse and determine molecular structures. Nuclear magnetic resonance (NMR) and mass spectrometry are indispensable tools in daily chemical research for rapidly analysing molecular structures, but, strictly speaking, they provide only speculative molecular structures that are sometimes assigned incorrectly. However, X-ray SCD provides direct structural information at the atomic level and is recognized as the most reliable structure determination method 1–3 . Unfortunately, X-ray SCD has some critical limitations. First, the crystallization of samples before measurement can not be automated and usually requires a time-consuming trial-and-error procedure. Second, the method is in principle not applicable to non-crystalline molecules. In this Article, we describe an advance in crystallographic analysis based on a new X-ray analysis protocol that does not require the crystallization of the sample molecules themselves. Our idea is to use networked porous metal complexes 4–7 as ‘crystalline sponges’ 8 . Owing to the high molecular-recognition ability of the pores, the crystalline sponges can absorb target sample molecules from their solution into the pores, rendering the incoming molecules regularly ordered in the crystal. Accordingly, the molecular structure of the absorbed guest will be displayed, along with the host framework, by the crystallographic analysis of the networked porous complexes. We emphasize that even trace amounts of samples (,0.1mg) can be analysed by this method because the experiment can be performed with only one tiny crystal (,0.1 mm to a side). In the following discussion, we thus describe the crystallographic analysis of non-crystalline compounds and nanogram–microgram-scale X-ray crystallography based on our method. The great advantage of trace-amount X-ray analysis is particularly emphasized by its application to liquid chromatography SCD analysis (see below), where high-performance liquid chromatography (HPLC) fractions are directly collected by the crystalline sponge and analysed by X-ray crystallography. Furthermore, we successfully determine the structure of a scarce marine natural product, miyakosyne A, including the absolute configuration of its chiral centre, which could not be determined by conventional chemical and spectroscopic methods. X-ray crystallography of liquid samples

The Vitreous State: Thermodynamics, Structure, Rheology, and Crystallization

Abstract: Introduction.- States of Aggregation, Thermodynamic Phases, and the Vitreous State.- Non-Equilibrium Thermodynamics and the Kinetics of Glass Transition and Stabilization.- General Approaches to the Description of the Structure of Glasses.- Statistical Physics of Under-Cooled Melts and Glasses.- Nucleation in Glass-Forming Systems.- Catalyzed Crystallization of Glass-Forming Melts.- Theory of Crystal Growth and Dissolution in Under-cooled Melts.- Growth of Clusters. Ostwald's Rule of Stages.- Kinetics of Overall Crystallization.- Liquid Phase Separation in Glass-Forming Melts.- Rheology of Glass-Forming Melts.- Concluding Remarks.

Millimeter-Size Single-Crystal Graphene by Suppressing Evaporative Loss of Cu During Low Pressure Chemical Vapor Deposition

Abstract: Millimeter-size single-crystal monolayer graphene is synthesized on polycrystalline Cu foil by a method that involves suppressing loss by evaporation of the Cu at high temperature under low pressure This significantly diminishes the number of graphene domains, and large single crystal domains up to ∼2 mm in size are grown

Liquid–Liquid Phase Separation in Highly Supersaturated Aqueous Solutions of Poorly Water-Soluble Drugs: Implications for Solubility Enhancing Formulations

Abstract: Highly supersaturated aqueous drug solutions are often generated during drug testing and upon delivery to the patient. The phase behavior of such solutions appears complex and poorly understood, with the formation of colloidal drug aggregates often being reported. In this study, the phase behavior of eight hydrophobic poorly water-soluble drug molecules in highly supersaturated aqueous solutions was examined, and colloid formation was explained in terms of liquid–liquid phase separation (LLPS). A relationship was found between the concentration at which LLPS was observed and the theoretically predicted amorphous “solubility” value, where the latter was predicted based on the thermodynamic properties of the crystalline solid/supercooled liquid and solution activity coefficients. A phase diagram for the ritonavir–water system as a function of temperature was used to demonstrate that LLPS occurs in the metastable region of the phase diagram, and thus LLPS is a precursor to crystallization. Using an amorphous...

Recent advances in the monitoring, modelling and control of crystallization systems

Abstract: Crystallization is one of the most important unit operations used for the separation and purification of crystalline solid products. Appropriate design and control of the crystallization process is paramount to produce crystalline products with tailor-made-properties. This paper provides an overview of selected recent developments in the modelling, monitoring and control of crystallization processes. We consider the topics discussed in this review to be enabling technologies for the development of the next generation of crystallization processes with significantly improved predictability, robustness and controllability.

