紫外测定壳聚糖脱乙酰度方法的探讨

分别采用直接、一阶导数、多波长和双内标等4种紫外分光光度法测定壳聚糖的脱乙酰度,评价4种紫外测定方法,并与胶体滴定、电位滴定和氢核磁3种测定方法进行了比较。结果表明,采取上述紫外法测定壳聚糖脱乙酰度值均高于胶体滴定和氢核磁测定值。故准确测定高脱乙酰度壳聚糖的脱乙酰度,紫外法非首选方法。     

红外光谱法测定壳聚糖脱乙酰度

以碱量法为对比方法,考察了基于A1655／A3450和A1320／A1420的2种红外光谱计算壳聚糖脱乙酰度方法的准确性。结果表明,红外光谱法虽精密度低于碱量法,但基于A1655／A3450的红外测试结果与碱量法基本相吻合;基于A1320／A1420加的红外光谱计算结果略高于碱量法,与商家标注值相吻合,且不受样品含少量水、残酸或残碱的影响。红外光谱法是一种较为理想的壳聚糖脱乙酰度测定方法,同时采用A1655／A3450和A1320／A1420计算更利于得到准确的测定结果。     

壳聚糖脱乙酰度测定方法的总结与比较

测定壳聚糖脱乙酰度(DD)的方法主要分为三类:①光谱法:紫外、红外光谱和核磁法;②破坏样品法:色谱法、差示扫描量热和元素分析法;③滴定法:酸碱、电位和胶体滴定等方法。对壳聚糖脱乙酰度测定方法进行总结与比较,为研究者选择最佳的壳聚糖脱乙酰度测定方法提供理论依据。     

Effects of the molecular weight and the degree of deacetylation of chitosan oligosaccharides on antitumor activity

Effects of the degree of deacetylation (DDA) and the molecular mass of chitosan oligosaccharides (CTS-OS), obtained from the enzymatic hydrolysis of high molecular weight chitosan (HMWC), on antitumor activity was explored. The DDA and molecular weights of CTS-OS were determined by matrix-assisted laser desorption/ionization-mass spectrometry (MALDI-TOF MS) analysis. The CTS-OS were found to be a mixture of mainly dimers (18.8%), trimers (24.8%), tetramers (24.9%), pentamers (17.7%), hexamers (7.1%), heptamers (3.3%), and octamers (3.4%). The CTS-OS were further fractionated by gel-filtration chromatography into two major fractions: (1) COS, consisting of glucosamine (GlcN)(n), n = 3-5 with DDA 100%; and (2) HOS, consisting of (GlcN)(5) as the minimum residues and varying number of N-acetylglucosamine (GlcNAc)(n), n = 1-2 with DDA about 87.5% in random order. The cytotoxicities, expressed as the concentration needed for 50% cell death (CC(50)), of CTS-OS, COS, and HOS against PC3 (prostate cancer cell), A549 (lung cancer cell), and HepG2 (hepatoma cell), were determined to be 25 μg·mL(-1), 25 μg·mL(-1), and 50 μg·mL(-1), respectively. The HMWC was approximately 50% less effective than both CTS-OS and COS. These results demonstrate that the molecular weight and DDA of chitosan oligosaccharides are important factors for suppressing cancer cell growth.     

The effect of reaction time and temperature during heterogenous alkali deacetylation on degree of deacetylation and molecular weight of resulting chitosan

The objective of the study is to elucidate the effect of reaction time and temperature during heterogenous alkali reaction on degree of deacetylation (DD) and molecular weight (MW) of the resulting chitosans, and to establish the reaction conditions to obtain desired DD and MW chitosan products. Chitin was extracted from red shrimp process waste. DDs and MWs were determined by infrared spectroscopy (IR) and static light scattering, respectively. The results are as follow: The DD and MW of chitin obtained were 31.9% and 5637 kDa, respectively. The DD of the resulting chitosan increased along with reaction time and/or reaction temperature. The DDs of the resulting chitosan that were obtained from 140°C were higher than those reacted at 99°C. The highest DD of the resulting chitosans after alkali deacetylation at 99 and 140°C were 92.2 and 95.1%, respectively. The DDs of chitosans increased fast at the beginning of reaction process then slowed over time. The reaction rate and rate constant of the deacetylation reaction decreased with increasing DD of the reactant. The MWs of chitosans decreased along with the deacetylation time. MW of those chitosans reacted at 140°C are smaller than those at 99°C. The rate of chitosan degradation was above 43.6%/h in the initial stage, then decreased to about 20%/h. The degradation rate constants raised substantially in the late stage. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2917–2923, 2003     

