荧光光谱跟踪结冷胶水溶液的溶液-凝胶转变

将异硫氰酸荧光黄(FITC)标记在结冷胶分子链,用荧光光谱跟踪了结冷胶水溶液凝胶化过程中FITC荧光强度和各向异性比的变化.结果表明在结冷胶的凝胶化转变中,FITC的荧光相对强度和各向异性随温度降低而增大,在某一温度荧光相对强度和各向异性比对温度的曲线出现了明显的转折点,这个转折点的温度低于流变温度扫描曲线中G′=G″的温度.利用荧光的方法确定物理交联体系的关于重均聚合度和凝胶分数的相关临界指数γ和β.γ和β不符合Flory-Stockmayer和逾渗模型的预测.     

凝胶中荧光颗粒原位电泳洗脱过量异硫氰酸荧光素用于图像分析北大核心CSCD

去除荧光标记后残余荧光染料可以提高荧光颗粒检测的灵敏度、准确度和效率。该文发展了一种原位电泳洗脱(electrophoretic elution,EE)模型,用于在荧光标记后快速去除多余的荧光探针,实现荧光颗粒的灵敏检测。将牛血清蛋白(BSA)和磁珠(MBs)作为模式蛋白和微颗粒,混合孵育获得MBs-BSA,用异硫氰酸荧光素(FITC)对MBs-BSA标记,得到MBs-BSA_(FITC)复合物。将含有多余FITC的MBs-BSA_(FITC)溶液与低凝聚温度琼脂糖凝胶溶液按1∶5的体积比混合,并将混合物凝胶和纯琼脂糖凝胶分段填充到电泳通道中。电泳过程中,利用颗粒尺寸与凝胶孔径的差异来保留MBs-BSA_(FITC),同时将游离的FITC洗脱。经过30 min的电泳洗脱,通道内多余的FITC清除率达到97.6%,同时目标颗粒荧光信号保留了27.8%。成像系统曝光时间为1.35 s时,电泳洗脱将颗粒与背景的荧光信号比(P/B ratio,PBr)从1.08增加到12.2。CCD相机的曝光时间增加到2.35 s,可以将PBr提高到15.5,可进一步实现对微弱荧光亮点的高灵敏检测。该模型有以下优点:(1)能对颗粒表面非特异性吸附的FITC实现有效洗脱,提高了检测的特异性;(2)能够将97%以上的游离FITC清除;(3)30 min内能够使凝胶内的背景荧光大幅降低,提高了PBr和检测灵敏度。因此,该方法具有在凝胶中进行基于磁珠/荧光颗粒点的免疫检测、在免疫电泳或凝胶电泳中对蛋白质/核酸条带进行荧光染色等领域的应用潜力。     

阳离子诱导海藻酸水溶液凝胶化的临界行为与自相似性

以作者对阳离子诱导海藻酸水溶液凝胶化的研究结果为中心,介绍了海藻酸钠水溶液随浓度增大和二价金属阳离子(Ca2 、Cu2 )的加入而发生的溶液-凝胶转变的临界点和相关临界指数,探讨了临界凝胶的自相似性和分形结构,以及动态标度理论对物理交联体系的适用性.基于对阳离子诱导海藻酸水溶液凝胶化及其临界行为的研究结果,提出了从凝胶化的出发点--溶液来对凝胶化进行分类的设想,根据起始组分分子链的长短将凝胶化过程分为生长型和交联型两类.     

目视化乙肝病毒基因芯片

优化了基于纳米金标记探针的目视化检测方法,将其用于检测从阳性血清中提取的乙肝病毒(HBV)基因,并与基于荧光素异硫氰酸酯(FITC)标记探针的荧光检测方法进行了比较.结果表明,目视化乙肝病毒基因芯片诊断方法操作简单,成本低廉.此类基因芯片在病毒基因检测领域将会有广泛用途.     

微囊化海藻酸离子移变凝胶的制备、结构与性能

通过静电脉冲技术制备了海藻酸-壳聚糖-海藻酸(Alginate-Chitosan-Alginate,ACA)微胶囊,红外光谱分析表明,ACA是一种以聚电解质配合物为囊膜,以海藻酸钠离子吸附剂为囊心物的微胶囊型离子吸附体系.扫描电镜测试表明,ACA吸附重金属离子的过程是微胶囊囊内海藻酸凝胶化的过程,其解吸附过程是海藻酸凝胶转变成海藻酸溶液的过程.与传统离子交换树脂相比,ACA对Pb²⁺的吸附具有较高的去除率、很强的富集能力和较低的极限吸附浓度,并且能够被多次重复使用.ACA的离子交换速率比传统离子交换树脂快得多,离子交换过程中,交换离子和吸附剂海藻酸分子的相互扩散大大提高了离子交换速率.     

