The Effect of Chitin Alkaline Deacetylation at Different Condition on Particle Properties

The abundant biopolymer chitin, found mainly in crustaceous exoskeleton, such as crab, shrimp and lobster, can be deacetylated to yield chitosan. This slightly different biopolymer is more reactive than chitin, being more effective for many applications in fields as environmental remediation, biomedical sciences, catalysis and so on. The main process for chitin deacetylation used sodium hydroxide solutions at high temperatures for long times to obtain chitosan with high deacetylation degree (DD). The present study has evaluated the effect from room temperature (RT), 363 and 393 K, hydroxide concentration (2.0 or 10.0 mol dm³) and time (3 and 24 h) on shrimp chitin deacetylation. Similar amounts of chitin and sodium hydroxide solutions were stirred jointly and the resultant solids were filtered and washed until pH 7, than dried at environmental conditions. The obtained samples were characterized by several techniques, such as elemental analysis, X-rays diffraction (XRD), laser scattering and absorption spectroscopy at infrared region with Fourier transform (FTIR), which was used for DD calculation. The results showed that all chitin-chitosan samples did not reach DD > 90%, as observed for some good commercial chitosans. The highest DD was obtained by the sample prepared at more drastic conditions, as expected, however the higher sodium hydroxide concentration leads to decrease of molecular mass when associated with high temperatures. The crystallinity was influenced mostly by reaction time, which change the positions and intensities as indicated by XRD main peaks, located at 9.3 and 19.4° 2Θ. Particle sizes were strongly diminished by treatment at 393 K, what imply also some increase at the pressure, favoring chain dissociation reactions. This work mapped several properties for chitin-chitosan samples achieved by the described conditions.     

Preparation of Chitin Hydrogel Under Mild Conditions

Both the amount of water and the number of calcium ions are main factors affecting the dissolution of chitin in calcium chloride dihydrate-saturated methanol (calcium solvent). The higher degree of N-acetylation of the chitin was also indicated by its higher solubility in calcium solvent. The chitin hydrogel was prepared by adding a large excess of water to the chitin solution with vigorous stirring, followed by extensive dialysis against water or by filtration to remove the methanol and calcium ions. The water content of the chitin hydrogel was approximately 94–96% (w/v) and could be controlled by centrifugation. The chitin gel was also prepared by the addition of a large excess of alcohol, such as ethanol and iso-propanol, and these protocols were found to be effective under anhydrous conditions because the alcohols were exchangeable with other organic solvents in solution. The chitin hydrogel was more susceptible to lysozyme than to chitinase, and showed and a poor susceptibility to chitosanase. A α-chitin-type crystalline structure was regenerated from chitin sheets prepared from both α-chitin and β-chitin solutions in calcium solvent, but the β-chitin-type sheet was formed from the β-chitin hydrogel prepared by mechanical agitation in water. The α-chitin hydrogel solidified when thawed after freezing, but the β-chitin hydrogel prepared by mechanical agitation maintained its gel form even after prolonged freezing. Animal studies revealed a low toxicity for the chitin sheet and an acceleration of epidermal cell regeneration.     

Comparative study on interaction between copper (II) and chitin/chitosan by density functional calculation

The DMol³ calculations, based on density functional theory (DFT), have been employed to investigate the interactions between Cu²⁺ and chitin/chitosan residues. The possible initial conformations were optimized at the generalized gradient approximation (GGA) level, with spin unrestricted approach, symmetric unrestriction, doublet multiplicity and BLYP/DND methods. For all initial complexes considered, the Cu²⁺ was completed with H₂O and/or OH⁻ groups to neutralize the initial complexes with hexacoordination geometries. The tendency of ligands to coordinate with Cu²⁺ is NH₂ > C₃OH > H₂O > NHCOCH₃, suggesting that amine groups (NH₂) on chitosan prefer to bind Cu²⁺ and acetamide groups (NHCOCH₃) on chitin lose their coordination with Cu²⁺ in aqueous solution. The geometries of bridge and pendant models have been comparatively analyzed. The results show that bridge model is more favorable than pendant model. In terms of the optimized geometries, the initial hexacoordination structures of Cu²⁺ designed seem more reasonable than initial tetracoordination ones designed.     

