Stimuli-responsive multilayer chitosan hollow microspheres via layer-by-layer assembly

Novel stimuli-responsive multilayer chitosan hollow microspheres with chitosan as the unique component have been fabricated by the sequential layer-by-layer electrostatic assembly technique from the sacrificial templates (polystyrene sulfonate, PSS) with chitosan (CS) as the polycation and carboxymethyl chitosan (CMCS) as the polyanion, respectively. Their hollow structure was confirmed by the TEM analysis. The DLS analysis indicated that the multilayer chitosan microcapsules were pH and ionic strength dual-responsive. Due to the biocompatibility of the single component chitosan used, the multilayer chitosan microcapsules are expected to be used in the controlled release of drugs.     

Bioactive polymeric formulations for wound healing

Ricinoleic acid (RA) has potential to promote wound healing because of its analgesic and anti‐inflammatory properties. This study investigates the synthesis and characterization of RA liposomes infused in a hydrogel for topical application. Lecithin liposomes containing RA were prepared and incorporated into a chitosan solution and were subsequently cross‐linked with di‐aldehyde β‐cyclodextrin (Di‐β‐CD). Chitosan/Di‐β‐CD concentrations and reaction temperatures were varied to alter gelation time, water content, and mechanical properties of the hydrogel in an effort to obtain a wide range of RA release profiles. Hydrogel cross‐linking was confirmed by spectroscopy, and liposome and carrier hydrogel morphology via microscopy. Chitosan, Di‐β‐CD, and liposome concentrations within the formulation affected the extent of matrix swelling, mechanical strength, and pore and overall morphology. Higher cross‐linking density of the hydrogel led to lower water uptake and slower release rate of RA. Optimized formulations resulted in a burst release of RA followed by a steady release pattern accounting for 80% of the encapsulated RA over a period of 48 hours. However, RA concentrations above 0.1 mg/mL were found to be cytotoxic to fibroblast cultures in vitro because of the oily nature of RA. These formulations promoted wound healing when used to treat full thickness skin wounds (2 cm²) in Wister male rats. The wound contraction rates were significantly higher compared to a commercially available topical cream after a time period of 21 days. Histopathological analysis of the RA‐liposomal chitosan hydrogel group showed that the epidermis, dermis, and subcutaneous skin layers displayed an accelerated yet normal healing compared to control group.     

Determination of Hydrogen Peroxide by Electrochemiluminescence Using a Chitosan–graphene Composite Film Doped Cadmium-Tellurium Quantum Dot Modified Glassy Carbon Electrode

Here is reported the novel determination of hydrogen peroxide by electrochemiluminescence using a chitosan–graphene composite film doped cadmium-tellurium quantum dot modified glassy carbon electrode. The cadmium-tellurium quantum dots were studied by absorption and fluorescence spectroscopy. Scanning electron microscopy and electrochemical impedance spectroscopy were used to characterize the structure morphology of the composite matrix. The electrochemiluminescence emission was linear with the concentration of hydrogen peroxide in the range of 3.5?×?10^?7 to 1.1?×?10^?5?M with a determination limit of 2.1?×?10^?7?M. Furthermore, the modified electrode showed excellent reproducibility and stability.     

Microencapsulation of DNA Within alginate microspheres and crosslinked chitosan membranes for in vivo application

Calf thymus DNA was microencapsulated within crosslinked chitosan membranes, or immobilized within chitosan-coated alginate microspheres. Microcapsules were prepared by interfacial polymerization of chitosan, and alginate microspheres formed by emulsification/ internal gelation. Diameters ranged from 20 to 500 Μm, depending on the formulation conditions. Encapsulated DNA was quantifiedin situ by direct spectrophotometry (260 nm) and ethidium bromide fluorimetry, and compared to DNA measurements on the fractions following disruption and dissolution of the microspheres. Approximately 84% of the DNA was released upon core dissolution and membrane disruption, with 12% membrane bound. The yield of encapsulation was 96%. Leakage of DNA from intact microspheres/capsules was not observed. DNA microcapsules and microspheres were recovered intact from rat feces following gavage and gastrointestinal transit. Higher recoveries (60%) and reduced shrinkage during transit were obtained with the alginate microspheres. DNA was recovered and purified from the microcapsules and microspheres by chromatography and differential precipitation with ethanol. This is the first report of microcapsules or microspheres containing biologically active material (DNA) being passed through the gastrointestinal tract, with the potential for substantial recovery.     

