低分子量壳聚糖制备与应用研究进展

低分子量壳聚糖因具有特殊的生物活性而日益受到人们的关注。本文概要介绍了近5年来国内外低分子量壳聚糖的研究进展,包括低分子量壳聚糖的制备方法,如酶降解法、酸水解法、氧化降解法、物理法等,以及低分子量壳聚糖在农业、医药、抗菌、化妆品、食品等方面的应用。     

低分子肝素/壳聚糖/海藻酸钠复合微囊的制备及释药性能

低分子肝素/壳聚糖/海藻酸钠复合微囊的制备及释药性能;壳聚糖; 海藻酸钠; 低分子肝素; 微囊; 释药性能     

用GPC研究壳聚糖氧化降解过程中的分子量及其分布

用凝胶渗透色谱法跟踪研究了过氧化氢对壳聚糖氧化降解过程中壳聚糖的分子量及其分布的影响,结果表明,反应温度、时间和过氧化氢用量对壳聚糖的降解程度及降解产品质量均有影响。     

低分子量N-羧丁酰壳聚糖的合成及其吸湿保湿性

低分子量N-羧丁酰壳聚糖的合成及其吸湿保湿性;低分子量壳聚糖;低分子量N-羧丁酰壳聚糖;吸湿性;保湿性     

小分子与高分子混合凝胶研究进展

凝胶作为一种半固态的软物质材料近年来得到很多关注。高分子和小分子都可以作为凝胶的胶凝剂,但是由于在形成过程中两者形成的结构交联与否对形成的凝胶影响很大,表现出了明显的不同。而小分子高分子混合凝胶能整合两者的优势,使混合凝胶兼具小分子凝胶的刺激响应性和高分子凝胶的力学性能。本文从高分子凝胶与小分子凝胶的差异化和互补性方面入手,总结了小分子和高分子的混合凝胶的研究进展。     

高分子量聚合物对溶剂诱导低分子量聚合物薄膜去润湿动力学的影响

采用偏光显微镜及椭偏仪等研究了单分散低分子量聚苯乙烯(PS)薄膜、 单分散高分子量PS薄膜以及将二者按不同质量比共混制备的PS薄膜, 在室温下用丙酮溶剂诱导其去润湿的过程. 实验发现, 按不同质量比共混的PS薄膜的去润湿动力学与单分散的PS薄膜去润湿动力学有较大区别. 按不同质量比共混的PS薄膜, 低分子量的PS更易于富集在薄膜的表面, 其去润湿的速度介于单分散低分子量PS薄膜与单分散高分子量PS薄膜的去润湿速度之间. 但共混薄膜的去润湿速率并非随着高分子量PS的加入呈现单调的变化, 这是由大量接触分子的形成抑制了去润湿所致.     

血清中低分子量蛋白质的提取和鉴定

采用改进的圆盘凝胶电泳提取人血清中低分子量蛋白质, 去除了血清中分子量大于3×104的蛋白质, 将提取的低分子量蛋白质热变性后直接在溶液中酶解成肽, 经液相色谱-质谱分析, 并进行Mascot数据库检索, 确认出人血清中97种蛋白质.     

Comparison of Fractionation Methods for the Characterisation of Short Chain Branching as a Function of Molecular Weight in Ethylene 1-Olefin Copolymers

Summary: Rapid and automated analysis of polyolefins is becoming essential for product development in industry. Quantifying short chain branching in ethylene 1-olefin copolymers is common practice. Several different methods are available to perform this type of analysis. Preparative fractionation followed by subsequent analysis of the fraction by SEC and NMR, SEC-FTIR and SEC-IR were studied towards their applicability in polyolefin research and product development environment. The method of choice is defined by prerequisites such as accuracy, labour and time demands but also in versatility and practicability. The most accurate method is limited in terms of sample throughput and the most practical method is limited towards resolution of very low branching. SEC-FTIR is capable to measure even heterogeneous low branched samples like bimodal high density polyethylene in rapid and satisfactory matter.     