Poly(butylene 2,5-furan dicarboxylate), a Biobased Alternative to PBT: Synthesis, Physical Properties, and Crystal Structure

Abstract: This paper describes the synthesis, crystal structure, and physicomechanical properties of a biobased polyester prepared from 2,5-furandicarboxylic acid (FDCA) and 1,4-butanediol. Melt-polycondensation experiments were conducted by a two-stage polymerization using titanium tetraisopropoxide (Ti[OiPr]4) as a catalyst. Polymerization conditions (catalyst concentration, reaction time and second stage reaction temperature) were varied to optimize poly(butylene-FDCA), PBF, and molecular weight. A series of PBFs with different Mw were characterized by DSC, TGA, DMTA, X-ray diffraction and tensile testing. Influence of molecular weight and melting/crystallization enthalpy on PBF material tensile properties was explored. Cold-drawing tensile tests at room temperature for PBF with Mw 16K to 27K showed a brittle-to-ductile transition. When Mw reaches 38K, the Young modulus of PBF remains above 900 MPa, and the elongation at break increases to above 1000%. The mechanical properties, thermal properties and crystal st...

Structural Electron Crystallography

Abstract: Introduction. Background: The Electron Microscope as a Crystallographic Instrument. Crystal Symmetry. Crystallization and Data Collection. Crystal Structure Analysis. Data Perturbations. Applications: Molecular Organic Structures. Inorganic Structures. The Alkanes. Alkane Derivatives. The Lipids. Linear Polymers. Globular Macromolecules. Index.

Nanoporous Organic Polymer/Cage Composite Membranes†

Abstract: Organic?organic composite membranes are prepared by in?situ crystallization of cage molecules in a polymer of intrinsic microporosity. This allows a direct one-step route to mixed-matrix membranes, starting with a homogeneous molecular solution. Extremely high gas permeabilities are achieved, even after ageing for more than a year, coupled with good selectivity for applications such as CO2 recovery.

The role of crystallization and phase separation in the formation of physically cross-linked PVA hydrogels

Abstract: The biocompatibility, processing ease, and mechanical properties of freeze-thawed poly(vinyl alcohol) (PVA)-based hydrogels have encouraged significant research toward developing this material for various biomedical applications. Crystallization that occurs during the freeze-thawing process is cited in the literature as the primary mechanism responsible for the resultant mechanical properties. Further analysis, however, shows the presence of two unique mechanisms that contribute to PVA's mechanical properties. During freeze–thaw cycling water freezes causing phase separation, which facilitates crystallization. The impact of phase separation during freeze–thaw cycling was investigated by comparing freeze-thawed and aged PVA hydrogels. Aged hydrogels were not prepared by freezing and, therefore, did not exhibit significant phase separation. The amount of phase separation was discerned using optical microscopy in the hydrated state. Crystallinity and mechanical properties were also evaluated as a function of the number of cycles (for freeze-thawed gels) and aging time (for aged gels). For freeze-thawed hydrogels, crystallinity deviated significantly from the trend observed in compressive modulus, indicating that crystallinity was not the only factor determining the hydrogel's mechanical properties. Phase separation was found to occur during freeze–thaw cycling independently of crystallization, especially at later freeze–thaw cycles (after the third). The trends observed for both crystallinity and modulus for aged hydrogels, however, were in better agreement with each other. Further evaluation of the mechanical properties of aged and freeze-thawed hydrogels with similar crystallinities indicated that freeze-thawed hydrogels have significantly higher modulus values (p < 0.05). As a result, phase separation, independently of crystallization, was determined to have a significant effect on gelation during freeze–thaw cycling. In particular, PVA-rich regions that are formed during phase separation, without additional cross-linking, are believed to have a significant effect on the resultant mechanical properties.

Proton-exchange mechanism of specific Cs+ adsorption via lattice defect sites of Prussian blue filled with coordination and crystallization water molecules

Abstract: We have revealed the fundamental mechanism of specific Cs+ adsorption into Prussian blue (PB) in order to develop high-performance PB-based Cs+ adsorbents in the wake of the Fukushima nuclear accident. We compared two types of PB nanoparticles with formulae of FeIII4[FeII(CN)6]3·xH2O (x = 10–15) (PB-1) and (NH4)0.70FeIII1.10[FeII(CN)6]·1.7H2O (PB-2) with respect to the Cs+ adsorption ability. The synthesised PB-1, by a common stoichiometric aqueous reaction between 4Fe3+ and 3[FeII(CN)6]4−, showed much more efficient Cs+ adsorption ability than did the commercially available PB-2. A high value of the number of waters of crystallization, x, of PB-1 was caused by a lot of defect sites (vacant sites) of [FeII(CN)6]4− moieties that were filled with coordination and crystallization water molecules. Hydrated Cs+ ions were preferably adsorbed via the hydrophilic defect sites and accompanied by proton-elimination from the coordination water. The low number of hydrophilic sites of PB-2 was responsible for its insufficient Cs+ adsorption ability.

