功能性大分子的相互作用及其应用研究

以葡甘聚糖、κ-卡拉胶、黄原胶、大豆分离蛋白为主要原料,研究了三种多糖之间以及多糖与蛋白质之间的相互作用.结果表明,多种多糖及多糖与蛋白质共混后在分子间力的作用下,呈现出良好的增效性,其综合性能(如凝胶强度、弹性、透明度等)得到了提高.利用这一性质,开发出了一种兼有膳食纤维和蛋白质的新型功能性基料.同时探讨了温度、时间、浓度、电解质各因素对多糖之间及多糖与蛋白质之间相互作用的影响,得出工艺配方,制成了多糖复合保健食品和仿生海洋产品.     

钙离子诱导的海藻酸钠/黄原胶凝胶化临界行为研究

研究了海藻酸钠/黄原胶混合体系的相行为及其对海藻酸钠-钙离子凝胶化临界行为的影响.当海藻酸钠浓度为0.5 wt%时,随着黄原胶的添加,混合体系出现相容、相分离及液晶3种不同的相行为.与纯黄原胶溶液相比,海藻酸钠/黄原胶混合溶液在更低的黄原胶浓度下开始形成液晶,这是由于混合体系中相分离的发生导致了黄原胶有效浓度升高.利用葡萄糖酸内酯(GDL)在线酸化Ca-EDTA,释放钙离子,研究了不同钙离子引入量时(f=[Ca2+]/[COO-])混合体系的黏弹性.Winter-Chambon分析发现临界凝胶点(f gel)随黄原胶浓度的增加而降低.当相分离发生时,临界凝胶点急剧降低,当液晶结构形成后,临界凝胶点呈现上升趋势.通过对比Winter-Chambon方法和临界凝胶点模量松弛法所测得的松弛临界指数(nw和nr),发现黄原胶的添加使海藻酸钠临界凝胶失去结构自相似性.相分离的发生导致临界凝胶结构排列更加致密,而液晶的出现使临界凝胶结构排列相对疏松.     

植物多糖干凝胶的制备及其力学性能

以植物多糖淀粉、魔芋葡甘聚糖（KGM）为基材,采用物理改性及共混的方法,原料经溶胶-凝胶,冷冻干燥过程得到植物多糖干凝胶。通过正交试验,得到了制备植物多糖干凝胶的原料配方。探讨了制胶温度、搅拌时间、搅拌速率、溶液PH、预冷冻时间等因素对植物多糖干凝胶弹性、硬度的影响。采用响应曲面法对制备条件进行优化,得到的最佳制备条件为：制胶温度90℃、搅拌速率800r／min、搅拌时间70min、溶液pH-9、预冷冻时间14h、预冷冻温度-40℃、冷阱温度-50℃、真空度12．5kPa。该干凝胶的弹性、硬度分别为1．812mm和5．382N。扫描电镜的观察表明,该植物多糖干凝胶呈立体三维多孔网络结构。     

黄原胶以三价铬交联的水凝胶的脱水行为

对黄原胶／三价铬水凝胶在７０，８０和９０℃下的脱水行为进行了研究．脱水与凝胶的交联密度即参与交联反应的三价铬的含量有密切联系．突发脱水之后的过程可以用一级反应动力学描述，反应速度常数随三价铬的浓度和温度的增高而增大，活化能为３４．５ｋｃａｌ／ｍｏｌ．一价盐（ＮａＣｌ）的含量对脱水过程没有影响．     

多糖共混及其分子设计

着重讨论了多糖共混过程中的凝胶化及其分子间的协同作用，并对多糖共混凝胶化中的构效关系，分子修饰及分子设计等问题进行了讨论。     

浅谈黄原胶及其在农药制剂加工中的应用

黄原胶是极具发展潜力的生物多糖,独特的分子结构使其具有良好的增稠、乳化和稳定作用,已被广泛应用于日用化工、石油开采、纺织印染、食品、医药、涂料、农药等众多工业领域,拥有广阔的市场前景。本文对黄原胶的结构、特性、生产工艺以及主要应用领域等进行了简单综述,总结了黄原胶在农药制剂加工中的应用现状,指出黄原胶优越的流变特性对悬浮剂、水乳剂、悬乳剂等农药制剂悬浮稳定性的提高具有重大意义,最后展望了黄原胶未来的发展前景。     

