过氧化氢在乙酸均相体系中对壳聚糖的降解

为制备分子量较低的可溶于水的壳低聚糖,研究了在乙酸均相体系中过氧化氢氧化降解壳聚糖的过程,采用凝胶渗透色谱法跟踪测定了壳聚糖氧化降解过程中分子量及其分布的变化,探索制备不同分子量壳低聚糖的适宜条件。     

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.     

壳聚糖在水溶液中的辐射降解反应

研究了壳聚糖在CH3COOH/NaCl缓冲溶液均相体系下的辐射降解反应,给出了H2O2、异丙醇、pH、样品初始分子量等因素对壳聚糖降解的影响,探讨了实验条件下溶液中不同自由基对壳聚糖降解的作用,并对辐照前后壳聚糖的结构进行了表征.结果表明,酸性条件下,壳聚糖的降解主要由.H和.OH自由基共同作用引起,加入H2O2或者通入N2O都能够略微提高.OH自由基浓度,对壳聚糖的降解有促进作用.加入异丙醇后,由于同时降低了.H和.OH自由基浓度,导致壳聚糖降解缓慢.当溶液的pH接近中性后,对壳聚糖的降解起主要作用的为.OH自由基,加入H2O2或者通入N2O都会增加.OH自由基的浓度,从而明显提高壳聚糖的降解速率.此外,研究发现低分子量的壳聚糖具有较快的降解速率.样品的UV、FTIR分析表明,辐照后除在壳聚糖分子链端生成羰基外,壳聚糖主链结构未见变化,脱乙酰度也没有显著改变,显示出辐射降解是一种有效的控制壳聚糖分子量方法.     

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     

羧甲基壳聚糖基生物医用材料降解代谢行为的研究进展

作为一种水溶性多糖高分子材料,羧甲基壳聚糖(carboxymethyl chitosan, CMCTs)具有优异的生物相容性和生物降解性以及保湿、止血、抗菌、可吸收等一系列优良的功能特性,因而被广泛应用于医工交叉领域。羧甲基壳聚糖进入体内后,在酶、氧、微生物、水等环境适宜时能够被降解,并经吸收、代谢、排泄。其体内降解速率主要取决于材料的尺寸、脱乙酰度、取代度、分子量等。了解羧甲基壳聚糖在动物体内的降解代谢行为,对羧甲基壳聚糖在转化过程中的质量控制和临床应用至关重要。然而就目前而言,羧甲基壳聚糖在生物体内降解代谢的影响因素及其体内吸收、分布、代谢、排泄规律缺乏系统性总结,这一现状从基础层面严重制约了其在生物医药领域的进一步发展。基于上述问题,本文对近年来羧甲基壳聚糖基生物医用材料的降解、代谢相关研究进行梳理和总结,重点阐述了羧甲基壳聚糖作为可降解材料的生物学特性、降解方式、代谢过程等,系统揭示羧甲基壳聚糖体内降解、代谢的规律,并对植入物尺寸、脱乙酰度、取代度、分子量、交联度及成分比例等影响羧甲基壳聚糖降解速率的主要因素进行归纳,以期为羧甲基壳聚糖基生物医用材料的研发和转化研究提供参考。     

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。     

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。     

壳聚糖的配位控制氧化降解及量子化学研究

提出一种新的壳聚糖降解法——金属配位控制氧化降解法，首先对壳聚糖实行人为特异性结构改造，将壳聚糖转化为壳聚糖金属配合物，再以H2O2对配合物进行氧化降解。对比金属配位控制氧化降解和直接氧化降解的反应结果，表明在相同降解条件下，前一种方法的降解速度明显高于后一种方法，且降解产物分子量分布较后者窄。半经验量子化学hyperchem6.01 ZIND0/1模拟计算结果显示，壳聚糖金属配合物高分子链上配位糖元对应的糖苷键比其他糖苷键更容易发生断裂，壳聚糖链断裂优先发生在该位置，降解反应具有更好的选择性和可控性。     

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     

壳聚糖修饰纳米纤维膜表面对氧化还原酶行为的影响

采用静电纺丝法制备了丙烯腈/丙烯酸共聚物(PANCAA)纳米纤维膜, 研究了纺丝液浓度对纤维形态的影响, 以扫描电子显微镜观察纤维形貌, 遴选得到最佳纺丝条件. 以1-乙基-3-(N,N-二甲基氨基丙基)碳二亚胺/N-羟基丁二酰亚胺(EDC/NHS)为偶联剂, 在纤维膜表面引入壳聚糖修饰层, 采用衰减全反射傅里叶变换红外光谱(ATR/FTTIR)、水接触角和称重法考察了修饰前后膜的变化. 通过戊二醛将过氧化氢酶固定到壳聚糖修饰的PANCAA纳米纤维膜上, 研究了壳聚糖及戊二醛浓度对固定化过氧化氢酶的影响, 结果表明, 在壳聚糖浓度为25 mg/mL及戊二醛质量分数为5%条件下, 壳聚糖修饰膜的固定化酶活性比空白膜提高了41.7%, 稳定性也得到了不同程度的提高.     

Synergetic degradation of chitosan with gamma radiation and hydrogen peroxide

Chitosan samples were irradiated by ⁶⁰Co γ-rays in the presence of hydrogen peroxide with radiation dose from 10 kGy to 100 kGy. The degradation was monitored by gel permeation chromatography (GPC), revealing the existence of a synergetic effect on the degradation. Structures of the degraded products were characterized with Fourier-transform infrared spectra (FT-IR), ultraviolet-visible spectral (UV-vis) analysis, and X-ray diffraction (XRD). Results showed that the crystallinity of chitosan decreases with degradation, and the crystalline state of water-soluble chitosan is entirely different from that of water-insoluble chitosan. An elemental analysis method was employed to investigate changes in the element content of chitosan after degradation. Mechanism of chitosan radiation degradation with and without hydrogen peroxide was also discussed.     