The Effect of Trifluoroacetic Acid on Molecular Weight Determination of Polyesters:An in Situ NMR Investigation

Due to the poor solubility of aromatic polyesters in common organic solvents,trifluoroacetic acid is usually used as a co-solvent to increase their solubility for characterizations.However,only few studies have reported the side reactions induced by it.We present here the application of in situ 1H-NMR techniques to explore its effect on the hydroxyl end-groups,which are usually used for the molecular weight determination of polyesters by end-group estimation method.Using bis(2-hydroxyethyl) terephthalate (BHET) as model compound,1H quantitative NMR results show the peak integration of hydroxyethyl end-groups decreased with time via a pseudo-first-order kinetics in d-trifluoroacetic acid/d-chloroform mixture solvent (1∶10,V∶V).This is due to the esterification of hydroxyethyl groups with trifluoroacetic acid,revealed by the 1H-13C gradient-enhanced heteronuclear multiple bond correlation (gHMBC) spectrum.The mixtures of dimethyl terephthalate and BHET with different molar ratios were used to represent poly(ethylene terephthalate) (PET) with different degrees of polymerization,and the effect of trifluoroacetic acid on the estimation of hydroxyethyl groups and subsequent molecular weight determination of polyesters was studied.Our results show that if a relative error of 5％ is allowed,the NMR measurements must be finished within 1.3 h of solution preparation at 25 ℃ in the mixture solvent.The results were confirmed in PET sample,while in poly(ethylene adipate),the obtained esterifaction constant is faster that those in aromatic system.The results can be applied to other polymer systems with alcohol functionalized groups,and used as a guideline for the characterization of polyesters and polyethers by end-group estimation method.     

分子量对壳聚糖溶致液晶性的影响

三种不同分子量的壳聚糖[脱乙酰度均为(84±1)%]在二氯乙酸溶液中都呈现胆甾型溶致液晶相.临界浓度随分子量增加而降低,但均比同样聚合度的甲壳素的高.用偏光显微镜法和激光小角散射法测得的胆甾液晶相的螺距很相近,在浓度相同时,其值随分子量的增加而减小.     

Progress in Molecular Dynamics and Hansen Solubility Parameters of Low Molecular Weight Gels北大核心CSCD

Recently,the use of computational methods such as Molecular Dynamics（MD）simulations and Hansen Solubility Parameters （HSPs）to study the behavior of small molecule gelators has attracted much attention. MD simulation is a computational method based on classical mechanics and is one of the preferred techniques for understanding the process of small molecule gelators. The MD simulation can more accurately analyze the gelation trend or assembly behavior of small molecule gelators,dynamically and graphically display the self-assembly process,effectively reveal the relationship between the structure of small molecule gelators and related gelation behavior,and quantitatively analyze non-covalent bond interactions such as hydrogen bonds,π-π stacking,van der Waals interactions,ionic bonding and solvophobic interactions. By performing molecular dynamics simulations on known gelators/non-gelators,parameters related to gelation behavior in the simulated data are extracted,and the linear correlation is measured by fitting the Pearson correlation coefficient to finally predict the gelation behavior of a certain class of small molecules. On the other hand,the empirical model developed according to the HSPs is the most representative,which consists of the energy of dispersion interaction（δd）,the energy of polar interaction（δp）and H-bonding energy（δh ）between molecules. These three parts determine the coordinate point of the three-dimensional space（Hansen space）. According to the range of the point,it can be determined whether the organic small molecule can form a gel in a specific solvent. In this paper,representative works published recently in the field of organic small molecule gels by using MD simulations and empirical models are reviewed. Some comments on the assembly behavior of gelators,the regulation and prediction of non-covalent bond interactions on gelation ability are made. © 2022, Science Press (China). All rights reserved.     

