Die Bestimmung der in autoxydierten, d. h. in hydroperoxidhaltigen olefinischen Fetts?uren und Fetten entstandenen CO-Gruppen

Ohne Zusammenfassung     

Diphenyl auf Citrusfruchtschalen

Ohne Zusammenfassung     

An all-purpose injection system for gas chromatographic analyses of biological samples.

A versatile injection system for the direct introduction of samples into the gas chromatograph (GC) is described. Several years of experience in biological and pharmaceutical chemistry have led to the construction and final modification of this device. No modification of the injection port of the GC is necessary.     

Die colorimetrische Bestimmung von 1-Monoglyceriden in Eiskrem

Ohne Zusammenfassung     

Bubble nucleation and cooperativity in DNA melting

The onset of intermediate states (denaturation bubbles) and their role during the melting transition of DNA are studied using the Peyrard-Bishop-Dauxois model by Monte Carlo simulations with no adjustable parameters. Comparison is made with previously published experimental results finding excellent agreement. Melting curves, critical DNA segment length for stability of bubbles, and the possibility of a two-state transition are studied.     

Liquid-phase microextraction of basic drugs--selection of extraction mode based on computer calculated solubility data

The extractability of 58 different basic drugs by 3-phase liquid-phase microextraction (LPME) was studied. Extraction recoveries were correlated to solubility data and log D data calculated with a commercial computer program. The basic drugs were extracted from 1.5 mL water samples (pH 13) through approximately 15 microL of dodecyl acetate immobilized within the pores of a porous polypropylene hollow fibre (organic phase), and into 15 microL of 10 mM HCl (acceptor solution) present inside the lumen of the hollow fibre. Compounds with a calculated solubility below 1 mg/mL at pH 2 were poorly recovered and remained principally in the organic phase. For these drugs, 2-phase LPME may be used as an alternative technique, where the aqueous acceptor phase is replaced by an organic solvent. In the solubility range 1-5 mg/mL, most drugs were effectively extracted (recovery >30%), whereas drugs belonging to the solubility range 5-150 mg/mL were all extracted with recoveries above 30% by 3-phase LPME. The hydrophilic nature of most drugs with solubilities above 150 mg/mL prevented them from entering the organic phase, and only those with log D >1.8 were effectively recovered by 3-phase LPME. For drugs with log D < 1.8 (and solubility >150 mg/mL), carrier-mediated LPME was found to be the preferred technique, where an ion-pair reagent (octanoic acid) was added to the sample. In the case of carrier-mediated LPME, the volume of sample was decreased to 100 microL to facilitate rapid extractions. Based on the present work, the extractability of new compounds may easily be predicted to speed up method development. Extractions were also accomplished from plasma samples, where interactions between proteins and the drugs may reduce the extraction recovery. However, dilution of the plasma samples with water and adjustment of pH into the alkaline region effectively suppressed drug-protein interactions for most of the drugs studied.     

The Solvent Effect on Spin Exchange in Long-Chain Nitroxide Biradicals

Intramolecular electron spin exchange, as a function of temperature and the solvent viscosity, polarity and relaxation properties of the solvent molecules, has been studied by X-band electron paramagnetic resonance (EPR) spectroscopy in two long-chain flexible nitroxide biradicals existing in fluid solutions in three spectroscopically different spatial conformations. Certain thermodynamic parameters of the conformational rearrangements were calculated from the EPR spectra. Spin exchange in two biradicals dissolved in five different alcohols was compared with that in a nonpolar solvent (toluene), polar protic (water) and aprotic (acetonitrile), and with thermodynamic characteristics of the solvents. Distinct correlations were found between macroscopic (solvent viscosity, polarity) and microscopic (solvent longitudinal relaxation time) characteristics of solvents, and thermodynamic parameters of the intramolecular conformational transitions. Authors' address: Van Anh Tran, Institute of Physical and Theoretical Chemistry, Graz University of Technology, Technikerstrasse 4, 8010 Graz, Austria     

Synthesis of the C-13 side chain precursors of the 9-dihydrotaxane analogue ABT-271

N-Boc-L-Leucinol was converted to two C-13 side chain precursors of the 9-dihydrotaxane analogue ABT-271. The trans-oxazolidine acid 4 and the cis-Boc-lactam 2b were prepared in 44% and 40% overall yield, respectively, and with excellent (>98%) stereochemical purity.     

Hyperbolic shock waves of the optical self-focusing with normal group-velocity dispersion

The theory of focusing light pulses in Kerr media with normal group-velocity dispersion in (2+1) and (3+1) dimensions is revisited. It is shown that pulse splitting introduced by this dispersion follows from shock fronts that develop along hyperbolas separating the region of transverse self-focusing from the domain of temporal dispersion. Justified by a self-similar approach, this property is confirmed by numerical simulations using an adaptive-mesh refinement code.