海藻酸盐水凝胶作为递送载体在组织再生中的应用

海藻酸盐是一类存在于褐藻中的线性亲水多糖,由D-甘露糖醛酸(M)和L-古洛糖醛酸(G)以不同比例的重复单元组成.它是用于水凝胶合成的天然生物材料之一,通过简单的离子交联,即可与Ca2+等多价无机阳离子发生"蛋盒反应",形成水凝胶.海藻酸盐骨架上存在大量–OH和–COOH极性基团,通过化学或物理方法对其进行修饰,使其可以在温度、pH、光等刺激的响应下实现细胞或生物活性分子的可控释放.目前组织再生领域的主要应用策略之一是利用生物相容性材料,结合生物活性分子和细胞,以促进受损组织的再生.水凝胶材料在保护嵌入的细胞并模仿天然细胞外基质方面具有潜力.海藻酸盐也因为其易于凝胶化和良好的生物相容性,被广泛用于组织再生领域.本综述中,我们总结了用于组织再生,特别在伤口愈合、骨和心脏修复领域的海藻酸盐水凝胶的不同交联方法,重点分析了对刺激具有响应性的海藻酸盐水凝胶的特征以及其作为递送载体在组织再生中的应用.     

用动态光散射跟踪钙-海藻酸水溶液凝胶化

海藻酸(alginate)是一种天然多糖,是直链键合的β-D-甘露糖醛酸(M)和α-L-古洛糖醛酸(G)的无规嵌段共聚物[1].在海藻酸水溶液中加入钙、铜、锌、铅等二价正离子,能够形成凝胶;其中钙-海藻酸凝胶在细胞输送、组织工程等领域受到人们的关注[2,3].影响海藻酸凝胶化的因素包括海藻酸的分子量和分子量分布、M/G值和序列分布、溶液浓度、正离子种类与浓度等[4,5].     

海藻酸-壳聚糖-海藻酸凝胶离子取代机理

研究了海藻酸-壳聚糖-海藻酸(ACA)凝胶的离子取代机理.光学显微镜照相法证实ACA离子取代过程中溶胶-凝胶相界面的存在.动边界模型描述ACA离子取代凝胶对二价离子的取代动力学过程,结果表明,模型可靠.离子取代凝胶对二价离子的取代属于颗粒扩散控制机理.与离子交换树脂比较,ACA离子取代速率要快得多,ACA离子取代过程不同于传统离子交换树脂离子交换过程,它是金属离子在溶胶凝胶相转移过程中的取代过程;ACA是一种崭新的离子移变凝胶型离子吸附剂.     

微波法制备氮掺杂碳点/海藻酸纳米复合物及其电沉积技术研究

以海藻酸为碳源,乙二胺为氮掺杂剂,采用简单方便的微波法制备得到氮掺杂碳点(N-CDs)/海藻酸纳米复合物.通过透射电镜观察到所制得的N-CDs/海藻酸纳米复合物有纳米粒子存在,它们的平均粒径为4.6 nm.荧光性能分析表明N-CDs/海藻酸纳米复合物在365 nm紫外光下呈现明显的蓝色荧光,并且其荧光发射性能具有激发光波长依赖性. N-CDs/海藻酸纳米复合物还保留了海藻酸与Ca~(2+)作用形成凝胶的性能以及与一些二价金属离子的配位能力,可以直接应用于阳极电沉积和配位电沉积.利用电沉积技术具有空间选择性和时间可控性的特点,可以在电极上构建不同形状和荧光图案的N-CDs/海藻酸电沉积膜,还可以对电沉积膜的厚度进行调控.此外,利用电沉积技术制备的N-CDs/海藻酸电沉积膜电极可用于进行电化学检测.     

