H_2O_2法氧化降解壳聚糖制备壳寡糖北大核心CSCD

壳聚糖不溶于水,限制了其广泛应用,故需将壳聚糖进一步降解成具有相同结构单元的壳寡糖。壳寡糖不仅易溶于水,而且具有更好的抑菌性效果和更广的抑菌谱,在医药、农业和工业等领域具有较好的应用前景。制备壳寡糖的方法主要有化学法、物理法和生物酶解法。其中,H_2O_2氧化降解法是一种高效、快速、无污染的方法,本文综述了H_2O_2法制备壳寡糖的反应机理、反应的影响因素及其应用前景。以及课题组通过使用黄粉虫的虫皮制备而得的CTS,在中性条件下用H_2O_2法进一步降解制备COS,得到的最优条件为:50℃、10%H_2O_2、1%CTS,反应5h,分子量7000Da左右,收率达到85%,产品颜色呈浅黄色。     

壳寡糖的酶法制备

通过还原端基、酶解产物聚合度、水解液调碱性后透光率的测定以及酶解产物的TLC、HPLC分析,研究了壳聚糖酶降解壳聚糖过程中壳聚糖浓度、酶用量、反应时间和pH对酶促反应速率和产物聚合度的影响。结果表明:壳聚糖酶在底物浓度0.03 g/mL、壳聚糖酶用量4~6 u/g、pH=5.8和水解200 min时,可得到以聚合度3~7为主的壳寡糖。     

非专一性酶催化壳聚糖水解反应的特性

某些非专一性酶对壳聚糖具有一定的降解作用，具有普遍的壳聚糖酶的活性。α-淀粉酶对壳聚糖的降解作用受温度、底物浓度、酶浓度、反应时间、pH等因素的影响，其最佳反应条件为壳聚糖浓度20g/L，酶浓度4g/L,pH值6.0，反应温度50℃。降解反应初期是以内切的方式进行，所得到的壳寡糖具有较低的分散度。     

溶菌酶降解壳聚糖条件的研究

研究了溶茵酶对壳聚糖的降解条件,结果表明：脱乙酰度约70％的壳聚糖较易被溶菌酶水解;水解反应的最适温度为55℃、pH值为4．0,低速摇床振荡对水解有利;在壳聚糖水解初期,溶液中还原糖浓度迅速增加,0．5h后水解速率逐渐减慢,至8h后还原糖浓度的增加已很缓慢;酶解液中还原糖的生成量瞳壳聚糖及溶茵酶浓度的增加而增大,当壳聚糖溶液浓度为20mg／mL、溶茵酶浓度为2．48mg／mL时,水解6h后,还原糖的含量可达6．758mmol／L。水解6h后酶解液中还原糖浓度与壳聚糖的浓度呈线性关系。     

氧化降解壳聚糖铜配合物制备低聚壳聚糖

氧化降解壳聚糖铜配合物制备低聚壳聚糖;壳聚糖铜配合物;壳聚糖;氧化降解;催化     

壳聚糖和壳寡糖的磷酸化研究

以甲磺酸为溶剂,壳聚糖(CTS)和壳寡糖(COS)为原料,分别与五氧化二磷反应合成其磷酸酯。用电位滴定法测定取代度(DS),并用红外光谱法(FT-IR)和差热分析法(DTA)进行结构表征。通过分析壳聚糖与壳寡糖磷酸化正交实验结果,得出了甲磺酸用量、五氧化二磷用量、温度和反应时间等因素对产物取代度的影响,优化了合成工艺,并通过结构分析对两者进行了比较。     

中性蛋白酶对壳聚糖的降解

用粘度测定法和还原糖测定法,研究了中性蛋白酶非专一性降解壳聚过程中温度,ｐＨ值,反应时间,酶浓度,底物浓度,金属离子及壳聚糖的脱乙酰度对中性蛋白酶降解壳聚糖反应速度的影响,确定了以壳聚糖为底物的中性蛋白酶的一些催化特性：最适温度为５０℃;最适ｐＨ值为６．０;米氏常数Ｋｍ值为１．１×１０＾－２ｇ／ｍＬ;一定浓度的Ｃｕ６２＋,Ｂａ＾２＋,Ｍｎ＾２＋抑制该酶的活性;     

壳聚糖超声可控降解及降解动力学研究

通过正交实验法考察了壳聚糖溶液浓度、反应温度、超声强度以及醋酸溶液浓度对超声降解反应的影响,确定了最佳反应条件,制备了一系列不同分子量的壳聚糖.研究了壳聚糖溶液浓度、反应温度以及壳聚糖原料分子参数与降解速率常数的关系.通过红外光谱、X-射线衍射和凝胶渗透色谱对降解产物进行了表征.结果表明,超声降解壳聚糖的最佳条件为10℃,壳聚糖溶液浓度2.5g/L.降解速率常数随壳聚糖溶液浓度和反应温度的降低而增大.高分子量和低脱乙酰度的壳聚糖原料有较高的降解速率和降解速率常数,壳聚糖原料的分子量对降解速率和降解速率常数的影响大于脱乙酰度对其的影响.超声波导致了壳聚糖分子量的降低和产物晶体结构的破坏,但没有改变产物的脱乙酰度和糖残基结构.     

