Chromatographic purification and properties of soluble single-walled carbon nanotubes.

We report an improved chromatographic purification of soluble single-walled carbon nanotubes (s-SWNTs) using gel permeation chromatography. Three fractions are separated by gel permeation chromatography, and the first fraction contains 74% of the s-SWNTs as detected by atomic force microscopy and UV and near-infrared spectroscopy.     

Isolation of fucoxanthin from edible brown algae by microwave-assisted extraction coupled with high-speed countercurrent chromatography

A rapid and efficient method for the separation and purification of fucoxanthin from edible brown algae by microwave-assisted extraction coupled with high-speed countercurrent chromatography was developed. The algae were first extracted using microwave-assisted extraction, then the dried extract was dissolved and directly introduced into the high-speed countercurrent chromatography system with a two-phase solvent system consisting of hexane-ethyl acetate-ethanol-water (5:5:6:4, v/v/v/v). The isolation was done in less than 75 min, and a total of 0.83 mg, 1.09 mg, and 0.20 mg fucoxanthin were obtained from 25.0 g fresh Laminaria japonica Aresch, 1.5 g dry Undaria pinnatifida (Harv) Sur, and 15.0 g dry Sargassum fusiforme (Harv) Setch, respectively. The purity of fucoxanthin determined by HPLC was over 90% and its structure was further identified by LC-ESI-MS and (1) H-NMR.     

大孔树脂-高速逆流色谱法分离纯化地黄中毛蕊花糖苷

该文建立了大孔树脂-高速逆流色谱分离中药材地黄中有效成分毛蕊花糖苷的方法。考察了4种大孔树脂对地黄粗提物中毛蕊花糖苷的静态吸附与解吸情况,其中D101大孔树脂对目标成分的吸附率与解吸率最理想,实验结果表明体积分数为10%的乙醇洗脱得到的毛蕊花糖苷含量最高,目标成分含量从4.9%提高到32.6%。最后,部分纯化的样品（165 mg）采用高速逆流色谱进一步纯化,两相溶剂系统由乙酸乙酯-正丁醇-水（1：4：5,v/v/v）组成,分离得到45 mg纯度为96%的毛蕊花糖苷。     

Separation of gallic acid from Cornus officinalis Sieb. et Zucc by high-speed counter-current chromatography

Gallic acid was separated from a n-butanol extract of the fruit of Cornus officinalis Sieb. et Zucc by high-speed countercurrent chromatography in two steps using two solvent systems composed of ethyl-acetate-ethanol n-butanol-water (5:1.8:6, v/v/v) and ethyl acetate-ethanol-water (5:0.5:6, v/v/v) successively. From 1 g of n-butanol extract the method produced 60 mg of gallic acid at a purity of 97%.     

Separation and purification of intermediates for the preparation of naproxen from synthetic mixtures by countercurrent chromatography

Three key intermediates in the preparation of the nonsteroidal anti‐inflammatory drug naproxen were successfully separated and purified with high purity from synthetic mixtures by countercurrent chromatography with a selected biphasic solvent system. The biphasic solvent system composed of n‐hexane/ethyl acetate/methanol/water (9:1:9:1, v/v/v/v) was selected according to partition performance of the three components using thin‐layer chromatography. Fifty milligrams of the synthetic mixture after the three‐step reaction was injected into a preparative countercurrent chromatography separation column and yielded 3.5, 14.0, and 8.0 mg of three key intermediates with 95.0, 99.0, and 98.0% purity, and the recovery of each component was 65.2, 71.2, and 69.6%, respectively. The results indicated that countercurrent chromatography is an efficient alternative and economical method for the separation and purification of intermediate components from synthetic mixtures.     

Near-edge X-ray absorption fine structure spectroscopy-assisted purification of single-walled carbon nanotubes

Single-walled carbon nanotubes were produced by the conventional arc discharge method, and purified with a two-step treatment. First, the raw soot containing single-walled carbon nanotubes was burned up at ca. 350 °C in air to remove amorphous carbon, and then it was treated by strong acidic solvents to remove metal catalysts. Near-edge X-ray absorption fine structure spectroscopy was applied to analyze the defects on single-walled carbon nanotubes in whole purification process, so the experimental conditions can be optimized, and finally high-purity single-walled carbon nanotubes were obtained as revealed by various spectroscopic characterizations such as scanning electron microscopy, transmission electron microscopy, thermogravimetric analysis, and Raman spectroscopy.     