壳聚糖及其在分析化学中的应用

综述了壳聚糖、甲壳素在污水处理、电化学、原子吸收光谱、高效液相色谱、吸光光度法中的应用。引用文献28篇。     

Morphology and permeability of cellulose/chitin blend membranes

A series of biodegradable cellulose/chitin blend membranes were successfully prepared from blend solution of cellulose and chitin in 9.5 wt% NaOH/4.5 wt% thiourea aqueous solution coagulating with 5.0 wt% (NH₄)₂SO₄. The influence of chitin content on the morphology and structure of the membranes was studied by scanning electron microscopy, environmental scanning electron microscopy and wide-angle X-ray diffractometry, as well as Fourier transform infrared spectroscopy. Using double-cell method and solution depletion method, the permeability and partition coefficients of three model drugs (ceftazidine, cefazolin sodium, and thiourea) were determined in phosphate buffer solution to clarify the diffusion mechanism governing transport of solutes in these membranes. Diffusion coefficients were calculated from the permeability and partition coefficients in terms of Fick's law. The effects of the chitin content, pH, ionic strength, molecular size and temperature on the drug diffusion were also studied. Our results revealed that all of the membranes had a porous-like structure. The introduction of chitin exhibited great influence on the morphology and crystal structure of the blend membranes, resulting in a significant different permeability. For the first time, a dual diffusion mechanism with some hindrance of molecular diffusion via polymer obstruction was employed to explain the transport of drugs in the membranes.     

热塑性甲壳素衍生物N,O-苄基壳聚糖的合成及表征

天然高分子的热塑化一直引起人们的极大关注．由于存在大量的分子内和分子间氢键,一般天然高分子都不能加热塑化,从而限制了其应用．纤维素和淀粉的热塑化改性已有了许多研究．典型的热塑性纤维素衍生物有乙基纤维素、醋酸纤维素和经丙基纤维素等[1,2],有些纤维素衍生物还具有热致液晶性．淀粉的某些衍生物也已有热塑性[3]．在分子结构上,甲壳素／壳聚糖比纤维素或淀粉多了乙酰氨基和氨基,更易形成氢键,分子间作用力更强．迄今,国内外已报道了大量甲壳素／壳聚糖衍生物,但均无热塑性．我们曾合成具有热塑性的氰乙基经丙基壳聚糖,但熔点与分解温度之间只有27℃E4J．热塑性甲壳素的研究不仅为甲壳素的加工利用开辟了新途径,而且也将为热致性甲壳素液晶的研究奠定基础,从而进一步丰富和深化目前以纤维素衍生物为主的热致胆舀液晶研究[5,6]．为此,本文研究了一种新的热塑性甲壳素衍生物,并从结构上讨论了其具有热塑性的原因．     

Porous nano-minerals substituted apatite/chitin/pectin nanocomposites scaffolds for bone tissue engineering

In the current study, a porous 3D scaffold using Gallium-Apatite/chitin/pectin (Ga-HA/C/P) nanocomposites scaffolds (NCS) were fabricated by freeze-drying process with applications in orthopedics (bone tissue engineering). Various NCSs (0%, 30%, 50 and 70%) were prepared and characterized for its chemical structure, crystalline phase, surface texture by using various techniques such as FT-IR, XRD and SEM-EDX, respectively. The analyses of physicochemical properties proved that the formulated scaffolds were highly porous, and mechanically stable with superior density. The nanocomposite scaffolds also presented with increased swelling ability, lower biodegradation rate and higher mechanical strength. Further, biocompatibility and cytotoxicity of Ga-HA/C/P nanocomposite scaffolds were studied using NIH3T3 cells and MG-63 cells revealed no toxicity and cells attached and proliferated on scaffolds. Further implantation of prepared NCS showed mature bone formation through formation of new bone cells and osteoblast differentiation. Also, Ga-HA/C/P nanocomposites scaffolds proved to be more effective than chitin-pectin composite scaffolds. Taking results together it can be inferred that the prepared nanocomposite scaffolds possesses the prerequisites and showed great potential for treating orthopedic applications.     

Adsorption Mechanism of Composite Whisker on Copper Ions and Lead Ions

A new kind of inorganic composite adsorbent based on chitin whiskers(CHW) and potassium tetratitanate whiskers(PTW) was synthesized via the thermal deposition to remove Cu²⁺ and Pb²⁺ from wastewater. CHW could be successfully coated on the surface of PTW when thermal treated 8 times. The adsorption process was better fitted with the Langmuir and Freundlich models. The adsorption process was more conformed to the Pseudo-second-order model. The results from XPS(X-ray photoelectron spectrum) further show that the adsorption mechanism between CHW-PTW and Cu²⁺, Pb²⁺ are both ion exchange and chemical adsorption. Thermodynamic parameters suggest that the adsorption processes are nonspontaneous. The adsorption of Cu²⁺ and Pb²⁺ is endothermic and exothermic, respectively.