海洋硫酸多糖911的荧光标记研究

硫酸多糖（911）的性末端的半缩醛基,通过还原胺化反应与酪胺（Tyr)的氨基共价偶联,911－Tyr中酪胺引入的仲氨基通过与异硫氰酸酯荧光素（FITC）进行亲核反应,实现对911还原末端的选择性荧光标记。用UV－Vis吸收光谱,^1H NMR和HPSEC对偶联与标记结果进行确证,从^1H NMR谱推测911与酪胺的偶联率及FITC为911－Tyr标记率分别为60％和80％。由于采用的是911末端选择性标记,对911的抗凝活性无明显影响,也无明显细胞的毒性。以荧光标记的911作为探针,对淋巴细胞有较强的选择性标记染色。该法适用于具有还原末端的多糖及寡糖的荧光标记。     

Gelation behavior of thermoplastic-modified epoxy systems during polymerization-induced phase separation

The rheological behavior and gelation characteristics of epoxy blends are of critical importance to property study and industrial application. In this work, we studied the rheological behavior and structural transition of different thermoplastics, including polyetherimide, polymethylmethacrylate, and polyethersulfone (PES), modified epoxy systems by using rheometry instrument, differential scanning calorimetry, time-resolved light scattering, and scanning electronic microscopes. At the same molecular weight level of thermoplastics, different epoxy blends show profound diversities on the rheological and gelation behavior due to the large differences in phase separation and curing process. For early phase-separation systems of PES-modified epoxy blends, two gel points are identified, which correspond to physical gelation and chemical gelation, respectively. With the variation of the PES molecular weight and curing rate, dramatic changes in gel time and critical exponent were observed. As the molecular weight of thermoplastics is increased, the gelation time becomes shorter and the gel strength gets lower, while the faster curing rate would increase the physical gel strength significantly.     

Viscoelastic properties of polyacrylonitrile gels: dependence of sol-gel transition on concentration and aging time

Dynamic viscoelasticity was observed for polyacrylonitrile solution in dimethylacetamide in the process of sol-gel transition. The gel was prepared by the freezing and thawing method, i.e., the solution was frozen at −50°C and then kept at 25°C so as to undergo gelation. The longer the freezing time, the shorter was the gelation time. Also the higher the concentration, the shorter the gelation time. The strength of the network, S and critical exponent n at the transition point were evaluated. The S value increased with increasing concentration and was constant in value in spite of the variation of freezing time when the concentration of the solution was constant.     

Accurate determination of the limiting anisotropy of rhodamine 101. Implications for its use as a fluorescence polarization standard

The S1-S0 limiting anisotropy of a widely used fluorophore, rhodamine 101, is determined with unprecedented accuracy. From time-resolved and steady-state fluorescence measurements in several solvents, it is shown that the limiting anisotropy of rhodamine 101 is for all practical purposes equal to the theoretical one-photon fundamental anisotropy value of 2/5, both in rigid and in fluid media. This fact, along with the favorable chemical and photophysical properties of rhodamine 101, point to its use as a standard for fluorescence polarization measurements. It is also shown that if the excitation pulse can be considered a delta impulse with respect to the time scale of the anisotropy decay (but not necessarily to the time scale of the intensity decay), then no deconvolution procedure is needed for anisotropy decay analysis.     

Physical gelation and macromolecular mobility of sustainable polylactide during isothermal crystallization

The mobility of free macromolecular chains is of importance to the growth of crystallites in a crystallizing sustainable polylactide (PLA), which was scarcely explored by rheology. In this study, the time‐resolved rheological properties for PLA during isothermal crystallization were investigated first, showing that the storage and loss modulus experience 2–3 decades of increase. The Avrami analysis reveals that the crystallization kinetics in rheological measurement protocol follows the homogeneous nucleation and three‐dimensional growth mechanism. The linear viscoelastic properties in the vicinity of physical gelation point were then studied at the inverse quenching temperature of 165 °C. The results show that physical gelation occurs when the critical absolute crystallinity reaches 13% as determined by the rheological method. Relaxation time spectra reveal that the interfacial relaxation is greatly retarded but the presence of growing spherulites possesses little constraint on the mobility of free chains in matrix especially before physical gelation point. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 1235–1244     

Diffusion NMR as a new method for the determination of the gel point of gelatin

The gelation of gelatin has been investigated using pulsed field gradient (PFG) NMR. For the first time, diffusion results have been used to determine the gelation point, which is indicated by a minimum in the self-diffusion coefficient of the free polymer fraction vs temperature. Biexponential analysis of the diffusion decay data allowing the diffusion of free and network-bound gelatin to be determined separately has been applied to provide an extended insight into the gelation process. Low-amplitude oscillatory shear rheology and time-resolved dynamic light scattering (DLS) as classical polymer characterization methods were applied as control experiments. All three methods yielded a gelation temperature of 24-25 degrees C for the cooling regime. Hysteresis effects could also be observed.     

