多糖凝胶的孔径和化学结构对单壁碳纳米管流动性和选择性分离的影响

基于凝胶柱色谱分离技术研究了单分散的单壁碳纳米管(SWCNTs)在不同化学结构多孔多糖凝胶中的流动特性以及对金属型(m-)/半导体型(s-)SWCNTs分离的影响.通过比较SWCNTs在一系列不同孔径的葡聚糖Sephacryl凝胶中的流动行为,发现减小孔径尺寸能够增强s-SWCNTs与凝胶之间的吸附作用力,使大直径的m-SWCNTs快速地流过凝胶颗粒,而选择性地保留了小直径的s-SWCNTs.进一步发现多糖凝胶化学结构比孔径尺寸在SWCNTs的m/s分离中起着更重要的作用.当基于葡聚糖结构的Sephacryl凝胶中的氨基结构被琼脂糖结构所取代时,如Superdex 200和Sepharose 2B凝胶会增强它们与SWCNTs之间的作用力,使SWCNTs的保留时间延长,降低了s-SWCNTs的选择性和纯度.此外,即使拥有与Sephacryl S100类似的孔径范围,当Sephacryl凝胶中的氨基被疏水环氧丙烷基团取代时,葡聚糖凝胶Sephadex G100与SWCNTs的作用力很弱,导致所有SWCNTs快速流动,无法实现SWCNTs的m/s分离.因而,我们认为凝胶孔径和化学结构共同影响并调控了SWCNTs的m/s分离的选择性、纯度以及分离效率.     

超声分散对单壁碳纳米管分离的影响

利用凝胶柱色谱技术, 研究者们通过两步或多步淋洗的方法实现了不同导电属性或电子结构单壁碳纳米管(SWCNTs)的分离, 并提出其分离机制主要是由不同导电属性和电子结构的SWCNTs 与凝胶填料之间作用力的差异所导致的. 基于凝胶柱色谱分离技术, 本文重点考察了超声时间对单壁碳纳米管单分散以及金属型/半导体型SWCNTs 分离的影响. 在一定的低超声功率下, 适当增加超声时间有利于SWCNTs 在十二烷基硫酸钠(SDS)溶液中的单分散. 紫外-可见-近红外(UV-Vis-NIR)吸收光谱、拉曼(Raman)光谱和荧光(PL)光谱表征结果表明, 2 h的超声条件是获得高纯度的金属型以及不同直径分布的半导体型SWCNTs 的最优条件. 我们认为不同超声时间对SWCNTs 分离的影响主要是改变了SWCNTs 的单分散性和长度, 调制了不同SWCNTs 与凝胶之间作用力的差异, 从而导致了不同SWCNTs分离结果.     

琼脂糖性质对凝胶电泳法分离金属性和半导体性单壁碳纳米管的影响

利用琼脂糖凝胶电泳分离单壁碳纳米管(SWCNTs)技术, 考察了MB, Agarose, Agarose B和LRU 4种琼脂糖对SWCNTs分离效率的影响. 紫外-可见-近红外(UV-Vis-NIR)吸收光谱研究结果表明, 不同的琼脂糖对SWCNTs中s-SWCNTs的分离效率影响较小, 而对m-SWCNTs的分离效率影响较大. 分析4种琼脂糖凝胶的凝胶强度和凝胶网孔尺寸等发现, 影响SWCNTs中m-SWCNTs分离效率的主要因素是琼脂糖的凝胶强度和琼脂糖凝胶形成的网孔尺寸, 小的凝胶网孔尺寸有利于m-SWCNTs富集, 高凝胶强度则不利于其富集.     

裙带菜中聚甘露糖醛酸的分离纯化与结构分析

以裙带菜(Undaria pinnatifida, wakame)为原料, 经水提醇沉、DEAE-Sepharose Fast Flow、Sephacryl S-300和Sephacryl S-200凝胶柱分离纯化, 得到2个酸性多糖UPPS03和UPPS04. 高效凝胶渗透色谱测试结果表明, 其为均一多糖, 平均分子量分别为3.6×104和1.1×104. 采用糖组成分析、高碘酸氧化及Smith降解、糖醛酸还原、甲基化、红外光谱和核磁共振等方法对该多糖的化学结构进行了表征. 结果表明, 2个多糖均为1,4连接的聚甘露糖醛酸.     

单一导电属性及手性单壁碳纳米管的分离技术

综述了基于生长后处理策略下单一导电属性及手性单壁碳纳米管(SWCNTs)分离技术的研究进展, 阐述了SWCNTs 的选择性分离原理, 并比较了不同分离技术在分离纯度、效率、成本以及可规模化等方面的优缺点, 为SWCNTs 分离技术的发展及应用提供了方向性指导.     

