Synthesis of β-SiAlON whiskers: dependence of uniform morphology upon preparation conditions

Abstract

Abstract

β-SiAlON whiskers with uniform morphology were prepared using reaction sintering method under different conditions. The effect of preparing conditions on the morphology of β-SiAlON whiskers was systematically studied by SEM, XRD, TEM and HRTEM. The results showed that single crystalline β-SiAlON whiskers with uniform morphology were successfully fabricated at 1773 K for 6 h under flowing nitrogen atmosphere. The well synthesised whiskers were of several hundreds of nanometres in diameter and a few hundreds of micrometres in length. Although the morphology and its size distribution are mainly determined by the reaction temperature and holding time, they can also be tailored by controlling the reaction atmosphere. The ratio of staring materials has no significant influence on the morphology of β-SiAlON whiskers. The growth of β-SiAlON whiskers follows a vapour–solid mechanism, and the formation of the belt-like whiskers is attributed to an anisotropic growth at the early nucleation/growth stage.     

Preparation and sorption studies of microsphere copolymers containing β-cyclodextrin and poly(acrylic acid)

Microsphere polymeric materials containing β-cyclodextrin (β-CD) and poly(acrylic acid) (PAA) with tunable morphologies were prepared in order to improve their sorption characteristics in aqueous solution. The microsphere polymeric materials were prepared using a (water/oil) micro-emulsion-evaporation technique to condense β-cyclodextrin (β-CD) with PAA at various comonomer ratios and mixing speeds. The β-CD microsphere copolymers were characterized using FTIR, TGA, DSC, SEM, elemental (C and H) microanalyses, and solid state ¹³C-NMR spectroscopy. The sorption properties of the polymeric materials at 295 K in aqueous solution containing p-nitrophenol (PNP) were studied using a dye-based method with UV–Vis spectrophotometry at pH 4.6 and 10.3. The sorption isotherms of copolymer/PNP systems were evaluated with various isotherm models (e.g., Langmuir, BET, Freundlich, and Sips). The Sips isotherm showed the best overall agreement with the experimental results and the sorption parameters provided estimates of the sorbent surface area (12.0–331 m²/g) and the sorption capacity (Q_m = 0.359–2.20 mmol/g at pH = 4.6; Q_m = 0.070–0.191 mmol/g at pH = 10.3) for the microsphere copolymer/PNP systems in aqueous solution. The nitrogen adsorption properties of the microporous copolymers in the solid state were obtained at 77K with BET surface areas ranging from 0.275 to 4.47 m²/g. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

The biomimetic catalytic synthesis of acetal compounds using β-cyclodextrin as catalyst

Based on the principle of biomimetic catalysis, β-cyclodextrin was applied to the acetalation reaction as a facile and efficient catalyst, and the synthesis was environmentally friendly with atomic economy. The influencing factors of the acetalation reaction e.g. the reaction time, the volume of water-carrying agent,the molar ratio of catalyst to benzaldehyde and the molar ratio of glycol to benzaldehyde had been studied.The yield of benzaldehyde glycol acetal would reach a maximum of 81.3% under the conditions approached.Six of other acetals were also synthesized. Moreover, a plausible reaction mechanism for the formation of acetal had been proposed.     

Inclusion complexes of eucalyptus essential oil with β-cyclodextrin: preparation,characterization and controlled release