以数字处理对魔芋葡甘聚糖膜面特征的初步研究

以天然生物材料为原料的绿色环保型膜材料取代塑料薄膜将是今后膜材料的发展趋势[1 4 ] 。从魔芋 (ＡｍｏｒｐｈｏｐａｌｌｕｓＫｏｎｊａｃＫ .ＫｏＣｈ)中提取出的魔芋精粉 ,其主要成分为葡甘聚糖 ,其优良的成膜性已引起人们的重视[4 5] 。分形维数在材料研究中得到了广泛的应用[6 ] ,本文以魔芋葡甘聚糖为主要原料制成膜 ,对膜的扫描电镜图象进行数字化处理 ,探讨膜面的微观形貌特征及制膜条件对膜面的影响。1　实验部分1 1　膜的制备以魔芋精粉 (四川安县魔芋精粉厂 )为主要原料 ,并添加明胶增强剂、甘油 (食品级 )增塑剂 (质量比为 1…     

黄原胶分子形貌的电镜研究

本文用扫描电镜研究了温度、超声波处理及浓度对黄原胶分子形貌的影响,并用透射电镜研究了黄原胶单分子的形貌及分子量。认为黄原胶分子在一般情况下具有较规则的二、三、四级结构,论述了其初、高级结构之间的关系,得出了黄原胶分子是由40余个亚基组成的右手双螺旋这一结论,计算出其分子量为6×10~6至25×10~6。     

磷酸化黄原胶/氧化石墨烯的合成及其对铀的选择性吸附

以氧化石墨烯(GO)为基体,黄原胶(XG)为交联剂,磷酸(P)为修饰剂制备了磷酸功能化黄原胶/氧化石墨烯凝胶(P-XG/GO),并应用于铀的选择性吸附。扫描电子显微镜(SEM)、X射线衍射(XRD)、傅里叶变换红外光谱(FT-IR)、Zeta电势分析等技术表明GO的交联和磷酸化成功。系统研究了溶液pH值、铀初始浓度、吸附时间和温度等因素的影响,得到了适宜吸附条件。吸附数据用Langmuir等温线模型拟合良好,最大吸附能力为495.05 mg/g。与准一级动力学模型相比,准二级动力学模型更好地拟合了吸附过程。     

脂肪酰谷氨酸与小分子有机凝胶

研究了脂肪酰谷氨酸作为凝胶因子在不同有机溶剂中的成胶性能。结果表明,小分子有机凝胶的形成及其稳定性与有机溶剂种类、凝胶因子浓度和凝胶因子中碳链长度密切相关。FT-IR表明,凝胶因子在有机溶剂中是通过氢键等非共价力相互作用而聚集、自我组装形成凝胶。利用光学显微镜观察发现,凝胶因子在不同有机溶剂中形成凝胶的微观结构不同。     

聚偏氟乙烯凝胶电解质组成间相互作用及其凝胶化研究

通过冷却聚偏氟乙烯 (PVDF) 丙烯碳酸酯 (PC)或PVDF PC LiClO4的溶液 ,制备了数个聚合物凝胶 .实验表明 ,聚合物凝胶的凝胶化时间 (tgel)与凝胶温度、聚合物浓度有关 ,且强烈地依赖于体系中盐的浓度 ,因为盐会缩短体系的tgel.凝胶体系中LiClO4的存在提高了其凝胶熔融温度 (Tgm) ,LiClO4的含量越大 ,相应凝胶的Tgm 越高 .用DSC和落球法所测凝胶的Tgm 有较大的差别 .这说明凝胶中可能存在热稳定性好和热稳定性相对较差的两种不同结构部分 .FT IR的研究结果表明 ,凝胶电解质的各组成 (LiClO4,PC和PVDF)间存在较强的相互作用 .对含盐和不含盐的两类凝胶体系的对比研究表明 ,两者不同的凝胶化现象和Tgm 归因于盐与聚合物或溶剂间的络合作用     

Hydrocolloid gels of polysaccharides and proteins

Recent developments from 1997 to 2000 in hydrocolloid gels which consist of dispersed phase (polysaccharide or protein) and dispersing medium (water) are reviewed in the present paper. Gels and gelling processes of polysaccharides such as gellan gum, methylcellulose, xyloglucan, curdlan, konjac glucomannan and starch are described. Fluid gels and galactomannan gels prepared by freeze-thaw cycling are also described. Effects of pH and ionic strength on the gelation of proteins such as casein and β-lactoglobulin are described. Fractal treatment is introduced to study the structure–property relationship for globular protein gels. Gels formed by different hydrocolloids are also described briefly.     

