PEGylation of chitosan for improved solubility and fiber formation via electrospinning

PEG-N-chitosan and PEG-N,O-chitosan were synthesized via reductive amination and acylation of chitosan, respectively. The structures were confirmed by FTIR and H¹NMR. The extents of PEGylation increased with reducing chain lengths of either chitosan (M _v = 137–400 kDa) or poly(ethyelene glycol) (PEG, M _n = 500–2 kDa). Water solubility were easily achieved at degree of substitution (DS) as low as 0.2 for either derivtive whereas the PEG-N,O-chitosan at DS = 1.5 was soluble in organic solvents, including CHCl₃, DMF, DMSO and THF. None of the aqueous solutions of PEG-N-chitosan or PEG-N,O-chitosan alone could be electrospun into fibers. Electrospinning of PEG550-N,O-chitosan145 at 25% in DMF produced fibrous structure intermixed with beads. The efficiency of fiber formation and the uniformity of fibers were improved by increasing the solution viscosity using a cosolvent or reducing the solution surface tensions with a non-ionic surfactant. Ultra-fine fibers with diameters ranging from 40 nm to 360 nm and an average diameter of 162 nm were efficiently generated from electrospinning of 15% PEG550-N,O-chitosan145 in 75/25 (v/v) THF/DMF cosolvents with 0.5% Triton X-100^TM.     

壳聚糖对Cd2+的吸附性能

壳聚糖(ｃｈｉｔｏｓａｎ,简称ＣＴＳ)是由虾、蟹壳脱钙、蛋白质和脂肪后、经化学改性得到的天然高分子聚合物,分子中存在能与金属离子配位的羟基或氨基,其配合物可作为絮凝剂和螯合吸附剂用于水处理[1 3]及湿法冶金[4]等。本文考察了壳聚糖对Ｃｄ2+的静态吸附性能。1　实验部分1.1　试剂与仪器壳聚糖(浙江玉环县化工厂);硫酸镉、硝酸镉(分析纯,广州化学试剂厂);碳酸镉(化学纯,上海试剂二厂),其余试剂均为分析纯。78 1型磁力加热搅拌器(江苏金坛市恒丰仪器厂),501型超级恒温器(上海实验仪器厂),ｐＨＳ 3型酸度计(上海第二分析仪器厂)。1…     

茜素红S荧光猝灭法测定壳聚糖含量

在pH 5.0的NaAc-HAc缓冲液中壳聚糖对茜素红S的荧光强度具有明显的猝灭作用,且猝灭程度F0/F与加入的壳聚糖浓度成线性关系,据此建立一种测定壳聚糖含量的荧光猝灭法。确定了最佳测定条件,线性回归方程为F0/F=-0.438 37 0.436 27c(mg·L-1),线性范围为0-16.667 mg·L-1,r=0.996,检测限为0.473 mg·L-1;平均回收率为100.60％,测定了样品中壳聚糖的含量,并考察了干扰因素对测定的影响。采用该方法可测定复杂样品中微量壳聚糖含量。     

A chitosan-based chemomechanical polymer triggered by stacking effects with aromatic effectors including aminoacid derivatives

Chitosan with a covalently attached anthrylunit is used as chemomechanical polymer, in which stacking and cation-π interactions allow aromatic effector compounds with positively charged nitrogen centers to trigger macroscopic motions in aqueous surrounding. Thus, only protonated heterocycles such as imidazole or histamine lead at pH 5 to expansion, in contrast to toluenesulfonic acid, or pyrazole and pyrimidine. Inorganic salts and pH influence the polymer swelling, and must be taken into account for the calculation of net effects induced by organic effectors. Reversible volume expansions on the top of the swelling effect of water alone are observed as function of different effector structures, showing, for example, 45% net effect with imidazole and 66% with benzimidazole. Aminoacids, for solubility reasons measured in the form of their methylesters, yield smaller expansions, showing, however, a regular and selective increase with the lipophilicity of the residues. The kinetics of effector uptake, which relates to the velocity of expansion, are measured with histamine and follow first order, with t_1/2=2.7 min for 50% absorption.     

天然高分子表面活性剂

综述了淀粉、纤维素和壳聚糖类表面活性剂的合成方法、性质及功能。     

Amperometric determination of bovine insulin based on synergic action of carbon nanotubes and cobalt hexacyanoferrate nanoparticles stabilized by EDTA

A simple approach is proposed for the synthesis of cobalt hexacyanoferrate nanoparticles (CoNPs) with uniform shape and size controlled by ethylene diamine tetraacetic acid (EDTA) as a stabilizer. A sensitive amperometric biosensor for insulin has been prepared using glassy carbon electrodes by solubilization of carbon nanotubes (CNTs) in chitosan (CHIT) together with CoNPs synthesized by the new methodology. The CoNP-CNT-CHIT organic–inorganic system exerts a synergistic effect, resulting in the remarkably enhanced insulin currents owing to the superior electron-transfer ability of CNTs and the excellent reversible redox centers of CoNPs. High-resolution transmission electron microscopy (HRTEM) was used to provide closer inspection of the CoNPs. The effects of alkali metal cations and the concentrations of CNTs and CoNPs on the voltammetric behavior of the film-modified electrode were also investigated. In pH 6.98 phosphate buffer (PB) at +0.7 V (vs. SCE) the insulin biosensor exhibits a linear response range of 0.1–3 μM with a correlation coefficient of 0.98, and the detection limit (S/N=3) is determined to be 40 nM, the stability of the biosensor was tested and found satisfactory. There is great promise for in vivo measurements of this important hormone.     