低分子量溴代聚苯乙烯的制备及应用

用溶液法合成了一系列低分子量的聚苯乙烯，其溴化产物（Ｂｒ－ＰＳ）的溴含量和热稳定性与美国同类产品Ｐｙｒｏ－Ｃｈｅｋ ＬＭ相当，分别用作聚苯乙烯树脂的阻燃剂，极限氧指数测定结果表明，其阻燃性也达到了Ｐｙｒｏ－Ｃｈｅｋ ＬＭ的水平。     

低温等离子体对超高分子聚乙烯纤维表面改性研究

介绍了低温等离子放电技术的概念、原理、实施方法及其在超高分子量聚乙烯（UHMWPE）纤维表面改性方面的应用。综述了国内外低温等离子体对UHMWPE纤维表面改性的最新研究成果,阐述了气体等离子体种类、处理功率和处理时间等因素对UHMWPE纤维表面改性效果的影响机理,以及低温等离子设备对UHMWPE纤维表面改性连续化的初步...     

应用壳聚糖-分子筛复合材料选择性吸附卷烟烟气中低分子醛酮

制备了3种壳聚糖-分子筛复合材料,并使用扫描电镜和ASAP 2020全自动吸附仪观测了复合材料的微观形态及其物理性质。对分别添加3种壳聚糖-分子筛复合材料、分子筛及壳聚糖的卷烟复合滤咀对主流烟气中低分子醛酮类化合物和其它有害物质(如焦油、尼古丁及一氧化碳等)的吸附效果进行了试验。结果表明:添加了壳聚糖-分子筛复合材料、分子筛及壳聚糖的卷烟滤咀对主流烟气中低分子醛酮类化合物均有较好的吸附作用,对焦油、烟碱量无明显影响;3种壳聚糖-分子筛复合材料对主流烟气中醛酮类化合物的吸附能力均优于其两种单体材料,该复合材料对一氧化碳有一定的吸附,且对抽吸品质有所改善,口感柔和,烟气刺激性降低。     

激光光散射表征聚N－异丙基丙烯酰胺的分子量分布

采用自由基聚合法合成了聚N-异丙基丙烯酰胺(PNIPAAM)样品,由激光光散射法(LLS),包括绝对累积散射光强的角度依赖性(静态LLS)和线宽分布的角度依赖性(动态LLS)表征了合成的PNIPAAM样品的分子量分布。通过对动态光散射测得的电场-电场时间相关函数的拉普拉斯变换,求得平动扩散系数分布G(D);结合静态和动态光散射测量的结果,即M_w和G(D),确定了PNIPAAM样品的平动扩散系数D对分子量M的标定关系式D=2.84×10^-4M^-0.55,并将G(D)转换成分子量分布F_w(M).     

Structural Studies for Specific Binding Capacity of β‐Cyclodextrin with Ibuprofen

Ibuprofen (Ibu) and β‐cyclodextrin (βCD) and its derivative (hydroxypropyl‐β‐cyclodextrin, HPβCD) complexes spatial geometry information were studyed. Firstly, phase solubility experiment was carried out for S‐(+)‐ibuprofen (SIbu) and cyclodextrins complex. The apparent stability constant (Kc) for 1:1 complexes are 1065 M‐1 (βCD) and 1476 M‐1 (HPβCD) respectively. Secondly, ¹H NMR and two‐dimensional rotating‐frame overhauser effect spectroscopy (2D ROESY) were used for binding study, and confirmed that benzene ring of Ibu is deeply included into the cavity and racemic Ibu (RSIbu) can be discriminated by βCD or HPβCD. Finally, docking model was given by theoretical investigation. The model with ‐4.77 kcal/mol binding energy matches experimental structure.     