A new method of preparing single-walled carbon nanotubes

A novel method of purification for single-walled carbon nanotubes, prepared by an arc-discharge method, is described. The method involves a combination of acid washing followed by high temperature hydrogen treatment to remove the metal nanoparticles and amorphous carbon present in the as-synthesized singlewalled carbon nanotubes. The purified single-walled carbon nanotubes have been characterised by low-angle X-ray diffraction, electron microscopy, thermo-gravi-metric analysis and Raman spectroscopy. Dedicated to Professor C N R Rao on his 70th birthday     

Isolation of three glucaric acids from Leonurus japonicus Houtt. by using high-speed countercurrent chromatography combined with semi-preparative high-performance liquid chromatography

The isomerism of glucaric acids and the complexity of the composition of Leonurus japonicus Houtt. increased the difficulty of the separation of glucaric acids from the herb. In the present study, three glucaric acids were isolated from Leonurus japonicus Houtt. by using high-speed countercurrent chromatography combined with semi-preparative high-performance liquid chromatography. Cation exchange resin chromatography was applied to remove the alkaloids and enrich the glucaric acid fractions. Preliminary separation of the glucaric acid extract by high-speed countercurrent chromatography was carried out at 45℃ by using an optimized solvent system of ethyl acetate/n-butanol/formic acid/water (1:1:0.01:2, v/v/v/v) with satisfied stationary phase retention and separation factor. The semi-preparative high-performance liquid chromatography was used for further separation and purification of the target fractions, and three monomeric compounds were obtained with purities of 90.0, 91.0, and 95.3%. UV spectroscopy, NMR spectroscopy, and mass spectrometry were employed to identify their structures, which were assigned as 2-syringyl glucaric acid, 2,4-disyringyl glucaric acid, and 3,4-disyringyl glucaric acid, respectively, and 2,4-disyringyl glucaric acid was reported for the first time.     

Application of highly sulfonated single-walled carbon nanotubes: An efficient heterogeneous catalyst for the one-pot synthesis of 14-aryl-14H-dibenzo[a,j]xanthenes under solvent-free conditions

Highly sulfonated single-walled carbon nanotube-catalyzed synthesis of 14-aryl-14H-dibenzo[a,j]xanthenes in excellent yields and very short reaction times. Sulfonated single-walled carbon nanotubes are prepared using a chemical and simple process and it characterized by Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, Thermal gravimetric analysis (TGA) and acid-base titration. The sulfonated single-walled carbon nanotube was easily separated by simple filtration and was recycled eight consecutive times without any loss in its activity.     

SEPARATION OF THE MINOR FLAVONOLS FROM FLOS GOSSYPII BY HIGH-SPEED COUNTERCURRENT CHROMATOGRAPHY

An effective high-speed countercurrent chromatography (HSCCC) method was established for further separation and purification of four minor flavonols in addition to five major flavonols which were reported by our previous study from extracts of Flos Gossypii. HSCCC was performed with three two-phase solvent systems composed of n-hexane-ethyl acetate-methanol-water (7.5:15:6:7, v/v), (2.5:15:2:7, v/v) and (0:1:0:1, v/v). The separation was repeated 3 times, and 3.8 mg of 8-methoxyl-kaempferol-7-O-β-D-rhamnoside (HPLC purity 98.27%), 6.7 mg of astragalin (HPLC purity 94.18%), 3.3 mg of 4'-methoxyl-quercetin-7-O-β-D-glucoside (HPLC purity 94.30%) and 8.2 mg of hyperoside (HPLC purity 93.48%) were separated from 150 mg of the crude sample. The chemical structures of the flavonols were confirmed by MS, (1)H NMR and (13)C NMR. Meanwhile, the results indicated that the target compound with smaller K value (<0.5) can be separated by increasing column length of HSCCC. And four separation rules of flavonols according to the present study and references were summarized, which can be used as a useful guide for separation of flavonols by HSCCC.     

