The use of selenophenyl galactopyranosides for the synthesis of α and β-(1→4)-C-disaccharides

Methyl α-C-lactoside {β-D-Gilp-C-(1→4)-α-D-Glcp-OMe} and its α anomer were expeditiously synthesized by radical coupling of various selenophenyl galactopyranosides onto methyl 2,3-di-O-benzyl-4-deoxy-4-C-methylene-α-D-xylo-hexopyranoside, which aretemporarily connected through a silaketal tether.     

Stereochemical differentiation and simultaneous analysis of 3-, 4-, and 5-hydroxyalkanoic acids from biopolyesters by multidimensional gas chromatography

The direct enantioselective analysis of 3-, 4-, and 5-hydroxy fatty acids from biological material has been achieved by enantioselective multidimensional gas chromatography (enantio-MDGC) with heptakis(2,3-di-O-methyl-6-O-tert-butyldimethylsilyl)- or (2,3-di-O-acetyl-6-O-tert-butyldimethylsilyl)-β-cyclodextrin as chiral stationary phase. All the bacteria investigated produced polyesters of enatiomerically pure (R) configured compounds.     

Multiresidue method using SPME for the determination of various pesticides with different volatility in confined atmospheres

An analytical method is described for assessing the vapour concentration of 11 pesticides (bioallethrin, chlorpyriphos methyl, folpet, malathion, procymidone, quintozene, chlorothalonil, fonofos, penconazole and trimethacarb) in confined atmospheres (e.g. a greenhouse after pesticide application). This study is a successful extension of a method previously developed by the authors for dichlorvos to much less volatile pesticides. Sampling was performed by using polydimethylsiloxane–solid phase micro-extraction (PDMS–SPME) fibres immersed in a 250-mL sampling flask through which air samples were dynamically pumped from the analysed atmosphere. After a 40-min sampling duration, samples were analysed by GC/MS.Calibration was performed from a vapour-saturated air sample. The linearity of the observed signal versus pesticide concentration in the vapour phase was proved from spiked liquid samples whose headspace concentrations were measured by using the proposed method. This procedure gave calibration curves with regression coefficients (R²) greater than 0.98, and the repeatability of these measurements was found with RSDs of 1.9–7.6%. As a field application test, this analysis procedure was used for the determination of gaseous procymidone concentrations as a function of time in the atmosphere of an experimental 8-m² and 20-m³ greenhouse. The pesticide was sprayed according to real cultivation conditions, and measurements were made for 80 h after application (8 measurements). The observed concentrations found ranged from 200 to 500 µg m^–3, thus indicating the level of contamination of the air breathed by people in such working conditions.Abbreviations GC/MS gas chromatography/mass spectrometry - SIM selective ion monitoring - FC43 perfluorotributylamine - RSD relative standard deviation - LOD limit of detection - LOQ limit of quantification     

NMR and in silico screening

NMR-based screening and virtual, or in silico, screening can be highly complementary and synergistic. NMR-based screening is a rapid and reliable method for validating hits that come from in silico screens. In addition, ligand-binding data derived from NMR-based screens can focus and direct subsequent in silico screening. We will first give a short overview of existing NMR and in silico screening methods, discuss the drawbacks associated with each, and finally present applications that highlight the combination of the two technologies.     

Characteristic fragmentation of bacteriohopanepolyols during atmospheric pressure chemical ionisation liquid chromatography/ion trap mass spectrometry

Bacteriohopanepolyols (BHPs) fragment via characteristic pathways during atmospheric pressure chemical ionisation liquid chromatography/ion trap mass spectrometry (APCI-LC/MS(n)). Comparison of the MS(2) spectra of bacteriohopane-32,33,34,35-tetrol (BHT) and 2 beta-methylbacteriohopane-32,33,34,35-tetrol has confirmed the previously proposed ring-C cleavage occurring between C-9 and 11 and C-8 and 14. This fragmentation, diagnostic of all hopanoids, also occurs in BHPs containing an amino group (-NH(2)) at C-35 although the higher relative stability of the ion limits this fragmentation to a minor process after protonation of the basic nitrogen function. Studies of a number of cell cultures including a prochlorophyte (Prochlorothrix hollandica) and a cyanobacterium (Chlorogloeopsis LA) demonstrate the power of this technique to detect composite BHPs with a complex biological functionality at C-35. We also report the first observation of intact pentafunctionalised bacteriohopanepolyols using this method.     