In this study, eucalyptus essential oil (EEO) was encapsulated into β-cyclodextrin (β-CD) by saturated aqueous solution method. The success of EEO encapsulation was confirmed by laser light scatting, scanning electron microscopy, Fourier transform infrared spectroscopy, differential scanning calorimeter and thermogravimetric analysis. Releasing characteristics experiments were carried out at various temperatures, relative humidity (RH), storage time and high temperature stability test. Release kinetics of EEO from the inclusion complexes was investigated by zero-order kinetics, first-order kinetics and Avrami’s equation. The result showed that the release model of EEO from inclusion complexes fitted better for Avrami’s equation. Kinetics analysis based on the Avrami’s equation revealed that the release of EEO was accelerated with the increases of RH and temperature. For storage time treatment, the volatilization of EEO was significantly inhibited after encapsulation. High temperature stability test further revealed that EEO was protected after having been encapsulated into β-CD. For all treatments, the release parameter n was between 0.5 and 1.0, which presenting a diffusion-limited and first-order mode. These results indicated that encapsulation enhanced the stability and prolonged the acting time of EEO, and the release rate of EEO can also be passively controlled by the ambient temperature, humidity and storage time.     

Determination of lisinopril using β-cyclodextrin/graphene oxide-SO3H modified glassy carbon electrode

An electrochemical method has been successfully demonstrated for sensitive determination of lisinopril with β-cyclodextrin-graphene oxide-SO₃H composite modified glassy carbon electrode (β-CD/GO-SO₃H/GCE). Cyclic voltammetry, differential pulse voltammetry, and chronocoulometry were used to investigate the electrochemical behavior of lisinopril at β-CD/GO-SO₃H/GCE. The cyclic voltammetric results indicate that β-CD/GO-SO₃H/GCE can remarkably enhance electroactivity toward the oxidation of lisinopril in buffer solutions. The electrochemical behavior was further exploited as a sensitive detection scheme for the lisinopril determination by differential-pulse voltammetry. Under optimized conditions, the concentration range and detection limit were 0.21–190.4 and 0.11 µM (S/N = 3), respectively. The method was successfully applied to assay the drug in human serum.     

Optimal design of nanofiltration system for surface water treatment☆

Both reverse osmosis (RO) and nanofiltration (NF) membranes have been increasingly used for water purification and desalination. However, the salt rejection of NF membranes is quite different from that of RO membranes, which makes a significant distinction in their process designs. This work started from the performance investigation of a single NF membrane element and then focused on the process design of the NF system for surface water treat-ment. In experimental tests, it was found that the observed rejection of the NF element becomes nearly constant when the concentrate flow is large enough, while the membrane flux of the NF element is quite stable regardless of the water flow across the membrane surface. These findings can be used to instruct the process design of the NF system for surface water treatment. In process design, a two-stage arrangement is sufficient for the NF system to reach the highest water recovery, while the RO system requires a three-stage arrangement.     

The chemical-enzymatic preparation and resolution of β-naphthyl alcohol

通过化学-酶相耦合的方法,成功制备出e.e.值>99%的S-β-萘乙醇,使其光学纯度达到了制备R-2-萘乙胺的要求。研究中以β-萘乙酮为原料,经硼氢化钠还原得到外消旋的β-萘乙醇。经过酶催化动力学拆分,β-萘乙醇中R型底物100%全转化为酯,S构型底物型被保留,这样体系中S构型底物的e.e.值达到近100%。本文还考察了若干因素对酶催化动力学拆分过程的影响,并最终确定了酶催化动力学拆分β-萘乙醇制备S-β-萘乙醇的最适条件：反应温度45 ℃,溶液为甲苯,底物浓度为100 mmol/L。     

Symmetry complementarity-guided design of anthrax toxin inhibitors based on β-cyclodextrin: Synthesis and relative activities of face-selective functionalized polycationic clusters

Three new series of potential anthrax toxin inhibitors based on the β‐cyclodextrin (βCD) scaffold were developed by exploiting face‐selective Cu^I‐catalyzed azide–alkyne 1,3‐cycloadditions, amine–isothiocyanate coupling, and allyl group hydroboration–oxidation/hydroxy → amine replacement reactions. The molecular design follows the “symmetry–complementarity” concept between homogeneously functionalized polycationic βCD derivatives and protective antigen (PA), a component of anthrax toxin known to form C₇‐symmetric pores on the cell membrane used by lethal and edema factors to gain access to the cytosol. The synthesis and antitoxin activity of a collection of βCD derivatives differing in the number, arrangement, and face location of the cationic elements are reported herein. These results set the basis for a structure–activity relationship development program of new candidates to combat the anthrax threat.     