Controllable gelation of methylcellulose by a salt mixture

The effects of a salt mixture consisting of a salt-out salt (NaCl) and a salt-in salt (NaI) on the sol-gel transition of methylcellulose (MC) in aqueous solution have been studied by means of micro differential scanning calorimetry and rheometry. The salt mixture was found to have a combined effect from the salt-out and salt-in salts in the mixture, and the salt effect was dependent on the water hydration abilities of the component ions and ion concentration. At a fixed total salt concentration, the sol-gel transition temperature nicely followed a rule of mixing: Tp = m1Tp1 + m2Tp2 where Tp, Tp1, and Tp2 are the gelation peak temperatures for the MC solutions with a salt mixture, NaCl, and NaI, respectively, and mi is the molar fraction of the salt component i in the salt mixture. The linear rule of mixing proved that the effects of NaCl and NaI on the sol-gel transition of MC are completely independent. In addition, the presence of a single salt or a salt mixture in a MC solution does not change the essential mechanism of MC gelation. Therefore, the sol-gel transition of MC can be simply controlled by a salt mixture consisting of a salt-out salt and a salt-in salt. The rheological results supported the micro thermal results excellently. But the gel strength of MC containing salts was influenced by both salt type and salt concentration.     

Specialist gelator for ionic liquids

Cyclo(l-beta-3,7-dimethyloctylasparaginyl-L-phenylalanyl) (1) and cyclo(L-beta-2-ethylhexylasparaginyl-L-phenylalanyl) (2), prepared from L-asparaginyl-L-phenylalanine methyl ester, have been found to be specialist gelators for ionic liquids. They can gel a wide variety of ionic liquids, including imizazolium, pyridinium, pyrazolidinium, piperidinium, morpholinium, and ammonium salts. The mean minimum gel concentrations (MGCs) necessary to make gels at 25 degrees C were determined for ionic liquids. The gel strength increased at a rate nearly proportional to the concentration of added gelator. The strength of the transparent gel of 1-butylpyridinium tetrafluoroborate ([C(4)py]BF(4)), prepared at a concentration of 60 g L(-1) (gelator 1/[C(4)py]BF(4)), was ca. 1500 g cm(-2). FT-IR spectroscopy indicated that a driving force for gelation was intermolecular hydrogen bonding between amides and that the phase transition from gel to liquid upon heating was brought about by the collapse of hydrogen bonding. The gels formed from ionic liquids were very thermally stable; no melting occurs up to 140 degrees C when the gels were prepared at a concentration of 70 g L(-1) (gelator/ionic liquid). The ionic conductivities of the gels were nearly the same as those of pure ionic liquids. The gelator had electrochemical stability and a wide electrochemical window. When the gels were prepared from ionic liquids containing propylene carbonate, the ionic conductivities of the resulting gels increased to levels rather higher than those of pure ionic liquids. The gelators also gelled ionic liquids containing supporting electrolytes.     

Studies on organogelation of self assembling bis urea type low molecular weight molecules

A novel class of toluene based bis urea compounds carrying linear fatty acid units and semicarbazide linkages has been synthesised. The compounds were exhibiting thermoreversible gelation at concentrations below 10 mg/mL in common organic solvents, both aliphatic and aromatic. The effect of the chain length variation of fatty acid units on gelation properties like gelation concentration, gelation time and gel melting temperatures were studied. Choosing a particular gelator of fixed chain length and a specific solvent, the effect of the concentration on the gelation properties were studied. The thermal studies using DSC revealed the presence of phase transitions corresponding to the premelting and melting of the gels during the heating cycle. The morphology of the xerogels studied using SEM revealed a three dimensional network structure while the WAXS studies showed no crystallinity in the xerogels. IR spectra of the gels (solvent subtracted) and solutions in the corresponding solvent showed that a high degree of inter-molecular H bonding exists and absorptions corresponding to NH stretching shifted to lower wave numbers. Thus simple bisurea type of compounds exhibiting gelation ability in a wide range of solvents can be used for making functional gels for various applications.     

Crystallization and thermoreversible gelation of poly(butylene terephthalate)–epoxy mixtures

The thermoreversible gelation of solutions of poly(butylene terephthalate) (PBT) and a liquid diglycidyl ether of bisphenol-A epoxy has been investigated. The morphology of the gels and the conditions under which they form have been characterized by optical microscopy, thermal analysis, and x-ray scattering. Gels were found to form under two different conditions and with different morphologies. Gels formed after a considerable delay when homogenous PBT-epoxy solutions were cooled to slightly below the dissolution temperature of crystalline PBT. These gels contained large, irregular PBT spherulites and smaller birefringent interspherulitic matter. The melting of these gels and the onset of macroscopic flow coincided with the melting of the interspherulitic matter, and occurred before the melting of the large spherulites. Thermoreversible gels formed very quickly when PBT-epoxy solutions were self-nucleated by heating a dispersion of crystalline PBT in epoxy slightly and briefly above the dissolution temperature and then cooling. These gels displayed only a weak background birefringence and were molten when the weak birefringence disappeared. In both cases, gelation occurred by the formation of a three-dimensional PBT network in the epoxy liquid, and the nodes of the network were crystalline PBT particles. $ 1994 John Wiley & Sons, Inc.     