增强型绿色荧光蛋白的色谱分离和纯化

增强型绿色荧光蛋白(EGFP)是生物领域常用的标记物。在前期成功克隆表达EGFP的基础上,本实验建立了两步分离纯化EGFP的色谱方法,并验证其分离纯化效果,检验EGFP的活性。首先用金属螯合亲和色谱柱HisTrap HP对EGFP的重组菌体破碎上清液进行初步分离,再用葡聚糖凝胶排阻色谱柱Sephadex G-10 HR对其进行脱盐纯化。采用丙烯葡聚糖凝胶排阻色谱柱Sephacryl S-300 HR和十二烷基磺酸钠-聚丙烯酰胺凝胶电泳(SDS-PAGE)检测分离纯化后的EGFP纯度。最后通过荧光分光检测器和非变性聚丙烯酰胺凝胶电泳(Native-PAGE)验证分离纯化后的EGFP是否具有荧光活性。结果表明该方法可以简便快速地分离纯化EGFP,纯度超过98%,同时保持了EGFP的荧光活性。     

单壁碳纳米管在胆酸类表面活性剂中的分散及手性碳管(6,5)的双水相分离方法

选用牛磺脱氧胆酸钠和脱氧胆酸钠等6种胆酸类表面活性剂,考察其对单壁碳纳米管(SWCNTs)的分散能力.紫外-可见-近红外吸收光谱测试结果表明,在超声功率为225 W,超声时间1 h的分散条件下,胆酸类表面活性剂均能对SWCNTs均匀分散,均可作为SWCNTs的分散剂.在相同条件下,质量分数为2%的牛磺脱氧胆酸钠对SWCNTs的分散能力最强,脱氧胆酸钠对SWCNTs的分散能力最弱.此外,还采用聚乙二醇/葡聚糖双水相系统对SWCNTs分散液进行了萃取分离,获得了纯度较高的手性SWCNTs(6,5).所筛选的SWCNTs分散剂及采用的双水相分离方法为单一手性SWCNTs的分离提供了一定的技术参考.     

琼脂糖凝胶电泳法分离金属性和半导体性单壁碳纳米管

琼脂糖凝胶电泳(AGE)是实现金属性单壁碳纳米管(m-SWCNTs)和半导体性单壁碳纳米管(s-SWCNTs)低成本、规模化分离的有效技术之一。本研究利用琼脂糖凝胶电泳分离单壁碳纳米管。通过紫外-可见-近红外吸收光谱和拉曼光谱对色谱带进行分段表征,发现电泳中迁移的最快的部分m-SWCNTs含量最高。考察了琼脂糖的浓度对SWCNTs中m-SWCNTs分离的影响。结果表明:高的琼脂糖浓度有利于m-SWC-NTs的富集,可以通过扩大电荷密度带来的迁移速率的差异来使SWCNTs中的m-SWCNTs得到更有效的分离。     

谷胱甘肽键合柱对蛋白的选择性研究

通过将谷胱甘肽键合到硅胶表面合成了同时具有弱阳离子交换(WCX)、疏水(HIC)和氢键作用的多功能色谱填料, 该固定相在HIC和WCX模式下对蛋白都有很好的分离效果. 实验通过计量置换保留模型对蛋白在谷胱甘肽键合柱上的色谱保留行为及机理进行了研究, 结果发现, 在流动相盐浓度较低时蛋白根据自身等电点高低通过静电作用力得以分离, 而在高盐浓度下疏水和氢键作用力共同决定蛋白的保留. 这种多作用力保留模式可有效提高色谱柱的选择性, 尤其为蛋白质、多肽及氨基酸的高效分离提供新的解决思路.     

氨基安替比林MIP-CEC整体柱的制备及电色谱性能研究

以氨基安替比林为模板分子,在内径100 μm的石英毛细管内采用原位聚合法制备了分子印迹毛细管整体柱,以电色谱模式分离了氨基安替比林及其结构类似物安替比林,在乙腈(体积分数15%)-磷酸二氢钠缓冲液(5 mmol/L)作为流动相(pH 7.0)条件下,18 min内完成分离,分离因子为1.37.考察了缓冲液中乙腈含量、pH值、离子强度对电渗流、溶质保留时间及分离因子的影响,探讨了整体柱识别机理.     

Influence of air oxidation on the surfactant-assisted purification of single-walled carbon nanotubes

Arc discharge single-walled carbon nanotube (SWCNT) soot was treated under different experimental conditions including gas- and liquid-phase oxidation, heat treatment in an inert gas, and hydrogen gasification. Afterward, the samples were dispersed in a surfactant and centrifuged at a moderately high speed. Near-infrared spectra of all the dispersions were compared with that of raw SWCNT soot. The relative intensity of SWCNT characteristic spectral bands strongly increased for air-oxidized samples after centrifugation, while it did not substantially change for samples oxidized with nitric acid or reduced with hydrogen. The relative SWCNT spectral intensity was associated to the sample purity through the so-called purity index, which was calculated from the S(22) band transition of semiconducting SWCNTs. Air-oxidized samples experienced a 7-fold increase in the purity index during centrifugation, while it increased by only 2-3 times for nonoxidized samples. Air oxidation specifically improves the preferential stability of SWCNTs over carbonaceous impurities in the dispersions, leading to the highest purity index values reported so far.     