Comparative Studies of the Redox Behaviour and the Antioxidative Activity of Arylnaphthoquinones

Summary.  Comparative studies of redox behaviour and antioxidative activity (AOA) were carried out with two series of arylnaphthoquinone derivatives. For the electrochemical investigations, a voltammetric procedure combined with a glassy carbon electrode was applied. The AOA was examined using the photo-chemiluminometric method with the Photochem^? measuring device according to Popov et al. and the chemical procedure with the radical quencher DPPH (diphenylpicrylhydrazyl). Both the redox potential and the antioxidative activity of the investigated compounds are influenced by their substituents. Compounds with the OH-group at position 3 are easiest to oxidize (E _p = 0.18 V; pH 7.4). The lag phases (AOA) of these compounds are five to ten times greater than those of the strong antioxidants ascorbic acid and Trolox^?. As suggested for other natural compounds, we also found a good correlation between the oxidation potential and the AOA. Therefore, it seems that a good antioxidative activity requires a low redox potential. Corresponding authors. E-mail: wurglics@pharmchem.uni-frankfurt.de Received March 1, 2002; accepted March 28, 2002     

Ion-pair mediated transport of angiotensin, neurotensin, and their metabolites in liquid phase microextraction under acidic conditions

This paper discusses the behaviour of angiotensin 1 and neurotensin together with their metabolites in a three-phase liquid phase microextraction under acidic conditions. Variations in donor phase, organic phase, and acceptor phase are studied with extraction recovery as response variable. It is proved that for all peptides the transport across the organic phase is mediated by heptane-1-sulphonic acid. n-Octanol gave overall best results as organic phase. A donor phase volume of 1.0 mL was chosen as a compromise between optimal recovery and robustness of the LPME device. The optimal pH of the donor phase (using acceptor phase of pH 2) was found to be different for the peptides, which opens opportunities for selective sample preparation. Decreasing the acceptor phase pH to 1.0 resulted in increased extraction recoveries. On using 1.0 mL of donor phase containing 50 mM heptane-1-sulphonic acid pH 3, n-octanol as organic phase immobilized in the pores of the fibre, and 20 microL of acceptor phase containing 0.1 mol/L HCl, extraction recoveries up to 82% (enrichment factor = 41) were achieved. To our knowledge this is the first report on liquid phase microextraction of angiotensins and neurotensins.     

Stereoelectronic substituent effects in polyhydroxylated piperidines and hexahydropyridazines

From the pK(a) values of the conjugate acids of a large series of hydroxylated piperidines and hexahydropyridazines, a consistent difference in basicity was found between stereoisomers having an axial or equatorial hydroxyl (OH) group either beta or gamma to the amine. Compounds with an equatorial OH group in the 3-position were 0.8 pH units more acidic than otherwise identical compounds with an axial OH group, whilst compounds with an equatorial OH group in the 4-position relative to the amine were 0.4 pH units more acidic than the corresponding compound with an axial OH. A similar effect was observed for the COOMe substituent. The difference in electron-withdrawing power of axial and equatorial substituents was explained by a difference in charge-dipole interactions in the two systems. Since this stereoelectronic substituent effect causes differences in basicity in different conformers, certain piperidines and hexahydropyridazines were found to change conformation upon protonation. A method for predicting the pK(a) of piperidines which takes stereochemistry into account is described.     

Influence of the particle size of the MgCl2 support on the performance of Ziegler catalysts in the polymerization of ethylene to ultra‐high molecular weight polyethylene and the resulting polymer properties

A highly systematic size series of Ziegler catalysts with similar porosities and surface textures are synthesized by varying the stirring speed during the MgCl₂ support synthesis. Besides the mean particle size, the only substantial difference observed between the various catalysts is the size and number of nodules per particle. Varying the mean diameter of the catalyst particles between 1.5 and 11.9 µm, leads to a pronounced impact on the activity in ultra‐high molecular weight polyethylene (UHMWPE) polymerization, while the M_w capabilities are only affected to a limited extend. In addition, it is observed that both the M_ws as the polymer bulk density (BD) increases during the course of the polymerization. This particularity allows to optimize the M_w and/or BD at a set polymer size, by tuning the catalyst particle size. This is particularly interesting in UHMWPE production, as control of the morphological and structural properties of the UHMWPE reactor powders are critical for efficient processing as well as the performance of the final product. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2679–2690