A novel microfluidic concept for bioanalysis using freely moving beads trapped in recirculating flows

There are only a few examples in which beads are employed for heterogeneous assays on microfluidic devices, because of the difficulties associated with packing and handling these in etched microstructures. This contribution describes a microfluidic device that allows the capture, preconcentration, and controlled manipulation of small beads (<6 microm) in etched microchannels using fluid flows only. The chips feature planar diverging and converging channel elements connected by a narrow microchannel. Creation of bi-directional liquid movement by opposing electro-osmotic and pressure-driven flows can lead to the generation of controlled recirculating flow at these elements. Small polymer beads can actually be captured in the controlled rotating flow patterns. The clusters of freely moving beads that result can be perfused sequentially with different solutions. A preliminary binding curve was determined for the reaction of streptavidin-coated beads and fluorescein-labelled biotin, demonstrating the potential of this bead-handling approach for bioanalysis.     

Template-Dependent Incorporation of Spin-Labeled Thymidine Analogs into Viral DNA

The synthesis of novel pppU_d analogs substituted at position C(5) with tethered nitroxide radicals is reported. It is shown that these analogs can serve as good substrates for E. coli DNA polymerase (Pol I) and T-4 DNA polymerase using lambda-phage DNA as template. The template-dependent incorporation of the substrates was established by radio-labeling and ESR experiments.     

Dischroïsme circulaire des alcaloïdes du groupe de l'hétéroyohimbane

Circular Dischroism of Heteroyohimbane-Type Alkaloids Circular dichroism cannot be used directly to determine the C (3)-configuration of heteroyohimbines. A preliminary chemical transformation is necessary.     

Synthese von Astaxanthin aus β-Jonon. I. Erschliessung der enantiomeren C15-Wittigsalze durch chemische und mikrobiologische Racematspaltung von (±)-3-Acetoxy-4-oxo-β-jonon

Synthesis of Astaxanthin from β-Ionone. I. A Route to the Enantiomeric C₁₅-Wittig Salts by Chemical and Microbial Resolution of (±)-3-Acetoxy-4-oxo-β-ionone Racemic 3-acetoxy-4-oxo-β-ionone ( 10 ) was synthesized from the industrially accessible intermediate β-ionone ( 5 ). Resolution of 10 into its enantiomers was achieved via the corresponding diastereomeric camphanates and by microbial resolution. Site-selective alkylation of racemic and of optically pure 3-acyloxy-4-oxo-β-ionones with vinyl magnesium chloride at ?70° furnished the corresponding 3-acyloxy-4-oxo-9-vinyl-β-ionols which could be transformed to the Wittig salts 1, 3 and 4 , respectively, following known procedures [1].     

Solute-solvent interactions in micellar electrokinetic chromatography: V. Factors that produce peak splitting

The experimental conditions that produce analyte peak splitting in micellar electrokinetic capillary chromatography (MEKC) have been systematically investigated. The system studied was a neutral phosphate buffer and sodium dodecyl sulfate (SDS) micelles as pseudostationary phase. A number of analytes showing a wide variety of hydrophobicity values and several organic solvents as sample diluents have been tested. Peak splitting phenomena are mainly due to the presence of organic solvent in the sample solution. They increase with the hydrophobicity of the analyte and decrease with the increase of the surfactant concentration. When hydrophobic compounds are analyzed the suggested ways to avoid split peaks are: (i) the use of 1-propanol or 1-butanol as sample diluent instead of methanol or acetonitrile or (ii) the use of high concentration of surfactant in the separating solution when the analyte must be dissolved in pure methanol or acetonitrile.     

Studies on the stability of the cyclobutane β-aminoacid skeleton: a cautionary tale

The 2-amino-1-cyclobutanecarboxylic acid skeleton undergoes facile retro-Mannich type ring opening in solution, which may lead to unexpected by-products during its synthesis or manipulation.     