Thermoreversible gelation of helical polypeptide/single‐walled carbon nanotubes and their solid‐state structures

Single‐walled carbon nanotubes (SWCNTs) have been functionalized with poly(γ‐benzyl‐L ‐glutamate)s (PBLGs) having well‐defined polymer molecular weight (M_n = 7.5–21.1 kg·mol^?1) and molecular weight distribution (PDI = 1.05–1.20) by a graft‐to method. Toluene solutions containing 5 wt % free PBLG and variable amounts of PBLG‐functionalized SWCNTs (PBLG‐SWCNTs) form gels at room temperature. Differential scanning calorimetry (DSC) analysis reveals that the gelation occurs thermoreversibly, in accord with previous studies on the pristine PBLG/toluene gels. The heat of gel melting (ΔH_m) is slightly elevated for the composite gels compared with the pristine gel, which suggests enhanced interactions between PBLGs in the former. But the gelation temperatures of the composites are unaffected by the presence of PBLG‐SWCNTs. Small‐angle X‐ray scattering (SAXS) analysis of the composite and pristine gels at different temperatures by the Guinier method suggests that PBLG‐SWCNTs promote interactions between PBLG rods, as indicated by the larger PBLG bundle size with increasing PBLG‐SWCNT content in the gel and the melt state. W/SAXS analysis of the dry gels reveals that PBLG‐SWCNTs induce significant changes in the PBLG packing order, resulting in a nematic phase, in contrast to a weakly ordered smectic C phase containing tilted PBLG rods that is observed in the pristine gel. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Sephacryl Gels: Physical Properties and Evaluation of Performance in Gel Filtration

Abstract

Sephacryl is a gel filtration medium composed of allyl dextran and N,N'-methylene bisacrylamide. Sephacryl S-200 SF has a fractionation range similar to that of Sephadex G-150. Sephacryl S-300 SF has a fractionation range more similar to Sephadex G-200 or Sepharose 6B, with an exclusion limit for globular proteins of about 10⁶ daltons. In typical applications, excellent resolution of protein mixtures was obtained at flow rates up to 30 cm/hr. Good correlation was established between elution volumes of proteins and their molecular weights. The gels contain few ionic groups, as determined by titration. Studies using Sephacryl S-200 at different pH values indicate that, above pH 3, protein does not interact with Sephacryl S-200 at moderate ionic strengths. However, below pH 3, protein binds strongly to the gel through hydrophobic interactions and/or hydrogen bonding. Most separations using Sephadex G-150 or Sephadex G-200 could be duplicated using Sephacryl S-200 or S-300 at much higher flow rates.     

Enrichment of large‐diameter semiconducting single‐walled carbon nanotubes by a mixed‐extractor strategy

In this work, we report a new mixed‐extractor strategy to improve the sorting yield of large‐diameter semiconducting single‐walled carbon nanotubes (s‐SWCNTs) with high purity. In the new mixed‐extractor strategy, two kinds of conjugated polymers with different rigidity, poly(9,9‐n‐dihexyl‐2,7‐fluorene‐alt‐9‐phenyl‐3,6‐carbazole) (PDFP) and poly(9,9‐dioctylfluorene‐alt‐benzothiadiazole) (P8BT), are used to sort large‐diameter s‐SWCNTs through two simple sonication processes. To our surprise, although PDFP itself shows no selectivity toward s‐SWCNTs, it can greatly enhance the sorting yield of P8BT. Using the PDFP/P8BT mixed‐extractor method, the yield of sorted s‐SWCNTs has been enhanced by 5 times with a purity above 99 % in comparison to that using P8BT single‐extractor method. In addition, the photoluminescence (PL) excitation maps shows that the PDFP/P8BT mixed‐extractor system not only enhances the sorting yield substantially, but also tends to be enrichment of (15,4) SWCNTs with the diameter of 1.36 nm.     

Flow of water through channels filled with deformable polymer gels

A mathematical model is developed for the flow of water through a channel impregnated with a polymer gel that is treated as an elastic and deformable porous medium. The model uses a Brinkman equation along with an experimentally observed velocity-dependent permeability. Numerical and approximate analytical solutions are given. These results show that the gel intrinsic properties, i.e., gel reference permeability and elastic index, control the water flow. First, the permeability of water flow through the gel increases with an increase of gel reference permeability. Second, the velocity of water decreases when the gel velocity exponent increases. Our theoretical results show that the velocity-dependent permeability of water flow through polymer gels is in fact an intrinsic property of the gel rather than a property of the channel or some interaction between the gel and the pore walls.     