Influence of degree of deacetylation on critical concentration of chitosan/dichloroacetic acid liquid‐crystalline solution

We prepared chitosans with various degrees of deacetylation (DDAs) by mixing completely deacetylated chitosan and acetic anhydride at room temperature without serious degradation and O‐substitution. We obtained a standard curve to measure DDA by plotting the IR absorbance ratio of A₁₅₆₀/A₂₈₈₀ against the known DDAs (from 1–100%) of 10 specimens. The effect of DDA on the critical concentration (C*) of chitosan/dichloroacetic acid solutions required to form mesophase was investigated by optical methods. A maximum C* value of 23 wt % appeared at a relative medium DDA (～20%). The effect was explained by the disordering of chains with medium composition ratios of the copolymer of glucosamine and N‐acetyl glucosamine. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1204–1208, 2002     

Investigation of different natural sources of chitin: influence of the source and deacetylation process on the physicochemical characteristics of chitosan

Several sea sources for chitin have been investigated, and the chitin content and crystallographic polymorph of the extracted chitin determined. Deacetylation of the chitin was carried out and the physicochemical characteristics of the resulting chitosan studied. The influence of the reaction parameters (reaction duration, temperature, nature of alkaline reagent, etc) was followed. Thus it became possible to determine adequate reaction conditions for obtaining chitosans with the required properties. The physicochemical characteristics of the obtained chitosan are closely related to the taxonomy of the source. New sea sources for chitin have been investigated and considered for industrial purposes. © 2000 Society of Chemical Industry     

Effect of degree of deacetylation of chitin on the properties of chitin crystallites

In the present article, chitin from crab shell was systematically deacetylated using a NaOH treatment with control of the reaction time. The degree of deacetylation, monitored using solid-state NMR, revealed that the reaction was pseudo-first order. Based on this, swollen and NaOH-saturated particles are proposed as the reaction system. The weight loss of the partially saponified and neutralized samples after HCl hydrolysis increased linearly with the degree of deacetylation. The crystallinity of the samples was found to increase after acid hydrolysis. According to conductimetric titration, the surface charge density of the crystallites, after acid hydrolysis, was found to increase with base treatment time. The effect of surface charge on the formation of a chiral nematic phase, due to the rodlike nature of the crystallites, was explored. These results show that because the contribution of charged particles to the ionic strength was significant the double layer compression was affected, especially since the surface charge density was close to the Manning limit. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:373–380, 1997     

常压和加压浸渍法制备壳聚糖性能对比

研究了常压和加压条件下碱液浓度和反应时间对壳聚糖性能的影响。与传统工艺相比,在不改变壳聚糖化学结构、晶型结构的条件下,压力浸渍法反应时间由6 h降到1 h,耗碱量降低了65%。结果表明,压力浸渍法可得到更高脱乙酰度和更高分子量的壳聚糖产品。     

黏均分子质量为1万左右的壳聚糖制备的研究

本文着重讨论了通过过氧化氧氧化法降解制备黏均分子质量在1万左右的壳聚糖。本实验采用了正交实验设计，探讨了制备条件对产物脱乙酰度、特性黏度、水溶性等的影响。最佳制备条件为：H2O2的质量分数为4％，CH3COOH的质量分数3．5％，壳聚糖的质量分数2％，时间4h，温度50℃。最佳制备条件得到的壳聚糖脱乙酰度为88．53％，黏均分子质量为9048。实验结果基本苻合预期的要求。     

