Evaluation of poly{-N-isopropylacrylamide-co-[3-(methacryloylamino)propyl]trimethylammonium} as a stationary phase for capillary electrochromatography

A cationic polyacrylamide-based stationary phase was synthesized and characterized for CEC. The stationary phase was prepared by radical copolymerization of N-isopropylacrylamide (NIPAAm) and (3-(methacryloylamino)propyl)trimethylammonium chloride (MAPTA), producing a copolymer attached to 5 microm porous silica particles. Fourier transform infrared spectroscopy and thermogravimetric analysis were used to characterize the copolymer. Under capillary electrochromatographic conditions, the poly-NIPAAm-co-MAPTA stationary phase showed to be stable in a wide pH range. The amino groups in the MAPTA provided an anodic EOF for CEC separation. The electroosmotic mobility changed less than 10% when the pH of the mobile phase was changed from 2 to 12. The run-to-run RSD of analyte migration time was less than 1.5% (n = 3), and the RSD of peak area was less than 3% (n = 3). The day-to-day RSD for migration time was less than 2% (n = 3). The polar groups present in the stationary phase contributed to the selectivity of the phase providing for hydrophilic interactions. In the separation of a series of neutral and acidic compounds, the stationary phase shows a mixed-mode separation mechanism with both hydrophobicity and hydrophilicity contributing to the separation.     

Stable helical polyguanidines: poly[N-(1-anthryl)-N'-[(R)- and/or (S)-3,7-dimethyloctyl]guanidines

Using chiral catalysts of (R)- and/or (S)-BINOL-Ti, the asymmetrical polymerization of achiral monomer, N-(1-anthryl)-N'-n-octadecylcarbodiimide, yielded soluble nonregioregular polyguanidines of Poly-R1 and Poly-S1. A racemization process occurred when the toluene solution of Poly-R1 was annealed at elevated temperatures (70-80 degrees C). Kinetic studies reveal this to be a slow process with an activation energy of ca. 36 kcal/mol. On the other hand, using titanium(IV) trifluoroethoxide catalyst, the polymerization of N-(1-anthryl)-N'-[(R)- and/or (S)-3,7-dimethyloctyl]carbodiimides afforded highly regioregular polyguanidines of Poly-R2 and Poly-S2. These polymers adopt stable helices in various solvents and elevated temperatures, whose kinetically controlled conformations and thermodynamically controlled conformations are essentially the same.     

Solvation of the Whelk-O1 chiral stationary phase: a molecular dynamics study

Density functional theory calculations and molecular dynamics simulations are employed to explore the solvation of the Whelk-O1 chiral stationary phase. First, a semi-flexible representation of the Whelk-O1 selective molecule is extracted from an extensive series of B3LYP/6-311+ G(2d,p) calculations. The resulting model is used to build a chiral surface, including end-caps, for molecular dynamics study of the interface between solvent and Whelk-O1. Three solvent environments in common use for Whelk-O1 HPLC have been examined: a normal-phase solvent of n-hexane/2-propanol; a reversed-phase solvent of water/methanol; and a supercritical solvent of CO(2) and methanol. In each case, we analyze the interface with an emphasis on solvent composition and solvent hydrogen bonding to the Whelk-O1 selector.     

Isomerization of N-[α-(Alkylthio)alkyl]- and N-[α-(Arylthio)alkyl]benzotriazoles

The thermal isomerizations of N-[α-(alkylthio)alkyl]- and N-[α-(arylthio)alkyl]benzotriazoles have been investigated under N₂ atmospheres (i) in toluene, xylene, MeOH, or EtOH, in the presence of acid catalysts and (ii) in the absence of solvent. The sulfide isomerization rates depend on the number of H-atoms carried by the C-atom attached to the N-atom of the benzotriazole: tertiary (no hydrogen) > secondary (1 hydrogen) > primary (2 hydrogens). The results support an isomenzation mechanism involving a heterolytic N? C bond cleavage with formation of sulfonium/carbonium and benzotriazolate ions.     

Bis[3-(triethoxysilyl)propyl]tetrasulfide: the first liquid sulfur-transferring agent useful for conversion of nucleoside phosphites to the phosphorothioates

This paper describes bis[3-(triethoxysilyl)propyl]tetrasulfide, which is the first liquid sulfur-transferring agent useful for the conversion of nucleoside phosphite intermediates in the synthesis of the phosphorothioates using a phosphoramidite strategy. This liquid reagent is preferable to existing solid sulfur-transferring agents, because it enables solid-phase synthesis with an automated DNA/RNA synthesizer, while avoiding the risk of accumulation of reagent deposits in the delivery tubes and valves of the synthesizer during sulfurization.     

新型N-[cis-3-(2-氯-3,3,3-三氟丙烯基)-2,2-二甲基环丙烷基羰基]-N'-芳氧乙酰肼的合成与生物活性

为了寻找高效、低毒的农药先导化合物,利用cis-3-(2-氯-3,3,3-三氟丙烯基)-2,2-二甲基环丙烷酰氯(1)与芳氧乙酰肼的缩合反应,合成了12种未见文献报道的目标化合物,其结构经IR,1H NMR,MS和元素分析测试技术确证.初步的生物活性测定结果表明,部分目标化合物在100 mg/L浓度下对双子叶植物(油菜)显示出良好的除草活性;同时,部分化合物在200 mg/L浓度下对蚕豆蚜虫(Aphis fabas)显示出较好的杀虫活性.