Fluorescence and β-cyclodextrin inclusion properties of three carbazole-based dyes

Fluorescence behavior of three carbazole-based dyes, 2-(9H-carbazol-9-yl) butanoic acid, 2-(1,4-dimethyl-9H-carbazol-9-yl)acetic acid and 3-(1,4-dimethyl-9H-carbazol-9-yl)propanoic acid were examined. General solvent effects of the butanoic and acetic acid derivatives in 23 different solvents was not well-described by the Lippert–Mataga equation, indicating a specific solvent effect due to intermolecular hydrogen bonding dominated fluorescence spectra. The emission wavelengths and fluorescence intensities were relatively stable in aqueous acetonitrile and aqueous methanol solutions. Their fluorescence intensities increased from low to high pH and also from high to low temperature. The acid dissociation constants of the three carbazole derivatives in their ground state were estimated to be in the range 3.2–4.8. The fluorescence intensities were also enhanced in the presence of β-cyclodextrin. The average stability constant of the inclusion complexes was 21.2 ± 13.4 at pH3 and 54.0 ± 7.0 at pH8. A molecular dynamics simulation indicated that the carbazole moiety was partially included into the β-cyclodextrin cavity leaving the carboxylic acid group exposed.     

Preparation and characterization of thermo-sensitive microspheres with β-cyclodextrin groups

采用沉淀聚合机理,由一步法和两步法制备聚（N-异丙基丙烯酰胺-甲基丙烯酸缩水甘油酯） [P(NIPAM-co-GMA)]温敏性微球。其中一步法是同时加入所有反应物反应成微球,而两步法是先加NIPAM成微球,再加入GMA,最终均生成P(NIPAM-co-GMA)微球;再将改性的乙二胺代环糊精（EDA-β-CD）通过化学反应引入到P(NIPAM-co-GMA)微球结构中,制备得到聚（N-异丙基丙烯酰胺-甲基丙烯酸-2-羟丙基乙二胺基环糊精） [P(NIPAM-co-GMA/β-CD)]共聚高分子微球。分别用扫描电镜、红外光谱、控温激光粒度仪及光学显微镜对产物的形貌、结构和温敏特性进行了表征。结果表明,两种方法制备的微球均具有良好的单分散性和球形度,均能成功地固载β-环糊精（β-CD）基团,并且都有温度响应特性;但是,同一步法制备的微球相比,两步法制得的微球粒径明显较大,且微球固载有更多的β-CD。     

Synthesis and drug-release properties of biodegradable hydrogels having β-cyclodextrin

A new β-cyclodextrin (β-CD) methacrylated monomer was synthesized from the reaction of β-CD, glycidyl methacrylate. Based on inclusion character of β-CD, a series of hydrogels were prepared by irradiating the mixtures of β-CD methacrylate monomer (β-CD-Met), poly(ethylene glycol) monoacrylate, poly(ethylene glycol)diacrylate, fumaric acid monoethyl ester-functionalized poly(lactic-co-glycolic) acid, 1-vinyl-2-pyrrolidone, N,N′-methylene bisacrylamide, and the photoinitiator. Gel percentages and equilibrium swelling ratios (%) of hydrogels were investigated. It was observed that equilibrium-swelling ratio increased with increasing β-CD-Met content in the hydrogel composition. SEM images demonstrated that β-CD-Met-based hydrogel have lots of voids on the fractured surface. In this study, ibuprofen (IBU) which is capable of forming inclusion complex with β-CD was chosen. For the hydrogel with maximum CD content, the IBU drug loading was found as 9 mg/g dry gel. It can be concluded that the inclusion complex-formation capability of β-CD moiety increases the drug release by improving the aqueous solubility of hydrophilic drugs.     