Zinc oxide nanoparticles: chemical mechanisms and classical and non-classical crystallization

Abstract: Among all the functional materials, ZnO plays an outstanding role in terms of chemical and physical properties, but also in terms of morphological variety and the number of reported synthesis approaches. Complex shapes and hierarchical architectures make ZnO a perfect example to study chemical and crystallization mechanisms. In this review article, we will discuss the nucleation and growth of ZnO nanostructures in liquid media by classical and non-classical (i.e., particle-based) crystallization pathways. We elaborate the chemical conditions and parameters that are responsible for the occurrence of one or the other pathway.

The roles of water molecules at the biointerface of medical polymers

Abstract: A number of biomaterials have been proposed, including hydrophilic, phase-separated and zwitterionic polymers. It has not been clearly elucidated which mechanisms are responsible for biocompatibility on a molecular level. Water interactions have been recognized as a fundamental part of the biological response to contact with biomaterials. We have proposed the ‘intermediate water’ concept; the water exhibited both clear peak for cold crystallization in differential scanning calorimetry chart and a strong peak at 3400 cm−1 in a time-resolved infrared spectrum. We found the localized hydration structure consisting of the three hydrated water in poly(2-methoxyethyl acrylate) (PMEA).

Liquid–liquid transition in a strong bulk metallic glass-forming liquid

Abstract: The nature of liquid–liquid phase transitions remains inconclusive, because direct experimental evidence is limited by crystallization. Wei et al. observe it in a bulk metallic glass former, which is characterized by heat capacity maxima and sudden changes in both viscosity and local structures.

Crystal Nucleation Kinetics from Induction Times and Metastable Zone Widths

Abstract: We compare two recently developed methods to determine crystal nucleation rates in stirred solutions by using isonicotinamide (INA) in ethanol as an example. The two developed methods make use of the stochastic nature of crystal nucleation, which is reflected in induction time and metastable zone width variations measured in sufficiently small volumes. These methods give easy experimental access to the nucleation rate parameters in solution under industrially realistic crystallization conditions. While the metastable zone width method is less labor intensive, the induction time method has higher accuracy and is easier to analyze.

Solvent additive effects on small molecule crystallization in bulk heterojunction solar cells probed during spin casting.

Abstract: Solvent additive processing can lead to drastic improvements in the power conversion efficiency (PCE) in solution processable small molecule (SPSM) bulk heterojunction solar cells. In situ grazing incidence wide-angle X-ray scattering is used to investigate the kinetics of crystallite formation during and shortly after spin casting. The additive is shown to have a complex effect on structural evolution invoking polymorphism and enhanced crystalline quality of the donor SPSM.

Archetypal sandwich-structured CuO for high performance non-enzymatic sensing of glucose.

Abstract: In the quest to enhance the selectivity and sensitivity of novel structured metal oxides for electrochemical non-enzymatic sensing of glucose, we report here a green synthesis of unique sandwich-structured CuO on a large scale under microwave mediated homogeneous precipitation conditions. The physicochemical studies carried out by XRD and BET methods show that the monoclinic CuO formed via thermal decomposition of Cu(2)(OH)(2)CO(3) possesses monomodal channel-type pores with largely improved surface area (~43 m(2) g(-1)) and pore volume (0.163 cm(3) g(-1)). The fascinating surface morphology and pore structure of CuO is formulated due to homogeneous crystallization and microwave induced self assembly during synthesis. The cyclic voltammetry and chronoamperometry studies show diffusion controlled glucose oxidation at ~0.6 V (vs. Ag/AgCl) with extremely high sensitivity of 5342.8 μA mM(-1) cm(-2) and respective detection limit and response time of ~1 μM and ~0.7 s, under a wide dynamic concentration range of glucose. The chronoamperometry measurements demonstrate that the sensitivity of CuO to glucose is unaffected by the absence of dissolved oxygen and presence of poisoning chloride ions in the reaction medium, which essentially implies high poison resistance activity of the sandwich-structured CuO. The sandwich-structured CuO also shows insignificant interference/significant selectivity to glucose, even in the presence of high concentrations of other sugars as well as reducing species. In addition, the sandwich-structured CuO shows excellent reproducibility (relative standard deviation of ~2.4% over ten identically fabricated electrodes) and outstanding long term stability (only ~1.3% loss in sensitivity over a period of one month) during non-enzymatic electrochemical sensing of glucose. The unique microstructure and suitable channel-type pore architecture provide structural stability and maximum accessible electroactive surface for unimpeded mobility of glucose as well as the product molecules, which result in the excellent sensitivity and selectivity of sandwich-structured CuO for glucose under non-enzymatic milieu.