Study on formation of gels formed by polymer and zirconium acetate

The gel system used in the preparation of dispersed particle gel for water shutoff treatments, which is composed of polyacrylamides and zirconium acetate, was investigated. The gelation process, the effects of various parameters on the gelation properties, the thermal stability, and the microstructure were addressed. The cross-linking reaction process is divided into three successive steps: induction, rapid cross-linking, and stabilization. High polymer and crosslinker concentrations reduce gelation time and increase gel strength. In addition, adding salts to the brine or increasing the temperature also decrease gelation time and increase gel strength. The optimum pH for the gel system is 7.49. In field applications, this gel system is recommended to be used within 130 °C using differential scanning calorimetry. The gel formed in a three-dimensional network structure was confirmed through environmental scanning electron microscopy.     

Thermal gelation of cellulose in a NaOH/thiourea aqueous solution

Utilizing a novel solvent of cellulose, 6 wt % NaOH/5 wt % thiourea aqueous solution, for the first time, we prepared the thermally induced cellulose gel. We investigated the thermal gelation of cellulose solutions with rheometry and the structure of the gel with 13C NMR, wide-angle X-ray diffraction, environmental scanning electron microscopy, and atomic force microscopy. The cellulose solutions revealed an increase in both the storage modulus (G') and the loss modulus (G") with an increase in the temperature during gelation. The temperature at the turning point, where G' overrides G" because of the onset of gelation, decreased from 38.6 to 20.1 degrees C with an increase of cellulose concentration from 4 to 6 wt %. Given enough time, G' of all solutions can exceed G" at a certain temperature slightly lower than the gelation temperature, indicating that the occurrence of the gelation is also a function of time. Each of the assigned peaks of NMR of the cellulose gel is similar to that of the cellulose solution, suggesting that the gelation resulted from a physical cross-linking. The gels were composed of relatively stable network units with an average diameter of about 47 nm. At either a higher temperature (at 60 degrees C for 30 s) or a longer gelation time (at 30 degrees C for 157 s), the gel in the 5 wt % cellulose solution could form. A schematic gelation process was proposed to illustrate the sol-gel transition: the random self-association of the cellulose chains having the exposed hydroxyl in the aqueous solution promotes the physical cross-linking networks.     

凝胶化反应中标度行为及凝胶化点关系

在苯乙烯(St)-二乙烯苯(DVB)自由基聚合的凝胶化反应过程中,定时取样,得到凝胶化点前后及直至反应终点的一系列溶胶样品,利用光散射技术研究了溶胶相的重均分子量M_w、尺寸均方旋转半径R_g的变化过程,建立了M_w、R_g和反应时间t的标度关系,并在此基础上提出一神新的准确求取凝胶化时间t_gel的方法.     

Physical gelation of water‐borne thermosetting resins by percolation theory—Urea‐formaldehyde,melamine‐urea‐formaldehyde,and melamine‐formaldehyde resins

Percolation and effective‐medium theories are applied for calculating the connectivity threshold of colloid particles of given shapes, observed during the physical gelation, distinguished from chemical gelation, of aminoplastic resins. The rigidity threshold, being the critical solid fraction at which a rigid network is first formed, was also calculated. For that purpose, it was assumed that the central forces that act between the colloidal particles and aggregates were not alone, thus corresponding to the case of physical gelation. It was shown that the observed change of morphology exhibited by such particles and aggregates as a function of time, from elongated to spherical, significantly delays the gel point. Consequently, the latter occurs only after a rather high fraction of solid phase (typically from 30 to 60%) is formed. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 971–978, 2008     

Solvent effects on the kinetics of gelation and the crosslink density of polysiloxane gels

A wide range of hydrocarbons were rapidly gelled by adding a polysiloxane copolymer in the presence of divinylbenzene and a platinum catalyst. The gel point was measured over a range of concentrations for hydrocarbons/solvents and organogels, using three separate methods: rheology, visual (tilt-tube) and FTIR. As the fraction of solvent was increased, the rate of reaction decreased, leading to an increase in the gelation time. The absolute value of the gel point depends upon the techniques used to measure it. For any particular system the gel point values always followed the order: rheology > visual > FTIR. The crosslink densities of the gel systems were determined using both swelling and thermomechanical analysis. The swelling measurements confirmed that the addition of large quantities of solvent markedly reduced the crosslink density of the obtained chemical gel networks, which helped in designing gels with suitable critical strength for effective field work. Also the effectiveness of gelation with the proposed gelling system for different hydrocarbons/solvents was evaluated, and discussed in relation to their dielectric properties.This paper is dedicated to Mike Owen on occasion of his winning the DeBruyn medal, the first silicon chemist to do so.