Hac/H2O2降解制高性能水溶性壳聚糖的工艺研究

研究了壳聚糖HAc介质中用H2O2进行氧化降解的情况,讨论了主要影响因素温度对降解反应速率和产品质量的影响,选定最佳温度75℃;依据壳聚糖浓度、反应时间、乙酸浓度、氧化剂与壳聚糖比例设计正交实验,详细分析了各个指标下所得数据,综合得出水溶性低聚糖制备的优化条件:n(氧化剂)∶n(壳聚糖单元)=2、t=4h、C壳聚糖)=3%、CHAc=3.5%     

Effect of cupric ion on thermal degradation of chitosan

The thermal degradation of chitosan and chitosan–cupric ion compounds in nitrogen was studied by thermogravimetry analysis and differential thermal analysis (DTA) in the temperature range 30–600°C. The effect of cupric ion on the thermal degradation behaviors of chitosan was discussed. Fourier transform-infrared (FTIR) and X-ray diffractogram (XRD) analysis were utilized to determine the micro-structure of chitosan–cupric ion compounds. The results show that FTIR absorbance bands of  N H,  C N ,  C O C etc. groups of chitosan are shifted, and XRD peaks of chitosan located at 11.3, 17.8, and 22.8° are gradually absent with increasing weight fraction of cupric ion mixed in chitosan, which show that there are coordinating bonds between chitosan and cupric ion. The results of thermal analysis indicate that the thermal degradation of chitosan and chitosan–cupric ion compounds in nitrogen is a two-stage reaction. The first stage is the deacetylation of the main chain and the cleavage of glycosidic linkages of chitosan, and the second stage is the thermal destruction of pyranose ring of chitosan and the decomposition of residual carbon, in which both are exothermic. The effect of cupric ion on the thermal degradation of chitosan is significant. In the thermal degradation of chitosan–cupric ion compounds, the temperature of initial weight loss (T_st), the temperature of maximal weight loss rate (T_max), that is, the peak temperature on the DTG curve, and the peak temperature (T_p) on the DTA curve decrease, and the reaction activation energy (E_a) varies with increasing weight fraction of cupric ion. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Studies on the effect of substitution degree on the liquid crystalline behavior of cyanoethyl chitosan

An alkali–chitosan method was employed to prepare cyanoethyl chitosan (CNCS) with different degrees of substitution (DS) from chitosan by controlling the reaction time. The effect of the DS (from 0.36 to 1.21) on the liquid crystalline behaviors of CNCS was investigated. The critical concentration and texture of CNCS liquid crystalline in dichloroacetic acid and formic acid showed no obvious dependence on the DS. However, increase of the DS could enhance the birefringence of liquid crystalline solutions under a polarized microscope, which implied improved liquid crystallinity. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 2057–2061, 2000     

低分子量壳聚糖的制备

利用H2O2的强氧化性制备低分子量分布的壳聚糖是将虾皮用HC l浸泡去除碳酸钙盐;再用稀碱除去蛋白质得甲壳素;然后浓碱在50℃与其反应,并控制反应时间,分别制备出脱乙酰度为85%,93%,99%的壳聚糖,最后用H2O2氧化不同脱乙酰化壳聚糖,得到不同低分子量的壳聚糖。其中,脱乙酰度为85%壳聚糖用不同浓度的H2O2降解,得到了4.7×105,3.5×105,2.5×105,1.2×105,8×105等5个不同分子量段的壳聚糖产品。H2O2浓度越大,降解所得壳聚糖的分子量就越小。     

Effect of degree of deacetylation on solubility of low‐molecular‐weight chitosan produced via enzymatic breakdown of chitosan