壳聚糖-对羟基苯甲酸酶法接枝及表征

从土豆中提取酪氨酸酶(tyr),以该酶催化氧化对羟基苯甲酸(BA)成活性邻醌,成功地实现了壳聚糖(Cs)上的接枝。通过UV-Vis、FTIR、TG-SDTA对其反应产物进行结构和性能的初步表征,由线性电位滴定法测得其接枝率为47%~58%。     

Cu(Ⅱ)对壳聚糖的配位控制降解

对壳聚糖进行液态均相络合反应制得壳聚糖铜配合物,IR、UV、元素分析及热重分析等检测证实了壳聚糖铜配合物中配位键的存在,且显示壳聚糖在形成配位结构后存在有利于降解的优势构象。以H₂O₂对壳聚糖-Cu(Ⅱ)络合物及壳聚糖进行氧化降解,考察降解过程中粘度的变化及降解产物分子量分布,在相同的降解条件下,壳聚糖铜配合物的降解速度明显高于壳聚糖,降解产物分子量分布较壳聚糖直接降解窄,结果进一步证明壳聚糖铜配合物中存在有利于降解的优势结构,同时证明以金属离子Cu(Ⅱ)对壳聚     

凝胶渗透色谱法研究壳聚糖生物材料酶降解过程的均匀性

壳聚糖是一种重要的生物医用材料,脱乙酰度是影响其生物降解性能的重要因素。运用凝胶渗透色谱研究了脱乙酰 度及相对分子质量分布相似、而聚合单元N-乙酰氨基-D-葡萄糖和D-氨基葡萄糖分布不同的两种壳聚糖材料在溶菌酶作用 下的降解过程,分析检测了壳聚糖材料在降解过程中的重均相对分子质量、相对分子质量多分散性和相对分子质量分布 的变化。发现聚合单元为随机分布的壳聚糖样品,其降解是均匀的;而聚合单元为段状分布的壳聚糖样品,其降解是非 均匀的;表明其聚合单元的分布方式决定壳聚糖材料酶降解过程的均匀性。     

Hydrolytic And Enzymatic Degradation Characteristics Of Biodegradable Aliphatic Polysters

Aliphatic polyesters, especially those derived from lactide (PLA), glycolide (PGA) and ε-caprolactone (PCL), are being investigated worldwide for applications in the field of surgery (suture material, devices for internal bone fracture fixation), pharmacology (sustained drug delivery systems), and tissue engineering (scaffold for tissue regeneration) [1,2]. This is mainly due to their good biocompatibility and variable degradability. These polymers present also a growing interest for environmental applications in agriculture (mulch films) and in our everyday life (packaging material)as the development of biodegradable materials is now considered as one of the potential solutions to the problem of plastic waste management.For both biomedical and environmental applications, it is of major importance to understand the degradation characteristics of the polymers. The hydrolytic degradation of aliphatic polyesters has been investigated by many research groups. Our group has shown that degradation of PLAGA large size devices is faster inside than at the surface. This heterogeneous degradation is due to the autocatalytic effect of carboxylic endgroups formed by ester bond cleavage. Moreover,degradation-induced morphological and compositional changes were also elucidated. In the case of PCL, the hydrolytic degradation is very slow due to its hydrophobicity and crystallinity.The enzymatic degradation of these polymers has been investigated by a number of authors. A specific enzyme, proteinase K, has been shown to have significant effects on PLA degradation. This enzyme preferentially degrade L-lactate units as opposed to D-lactate ones, amorphous zones as opposed to crystalline ones [3]. The enzymatic degradation of PCL polymers has also been investigated. A number of lipase-type enzymes were found to significantly accelerate the degradation of PCL despite its high crystallinity. In the case of PLA/PCL blends, the two components exhibited well separated crystalline domains. The selective degradation of PCL or PLA components by enzymes revealed the inner morphology of the blends with formation of microsphere-like or island-like structures [5].     

