Rod-like Crystals Research Articles

Impact of crystallization conditions and filtration cake washing on the clustering of metformin hydrochloride crystals

Crystallization is one of the basic methods employed in the pharmaceutical and chemical industry to produce powder products with controlled purity. Crystallization is commonly associated with the filtration and drying of solid material, where these unit operations can significantly affect the properties of the final material. This study focuses on the interplay of crystallization, filtration, cake washing, and drying to prevent the formation of crystal clusters. In this work, metformin hydrochloride crystalizing in rod-like crystals is used as a model drug. First, the crystallization parameters, such as stirring speed, cooling rate, impeller type, and solvent type, were varied. It was found that in all cases, metformin hydrochloride crystalizes in single rod-like crystals with various crystal size distribution, where the cooling rate and solvent type lead to non-uniform crystal growth demonstrated by very polydisperse crystal size distribution. Experimental results and Computational Fluid Dynamics simulation confirmed that stresses during crystallization were not sufficient to cause significant crystal breakup. In the next step, filtration connected with filter cake washing and subsequent drying was used to study the formation of crystal clusters. It was found that crystal cake was significantly stronger for the non-washed samples than for washed cake. Both the measured apparent elasticity modulus and the apparent hardness confirmed a strong impact of the washing solvent, allowing quality control when developing a crystal production process.

A Smart Molecule Showing Spin Crossover Responsive Aggregation-Induced Emission

A Smart Molecule Showing Spin Crossover Responsive Aggregation-Induced Emission

Controllable photomechanical bending of metal-organic rotaxane crystals facilitated by regioselective confined-space photodimerization

Molecular machines based on mechanically-interlocked molecules (MIMs) such as (pseudo) rotaxanes or catenates are known for their molecular-level dynamics, but promoting macro-mechanical response of these molecular machines or related materials is still challenging. Herein, by employing macrocyclic cucurbit[8]uril (CB[8])-based pseudorotaxane with a pair of styrene-derived photoactive guest molecules as linking structs of uranyl node, we describe a metal-organic rotaxane compound, U-CB[8]-MPyVB, that is capable of delivering controllable macroscopic mechanical responses. Under light irradiation, the ladder-shape structural unit of metal-organic rotaxane chain in U-CB[8]-MPyVB undergoes a regioselective solid-state [2 + 2] photodimerization, and facilitates a photo-triggered single-crystal-to-single-crystal (SCSC) transformation, which even induces macroscopic photomechanical bending of individual rod-like bulk crystals. The fabrication of rotaxane-based crystalline materials with both photoresponsive microscopic and macroscopic dynamic behaviors in solid state can be promising photoactuator devices, and will have implications in emerging fields such as optomechanical microdevices and smart microrobotics.

Structural Isomerization in Cu(I) Clusters: Tracing the Cu Thermal Migration Paths and Unveiling the Structure-Dependent Photoluminescence

Structural Isomerization in Cu(I) Clusters: Tracing the Cu Thermal Migration Paths and Unveiling the Structure-Dependent Photoluminescence

Preparation of high-strength porous mullite ceramics and the effect of hollow sphere particle size on microstructure and properties

Porous mullite ceramics with high strength were successfully prepared by protein foaming method with fly ash hollow spheres as raw materials. When sintering temperature was increased from 1450 °C to 1550 °C, short rod-like mullite crystals in three-dimensional skeleton grew into interlocking microstructure, effectively enhancing compressive strength and flexural strength of mullite ceramic samples. Using hollow spheres with smaller particle sizes decreased open porosity of samples. However, the effect on total porosity was negligible. Moreover, smaller hollow spheres promoted a shift in median pore size of samples to smaller diameters (87.01 μm→61.66 μm→54.61 μm→36.81 μm). Both compressive strength and flexural strength of samples were significantly improved by reducing particle size of fly ash hollow spheres. Samples produced with the smallest hollow spheres (S4) exhibited low thermal conductivity of 0.401 W m−1 K−1 as well as high compressive strength of 18.10 MPa and flexural strength of 8.69 MPa. These characteristics are significantly superior to those of traditional mullite-based porous ceramics, indicating the effectiveness of the proposed preparation method.