Chitosan has emerged as a unique biomaterial, possessing scope in diverse applications in the biomedical, food and chemical industries. However, its high molecular weight is a concern when handling the polymer. Various techniques have been explored for depolymerization of this polymer, wherein enzymes have emerged as the most economic method having minimum degrading effect on the polymer and resulting in formation of side products. Chitosan can be depolymerized using a broad range of enzymes. In this study, various enzymes like α‐amylase, papain, pepsin and bromelain were employed to depolymerize chitosan and convert it into its lower molecular weight counterpart. Further, attempts were made to elucidate the process of depolymerization of chitosan, primarily by determining the change in its viscosity and hence its molecular weight. The process of depolymerization was optimized using a one‐factor‐at‐a‐time approach. The molecular weight of the resultant chitosan was estimated using gel permeation chromatography and infrared spectroscopy. These studies revealed a considerable decrease in molecular weights of chitosan depolymerized by pepsin, papain, bromelain and α‐amylase, resulting in recovery of the low‐molecular‐weight chitosan of 76.09 ± 5, 74.18 ± 5, 55.75 ± 5 and 49.18 ± 5%, respectively. Maximum yield and depolymerization were obtained using pepsin and papain due to their enzymatic recognition pattern, which was also validated using studies involving molecular dynamics. © 2019 Society of Chemical Industry     

超声降解造纸黑液的初步研究

超声降解水体中有机污染物是近年来兴起的一项极具发展前景的新型水处理技术，在超声作用下，液体产生超声空化效应，可有效降解水中一些难降解大分子有机物，利用超声技术（US）及超声与组合高级氧化技术（AOPs)，例如US－H2O2，US－H2O2－FeSo4对造纸废水进行处理，试验结果表明，此技术可一定程度降解造纸废水中大分子有机物，造纸废水的CODCr及TOC均有一定程度降低，有望成为生化法处理造纸废水的前处理技术。     

超声波法黄原酸化壳聚糖的制备

介绍了制备黄原酸化壳聚糖(XCTS)的常规方法和超声波法, 使用元素分析、FT-IR、XRD、SEM和TG对其结构进行表征, 并分析了物料比、超声波功率、反应温度、反应时间和碱浓度对超声波法制备XCTS的影响。结果表明超声波法能明显加快制备黄原酸化壳聚糖的速度, 增加产量, 同时提高产物的硫含量, 其最佳工艺:壳聚糖与二硫化碳的质量体积比为1:2(g/mL), 超声波功率为150W, 超声波作用时间为60min, NaOH的质量分数为15%。     

超声辐射下非均相甲壳素脱乙酰化反应动力学

在超声辐射条件下进行了甲壳素非均相脱乙酰化反应动力学研究。结果表明,超声辐射条件下,甲壳素的脱乙酰度明显提高,反应过程符合准一级动力学关系,反应控制为扩散控制,其表观活化能为3.45 kJ/mol。     

酶载体壳聚糖制备的研究

本文分别采用电热法、连续微波法和问歇微波法制备了几种性能不同的壳聚糖,并对产品的脱乙酰度和分子量进行了比较.结果表明,间歇微波法制备的壳聚糖具有制备时间短、产品脱乙酰度高和分子量大等特点,能更好地满足酶载体的要求.     

Molecular weight effect on antimicrobial activity of chitosan treated cotton fabrics

The effect of the molecular weight of chitosan on antimicrobial activity was investigated using three chitosans of different molecular weights [1800 (water soluble), 100,000, and 210,000] and similar degrees of deacetylation (86–89%). Cotton fabrics were treated with chitosan by the pad–dry–cure method. The molecular weight dependence of the antimicrobial activity of chitosan was more pronounced at a low treatment concentration. Chitosans with molecular weight of 100,000 and 210,000 effectively inhibited Staphylococcus aureus at a 0.5% treatment concentration. Chitosan with a molecular weight of 1800 was effective against S. aureus at a 1.0% treatment concentration. Escherichia coli was effectively inhibited by chitosan with a molecular weight of 210,000 at a 0.3% treatment concentration and by chitosans with a molecular weight of 1800 and 100,000 at a 1.0% treatment concentration. Proteus vulgaris was effectively inhibited by chitosans with molecular weight of 100,000 and 210,000 at a 0.3% treatment concentration and by chitosan with a molecular weight of 1800 at a 0.5% treatment concentration. None of the chitosans significantly inhibited Klebsiella pneumoniae and Pseudomonas aeruginosa below a 1.0% treatment concentration. Chitosans with high molecular weights were more effective in inhibiting bacterial growth than chitosans with low molecular weights. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2495–2501, 2001