Synthesis and Characterization of the Inclusion Complex of β-cyclodextrin and Azomethine

A β-cyclodextrin (β-Cyd) inclusion complex containing azomethine as a guest was prepared by kneading method with aliquot addition of ethanol. The product was characterized by Fourier Transform Infrared (FTIR) spectrometer, ¹H Nuclear Magnetic Resonance (¹H NMR) and Thermogravimetric Analyzer (TGA), which proves the formation of the inclusion complex where the benzyl part of azomethine has been encapsulated by the hydrophobic cavity of β-Cyd. The interaction of β-Cyd and azomethine was also analyzed by means of spectrometry by UV-Vis spectrophotometer to determine the formation constant. The formation constant was calculated by using a modified Benesi-Hildebrand equation at 25 °C. The apparent formation constant obtained was 1.29 × 10⁴ L/mol. Besides that, the stoichiometry ratio was also determined to be 1:1 for the inclusion complex of β-Cyd with azomethine.     

Inductive effect of MXene membrane influenced by β-cyclodextrin intercalation

Two-dimensional nanomaterials could be potentially applied in the field of brain–computer interface due to their significant inductive effect during ion permeation. In order to tune the inductive signal through the microstructure, a membrane based on MXene-grafted β-cyclodextrin (β-CD) was prepared, and its electrochemical performance was recorded. The experimental results confirmed that β-CD has been successfully intercalated into the gallery between the MXene sheets, and the intercalation induced a weaker inductive effect of MXene in the ion diffusion process. Moreover, the results indicated that easier ion diffusion through the membrane could result in weaker inductance. Besides, the experimental results were roughly analyzed by the back-propagation (BP) neural network to compare the contribution of the influence factors. The results suggested that tunable inductance can be achieved by constructing a certain interlay spacing of MXene, which could be potentially used to design microsized inductors in biological applications.     

Shape-selective separation of geraniol and nerol via noncovalent interactionswith β-cyclodextrin

In this paper, selective separation of the isomeric compounds geraniol and nerol, based on the preferential affinity of β-cyclodextrin (β-CD) for geraniol was investigated. To demonstrate the potential application of β-CD for separation of geraiol from nerol, the structure of the inclusion complexes was characterized with various physico-chemical techniques. The selective noncovalent binding property of β-CD was confirmed by quantum-chemical calculations. For the mixture, which contains 50 wt% of geraniol and nerol, respectively, 96% of geraniol in complex can be obtained, and the similar separation efficiency was found after use for three times.     

A novel bridged organocobaloxime/ β-cyclodextrin inclusion complex produced by a β-cyclodextrin induced reaction

A cobalt-to-oxime carbon bridged organocobaloxime/β-cyclodextrin inclusion complex has been formed in a β-cyclodextrin induced reaction, which was confirmed by X-ray structure analysis and FAB-MS.     

Preparation and electrochemical behavior of water-soluble inclusion complex of ferrocene with β-cyclodextrin polymer

A new water-soluble inclusion complex of ferrocene (Fc) with β-cyclodextrin polymer (β-CDP) was prepared by a facile strategy and characterized by ¹H NMR spectroscopy, elemental analysis, powder X-ray diffractometry, thermogravimetry, UV–vis spectroscopy and cyclic voltammetry. Compared with Fc and the inclusion complex of Fc with β-cyclodextrin (Fc-β-CD), the solubility of ferrocene-β-cyclodextrin polymer (Fc-β-CDP) was greatly enhanced due to the water-soluble β-CDP host. The ratio of β-cyclodextrin (β-CD) unit in β-CDP to Fc was determined as 1:1. At 25 °C, the dissociated constant of Fc-β-CDP was measured as 3.65 mM by UV–vis spectroscopy and cyclic voltammetry. The electrochemical properties of Fc-β-CDP in water were studied. The diffusion coefficients of oxidation state and reduction state were calculated as 3.52 × 10⁻⁷ cm² s⁻¹ and 3.93 × 10⁻⁷ cm² s⁻¹. The resulting value of standard rate constant was measured as 1.95 × 10⁻³ cm s⁻¹. The diffusion activation energy was calculated as 21.8 kJ mol⁻¹.     