Strength development and microstructure of recycled gypsum-soda residue-GGBS based geopolymer

The utilization of waste materials in road construction is one type of sustainable infrastructure practice, which reduces the dependence on natural resources. The waste, including recycled gypsum powder (from construction and demolition waste), soda residue (from the Na2CO3 industry), and ground granulated blast-furnace slag (GGBS), are favorable supplementary cementitious materials. This paper aims to evaluate the recycled potential of gypsum waste and wet-basis soda residue combined with GGBS to prepare geopolymer for subgrade applications. In this regard, the geopolymer mixture containing 0%, 5%, 10% recycled gypsum and 60%, 70%, 80% soda residue by dry weight will be prepared as partly substitute for GGBS. The mechanical performance will be measured using unconfined compression strength (UCS) and studied strength mechanism via scanning electron microscopy (SEM), X-ray diffraction (XRD), and thermogravimetric analysis (TGA). Test results reveal that the strength of the RG-SR-GGBS based geopolymer decreased with increasing SR dosage and increased with increasing curing age. Excessive dosing of 10% recycled gypsum as a partial substitute for GGBS was detrimental to the strength of geopolymer, while a 5% dose was beneficial to increase the UCS value. The geopolymer of group SR60-RG5-S35 achieved a maximum UCS value of 9310 kPa at the curing age of 28 days. Ettringite (AFt) is a stable hydration product only if there is a sufficient supply of sulphate from recycled gypsum. Many rod-like AFt crystals form cavities in the geopolymer thus reducing the UCS value, while the right amount of AFt fills the capillary pores and increases the structural density and strength. GGBS was activated by the alkalinity of soda residue to generate dense calcium silicate hydrate (C-S-H gel), which is the main reason for the strength development.

Electrically Switchable Anisometric Carbon Quantum Dots Exhibiting Linearly Polarized Photoluminescence: Syntheses, Anisotropic Properties, and Facile Control of Uniaxial Orientation.

Carbon quantum dots (CQDs) have been extensively explored in diverse fields because of their exceptional features. The nanometric particles with photoluminescence (PL) benefit various optical and photonic applications. However, the majority of previous reports have mainly focused on either unpolarized or circular-polarized (CP) PL. Linearly polarized (LP) emission of CQDs is limited mainly because of their isometric shape and difficulties in macroscopic orientation control. Herein, we report syntheses of anisometric CQDs and facile control of the uniaxial orientation on a macroscopic scale, which results in linearly polarized photoluminescence (LP-PL). The anisometric CQDs are synthesized from rigid-rod-shaped precursors and evenly dispersed in the rod-like liquid crystal (LC) host. As-synthesized CQDs exhibit a PL quantum yield as high as 35% in chloroform. In addition to uniform alignment, facile directional switching of the elongated CQD is established by employing the electrical responsiveness of the CQD and host LC. Therefore, the dichroic photophysical properties of anisometric CQDs have been beneficially adopted for fabrications of polarization-sensitive and electrically switchable PL devices. Also, anisometric CQDs are embedded in polymer films with molecular orientational patterns and clearly recognized by LP-PL.

Structure and Properties of Organogels Prepared from Rapeseed Oil with Stigmasterol.

This work used the natural ingredient stigmasterol as an oleogelator to explore the effect of concentration on the properties of organogels. Organogels based on rapeseed oil were investigated using various techniques (oil binding capacity, rheology, polarized light microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy) to better understand their physical and microscopic properties. Results showed that stigmasterol was an efficient and thermoreversible oleogelator, capable of structuring rapeseed oil at a stigmasterol concentration as low as 2% with a gelation temperature of 5 °C. The oil binding capacity values of organogels increased to 99.74% as the concentration of stigmasterol was increased to 6%. The rheological properties revealed that organogels prepared with stigmasterol were a pseudoplastic fluid with non-covalent physical crosslinking, and the G’ of the organogels did not change with the frequency of scanning increased, showing the characteristics of strong gel. The microscopic properties and Fourier transform infrared spectroscopy showed that stigmasterol formed rod-like crystals through the self-assembly of intermolecular hydrogen bonds, fixing rapeseed oil in its three-dimensional structure to form organogels. Therefore, stigmasterol can be considered as a good organogelator. It is expected to be widely used in food, medicine, and other biological-related fields.

