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研究了β分子筛的物化性质对其催化活性的影响。实验发现,β分子筛对甲基叔丁基醚(MTBE)反应的催化活性是各类酸中心共同作用的结果,但强Lewis酸密度对其活性的影响较大;比表面积、二次孔体积及微孔比表面积等因素与异丁烯转化率无明显的相关性;C4原料中的惰性组分对MTBE反应的影响较小,但以混合C4为原料时MTBE反应的初始反应速率较低。  相似文献
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It is always difficult to achieve pure hydroxyapatite (HA) and tricalcium phosphate (TCP) at high temperatures by using non-alkoxide-based sol?Cgel techniques and other related techniques, which have limited their application. In this paper, our study brought to light that the reason for that was a non-uniform mixing of the reactants at molecular-level, which led to different Ca/P ratios and hence to the occurrence of three high temperature stable phases of HA, TCP and CaO at high temperatures. A series of experiments were designed to demonstrate this proposed hypothesis. Our study firstly revealed that by introducing ethylene glycol into the sol?Cgel system, the uniform mixing of the reactants at molecular-level could be obtained and then pure HA and TCP phases were achieved at high temperatures.  相似文献
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Degradation profiles and surface wettability are critical for optimal application of electrospun fibrous mats as drug carriers, tissue growth scaffolds and wound dressing materials. The effect of surface morphologies and chemical groups on surface wettability, and the resulting matrix degradation profiles were firstly assessed for electrospun poly(d,l-lactide) (PDLLA) and poly(d,l-lactide)-poly(ethylene glycol) (PELA) fibers. The air entrapment between the fiber interfaces clarified the effects of various surface morphologies on the surface wettability. Chemical groups with lower binding energy were enriched on the fiber surface due to the high voltage of the electrospinning process, and a surface erosion pattern was detected in the degradation of electrospun PDLLA fibers, which was quite different from the bulk degradation pattern for other forms of PDLLA. Contributed by the hydrophilic poly(ethylene glycol) segments, the degradation of electrospun PELA fibers with hydrophobic surface followed a pattern different from surface erosion and typical bulk degradation.  相似文献
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The recurrence of acute gout attacks remains an unsolved problem in clinical therapy. In order to tackle this problem, poly(ε‐caprolactone) (PCL)/gelatin composite fibrous devices loaded with luteolin are presented via electrospinning for the therapy of gout and its recurrence. The luteolin‐loaded fibrous device has the capability of inhibiting metabolic activities and reducing inflammation‐associated cytokine productions (TNF‐a, IL‐1β, IL‐6) that are secreted by lipopolysaccharide stimulated RAW 264.7 macrophages. The device can also suppress the reaction activities of xanthine oxidase for 7 d in vitro. In vivo, acute gout model is established by injecting monosodium urate (MSU) crystals into New Zealand rabbits' knees, then the luteolin‐loaded PCL/gelatin (5:5) nanofiber device is implanted near the gout sites. The results show that the device can alleviate the acute gouty arthritis. In the mean time, the luteolin‐loaded PCL fiber device with a longer drug release profile is implanted in a recurrent gout model, which is constructed by injecting MSU crystals into rabbits' knees three times. The results on day 21 reveal that this device has the potential to overcome the recurrence of gout. Therefore, the drug‐loaded polymer fiber device can be an inspiration for potential gout therapy to overcome recurrent attacks.

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Considerable efforts have been devoted to enhancing the cell penetration of nanoparticles by coating cell‐penetrating peptides (CPPs) on the surface. However, the internalization mechanism for a CPP at different concentrations varies a lot. It is acknowledged that the mechanism is restricted to endocytic pathway at relatively low concentrations; however, direct translocation becomes dominant at high concentrations. This raises an interesting question on how the surface Tat coating density of the nanoparticles would influence their cell–membrane interaction and the consequent internalization behavior. This study systematically investigates the effect of Tat peptides on the internalization behavior of polymeric micelles by tuning surface Tat coating density, incubation concentrations, incubation time, and other factors using poly(ethylene glycol)–poly(ε‐caprolactone) copolymer (PEG‐PCL) micelles. It is found that both energy‐dependent and energy‐independent pathways are involved in the cellular uptake process, and the Tat‐conjugated polymeric micelles strongly accumulated on the cell surface at initial stage. The membrane‐anchoring and internalization rate increase with the increasing Tat coating density. Furthermore, the increasing of Tat coating density accelerates the energy‐independent pathway. It is envisioned that this finding will further shed light on the surface modification of nanoparticles for enhanced cell penetration and direct translocation into cell cytoplasm.  相似文献
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Fluorescein isothiocyanate (FITC), a fluorescent probe, is coupled to amphiphilic monomethoxy poly(ethylene glycol)‐block‐poly(ε‐caprolactone) (mPEG‐PCL) copolymers. FITC‐labeled mPEG‐PCL copolymers self‐assemble into micelles through the solvent evaporation method. The cellular internalization is examined using fluorescence microscopy on incubation of NIH‐3T3 fibroblasts with micelles or free FITC solution. The effect of the hydrophilic/hydrophobic ratio on the endocytosis mechanisms is evaluated by fluorescence microscopy on culturing of human hepatoblastoma cells and human umbilical vein endothelial cells, individually, mixed with the micelles holding the same parameters including micelle size, shape, and surface charges.

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This study was aimed to design core–sheath‐structured polymeric fibers for protein delivery through emulsion electrospinning to enhance the encapsulation efficiency (EE), structural integrity, and activity retention, and to achieve controllable protein release. Integral core–sheath structure was achieved for electrospun fibers with lysozyme loading efficiency of 93.3% and the specific activity retention (SAR) of 64.6%, while the surface protein content (SP) was as low as 4.2%. The emulsion components were optimized to minimize the burst release and extend the release period, and the release profiles were found to be closely related with the fiber characteristics such as the SPs. An initial burst release as low as 6.2% followed by gradual release for 33 days was indicated from poly(ethylene glycol)‐poly(DL ‐lactide) (PELA) fibers. The gradual protein release was determined by a competition of fiber collapse leading to accelerated release and fiber fusion leading to decelerated release. Dependent on the matrix polymer and protein encapsulated, the degradation behaviors of the fiber matrices were correlated with the release rate and the effective lifetime of the drug release. The core–sheath‐structured ultrafine fibers could protect the structural integrity and bioactivity of encapsulated lysozyme, and an increase in the protective effect was demonstrated for fibers prepared from PELA matrix. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献
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