Modular synthesis of heparin oligosaccharides

A general, modular strategy for the first completely stereoselective synthesis of defined heparin oligosaccharides is described. Six monosaccharide building blocks (four differentially protected glucosamines, one glucuronic and one iduronic acid) were utilized to prepare di- and trisaccharide modules in a fully selective fashion. Installation of the alpha-glucosamine linkage was controlled by placing a conformational constraint on the uronic acid glycosyl acceptors thereby establishing a new concept for stereochemical control. Combination of disaccharide modules to form trans-uronic acid linkages was completely selective by virtue of C2 participating groups. Coupling reactions between disaccharide modules exhibited sequence dependence. While the union of many glucosamine uronic acid disaccharide modules did not meet any problems, certain sequences proved not accessible. Elaboration of glucosamine uronic acid disaccharide building blocks to trisaccharide modules by addition of either one additional glucosamine or uronic acid allowed for stereoselective access to oligosaccharides as demonstrated on the example of a hexasaccharide resembling the ATIII-binding sequence. Final deprotection and sulfation yielded the fully synthetic heparin oligosaccharides.     

Adhesion forces between wetted solid surfaces

We investigate in this paper the influence of wetting films on the adhesion forces between macroscopic solid surfaces connected by a liquid bridge. We show that the capillary forces are dependent on the interactions governing the wetting layers, and that those interactions may be determined from the measurement of the capillary force in the presence of a condensable vapor. We illustrate those results with a surface force apparatus experiment where the capillary force between high-energy surfaces is measured for different liquid pressures.     

An Alternative Method for the Preparation of Diphenylboron Chelates. The Crystal and Molecular Structures of (Pyridine‐2‐acetyloximato)diphenylboron and (1‐Phenylazo‐2‐naphtholato)diphenylboron

A convenient method for the preparation of diphenylboron chelates from ammonium tetraphenylborate is described. A variety of five‐ or six‐membered O,O‐, N,O‐ and N,N‐chelates were obtained in yields from 60 to 90 %. The isolated compounds were characterized by elemental analysis, IR spectroscopy and multinuclear magnetic resonance spectroscopy (¹H, ¹³C, and ¹¹B). The crystal and molecular structures of (pyridine‐2‐acetyloximato)diphenylboron and (1‐phenylazo‐2‐naphtholato)diphenylboron were determined by X‐ray diffraction on single crystals.     

L?slichkeitsbestimmungen an schwer l?slichen Stoffen I. Die Wasserl?slichkeit des Magnesiumoxyds

Zusammenfassung Die Löslichkeit von Magnesiumoxyd in Wasser wurde neu bestimmt. Die Untersuchung geschah in der Absicht, gleichzeitig eine für Löslichkeitsbestimmungen auch anderer, noch schwerer löslicher Oxyde brauchbare Methode zu ermitteln.Es ergab sich, dass eine exakte Bestimmung der Löslichkeit des Magnesiumoxyds sowohl gewichtsanalytisch wie alkalimetrisch möglich ist, undzwarletzteres auf Grund derLeitfähigkeitstitration Die Löslichkeitsbestimmung durch Leitfähigkeitstitration lässt sich auch auf noch wesentlich schwerer lösliche Oxyde übertragen.Verwendung von recht reinem Wasser (Leitfähigkeitswasser) und Vorbeugung jeden Kohlendioxydzutritts während des Arbeitens erwies sich als wichtig für eine exakte Bestimmung der Löslichkeit. Unter Beachtung dieser Vorsichtsmafsregeln liessen sich auch unmittelbar aus der spezifischen Leitfähigkeit unter Verwendung der Ionenbeweglichkeiten Werte errechnen, die mit den gewichtsanalytisch und konduktotitrimetrisch erhaltenen hinlänglich, übereinstimmen, besonders wenn bei der Auswertung jener auf den (sehr geringen) Kohlendioxydgehalt des verwendeten Leitfähigkeitswassers Rücksicht genommen wurde.Während früher Koh1rausch auf konduktometrischem Wege etwa 0,2, Fresenius dagegen gewichtsanalytisch 0,45 Millimol pro Liter als Löslichkeit des Magnesiumoxyds gefunden hat, fanden wir nach genügender Ausschaltung der durch Kohlendioxydzutritt bedingten Fehlerquellen den Wert 0,35 Millimol nach der Methode von Kohlrausch und 0,40 Millimol nach der Methode von Fresenius. Nach der von uns erstmalig für Löslichkeitsbestimmungen nutzbar gemachten Methode der Leitfähigkeitstitration fanden wir den Wert 0,39 Millimol pro Liter.Der zur Zeit fast allgemein als gültig angenommene Wert von Kohlrausch für die Löslichkeit des Magnesiumoxyds ist demnach durch einen etwa doppelt so hohen zu ersetzen. *** DIRECT SUPPORT *** A0025285 00002