Effects of various liquid organic solvents on solvent-induced crystallization of amorphous poly(lactic acid) film

Abstract: The effects of 60 organic solvent on poly(lactic acid) (PLA) were systematically investigated using the Hansen solubility parameter (HSP). The hydrogen bonding solubility parameter accurately reflects the solubility of PLA films using HSP but it depends on hydrogen bonding, as well as dispersion and polar parameters. The PLA films immersed in organic solvent became cloudy and showed no changes in chemical structure. However, solvent-induced crystallization of the PLA films was observed. Crystalline structures do not dependent on the organic solvent but on the degree of swelling. The organic solvent-induced crystallization formed a crystallized mixture of a- and β-forms. The density of the crystalline PLA films was lower than that of amorphous PLA films. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Evolution of Supersaturation of Amorphous Pharmaceuticals: The Effect of Rate of Supersaturation Generation

Abstract: The combination of a rapidly dissolving and supersaturating "spring" with a precipitation retarding "parachute" has often been pursued as an effective formulation strategy for amorphous solid dispersions (ASDs) to enhance the rate and extent of oral absorption. However, the interplay between these two rate processes in achieving and maintaining supersaturation remains inadequately understood, and the effect of rate of supersaturation buildup on the overall time evolution of supersaturation during the dissolution of amorphous solids has not been explored. The objective of this study is to investigate the effect of supersaturation generation rate on the resulting kinetic solubility profiles of amorphous pharmaceuticals and to delineate the evolution of supersaturation from a mechanistic viewpoint. Experimental concentration-time curves under varying rates of supersaturation generation and recrystallization for model drugs, indomethacin (IND), naproxen (NAP) and piroxicam (PIR), were generated from infusing dissolved drug (e.g., in ethanol) into the dissolution medium and compared with that predicted from a comprehensive mechanistic model based on the classical nucleation theory taking into account both the particle growth and ripening processes. In the absence of any dissolved polymer to inhibit drug precipitation, both our experimental and predicted results show that the maximum achievable supersaturation (i.e., kinetic solubility) of the amorphous solids increases, the time to reach maximum decreases, and the rate of concentration decline in the de-supersaturation phase increases, with increasing rate of supersaturation generation (i.e., dissolution rate). Our mechanistic model also predicts the existence of an optimal supersaturation rate which maximizes the area under the curve (AUC) of the kinetic solubility concentration-time profile, which agrees well with experimental data. In the presence of a dissolved polymer from ASD dissolution, these observed trends also hold true except the de-supersaturation phase is more extended due to the crystallization inhibition effect. Since the observed kinetic solubility of nonequilibrium amorphous solids depends on the rate of supersaturation generation, our results also highlight the underlying difficulty in determining a reproducible solubility advantage for amorphous solids.

Nucleation from Solution

Abstract: The formation of crystalline solids from solution is fundamental to many natural and industrial processes. Crystallization may even be the key to the formation of life itself ( 1 ). The crystallization process begins with nucleation, which plays a central role in determining the structure and size distribution of the crystals. In the past decade, experimental and molecular modeling studies of ionic materials such as calcium carbonate, proteins, and organic molecular crystals has suggested that nucleation of solids from solution does not proceed via the classical pathway but follows much more complex routes. These routes are generally referred to as two-step nucleation, but actually encompass a number of potential mechanisms ( 2 – 4 ). On page 885 of this issue, Wallace et al. ( 5 ) use molecular simulations to probe CaCO3 nucleation. The results provide evidence for a dense liquid-liquid phase in which solvated CaCO3 clusters come together during nucleation.

Crystallization Behavior of Polylactide/Graphene Composites

Abstract: Polylactide (PLA) composites containing graphene nanosheets were prepared by the approach of solution mixing for a crystallization study. The results revealed that the graphene nanosheets are well distributed in the PLA matrix, leading to an evident viscosity increase despite their dispersion as multilayered structures in stack form. Both the cold and melt crystallization behaviors of PLA were found to depend strongly on the presence of the graphene nanosheets. During cold crystallization, the graphene nanosheets merely act as an inert filler, and the increased viscosity results in a decrease of the overall crystallization rate of the composite relative to neat PLA. However, the graphene nanosheets can act as a heterogeneous nucleating agent, which is their dominant role during melt crystallization. As a result, the composite shows a higher crystallization rate than neat PLA under these conditions.