Novel synthesis of macroporous poly(N-isopropylacrylamide) hydrogels using oil-in-water emulsions

Porous N-isopropylacrylamide (NIPA) hydrogels having a unique structure, that is, spherelike cavities distributed randomly and a homogeneous network in the gel phase, were successfully synthesized by means of an emulsion templating method; this method involves the synthesis of NIPA gels in an oil-in-water (O/W) emulsion by free radical copolymerization with a cross-linker, followed by washing (removal) of the dispersed oil as a pore template (porogen). The synthesis conditions, O/W volume ratio, amount of added surfactant, and monomer concentration affect the internal pore structure, equilibrium swelling, and swelling/shrinking kinetics. A porous hydrogel swollen at 10 degrees C has a pore diameter distribution in the range of 1-40 microm, which was observed with a scanning electron microscope. Scanning electron micrographs and swelling degree reveal that the pore size and porosity can be adjusted by varying the O/W volume ratios and surfactant amounts. The porous hydrogels show very rapid swelling/shrinking in accordance with the temperature swing. The fast response is attributed to the convection flow of water through the macropores. In addition to a faster response gel, the emulsion templating method can yield potentially intelligent gels in which the pores function as spaces for reaction, separation, and storage.     

硅胶表面结构的热稳定性研究

本文研究了热处理(200-1100℃)对自制的一种硅胶的表面结构的影响;测定了BET比表面(低温氮气吸附法)、孔体积、乙醇的吸附-脱附等温线,计算了孔径分布,求得了最可几Kelvin半径。结果表明,杂质的存在明显地降低硅胶的热稳定性。在发生熔结以前,孔径分布基本不变,当发生熔结时,孔半径显著减小。红外光谱的测定表明,随着热处理温度的升高,硅胶表面缔合羟基(～3500cm^-1)迅速减少,在～800°时已去除殆尽,而自由羟基(～3720cm^-1)减少缓慢,在1100℃时才迅速消失。X-射线衍射图表明,发生熔结后的硅胶显示有β-鳞石英的衍射峰,说明出现了有序晶相。对上述实验结果,文中作了初步的解释。     

Fluorophore and dye-assisted dispersion of carbon nanotubes in aqueous solution

DNA short oligo, surfactant, peptides, and polymer-assisted dispersion of single-walled carbon nanotube (SWCNTs) in aqueous solution have been intensively studied. It has been suggested that van der Waals interaction, π-π stacking, and hydrophobic interaction are major factors that account for the SWCNTs dispersion. Fluorophore and dye molecules such as Rhodamine B and fluorescein have both hydrophilic and hydrophobic moieties. These molecules also contain π-conjugated systems that can potentially interact with SWCNTs to induce its dispersion. Through a systematic study, here we show that SWCNTs can be dispersed in aqueous solution in the presence of various fluorophore or dye molecules. However, the ability of a fluorophore or dye molecule to disperse SWCNTs is not correlated with the stability of the fluorophore/dye-SWCNT complex, suggesting that the on-rate of fluorophore/dye binding to SWCNTs may dominate the efficiency of this process. We also examined the uptake of fluorophore molecules by mammalian cells when these molecules formed complexes with SWCNTs. The results can have potential applications in the delivery of poor cell-penetrating fluorophore molecules.     

Direct measurement of the interactions of amide solvents with single-walled carbon nanotubes using isothermal titration calorimetry

The interaction enthalpy of amide solvents with single-walled carbon nanotube (SWCNT) dispersions is measured using isothermal titration calorimetry (ITC). N,N-Dimethyl-formamide (DMF) and N-methyl-2-pyrilidone (NMP) were used to make dispersions of highly purified (6,5) SWCNTs. Using isothermal titration calorimetry, the ΔH and K(A) terms related to the solvent-nanotube interactions were measured, and ΔG and ΔS of the interaction were determined. It was found that the interaction enthalpy of NMP with SWCNTs dispersed in DMF was exothermic. The addition of a second solvent into a NMP or DMF dispersion produced spontaneous exfoliation of SWCNT bundles as the solvent properties became more favorable. During the titration, a positive change in interaction entropy within the dispersed system due to the unbundling of SWCNTs was measured. From blank titrations of pure DMF into pure NMP and the reverse, dilution enthalpies were also calculated and compared to the literature, along with the corresponding enthalpic interaction coefficients, h(xx) and h(xxx). From our results, ITC appears to be a viable technique for measuring the interaction of solvent molecules with the surface of SWCNTs and for measuring the effect of mixed solvent properties on SWCNT dispersions.