Effect of deacetylation rate on gelation kinetics of konjac glucomannan

Effect of deacetylation rate on the gelation behaviors on addition of sodium carbonate for native and acetylated konjac glucomannan (KGM) samples with a degree of acetylation (DA) range of 1.38-10.1 wt.% synthesized using acetic anhydride in the presence of pyridine as catalyst was studied by dynamic viscoelastic measurements. At a fixed alkaline concentration (C(Na)), both the critical gelation times (t(cr)) and the plateau values of storage moduli (G'(sat)) of the KGM gels increased with increasing DA. While at a fixed ratio of alkaline concentrations to values of DA (C(Na)/DA), the similar t(cr) and (G'(sat)) values independent of DA were observed. On the whole, increasing KGM concentration or temperature shortened the gelation time and enhanced the elastic modulus for KGM gel. The effect of deacetylation rate related to the C(Na)/DA on the gelation kinetics of the KGM samples were discussed.     

Gelation of native beta-lactoglobulin induced by electrostatic attractive interaction with xanthan gum

The mechanism and kinetics of the electrostatic gelation of native beta-lactoglobulin-xanthan gum mixtures in aqueous solution is reported. The total biopolymer concentration at which gelation was obtained was extremely low (0.1 wt %) compared to the usually tested concentrations for protein-polysaccharide mixed gels (4-12 wt %). This is, to our knowledge, the first time that oppositely charged proteins and polysaccharides are reported to form a gel without applying any treatment to denature the protein (e.g. heating, enzymatic hydrolysis) and at such low concentrations. Static light-scattering and viscoelastic measurements allowed determination of the gelation kinetics. It was found that the gelation process initiated following a similar path as that of an associative phase separation process, i.e., with the formation of primary and interpolymeric electrostatic complexes. However, interpolymeric complexes were able to form clusters and junction zones that resulted in the freeze-in of the whole structure at the point of gelation. The formed gel is therefore a coupled-gel, that is, a gel that has junction zones involving two different molecules. The structuration of xanthan gum, even at these low concentrations, may have played a role in the structuration process. Due to the electrostatic nature of the gels, there was an optimum pH and macromolecular ratio at which the stability of the gels was maximal. This was related to the existence of a stoichiometric electrical charge equivalence pH, where molecules carry equal but opposite charges and protein-polysaccharide interactions are at their maximum.     

Host–Guest Chemistry Within Cellulose Nanocrystal Gel Receptors

Cellulose nanocrystals (CNCs) spontaneously assemble into gels when mixed with a polyionic organic or inorganic salt. Here, we have used this ion-induced gelation strategy to create functional CNC gels with a rigid tetracationic macrocycle, cyclobis(paraquat-p-phenylene) ( CBPQT ⁴⁺). Addition of [ CBPQT ]Cl₄ to CNCs causes gelation and embeds an active host inside the material. The fabricated CNC gels can reversibly absorb guest molecules from solution then undergo molecular recognition processes that create colorful host–guest complexes. These materials have been implemented in gel chromatography (for guest exchange and separation), and as elements to encode 2- and 3-dimensional patterns. We anticipate that this concept might be extended to design a set of responsive and selective gel-like materials functioning as, for instance, water-pollutant scavengers, substrates for chiral separations, or molecular flasks.     

Ion gels by self-assembly of a triblock copolymer in an ionic liquid

We report a new way of developing ion gels through the self-assembly of a triblock copolymer in a room-temperature ionic liquid. Transparent ion gels were achieved by gelation of a poly(styrene-block-ethylene oxide-block-styrene) (SOS) triblock copolymer in 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]) with as low as 5 wt % SOS triblock copolymer. The gelation behavior, ionic conductivity, rheological properties, and microstructure of the ion gels were investigated. The ionic conductivity of the ion gels is only modestly affected by the triblock copolymer network. Its temperature dependence nearly tracks that of the bulk ionic liquid viscosity. The ion gels are thermally stable up to at least 100 degrees C and possess significant mechanical strength. The results presented here suggest that triblock copolymer gelation is a promising way to develop highly conductive ion gels and provides many advantages in terms of variety and processing.