Preparation and characterization of polyseudorotaxanes based on adamantane-modified polybenzoxazines and β-cyclodextrin

β-Cyclodextrin (β-CD) forms inclusion complexes (ICs) with adamantane-modified benzoxazines (2 benzoxazine and 3 benzoxazine). These benzoxazines can readily penetrate into the CD's hydrophobic cavity, causing turbidity of their solutions, from which fine crystalline powders are obtained. We characterized these complexes by powder X-ray diffraction, ¹³C and ¹³C CP/MAS NMR spectroscopies, DSC, and TGA. The X-ray diffraction and solid-state ¹³C CP/MAS NMR spectroscopy indicate that the IC domains of the polypseudorotaxanes maintain their channel-type structures after the ring-opening curing reactions have occurred. Furthermore, DSC measurements indicate that complexing the adamantane-modified benzoxazine units with β-CDs result in stiffer main chains and, thus, higher glass transition temperature. TGA also indicates that the inclusion complexes have enhanced its thermal stability.     

Crosslinking of β-cyclodextrin and combining with ammonium polyphosphate for flame-retardant polypropylene

This work presents the synthesis of crosslinked hexamethylene diisocyanate β-cyclodextrins (HDI-CDs) by reacting β-cyclodextrin (β-CD) with HDI as a crosslinking agent at different feed ratios. As a novel char-forming agent, the HDI-CDs are combined with ammonium polyphosphate (APP) and applied in polypropylene (PP) to form intumescent flame-retardant composites. The structure of HDI-CDs is characterized by Fourier transform infrared spectra (FTIR), ¹³C nuclear magnetic resonance spectroscopy, and nitrogen adsorption–desorption test. The thermogravimetric analysis (TGA) results indicate that HDI-CDs have better char-forming performance than β-CD. FTIR spectra, X-ray diffraction, and Raman spectra characterization demonstrate that the reaction between HDI-CDs and APP contributes to the formation of a more stable char layer than β-CD and APP. According to the results of TGA, scanning electron microscopy, limiting oxygen index (LOI), UL-94, and X-ray photoelectron spectroscopy test, when the crosslinking degree of HDI-CDs is high enough (not less than β-CD:HDI = 1:3.6), the PP/APP/HDI-CDs composites can form a compact and dense char layer during combustion. Among all composites, PP/APP/HDI-CD(4) shows the best flame-retardant performance, which can pass the UL 94 V-0 rating with an LOI value of 32.8% when the loading of flame retardants is 28 wt %. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48320.     

UV photopolymerized hydrogels with β-cyclodextrin moieties

Hydrophilic hydrogels based on poly(ethylene glycol)–poly(propylene glycol)–poly(ethylene glycol) block copolymers have potential applications in drug delivery, tissue engineering and other biomedical devices due to their excellent biocompatibility and environmental sensitivity. However, they also exhibit some shortcomings in terms of swelling and mechanical properties as well as affinity for water-insoluble or hydrophobic drug molecules. To address these limitations, new polymeric hydrogels with β-cyclodextrin moieties were prepared by UV photo-polymerization of maleic anhydride-substituted β-CD (MAH-CD) and the block copolymer macromer from Pluronic F68 and poly(ɛ-caprolactone). Their swelling and dynamic rheological properties were investigated with respect to the effects of feed compositions. It was found that the swelling ratio, storage modulus and loss modulus of the resulting hydrogel increased with the increase of MAH-CD amount. Incorporation of MAH-CD resulted in strong viscoelastic system with dominating elastic behavior.