Generating TON zeolites with reduced [0 0 1] length through combined mechanochemical bead-milling and porogen-directed recrystallization with enhanced catalytic property in hydroisomerization

Mechanochemical bead-milling of micron-meter sized zeolites to nanometers provides an effective route to enhance their diffusion and catalytic properties. This post-synthetic method is particularly important to reduce crystals of unidimensional zeolites preferentially along their channel direction, as direct synthesis is difficult to achieve since they habitually grow into rod-like crystals. The milling process is often escorted by surface amorphorization and structure degradation, hence, a subsequent recrystallization is often entailed to restore crystallinity. Herein, taken ZSM-22 as an example, it is demonstrated that secondary crystal growth and coalescence during recrystallization, a process that often offset the effect of milling, could be suppressed by the introduction of porogens in the post-milling recrystallization process. The combined bead-milling and porogen-directed recrystallization method allows the preparation of highly crystalline TON crystals with an axis length of largely 100–300 nm, which is record short in axis [001] channel length. The Si/Al ratio could be manipulated between 40 and 300, permitting the influence of acidity and diffusion to be evaluated. The catalytic assessments in n-heptane hydroisomerization demonstrate that isomer yields can be enhanced from 56% for parent material to up to 74% for an optimized catalyst with Si/Al of 200. Correlating of zeolite structure, kinetic studies and catalytic behavior discloses that low acid site density and improved diffusion property are critical factors to decrease cracking probability and improve isomerization selectivity. This study opens new ways to tailor diffusion properties of unidimensional zeolites, and are potentially extendable to other zeolites.

Microstructure and Mechanical Properties of Li2Si2O5 Whisker-Reinforced Glass-Ceramics

Lithium disilicate (Li2Si2O5) glass-ceramics are an ideal material for dental restoration; however, their intrinsic brittleness and low defect tolerance limit the scope of their clinical applications. In this study, Li2Si2O5 whiskers were creatively synthesized via a mild-condition hydrothermal reaction. Self-reinforced Li2Si2O5 glass-ceramics were sintered by introducing the Li2Si2O5 whiskers, and their effects on phase, microstructure, and mechanical properties were systematically studied. The crystal-growth and toughening mechanisms were also discussed. The results showed that the Li2Si2O5 whiskers played an important role in inducing crystallization, and improving the microstructure and properties of the glass-ceramics. With increasing amounts of Li2Si2O5 whiskers, the crystallinities increased slightly, and the average crystal size also increased. The microstructure was composed of crystals of bimodal size distributions, in which some large, rod-like Li2Si2O5 crystals epitaxially grew along with the whiskers, and small crystals directly crystallized from the parent glass-ceramic powders. The Li2Si2O5 glass-ceramics exhibited high flexural strength (389.5 ± 11.77 MPa, LDW3), and fracture toughness (3.46 ± 0.10 MPa·m1/2, LDW5). The improved properties were attributed mainly to crack deflection and bridge-toughening mechanisms.

Experimental investigation and thermodynamic calculation of ternary Al–Ca–Mg phase equilibria

Abstract The ternary Al –Ca –Mg phase equlibria were investigated using X-ray diffraction methods, metallography, scanning electron microscopy with energy- and wave-length-dispersive X-ray microanalysis, and differential thermal analysis. The phase diagram was determined in the complete composition range. Large ternary solubilities were found for the binary phases CaMg2, Al2Ca and Al3Ca8. Microstructures of samples with compositions near the ternary monovariant eutectic L → CaMg2 + Al2Ca show remarkable rod-like crystals that are identified as intergrowth between CaMg2 and Al2Ca. A consistent thermodynamic model was developed using the Calphad method incorporating all experimental data. It was used to calculate all pertinent phase equilibria of the Al –Ca –Mg system.

Fabrication of Monetite by a Controlled Phase Transformation of Three Dimensionally Printed Calcium Sulfate Construct

M onetite is one of the calcium phosphates that has been used for bone regeneration and repair. Comparing to the widely used hydroxyapatite, monetite displayed greater resorption at physiological pH and could induce osteoclast resorption. Fabrication of a shape-customizable monetite construct by using a powder-based three dimensional printing (3DP) technique in combination with a phase transformation at low temperature was studied. Phase transformation of 3D printed calcium sulfate-based sample was carried out in 1M disodium hydrogen phosphate solution at pH5. Various processing parameters were then varied including temperatures (37 oC, 65 oC and 100 oC), sample weight to solution volume ratios (1:20, 1:30, 1:40 and 1:50) and soaking periods (24 h, 48 h, 72 h, 96 h and 120 h). It was found that a temperature of 100 oC, a sample weight to volume ratio of 1:50 and a time greater than 48 h were needed to fully transform the as-printed sample to monophasic monetite without causing the destruction of the structure or the incomplete transformation. Consistently, the microstructure of samples changed from rod-like crystals of calcium sulfate to petal-like crystals of monetite during the transformation process. Density, compressive modulus and strength decreased with soaking times during the course of transformation, but they did not further change with times after complete transformation. In vitro resorbability showed that 3D printed resorbed without conversion to other phase and its weight loss and ions release were greater than those of 3D printed hydroxyapatite indicating its greater resorption potential.