Oxidative degradation of chitosan under the action of hydrogen peroxide

The reaction of chitosan with hydrogen peroxide in homogeneous medium and the influence of iron(II) sulfate, copper(II) chloride, and disodium ethylenediaminetetraacetate on oxidative degradation of chitosan were studied by the rheology method.     

Synergistic degradation to prepare oligochitosan by γ-irradiation of chitosan solution in the presence of hydrogen peroxide

Synergistic degradation of chitosan by γ-irradiation of chitosan solution (3%) in the presence of hydrogen peroxide (0.25%, 0.5% and 1%) was investigated. The efficiency of the degradation process was demonstrated by gel permeation chromatography (GPC) analysis of the average molecular weight of degraded chitosan (oligochitosan). Structures of resultant oligochitosan were characterized by Fourier-transform infrared spectra (FT-IR) and X-ray diffraction (XRD). Results showed that oligochitosan with Mw from 5000 to 10,000 could be efficiently prepared by γ-irradiation of chitosan solution containing a small amount of hydrogen peroxide at low dose less than 10 kGy. There was almost no significant change in the main chain structure of oligochitosan; however, the obtained oligochitosans lost about 10% of amino groups and the formation of carboxyl groups could not be specified by FT-IR spectra. The morphology state of oligochitosan was essentially amorphous, which differs from that of original chitosan. The combined γ ray/H₂O₂ method is significantly efficient for scale-up manufacture of oligochitosan.     

甲壳低聚糖表面活性剂的制备及其表面活性研究

通过氧化降解壳聚糖制得水溶性甲壳低聚糖，再与二甲基十二烷基缩水甘油基氯化铵反应，得到了季铵盐型阳离子甲壳低聚糖表面活性剂。用红外光谱、核磁共振(^1H，^13C)、元素分析等分析手段对产物进行了结构表征，并研究了取代度对产物表面活性的影响规律。     

H2O2在苯酚降解过程中的作用研究

H2O2浓度是影响苯酚降解程度的重要因素之一。实验表明,不同浓度的H2O2在苯酚降解过程中所起的主要作用也不相同。在环状有机物的降解过程中,苯酚往往作为副产物出现,因此,苯酚的降解程度也往往影响到这些环状有机物的降解程度。H2O2在光氧化、光催化氧化和光电催化氧化的条件下均能影响苯酚的降解程度。在后两种条件下,H2O2还影响到用作光催化剂的TiO2的活性。     

有序介孔锰氧化物催化过氧化氢降解水中诺氟沙星

采用硬模板法制备了有序介孔氧化锰,并用过氧化氢氧化诺氟沙星的降解率及其抗菌活性变化评价了其催化活性.研究发现,有序介孔锰氧化物表现出较高的催化活性;低pH有利于提高其催化活性.与单独过氧化氢氧化过程相比,有序介孔锰氧化物的存在明显减弱了诺氟沙星的抗菌活性.叔丁醇对催化体系的抑制作用表明有序介孔锰氧化物促进了过氧化氢分解生成羟基自由基.通过对诺氟沙星在催化过程中的分解产物鉴定,提出了可能的分解途径.     

Induced degradation of chitosan,conjugated with block copolymerization with acrylamide

Synthesis of block copolymers of chitosan with acrylamide, involving formation of acrylamide blocks on glucosamine blocks generated by induced degradation of chitosan macromolecules by the hydrogen peroxide-ascorbic acid system, was studied.     

Grafting onto chitosan. I. Graft copolymerization of methyl methacrylate onto chitosan with Fenton's reagent (Fe2+−H2O2) as a redox initiator

Poly(methyl methacrylate) has been grafted onto chitosan by using Fenton's reagent as a redox initiator in an aqueous medium. Initiation by Fenton's reagent was carried out in the presence of atmospheric oxygen. The percentages of grafting, efficiency, and homopolymer were found to depend on chitosan (RchitOH), ferrous ammonium sulfate (FAS), hydrogen peroxide, monomer (MMA) concentrations, reaction temperature, and reaction time.     

Electrodeposition of chitosan enables synthesis of copper/carbon composites for H2O2 sensing

This work presents a novel approach in synthesizing copper (Cu)/carbon composite materials by electrodeposition of the biopolymer chitosan, a renewable carbon precursor, on a copper anode, followed by pyrolysis of the electrodeposited chitosan gel. The amount of copper in the Cu/carbon composite material can be controlled by modifying the pH of the chitosan solution from which the electrodeposition is performed. This further influences the physical properties of the composite material. Here we show a 14 fold increase in electrical conductivity of the Cu/carbon composite, when compared to the material without copper inclusions. Metal/carbon composite materials have a wide range of applications already reported in the literature. As a proof of concept, we demonstrate the electrochemical sensing capability of this Cu/carbon material for non-enzymatic detection of hydrogen peroxide, achieving a sensitivity of 58.9 μA/mM cm², which is comparable to state of the art non-enzymatic hydrogen peroxide sensors. The anodic electrodeposition of chitosan proves to be a simple and straightforward medium for synthesis of Cu/carbon composites. We speculate that this method can be extended to obtain other metal/carbon composites as a low-cost alternative for the fabrication of functional composite electrodes.