Performance and selectivity of polymeric pseudostationary phases for the electrokinetic separation of amino acid derivatives and peptides

Two polymeric pseudostationary phases, one an acrylamide polymer and the second a siloxane polymer, have been investigated for the separation of naphthalene-2,3-dicarboxaldehyde (NDA)-derivatized amino acids and small peptides. The dervatized amino acids were detected by UV absorbance and laser-induced fluorescence (LIF) detection. The polymers provided very high efficiency and good selectivity for the separation of the amino acids. The separation selectivity using the polymers was significantly different from that of SDS micelles, and there were subtle differences in selectivities between the polymers. Although very good detection limits were obtained with LIF detection, a significant background signal was observed when the polymers were not washed to remove fluorescent impurities. The polymers did not separate the peptides very well. It is postulated that the fixed covalent structure of the polymers prevents them from interacting strongly or efficiently with the peptides, which are large in relation to the analytes typically separated by electrokinetic chromatography using polymers.     

Enantioseparation of dipeptides by capillary electrochromatography on a teicoplanin aglycone chiral stationary phase

This work deals with investigations on the enantioseparation of glycyl-dipeptides by capillary electrochromatography (CEC) on a capillary packed with teicoplanin aglycone immobilized on 3.5 μm silica gel. The results were compared to those obtained with micro-HPLC using the same chiral stationary phase. Polar organic and reversed-phase mode were checked, whereby the latter showed better results. Out of 12 glycyldipetides investigated, all compounds showed baseline separation with R_s values up to 20. Plate numbers were in the range of 10 000–300 000/m. The choice of organic modifier was found to be crucial. While methanol increased retention time, acetonitrile reduced it. A ternary mixture of ethanol–acetonitrile–aqueous triethylamine acetate solution pH 4.1 was found to be a useful compromise, providing excellent resolution with retention times less than 25 min. Efficiency and resolution were generally found to be higher in CEC than with micro-HPLC.     

Statistical versus non-statistical photo-fragmentation of protonated GWG tri-peptide induced by UV excitation

A new experimental method is described in which photo-induced fragmentation of protonated molecules in an electric field is investigated by the detection in coincidence of the ion and neutral fragments. This technique allows measuring fragmentation times, in the tens of nanosecond range, for each fragmentation channel independently. As an example, the method has been used to study the photo-fragmentation of the protonated tri-peptide GWG. It is shown that the various fragmentation channels have different fragmentation times. This is a clear signature of non-ergodic mechanisms occurring during fragmentation of such a large molecule.     

Synthesis and structures of helical polycyclic aromatic hydrocarbons bearing aryl substituents at the most sterically hindered positions

A three-step synthetic sequence starting from condensation between a benzannulated enediyne and an aryl tert-butyl ketone was established to provide easy access to angularly fused polycyclic aromatic hydrocarbons bearing one or two aryl substituents at the most sterically hindered positions to cause helical twists. The dynamic behaviors involving the helix inversion and the restricted rotation of the aryl substituents were investigated by temperature-dependent NMR studies. The X-ray structure of an indeno-fused 1-phenylpentahelicene derivative showed severe distortion of the [5]helicene system from planarity.     

Callipeltins F-I: new antifungal peptides from the marine sponge Latrunculia sp.

Four new antifungal peptides, callipeltins F-I, were isolated from the marine sponge Latrunculia sp., collected off Vanuatu islands. Their structures were elucidated by NMR and MS analysis. The new callipeltins exhibited anti Candida activity in the 10⁻⁴ M range.     

Control of helicity in C3-symmetric systems by peptide-like β-turns

Cyclic imidazole-containing hexapeptides with three arms bound to the peptide scaffold via the secondary nitrogen atoms of the imidazoles are presented; these arms, together with a part of the macrocycle, form peptide-like β-turns making their helicity predeterminable and allowing the diastereoselective synthesis of Λ-metal complexes.     

Nucleoside derived amino acids (NDA) in foldamer chemistry: synthesis and conformational studies of homooligomers of modified AZT

Homo short-oligomers of a novel trans-β-amino acid derived from AZT were synthesized and characterized. These adopt right-handed helical turns with their bases positioned systematically along the helix axis. These studies open up new possibilities for synthesizing nucleoside derived functional foldamers.     

光学活性三嵌段刚柔共聚物的合成和在二氧六环/水中的自组装

刚柔嵌段聚合物作为多层次有序高级结构的构筑单元正受到广泛的关注．与仅由柔性链段连接而成的嵌段聚合物相比,一方面,刚性链段和柔性链段的相分离与刚性链段倾向于有序取向间的竞争,使其自组装能力增强;另一方面,可在刚性链段引入某些功能基团,从而赋予超分子聚集体识别、传感、催化、光电等特殊的性质．     

16单元矩形径向线螺旋阵列天线的理论分析和数值模拟

 提出了一种16单元矩形径向线螺旋阵列天线。介绍了该矩形阵列天线的提出背景以及工作原理,分析了两种电磁组合探针的耦合特性,设计并数值模拟了中心频率为4.0 GHz的16单元矩形径向线螺旋阵列天线。模拟结果表明：该口径为180 mm×180 mm 的天线在中心频率4.0 GHz 下,增益为18.24 dB,轴向轴比值1.065;在3.8～4.2 GHz的频率范围内增益大于17.89 dB,轴向轴比值小于1.2,反射系数小于0.15,口径效率大于85％。