NEXAFS光谱分析聚合物修饰的单壁碳纳米管

利用C1s、O1s、N1s近边X射线吸收精细结构(Near Edge X-Ray Absorption Fine Structure,NEXAFS)光谱对聚合物修饰的碳纳米管进行了分析,研究了氧化及偶联聚合物对碳纳米管结构的影响。氧化碳纳米管及十八胺修饰的、聚合物/十八胺双修饰的碳纳米管的NEXAFS光谱均出现了碳/氧K边π*(C=O)和σ*(C-O)共振峰;而十八胺修饰的、聚合物/十八胺双修饰的碳纳米管则出现了氮K边π*(N-C=O)和σ*(N1s)共振峰。分析表明,NEXAFS光谱可有效表征聚合物修饰的碳纳米管。     

Biphasic alcoholysis coupled with high-speed countercurrent chromatography for high performance on separating phorbol from Croton tiglium Linn extracts

Phorbol is a tetracyclic diterpenoid found in Euphorbia tirucalli, Croton tiglium, and Rehmannia glutinosa, and is nuclear of various phorbol esters. The rapid obtaining of phorbol with high purity highly contributes to its application, such as synthesizing phorbol esters with designable side chains and particular therapeutic efficacy. This study introduced a biphasic alcoholysis method for obtaining phorbol from croton oil by using polarity imparity organic solvents in both phases and established a high-speed countercurrent chromatography method for simultaneous separation and purification of phorbol. The optimized operation conditions of biphasic alcoholysis were a reaction time of 91 min, a temperature of 14°C, and a croton oil-methanol ratio of 1:30 (g:ml). The phorbol during the biphasic alcoholysis was 3.2-fold higher in content than that obtained in conventional monophasic alcoholysis. The optimized high-speed countercurrent chromatography method was using the ethyl acetate/n-butyl alcohol/water at 4.7:0.3:5 (v:v:v) with Na₂SO₄ at 0.36 g/10 ml as the solvent system, using the mobile phase flow rate of 2 ml/min, the revolution of 800 r/min, under which the retention of the stationary phase was achieved at 72.83%. The crystallized phorbol following high-speed countercurrent chromatography was obtained as high purity of 94%.     

Application of centrifugation to the large-scale purification of electric arc-produced single-walled carbon nanotubes

We report a further advance in the bulk purification of nitric acid-treated single-walled carbon nanotubes (SWNTs) by use of high-speed centrifugation. We have already shown that low-speed centrifugation is effective in removing amorphous carbon (AC). In these earlier experiments, the AC preferentially suspends in aqueous dispersions on low-speed centrifugation (2000g), leaving the SWNTs in the sediment. In a surprising reversal, we now show that high-speed centrifugation (20000g) of well-dispersed preparations is effective in sedimenting carbon nanoparticles (CNP), while leaving the SWNTs suspended in aqueous media. Taken together, these two techniques allow the bulk scale (10 g) purification of SWNTs by efficiently separating the two main contaminants, in an industrially viable process. We show that the mechanism of these separations is based on the differential charging (zeta-potential) of the AC, CNPs, and SWNTs that comes about during the chemical processing. Due to their more robust structure, nitric acid oxidation leaves the CNPs with a surface charge density lower than that of the SWNTs, and thus the CNPs do not form stable dispersions in aqueous media during high-speed centrifugation. The efficiency of the process was confirmed by the high purification recovery factor (PRF = 90%), which is a measure of the fractional quantity of the product recovered after the purification. We demonstrate that the purity of SWNTs significantly affects their mechanical and electrical properties.     

Effect of chemical potential on the computer simulation of hydrogen storage in single walled carbon nanotubes

Hydrogen is a kind of clean, sustainable and renewable energy carrier. Of the problems to be solved for the utilization of hydrogen energy, how to store and transport hydrogen has been given high priority on the research agenda. Recently, carbon nanotubes (CNTs) were reported to be very promising candidates for hydrogen uptake[1], which may have possibility to satisfy the benchmark set by the US Department of Energy (DOE) Hydrogen Plan for fuel cell powered vehicles: a gravimetric density …     

Solid-phase extraction-capillary electrophoresis-mass spectrometry for the determination of tetracyclines residues in surface water by using carbon nanotubes as sorbent material

Last years chemical properties of carbon nanotubes (CNTs) have attracted high interest. One of the most important issues is the capability of CNTs to adsorb analytes on its surface. In this work, such property has been used to preconcentrate trace tetracyclines from environmental water samples at the trace level. Multi-walled carbon nanotubes (MWNTs) have showed higher capacity than other two single-walled carbon nanotubes (SWNTs). Preconcentration of the samples was performed in a flow system at-line coupled to the CE-MS equipment. The preconcentration of tetracyclines on MWNTs followed by capillary electrophoresis-mass spectrometry allows the detection of 0.30-0.69 microg/L of tetracyclines for the analysis of 10 mL of samples. Recoveries for the analysis of spiked samples ranged from 98.6 to 103.2% and the precision from 5.4 to 8.2%. Separation of tetracylines in the electrophoretic system was achieved using 50 mM formic acid at pH 2.0 as a background electrolyte. Atmospheric pressure electrospray ionization mass spectrometry detection was accomplished using 50:50 (v/v) methanol/water containing 0.5% (v/v) formic acid as a sheath liquid.     

