Evaluation of different operation modes of high performance liquid chromatography for the analysis of complex mixtures of neutral oligosaccharides

Chromatographic methods based on different HPLC operation modes, reverse phase (RP), high performance anion exchange chromatography (HPAEC), graphitized carbon chromatography (GCC) and hydrophilic interaction liquid chromatography (HILIC), have been developed and compared for the analysis of complex mixtures of neutral oligosaccharides with functional properties. Whereas GCC gave the best chromatographic separation of isomeric oligosaccharides with the same molecular weight (R(s) values in the range 1.0-4.0 and 2.4-5.6 for tetra- and pentasaccharides, respectively), HILIC provided the best results for mixtures including oligosaccharides of different degrees of polymerization (R(s) values of maltooligosaccharides between 3.4 and 6.2). Validation of the HILIC LC-MS method proved its utility for the analysis of oligosaccharide mixtures with functional properties: relative standard deviations lower than 10%, LOD's and LOQ's in the range 12.7-130.2 ng mL(-1) and 39.3-402.2 ng mL(-1), respectively, and linearity up to 10-20 μg mL(-1). Quantitative data for fructooligosaccharides, gentiooligosaccharides and dextransucrase cellobiose acceptor oligosaccharides were obtained by using this method.     

Quality assurance for molecular epidemiology of tuberculosis methods in the mycobacterium reference laboratory

In the National Mycobacterium Reference Laboratory of the Israeli National Public Health Laboratory (hereafter referred to as “the laboratory”), three methods are employed for the molecular epidemiology of Mycobacterium tuberculosis: IS6110 restriction fragment length polymorphism typing (RFLP typing), 43 spacer oligonucleotide typing (spoligotyping), and 24 loci Mycobacterial Interspersed Repeating Unit—Variable Number of Tandem Repeats typing (MIRU-VNTR typing). In this article, we describe the main practical aspects concerning quality assurance of these methods that are based on standardized, internationally agreed upon conditions, including consensus reference strains and markers. All three methods were validated by classical epidemiology (confirmed transmission) and clinical information. The laboratory has introduced a new 5 colors, 4 primer sets multiplex modification of the optimal 24-miru typing system that includes an easily produced in-house internal standard for the high-throughput capillary electrophoresis system. Quantitative measurement of the internal standards yielded statistics for measurement uncertainty that include the frequency distribution, mean, standard deviation, 95% confidence interval and coefficient of variation. Use of the new internal standard developed in our laboratory allowed us to introduce the first quantitative evaluation of the system performance of the AB3130xl capillary electrophoresis genetic analyzer for MIRU-VNTR typing. The results are discussed in terms of expected accuracy and precision of MIRU-VNTR results, and possible implications for forensic microsatellite typing which may be much more sensitive to the observed intra- and inter-plate variation.     

Efficient synthesis and free-radical scavenging capacity of new 2,4-substituted tetrahydroquinolines prepared via BiCl<Subscript>3</Subscript>-catalyzed three-component Povarov reaction,using <Emphasis Type="Italic">N</Emphasis>-vinylamides

Efficient synthesis of new structurally different 2-(het)aryl-4-amidyl-substituted tetrahydroquinolines 8–29 is reported. The synthesis based on BiCl₃-catalyzed three-component Povarov reaction between anilines, (het)aryl aldehydes and enamides offers a fast, safe, and cheap way for efficient tetrahydroquinoline libraries construction. Using N-vinylamides (N-vinylpyrrolidin-2-one and N-vinylacetamide) in this reaction, it was possible to obtain two series of different cis tetrahydroquinolines with antioxidant properties. Among 14 tested compounds, 7 tetrahydroquinolines revealed a prominent anti-radical capacity, equal or higher than that of the commercial antioxidants. Being the most active molecule, the N-[2-(α-furanyl)-6-methoxy-1,2,3,4-tetrahydroquinolin-4-yl] acetamide 21 was ca. 2.2-fold more potent than the well-known antioxidant, vitamin E (α-tocopherol).     

Diffusion through a cluster of small windows and flux regulation in microdomains

The way the arrangement of small conductors of ionic current on biological membranes regulates flux is an open physical question. We study this problem by a model of diffusion through a cluster of channels in an impermeable biological cell membrane. We show that the flux depends on the relative distance between the channels and show that moving two contiguous channels apart may increase the flux by nearly 50%. Brownian simulations in 2 and 3 dimensions agree with the theoretical results.     

Electron beam patterning for writing of positively charged gold colloidal nanoparticles

Synthesis at the nanoscale has progressed at a very fast pace during the last decades. The main challenge today lies in precise localization to achieve efficient nanofabrication of devices. In the present work, we report on a novel method for the patterning of gold metallic nanoparticles into nanostructures on a silicon-on-insulator (SOI) wafer. The fabrication makes use of relatively accessible equipment, a scanning electron microscope (SEM), and wet chemical synthesis. The electron beam implants electrons into the insulating material, which further anchors the positively charged Au nanoparticles by electrostatic attraction. The novel fabrication method was applied to several substrates useful in microelectronics to add plasmonic particles. The resolution and surface density of the deposition were tuned, respectively, by the electron energy (acceleration voltage) and the dose of electronic irradiation. We easily achieved the smallest written feature of 68?±?18 nm on SOI, and the technique can be extended to any positively charged nanoparticles, while the resolution is in principle limited by the particle size distribution and the scattering of the electrons in the substrate.

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Acylphosphonamidates and α-hydroxyiminophosphonamidates. Synthesis of N-acylphosphordiamidates by Beckmann rearrangement. Crystal structure of (E)-α-hydroxyiminobenzyl-1-pyrrolidinylphosphinate

Reaction of methyl benzoylphosphonochloridate (3) with a secondary or primary series of amines yielded methyl benzoylphosphonamidates, 4a-e. The latter compounds reacted with hydroxylamine to yield a-hydroxyiminobenzylphosphonamidates (5a-e), largely as (E)-isomers. The structure of methyl (E)-a-hydroxyimino-benzyl-1-pyrrolidinylphosphinate (5b) was determined by single-crystal X-ray crystallography. Heating oximes 5a-e in boiling toluene caused them to undergo Beckmann rearrangement to N-benzoylphosphordiamidates 6a-e. © 1996 John Wiley & Sons, Inc.