Preparation and characterization of chitosan-clay nanocomposites with antimicrobial activity

Chitosan-montmorillonite nanocomposites were prepared by an ion exchange reaction between water soluble oligomeric chitosan and a Na⁺-montmorillonite. The chitosan-montmorillonite nanocomposites were rapidly prepared within 1 h due to the high affinity between the chitosan and the montmorillonite clay host. The basal spacings of the composites were in a range of 14.5-19.6 Å depending on the mixing ratio of chitosan to clay. According to the thermogravimetric analysis (TG) and powder X-ray diffraction analysis the thermal stability of chitosan was remarkably improved in the interlayer space due to the strong electrostatic interaction of cationic chitosan molecules with anionic silicate layers. From the antimicrobial activity test it was found that the nanocomposites showed a synergistic effect in the antimicrobial activity against to Escherichia coli and Staphylococcus aureus.     

Preparation of glycerol plasticized chitosan films using AlCl3·6H2O as the solvent: optical,crystalline, mechanical and barrier properties

Chitosan films plasticized with the complex of AlCl₃·6H₂O and glycerol were prepared by using AlCl₃·6H₂O as the solvent. The effect of AlCl₃·6H₂O and glycerol complex with Chitosan was studied by SEM, XRD, TGA, and tensile testing. The complex would increase the water resistance and destroy the crystals of chitosan film. The TGA results proved that the chitosan film plasticized with the complex showed higher thermal stability at the temperature below 200?°C than pure chitosan film. With the addition of the complex of AlCl₃·6H₂O and glycerol, the tensile strength of chitosan film decreased and the elongation at break increased.     

Degradation of chitosan with self-resonating cavitation

For the degradation of chitosan, a novel physical method of self-resonating cavitation with strong cavitation effects was investigated in this paper. The effects of initial concentration, pH, temperature, inlet pressure and cavitation time on the degradation efficiency of chitosan were evaluated. It was found that the degradation efficiency was positively correlated with temperature and cavitation time, but was negatively correlated with the solution concentration. The degradation efficiency was maximized at pH of 4.4 and inlet pressure of 0.4 MPa. Under the experimental conditions, the intrinsic viscosity of chitosan solution was reduced by 92.2%, which was twice as high as the degradation efficiency where a Venturi tube cavitator was used. The viscosity-average molecular weights of initial and degraded chitosan were 651 and 104 kD, respectively. The deacetylation degree of chitosan slightly decreased from 89.34% to 88.05%. Structures and polydispersity of initial and degraded chitosan were measured by Fourier-transform infrared spectroscopy (FT-IR), nuclear magnetic resonance hydrogen spectroscopy (¹H NMR), X-ray diffraction (XRD) and gel permeation chromatography (GPC). The results showed that the degradation process did not change the natural structure of chitosan. XRD peaks of the original chitosan were observed at 2θ of 9.59° and 20.00°, and the one at 2θ of 20.00° was obviously weakened after the degradation process, which indicated that the crystallinity of chitosan decreased significantly after the degradation. The polydispersity index of chitosan samples decreased from 3.17 to 2.75, indicating that the molecular-weight distribution of products after the degradation was more concentrated. The results proved that self-resonating cavitation prompted the degradation of chitosan and could reduce the polydispersity of the products for the production of oligochitosan with homogeneous molecular weights.     

海藻酸钠和壳聚糖静电复合弹性支架的制备和表征

通过静电作用和相分离技术制备海藻酸钠/壳聚糖静电复合弹性支架,研究了冷冻温度和固含量对支架材料孔径的影响及组分比对材料力学性能、亲水性、降解性能和生物相容性的影响.固含量为2%(质量分数)及冷冻温度为-24℃时,支架孔径为110~170μm,并且亲水性良好,平衡溶胀度大于1400%.改变固含量和组分比可调控材料的力学性能;循环力学测试表明,湿态支架具有良好的弹性和一定的耐疲劳性;降解速率可由组分比调控;兔脂肪干细胞(rASCs)在支架上的培养结果表明,羧基和氨基摩尔比为2∶1和1∶1时细胞以聚集体存在;羧基和氨基摩尔比为1∶2时细胞黏附于支架上,实现细胞黏附/聚集体的调控.