UV-light mediated decomposition of a polyester for enrichment and release of semiconducting carbon nanotubes

Purification of single-walled carbon nanotubes using conjugated polymers to selectively disperse either semiconducting or metallic nanotubes is effective and has received significant attention. However, the interaction between the conjugated polymer and the nanotube surface is very strong, making it difficult to remove the adsorbed polymer. Here, we report a poly(carbazole-co-terephthalate) polymer that is not only selective for semiconducting carbon nanotubes but can also be largely removed from the nanotube surface via irradiation with UV light. Irradiation of the polymer-nanotube dispersion causes degradation of ester linkages in the polymer backbone, effectively cutting the polymer into fragments that no longer bind strongly to the nanotube surface. Characterization of the electronic nature of the samples was carried out via the combination of absorption, Raman, and fluorescence spectroscopy. In addition, thermogravimetric analysis allowed determination of the amount of polymer left on the nanotube surface after irradiation and indicated that a large proportion of the polymer is removed. The reported methodology opens new possibilities for purification of semiconducting single-walled carbon nanotubes and their isolation from the polymeric dispersant.     

Epoxidation and deoxygenation of single-walled carbon nanotubes: quantification of epoxide defects

Epoxidation of single-walled carbon nanotubes (SWNTs) may be carried out by the reaction of SWNTs with either trifluorodimethyldioxirane or 3-chloroperoxybenzoic acid; the resulting O-SWNTs are spectroscopically similar to those formed by ozonolysis. Quantification of the epoxide substituents is possible through the catalytic de-epoxidation reaction using MeReO3/PPh3 and the 31P NMR spectroscopy. The de-epoxidation methodology may be used to determine that wet air oxidation is preferable to either acid or O2/SF6 purification. We have demonstrated that previously assumed "pure" SWNTs are actually "doped" to a level of at least 1 oxygen per 250 carbon atoms.     

Water-solubilization of nucleotides-coated single-walled carbon nanotubes using a high-speed vibration milling technique

[reaction: see text] Pristine single-walled carbon nanotubes (SWNTs) and nucleotides mixed using a mechanochemical high-speed vibration milling technique (HSVM) are soluble in an aqueous solution, and the solubilities of SWNTs depend significantly on the number of phosphate groups and the kinds of bases employed.     

大孔树脂-高速逆流色谱分离纯化薇甘菊中的黄酮类化合物

该文建立了大孔树脂-高速逆流色谱分离薇甘菊中黄酮类物质的方法。分离条件为:采用大孔树脂AB-8,洗脱液为50%（v/v）乙醇水溶液,高速逆流色谱溶剂体系为正丁醇-乙酸-水（4：1：5,v/v）。从薇甘菊中分离到4种黄酮类物质:槲皮素-3-O-芸香糖苷（纯度90.2%）、山奈酚-3-O-芸香糖苷（纯度98.55%）、木犀草苷（纯度98.33%）和紫云英苷（纯度99.23%）。建立的大孔树脂-高速逆流色谱方法简单、高效,可扩展应用于从其他植物中分离黄酮类物质。     

Preparative isolation of osthol and xanthotoxol from Common Cnidium Fruit (Chinese traditional herb) using stepwise elution by high-speed counter-current chromatography

Preparative high-speed counter-current chromatography (HSCCC) was successfully used for isolation and purification of osthol and xanthotoxol from Cnidium monnieri (L.) Cusson (Common Cnidium Fruit) using stepwise elution with a pair of two-phase solvent systems composed of n-hexane-ethyl acetate-methanol-water at (1:1:1:1, v/v), and (5:5:6:4, v/v), which had been selected by analytical high-speed counter-current chromatography. Using a preparative unit of the HSCCC centrifuge, about a 308 mg amount of the crude extract was separated, yielding 88.3 mg of osthol and 19.4 mg of xanthotoxol at a high purity of over 98%.