Chiral separation of highly negatively charged enantiomers by capillary electrophoresis

The separation of two highly negatively charged enantiomeric organic disulfates containing two chiral centers was investigated by capillary electrophoresis using cyclodextrin based chiral selectors added to the run buffer. The optimum separation for the enantiomers was achieved in less than 3 min at 25 degrees C with a run buffer of 10 mM glycine pH 2.4 and 5 mM QA-beta-CD, which is a positively charged quaternary ammonium beta-cyclodextrin derivative. The method resulted in baseline resolution, excellent linearity, and highly reproducible migration times allowing facile evaluation of the enantiomeric purity of the individual isomers. Detection limits for the enantiomeric pair were determined to be 0.3 ng/microl (S/N = 3). The nature of the selector-enantiomer interaction and a quantitative measurement of the apparent stability constants that governed chiral discrimination of the enantiomers with QA-beta-CD were also investigated by UV-Vis spectroscopy and electrospray ionization mass spectrometry.     

Total synthesis and selective activity of a new class of conformationally restrained epothilones

Stereoselective total syntheses of two novel conformationally restrained epothilone analogues are described. Evans asymmetric alkylation, Brown allylation, and a diastereoselective aldol reaction served as the key steps in the stereoselective synthesis of one of the two key fragments of the convergent synthetic approach. Enzyme resolution was employed to obtain the second fragment as a single enantiomer. The molecules were assembled by esterification, followed by ring-closing metathesis. In preliminary cytotoxicity studies, one of the analogues showed strong and selective growth inhibitory activity against two leukemia cell lines over solid human tumor cell lines. The precise biological mechanism of action and high degree of selectivity of this analogue remain to be examined.     

In Situ Self Assembly of Thiolated ortho‐Quinone Capped Electrocatalysts for Bioanalytical Applications

Thiolated o‐quinone‐capped electrocatalysts modeled on the naturally occurring o‐quinone cofactor pyrroloquinoline quinone (PQQ) were designed and synthesized for the development of biosensor devices. The o‐quinone‐capped electrocatalysts self assembled on gold electrodes through a thiolated phenyleneethynylene linkage to form a monolayer less than 2 nm in thickness. Cyclic voltammetric measurements demonstrated reversible electrochemical properties between the quinone and hydroquinone forms of the head group. In an amperometric sensing mode, the modified electrodes reproducibly detected ethanethiol at micromolar levels demonstrating their robust electrocatalytic activity toward thiols. Their redox cycling and electrocatalytic properties show promise for detection of biologically important thiols and other nucleophiles.     

Separation of the enzyme cofactor pyrroloquinoline quinone and three isomeric analogues by capillary electrophoresis with ion-pairing media

The enzyme cofactor pyrroloquinoline quinone (PQQ) was successfully separated from three closely related isomeric analogues by capillary electrophoresis with ultraviolet detection. Rapid and efficient separation of all four negatively charged isomers with baseline resolution was achieved by the addition of low concentrations (1-5 mM) of short chain tetraalkylammonium (TAA) salts to the capillary buffer. The TAA cations act as ion-pairing agents and promote differential migration of the isomers with only a minimal reduction in the electroosmotic flow. The effects of the TAA salt concentration and the alkyl chain length were examined. Detection limits of PQQ and its isomers were in the range of 7-15 microM with mass detection limits of 98-210 fmol.     

Conductive polymeric ionic liquids for electroanalysis and solid-phase microextraction