钨磷酸催化H2O2氧化降解壳聚糖

钨磷酸催化H2O2氧化降解壳聚糖;壳聚糖;钨磷酸;H2O2;催化降解     

In-Vitro Degradation and Cytotoxicity of Gelatin/Chitosan Microspheres for Drug Controlled Release

The composite microspheres based on gelatin (Gel) and chitosan (Cs) loaded with 5-fluorouracil (5-FU) were fabricated using glutaraldehyde (GA) as a crosslinker. The in-vitro degradation behaviors of the Gel/Cs microspheres, including the changes of pH value, mass loss and microsphere morphology, were studied. The in-vitro cytotoxicites of Gel/Cs microspheres loaded and unloaded with 5-FU were carried out with MCF-7 breast cancer cell line. The empty Gel/Cs microspheres showed a smooth surface and were evenly distributed; however, there was much aggregation observed for the microspheres loaded with 5-FU. The degradation results showed that the pH values of both PBS and PBS-lysozyme solutions increased with increasing degradation time but the increase of pH value of PBS-lysozyme solution was quicker than that of PBS solution. The aggregated Gel/Cs microspheres lose their shape and many fibers were found after 21 days in PBS solution; while the Gel/Cs microsphere disappeared in PBS-lysozyme solution. The mass loss of the Gel/Cs microspheres in PBS-lysozyme solution was larger than that of the Gel/Cs in PBS solution. The results indicated that lysozyme can accelerate the degradation of Gel/Cs microspheres. The cytotoxicity results showed that the cell viability decreased with increasing glutaraldehyde content for the empty Gel/Cs microspheres; however, the cell viability increased with increasing glutaraldehyde content for the Gel/Cs microspheres loaded with 5-FU. Therefore, the Gel/Cs microspheres can be offered as drug carrier candidates for long-term applications of anti-cancer drugs.     

Selective Modification of Chitin and Chitosan: En Route to Tailored Oligosaccharides

Chitin and chitosan are attractive biopolymers with enormous structural possibilities for chemical modification, creating platforms for new chemical entities with a broad scope of applications, ranging from material science to medicine. During the last few years, incredible efforts have been dedicated to the regioselective modification of these biopolymers paving the way for improved properties and tailored activities. Herein, the most recent advances in chitin/chitosan regioselective modification, reaction conditions, selectivity, and the impact on its applications are highlighted. Moreover, the recent focus on chitooligosaccharides, their regioselective and chemoselective functionalization, as well as their role in biological studies, including molecular recognition with several biological targets are also covered.     

Assessment of the Effects of Chitosan,Chitooligosaccharides and Their Derivatives on Lemna minor

Chitosan, chitooligosaccharides and their derivatives’ production and use in many fields may result in their release to the environment, possibly affecting aquatic organisms. Both an experimental and a computational approach were considered for evaluating the effects of these compounds on Lemna minor. Based on the determined EC₅₀ values against L. minor, only D-glucosamine hydrochloride (EC₅₀ = 11.55 mg/L) was considered as “slightly toxic” for aquatic environments, while all the other investigated compounds, having EC₅₀ > 100 mg/L, were considered as “practically non-toxic”. The results obtained in the experimental approach were in good agreement with the predictions obtained using the admetSAR2.0 computational tool, revealing that the investigated compounds were not considered toxic for crustacean, fish and Tetrahymena pyriformis aquatic microorganisms. The ADMETLab2.0 computational tool predicted the values of IGC₅₀ for Tetrahymena pyriformis and the LC₅₀ for fathead minnow and Daphnia magna, with the lowest values of these parameters being revealed by totally acetylated chitooligosaccharides in correlation with their lowest solubility. The effects of the chitooligosaccharides and chitosan on L. minor decreased with increased molecular weight, increased with the degree of deacetylation and were reliant on acetylation patterns. Furthermore, the solubility mainly influenced the effects on the aqueous environment, with a higher solubility conducted to lower toxicity.     

Development of Reasonably Stable Chitosan Based Proton Exchange Membranes for a Glucose Oxidase Based Enzymatic Biofuel Cell

Chitosan based reasonably stable membranes were prepared as polymeric electrolyte and separator for enzymatic fuel cell applications. Glucose oxidase (GOx) bioanode centered biofuel cell with the developed chitosan membranes performed much better in stability with high current densities than that of the biofuel cell utilizing a 125 μ‐thick perfluorosulfonic acid‐type membrane (i. e. Nafion® 115). Proposed chitosan membrane structural stability was enhanced by employing cellulosic support materials and chemical crosslinking. The effects of pH, buffer type, buffer concentration, temperature on the manufactured chitosan membranes along with the biofuel cell system were investigated. The biofuel cell operation parameters were optimized for the current density and stability aspects and more than 3 mA cm^?2 current density was acquired from the cell at optimum conditions. Operational half‐life of the chitosan membrane was found as higher than the half‐life of the GOx immobilized bioanode. Therefore, this result indicates that chitosan membrane structural stability was not a limiting issue for the biofuel cell lifespan.