Photoinduced Bending Crystals of a Rhodium Dithionite Complex with n-Methoxybutyl Moieties

Abstract A newly synthesized photochromic rhodium dithionite complex with n-methoxybutyl moieties has been found to provide rod-like millimeter-size crystals exhibiting photoinduced bending; the crystals show an intriguing behavior which the bending and unbending occur upon photoirradiation from the same side of the crystal. The bending mechanism was clarified by single crystal X-ray diffraction experiments.

Antibacterial activity of V- doped rod-like MgO crystals decorated with nanoflake layer

In present study, we report a V doping fabrication method for obtaining rod-like MgO crystals decorated with a nanoflake layer. This novel structure has only been minimally reported in literature. Pure MgO and Mg2V2O7–MgO composite materials were obtained by precipitation and impregnation methods, with vanadium added concentrations of 0–9%. The influence of V doping on crystal structure and particle morphology of MgO was investigated by scanning electron microscopy (SEM). X-ray diffraction (XRD) analysis demonstrated that MgO has a cubic structure, while X-ray photoelectron spectroscopy (XPS) revealed that V5+ exists on the surface of MgO. The specific surface areas and pore sizes of MgO composites were calculated by BET and BJH analysis. These techniques revealed that specific surface area and pore size of MgO increased due to vanadium doping. The antibacterial effects of Mg2V2O7–MgO composite materials against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) were assessed using a bacterial killing/colony-forming unit (CFU) assay and bacteriostatic ring method. Our results demonstrate that V doping dramatically improved antimicrobial properties of MgO, with 7 mol% doping inducing the best antibacterial activity. The antibacterial mechanisms of Mg2V2O7–MgO composite material were also proposed.

Initial decomposition step and bimolecular hydrogen transfer of 3, 3′-diamino-4, 4′-azoxyfurazan under high pressure and high temperature

3, 3′-diamino-4, 4′-azoxyfurazan (DAAF) is a promising energetic furazan compound. Few works about its chemical and physical properties under high pressure and high temperature are reported so far. Here the thermal decompositions of DAAF under high temperature and/or high pressure with neon gas or liquid water were studied using Raman spectra. Under high temperature and ambient pressure, the decomposition sequence of DAAF begins with the unimolecular homolysis of CNazoxy and further followed by the cleavage of NH in NH2 group and the rupture of furazan ring. Application of high pressure induces the different initial decomposition process accompanied the variation of the intermolecular and intramolecular interactions. The initial step of DAAF is the breakdown of NH at 473 K and 0.9 GPa, which facilitates the bimolecular hydrogen transfer from NH2 group to Oazoxy-N and finally induces the dissociation of the O from azoxy group. It results in the formation of DAAzF at 483 K when using neon as pressure transmitting medium. Moreover, big and fine rod-like DAAzF crystals are formed above 493 K at 0.8 GPa employing water as pressure transmitting medium. The existence of super high temperature water leads to the bimolecular hydrogen transfer and dissociation of Oazoxy from DAAF more easily for the interaction of Oazoxy…H and more DAAF crystals transformation into DAAzF.

Bioinspired Crosslinked Nanocomposites of Polyvinyl Alcohol‐Reinforced Cellulose Nanocrystals Extracted from Rice Straw with Ethanedioic Acid

In this study, cellulose nanocrystals (CNC) were extracted from rice straw and incorporated into polyvinyl alcohol (PVOH) as reinforcement nanofillers. Multiple nanocomposites with different CNC contents were prepared. Extracted CNC appear as long, well‐defined rodlike crystals with a high aspect ratio (41). Nanocomposites with 3 wt% of CNC significantly exhibit improved tensile strength (60.4%) and maximum degradation temperature (287°C). Moreover, they demonstrate a decrease in water vapor permeability rate and in the swelling and solubility indices of PVOH/CNC. Significant improvements were observed when nanocomposites were crosslinked specifically in terms of tensile strength (104.8%) and maximum degradation temperature (364°C). They also demonstrate greatly reduced water vapor permeability rate, swelling, and solubility indices. The optimum CNC amount for both nanocomposites is 3 wt%.

The effect of the structure of a helical nanofilament of the B4 phase of bent-core liquid crystals on the nano-phase separation mixed with a rod-like cholesteric liquid crystal mixture.