Three novel electropolymerizable thiophene-based ionic liquids (ILs) were synthesized and characterized as potential candidates for developing selective extraction media for chemical analysis. Electropolymerization of the bis[(trifluoromethyl)sulfonyl]imide ([NTf₂]^-) analogs successfully produced uniform polymeric thin-films on macro- and microelectrode substrates from both vinyl and methylimidazolium IL monomer derivatives. The resultant conducting polymer IL (CPIL) films were characterized by electrochemical methods and found to exhibit attractive behavior towards anionic species while simultaneously providing an exclusion barrier toward cationic species. Thermogravimetric analysis of the thiophene-based IL monomers established a high thermal stability, particularly for the methylimidazolium IL, which was stable until temperatures above 350 °C. Subsequently, the methylimidazolium IL was polymerized on 125 μm platinum wires and utilized for the first time as a sorbent coating for headspace solid-phase microextraction (HS-SPME). The sorbent coating was easily prepared in a reproducible manner, provided high thermal stability, and allowed for the gas chromatographic analysis of polar analytes. The normalized response of the poly[thioph-C₆MIm][NTf₂]-based sorbent coating exhibited higher extraction efficiency compared to an 85 μm polyacrylate fiber and excellent fiber-to-fiber reproducibility. Therefore, the electropolymerizable thiophene-based ILs were found to be viable new materials for the preparation of sorbent coatings for HS-SPME.     

Functional neural network analysis in frontotemporal dementia and Alzheimer's disease using EEG and graph theory

Background  

Although a large body of knowledge about both brain structure and function has been gathered over the last decades, we still have a poor understanding of their exact relationship. Graph theory provides a method to study the relation between network structure and function, and its application to neuroscientific data is an emerging research field. We investigated topological changes in large-scale functional brain networks in patients with Alzheimer's disease (AD) and frontotemporal lobar degeneration (FTLD) by means of graph theoretical analysis of resting-state EEG recordings. EEGs of 20 patients with mild to moderate AD, 15 FTLD patients, and 23 non-demented individuals were recorded in an eyes-closed resting-state. The synchronization likelihood (SL), a measure of functional connectivity, was calculated for each sensor pair in 0.5–4 Hz, 4–8 Hz, 8–10 Hz, 10–13 Hz, 13–30 Hz and 30–45 Hz frequency bands. The resulting connectivity matrices were converted to unweighted graphs, whose structure was characterized with several measures: mean clustering coefficient (local connectivity), characteristic path length (global connectivity) and degree correlation (network 'assortativity'). All results were normalized for network size and compared with random control networks.     

Selective leaching of trace heavy metals associated with suspended matter in fresh waters

Summary River and pond waters, less than 400 ml, are filtered through 47 mm-diam. Nuclepore polycarbonate membrane filters of 12-, 5-and 0.4-m pore sizes sequentially for size fractionation of suspended matter. Each filter along with collected suspended matter (ca. 1 mg) is ultrasonically treated with 1 ml of chloroform and 0.5 ml of leaching solvent (1M ammonium acetate soln. or 0.1 M hydrochloric acid) in a test tube for 1 min. The filter is completely dissolved in the organic phase, while the suspended matter remains in the aqueous phase enabling a rapid leaching. The leaching solvent is then analyzed by graphite-furnace atomic absorption spectrometry for chromium, copper and cadmium. The proposed technique is more sensitive than the conventional leaching technique, which requires at least 4 ml of leaching solvent.

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Selektive Abtrennung von Schwermetallspuren von suspendierten Teilchen in Frischwasser

Zusammenfassung Fluß- bzw. Teichwasser wird in Mengen von weniger als 400 ml durch Polycarbonat-Membranfilter mit einem Durchmesser von 47 mm und einer Porengröße von 12, 5 bzw. 0,4m zwecks Fraktionierung der suspendierten Teilchen filtriert. Jedes Filter wird zusammen mit der darauf gesammelten Materie (ca. 1 mg) mit 1 ml Chloroform und 0,5 ml Auslaugmittel (1 M Ammoniumacetat oder 0,1 M Salzsäure) 1 min in einem Reagensglas mit Ultraschall behandelt. Das Filter löst sich in der organischen Phase vollständig, während die suspendierten Teilchen in der wäßrigen Phase rasch ausgelaugt werden. Die so erhaltene Lösung wird in einem Graphitofen durch Atomabsorptions-Spektrometrie auf Chrom, Kupfer und Cadmium analysiert. Die empfohlene Vorgangsweise ist empfindlicher als das konventionelle Auslaugverfahren, wofür wenigstens 4 ml Auslaugmittel benötigt werden.