壳聚糖衍生物的制备及其吸附性能

壳聚糖衍生物的制备及其吸附性能曲荣君，马千里，郑秀丽，孙言志（烟台师范学院化学系烟台２６４０２５）关键词壳聚精衍生物，制备，吸附壳聚糖（ＣＴＳ）是重金瞩离子的吸附剂￣［１，２］，由于壳聚精分子中的－ＮＨ＿２在ｐＨ较低的水溶液易形成而使ＣＴＳ溶于水，造...     

A highly efficient transacetalization of 2-formylpyrrole acetals in alkaline media

The reaction of 2-formylpyrrole acetals with sodium alkoxide in alcohols at reflux temperature smoothly proceeded to generate corresponding transacetalization products in nearly quantitative yields.A plausible mechanism involving the formation of a highly reactive intermediate azafulvene species was proposed to explain the observed transformation.     

Serendipitous synthesis of 3-hydroxy tetrahydrofurans from tin catalyzed sulfonylation of acyclic 1,2,4-triols

The reaction of syn-1,2,4-triols under sulfonylation conditions catalyzed by Bu₂SnO (5 mol %) results in cyclization and the formation of 3-hydroxy tetrahydrofurans (56-85%) while the anti-1,2,4-triols react to give C1-O-sulfonyl derivatives in good yields (66-83%) and the cyclization product in poor yield (5-12%). A mechanism that justifies these observations is proposed to occur via the tosylation of the primary hydroxyl followed by an intramolecular tin acetal rearrangement to a 1,3-stannylene which then undergoes a 5-exo-tet-cyclization. The difference in rates of cyclization reactivity is due to the energetically more stable tin acetals of syn-1,3-diols compared to those of anti-1,3-diols.     

聚乙烯醇／壳聚糖共混膜优先透醇性能的研究

聚乙烯醇／壳聚糖共混膜优先透醇性能的研究王新平，沈之荃，张富尧，林荣轩（浙江大学高分子系，化学系，杭州，３１００２７）关键词渗透蒸发，聚乙烯醇／壳聚糖共混物膜，乙醇水溶液本文首次报道利用亲水性的聚乙烯醇和壳聚糖制得具有很高的乙醇优先透过选择性的透醇型...     

相转移催化合成增塑剂BBP和水杨醛的研究

相转移催化合成增塑剂ＢＢＰ和水杨醛的研究郭锡坤，高文华，曾东宇（汕头大学化学系，汕头５１５０６３）关键词相转移催化，季铵盐，聚乙二醇，邻苯二甲酸丁苄酯，水杨醛，增塑剂邻苯二甲酸丁苄酯（增塑剂ＢＢＰ）是一种优良的增塑剂．邻羟基苯甲醛（水杨醛）不仅是重要...     

Hydroxypropyl chitosan bearing beta-cyclodextrin cavities: synthesis and slow release of its inclusion complex with a model hydrophobic drug

Hydroxypropyl chitosan-graft-carboxymethyl beta-cyclodextrin (HPCH-g-CM beta-CD) was synthesized by grafting CM beta-CD onto HPCH using water soluble 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) as the condensing agent. Due to the presence of hydrophobic beta-CD rings onto the HPCH backbone, this polymer can be used as a matrix for controlled drug release. The adsorption of a hydrophobic model drug, ketoprofen, by HPCH-g-CM beta-CD microparticles (using tripolyphosphate as an ionic crosslinking agent) fitted well in the Langmuir isotherm equation. The drug dissolution profile showed that HPCH-g-CM beta-CD microparticles provided a slower release of the entrapped ketoprofen than chitosan, and the release behavior was influenced by the pH value of the medium. These results suggest that beta-CD grafted with chitosan derivatives may become a potential biodegradable delivery system to control the release of hydrophobic drugs with pH-responsive capability.