1,3-Dipolar cycloaddition of stabilised and non-stabilised azomethine ylides derived from uracil polyoxin C (UPoC): access to nikkomycin analogues

Cascade thermal and decarboxylative cycloaddition reactions of uracil polyoxin C (UPoC) with mono- and di-carbonyl compounds in the presence of a dipolarophile leads, via stabilised and non-stabilised azomethine ylides respectively, to a series of polyoxin cycloadducts related to Nikkomycin B in good to excellent yields and high diastereoselectivity.     

Surface characteristics of chitin-based shape memory polyurethane elastomers

Shape memory polyurethanes (SMPUs) were prepared from polycaprolactone diol 4000 (PCL 4000), 1,4-butanediol (BDO), chitin, dimethylol propionic acid (DMPA), triethylamine (TEA) and 4,4′-diphenylmethane diisocyanate (MDI), and the structures of the synthesized materials were verified by infrared spectroscopy. The effects of chitin and DMPA contents in the polyurethane formulation on surface properties were investigated. DMPA provides function of making hydrophilic polyurethanes. The crystalline structure of chitin enhanced the hydrophobicity of the synthesized materials. Contact angle, water absorption, surface free energy, work of water adhesion and swelling behavior of the synthesized polyurethanes were affected by varying the DMPA and chitin contents. The interactions of the PU films with solvents on the surface were clearly related to the contents of DMPA and chitin in the final polyurethane formulation.     

Acetylation of Cellulose Nanowhiskers with Vinyl Acetate under Moderate Conditions

A novel and straightforward method for the surface acetylation of cellulose nanowhiskers by transesterification of vinyl acetate is proposed. The reaction of vinyl acetate with the hydroxyl groups of cellulose nanowhiskers obtained from cotton linters was examined with potassium carbonate as catalyst. Results indicate that during the first stage of the reaction, only the surface of the nanowhiskers was modified, while their dimensions and crystallinity remained unchanged. With increasing reaction time, diffusion mechanisms controlled the rate, leading to nanowhiskers with higher levels of acetylation, smaller dimensions, and lower crystallinity. In THF, a solvent of low polarity, the suspensions from modified nanowhiskers showed improved stability with increased acetylation.

     

过氧化氢甲壳素脱色反应条件与分子量研究

研究了不同条件下过氧化氢对虾壳甲壳素脱色的影响。实验结果表明，脱色反应速率在PH为10．5时达到最大，升高温度，增加过氧化氢浓度加快脱色的进行，甲壳素脱乙酰后脱色时间大大缩短，为之前的1／2，过氧化氢脱色降低了产物的分子量，并且产物分子量随脱色温度的升高而降低，借此可以通过改变脱色条件来控制产物分子量，虾壳甲壳素在40℃，PH为10．5c(H2O2）为3％时反应47min即可脱色，收率为96．2％，壳聚糖在此条件下用过氧化氢脱色后分子量为脱色前的59％，过氧化氢色后的甲壳素与精制甲壳素的红外图谱相吻合。     

IMPROVING NONTHROMBOGENICITY OF CHITIN WITH ZWITTERIONIC STRUCTURE OF SULFOBETAINE

In order to improve the nonthr0mbogenicity of chitin, a new monomer, N, N-dimethyl(β-hydroxyethyloxyethyl) ammonium propanesulfonate (DHAPS) was designed, synthesized and grafted onto the chitin membrane by using hexamethylene diisocyanate (HDI) as a coupling agent. Surface analysis of the grafted membranes by ATR-FTIR and XPS confirms that DHAPS has been successfully grafted onto the membrane surface. The platelet resistant property of the grafted membranes was evaluated by a platelet-rich plasma adhesion method. The results showed that platelet-adhesive resistance of the modified membrane has been greatly improved.     

Positive effects and mechanism of ultrasound on chitin preparation from shrimp shells by co-fermentation