We studied the structure of a helical nano-filament of the B4 phase in mixtures of a cholesteric liquid crystal mixture and a bent-core molecule using a resonant soft X-ray scattering (RSoXS) technique. In this system, nanophase separation occurs and it was already found that an unexpected new functional chiral smectic structure in the rod-like molecule rich region is constructed by the strong interaction between bent-core and rod-like molecules. In this paper, we focused on the structure of the helical filament in the bent-core liquid crystalline molecule rich region in this mixing system, and it was found that the pitch of the helical filament decreases and the coherence of the helical structure increases.

Porous SB-Cu1 two-dimensional metal-organic framework: The green catalyst towards C[sbnd]N bond-forming reactions

The main advantage of metal-organic frameworks (MOFs) catalysts over other heterogeneous catalysts is that they can be designed to have reaction sites within molecularly well-defined and tunable structures to achieve high catalytic performance. In recent years, several types of metal-organic frameworks with copper(II) have been synthesized for a wide range of applications but there is still few reports for MOFs containing copper(I). Herein, the rod-like crystals SB-Cu1 were synthesized through coordination bonding of bbp ligand and CuI. Inside porous two-dimensional SB-Cu1 each Cu(I) center lies in a tetrahedral coordination sphere of pyridyl groups. This study demonstrates that SB-Cu1 with its desirable features: high porosity, open metal sites (Cu (I)) and benzimidazole (brønsted base) could play as a dual heterogeneous catalyst for C-N forming reactions to synthesize products in good to excellent yields(70–85%). In this work, ethanol as green solvent and a wide variety of imidazole, pyrrole, amine and aryl halide have been used for preparing products. Also, the MOF catalyst was recovered and reused at least five times without loss of activity.

Electrophoresis-Aided Biomimetic Mineralization System Using Graphene Oxide for Regeneration of Hydroxyapatite on Dentin.

Graphene oxide (GO) is an emerging luminescent carbon nanomaterial with the ability to foster hydroxyapatite (HA). A specially designed electrophoresis system can be used to accelerate the mineralization process. The aim of this study was to promote HA crystal growth on demineralized dentin using a GO incorporated electrophoresis system. GO was successfully synthesized by carbonization of citric acid and its presence was confirmed by Fourier transform infrared and UV-visible spectrophotometry evaluation. Dentin slices were placed in demineralized solution and divided into control (without the electrophoresis system) and experimental group. Demineralized dentin slices in the experimental group were remineralized using the electrophoresis system for 8 h/1.0 mA, with one subgroup treated without GO and the other with GO. Energy dispersive spectroscopy evaluation showed that the calcium/phosphate ratio of the crystal formed in control and experimental group with addition of GO was close to natural hydroxyapatite. However, scanning electron microscopy evaluation showed that the exposed dentinal tubules were occluded with rod-like crystals, which is similar to native enamel morphology, in the experimental group with addition of GO compared to the flake-like crystal in the control group. Mechanical evaluation revealed that the nanohardness and modulus of remineralized dentin were significantly higher in the experimental group. In conclusion, GO is a promising material to remineralize dentin and the introduction of an electrophoresis system can accelerate its process.

The combined effect of thermal-acid hydrolysis, periodate oxidation, and iodine species removal on the properties of native tapioca (Manihot esculenta Crantz) starch

Through a four-step top-down approach, native tapioca starch (NTS) was thermally acid-hydrolyzed, periodate-oxidized with subsequent removal of iodine species (i.e., IO4(−), IO3(−), I(−), and I2), and dialdehyde tapioca starch (DTS) alcohol-precipitation. The percent yield was ∼91%. Analyses confirmed the presence of aldehydic functionalities (∼71%), effectual iodine species removal (∼98%), and enhanced water-solubility (∼96.57%). Besides, the combined treatment significantly reduced the Mw (∼57.81 kDa) and ameliorated homogeneity as well as thermal stability (Tmax ∼ 667.15 °C). Structural-spectral characterization also confirmed the presence of aldehydic functionality, polymorphic transition (C- to A-type), and a higher degree of crystallinity (∼91.77%), the latter further corroborated by thermal analysis. The morphological study revealed that the combined treatment reduced size (∼393.55-nm-diameter and ∼5.22-μm-length) and changed shape into rod-like crystals. DTS showed considerably and significantly low cytotoxicity to HaCaT cells in vitro at the concentrations assayed over the test period (24 h). DTS's conformation was most stable at −289 kcal/mol and −151.7 au heat formation and minimum potential energies, respectively. Overall, these results demonstrated that the combined treatment had no deleterious effects on NTS's properties, thus yielded DTS with ideal properties for multifarious uses.