Evaluation of Antibacterial and Antifungal Properties of Low Molecular Weight Chitosan Extracted from Hermetia illucens Relative to Crab Chitosan

This study shows the research on the depolymerisation of insect and crab chitosans using novel enzymes. Enzyme preparations containing recombinant chitinase Chi 418 from Trichoderma harzianum, chitinase Chi 403, and chitosanase Chi 402 from Myceliophthora thermophila, all belonging to the family GH18 of glycosyl hydrolases, were used to depolymerise a biopolymer, resulting in a range of chitosans with average molecular weights (M_w) of 6–21 kDa. The depolymerised chitosans obtained from crustaceans and insects were studied, and their antibacterial and antifungal properties were evaluated. The results proved the significance of the chitosan’s origin, showing the potential of Hermetia illucens as a new source of low molecular weight chitosan with an improved biological activity.     

EFFECT OF MOLECULAR WEIGHT OF PEO ON THE STRUCTURE AND PROPERTIES OF PDMAEMA/PEO HYDROGELS

A new kind of binary hydrogels composed of poly(dimethylaminoethylmethacrylate) (PDMAEMA) and poly(ethylene oxide) (PEO) with varying weight average molecular weights ((M)w = 5 × 104, 1 × 105 and 2.5 × 106) were prepared by y-irradiation technology. The properties of PDMAEMA/PEO hydrogels obtained were evaluated in terms of gel fraction, gel strength, thermal characterization and swelling behavior. The gel strength and swelling degree of the hydrogels could be improved obviously after adding PEO into the PDMAEMA system, while the degree of improvement decreased with increasing (M)w of PEO. The temperature sensitivity of PDMAEMA/PEO was retained only in the sample with PEO of (M)w = 5 × 104, and the pH sensitivity was retained in samples with PEO of (M)w = 5 × 104 and 1 × 105. When DMAEMA/PEO mixtures containing PEO of (M)w = 5 × 104 were irradiated, the main reaction could be the cross-linking of DMAEMA, and the linear PEO molecular chains could penetrate into the cross-linked network of PDMAEMA. With increasing Mw of PEO, some side reactions were induced, such as grafting of DMAEMA onto PEO molecules, the scission or cross-linking of PEO.     

Physicochemical Study of Ribavirin Complexes with α-, β- and γ-Cyclodextrins

The aim of this work was to characterise interactions between ribavirin (RBV) and native cyclodextrins (CDs). The extent of complexation in solution has been evaluated by high performance liquid chromatography (HPLC) and nuclear magnetic resonance (NMR). Thermogravimetry (TG), differential scanning calorimetry (DSC) and infrared spectroscopy (FT-IR) were used to characterise the solid state of all the binary systems. Complexation of RBV with α-, β-, and γ-CDs was proved by FT-IR, HPLC and thermal analysis. The 1:1 stoichiometry for the complexes was obtained by HPLC. The stability constants for RBV with α-, β- and γ-CD were determined to be 1493, 2606, and 1179 M⁻¹, respectively. Consequently β-CD was the most suitable of the three complexing agents since it showed the highest stability constant. RBV appears not included inside the cavity of the CD because H-3 and H-5 protons were not shifted in the presence of the molecule as proved by NMR. The 2D ROESY spectra did not show any dipolar proton interaction of the RBV with the CDs. Thus the complexation does not seem to be a host–guest inclusion complex but an external intermolecular complex. FT-IR spectral changes due to the RBV carboxamide group vibrations with the CDs confirm this association.     

甲烷氧化细菌生物催化合成聚-β-羟基丁酸酯的分子量调控

在甲烷氧化细菌Methylosinus trichosporium IMV3011细胞内生物催化合成聚-β-羟基丁酸酯(PHB)的过程中,对影响聚合物分子量的各种因素进行了研究.发现碳源、培养基组分NH4+,NO3-,HPO24-,Mg2+,某些导向PHB合成的关键中间产物以及PHB的提取方法均会对PHB的分子量产生影响.同时,通过对胞内PHB合成酶系中关键作用酶的活性变化进行研究,发现β-酮硫解酶催化着控制进入PHB循环入口的关键反应,而PHB分子量的变化则主要取决于PHB合成酶和PHB降解酶的协同作用.