The objective of this study is to explore the effect and mechanism of ultrasound on chitin extraction from shrimp shells powder (SSP) by the co-fermentation of Bacillus subtilis and Acetobacter pasteurianus. After pre-treating the SSP with high-intensity ultrasound (HIU) at 800 W, the protease activity in the fermentation solution reached 96.9 U/mL on day 3, which was significantly higher than for SSP that had not been pre-treated with ultrasound (81.8 U/mL). The fermentation time of the chitin extraction process was 5.0 d without ultrasound pre-treatment, while it was shortened to 4.5 d when using ultrasound at 800 W to treat SSP. However, there were no obvious differences when we applied ultrasound at low power (200 W, 400 W). Furthermore, chitin purified from shrimp shells pre-treated with HIU at 800 W exhibited lower molecular weight (11.2 kDa), higher chitin purity (89.8%), and a higher degree of deacetylation (21.1%) compared to SSP with no ultrasound pre-treatment (13.5 kDa, 86.6%, 18.5%). Results indicate that HIU peels off the protein/CaCO₃ matrix that covers the SSP surface. About 9.1% of protein and 4.7% of Ca²⁺ were released from SSP pre-treated with HIU at 800 W. These figures were both higher than with no ultrasound pre-treatment (4.5%, 3.2%). Additionally, the amount of soluble protein extracted from SSP through HIU at 800 W was 50% higher than for the control sample. SDS-PAGE analysis indicated that the soluble protein was degraded to the micromolecule. It also revealed that HIU (600, 800 W) induced the secondary and tertiary structure destruction of protein extracted from SSP. In conclusion, HIU-induced degradation and structural damage of protein enhances the protein/CaCO₃ matrix to be peeled off from SSP. Also, in the co-fermentation process, an increase of protease activity further accelerates deproteinization.     

Enhanced adsorption of Congo red using chitin suspension after sonoenzymolysis

In the present work, chitin suspensions after enzymolysis and sonoenzymolysis were taken as adsorbents to evaluate the adsorption properties of Congo red (CR) dyes. Compared with untreated chitin suspension, the CR adsorption performance was significantly improved after enzymolysis and even more after sonoenzymolysis. According to different adsorption kinetic and isotherm models, Langmuir isotherm and the pseudo-second order model were more reliable to describe the adsorption process of CR onto different chitin samples and demonstrated a monolayer and favorable physisorption process. What’s more, negative values of ΔG (Gibbs free energy change) and the shifts to higher negative values with the temperature increasing from adsorption thermodynamic study proved a spontaneous CR adsorption process. The structural characterization before and after adsorption further verified the physical adsorption between chitin and CR, and a larger specific area and higher porosity of chitin suspension was obtained after sonoenzymolysis with more available active sites.     

纳米甲壳素的制备、改性及应用研究进展

甲壳素是一种天然高分子化合物,具有来源广、可降解、生物相容、无毒和低抗原性等性质,但由于不溶于水和大多数有机溶剂,使其应用受到限制。由甲壳素制备的纳米甲壳素(甲壳素纳米晶须和甲壳素纳米纤维)能够在水中形成稳定均匀分散液,不仅具有甲壳素的性质,还有高长宽比、高表面积、低密度等性质,在其表面的羟基、N-乙酰基以及残留的胺基还可化学改性。本文综述了纳米甲壳素的制备,包括盐酸酸解、机械处理、2,2,6,6-四甲基哌啶-1-氧自由基(TEMPO)氧化、静电纺丝、溶解再生和脱N-乙酰基法,介绍了纳米甲壳素化学改性以及在增强、吸附和生物活性等方面应用。     

SEM characterization of anatomical variation in chitin organization in insect and arthropod cuticles

The cuticles of insects and arthropods have some of the most diverse material properties observed in nature, so much so that it is difficult to imagine that all cutciles are primarily composed of the same two materials: a fibrous chitin network and a matrix composed of cuticle proteins. Various factors contribute to the mechanical and optical properties of an insect or arthropod cuticle including the thickness and composition. In this paper, we also identified another factor that may contribute to the optical, surface, and mechanical properties of a cuticle, i.e. the organization of chitin nanofibers and chitin fiber bundles. Self-assembled chitin nanofibers serve as the foundation for all higher order chitin structures in the cuticles of insects and other arthropods via interactions with structural cuticle proteins. Using a technique that enables the characterization of chitin organization in the cuticle of intact insects and arthropod exoskeletons, we demonstrate a structure/function correlation of chitin organization with larger scale anatomical structures. The chitin scaffolds in cuticles display an extraordinarily diverse set of morphologies that may reflect specific mechanical or physical properties. After removal of the proteinaceous and mineral matrix of a cuticle, we observe using SEM diverse nanoscale and micro scale organization of in-situ chitin in the wing, head, eye, leg, and dorsal and ventral thoracic regions of the periodical cicada Magicicada septendecim and in other insects and arthropods. The organization of chitin also appears to have a significant role in the organization of nanoscale surface structures. While microscale bristles and hairs have long been known to be chitin based materials formed as cellular extensions, we have found a nanostructured layer of chitin in the cuticle of the wing of the dog day annual cicada Tibicen tibicens, which may be the scaffold for the nanocone arrays found on the wing. We also use this process to examine the chitin organizations in the fruit fly, Drosophila melanogaster, and the Atlantic brown shrimp, Farfantepenaeus aztecus. Interestingly many of the homologous anatomical structures from diverse arthropods exhibit similar patterns of chitin organization suggesting that a common set of parameters, govern chitin organization.