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Reverse Polarity (reverse + polarity)
Selected AbstractsThe autocorrelation matrix probing biochemical relationships after metabolic fingerprinting with CEELECTROPHORESIS, Issue 7 2009Santiago Angulo Abstract Fingerprinting together with statistical analysis is often employed to compare samples in metabonomic studies of a disease. Correlation algorithms can aid by extracting information based on the variation patterns of key metabolites. This information can be linked to metabolite identification or to specific up/down-regulated biochemical pathways. Matlab-based software employing the Pearson's correlation algorithm was applied to urine electropherograms from 20 mice infected with the schistosoma parasite. The fingerprints were the sum of electropherograms analysed with normal and reverse polarity, in two different modes MEKC and CZE and with two different capillaries (uncoated and polyacrylamide coated) to provide a broad picture of the samples. Hippurate, a metabolite that was depleted in the infected group and is present in both polarities, was chosen as a test variable; it correlated with itself to a p value of <0.000. Phenylacetylglycine, a metabolite shown as over expressed in the disease, was positively correlated to three metabolites in its same pathway with a correlation coefficient of 0.7 and p<0.000 to phenylalanine, 0.7 and p<0.000 to 2-hydroxyphenylacetic and 0.55 and p<0.003 to phenylacetate. The study shows that the autocorrelation matrix is able to provide extra information from data files acquired by CE analyses. It underlined an up-regulated metabolic path by association in the schistosoma infection model. [source] Determination of ribavirin in human serum and plasma by capillary electrophoresisELECTROPHORESIS, Issue 10-11 2004Michael C. Breadmore Abstract The electrophoretic separation of ribavirin and 5-methylcytidine (internal standard) by capillary electrophoresis was examined. Separation was achieved using reverse polarity in a 100 mM borate electrolyte, pH 9.1, with 5 mM spermine added to reduce the electroosmotic flow. Sample preparation based on acetonitrile protein precipitation was found to be unsuitable for ribavirin analysis in patient samples due to insufficient sensitivity and interferences. Solid-phase extraction employing phenyl boronic acid cartridges provided cleaner separations. Using this approach with 500 ,L sample and reconstitution of the dried extract into 100 ,L of 33% v/v 100 mM phosphate buffer, pH 6.4 / 67% v/v acetonitrile, the detection and quantitation limits were determined to be 0.05 and 0.10 ,g/mL, respectively, a sensitivity that is suitable for therapeutic drug monitoring of ribavirin in human plasma and serum samples. The method was validated and compared to a high-performance liquid chromatography (HPLC) method, showing excellent agreement between the two for a set of samples that stemmed from patients being treated with ribavirin and interferon-,-2b for a hepatitis C virus infection. [source] Dual stacking of unbuffered saline samples, transient isotachophoresis plus induced pH junction focusingELECTROPHORESIS, Issue 10 2003Sang-Hee Shim Abstract A dual stacking mechanism based on transient isotachophoresis (TITP) and induced pH junction focusing is demonstrated as a means to increase the concentration sensitivity in capillary electrophoresis of highly saline samples. When stacking was carried out with an unbuffered saline sample of fluorescein between two zones of low mobility background electrolyte at high pH under an electric field of reverse polarity, two transient peaks at both boundaries of the sample zone were observed. One peak at the rear boundary could be inferred as a transient isotachophoretic stacked zone. Through computer simulations of an unbuffered sample with a high concentration of sodium chloride, we showed that the fast moving zones of sodium and chloride ions induced pH changes at both boundaries to satisfy the electroneutrality condition and that the peak at the front boundary was due to the induced pH junction. To verify the pH changes, an indicator, thymol blue, was added to an NaCl solution and the color changes under an electric field were observed. The proposed mechanism was supported by observing the dual stacking procedure for an unbuffered sample of 4-nitrophenol and measuring additional sensitivity enhancements by dual stacking for ten weakly acidic compounds. For the ten analytes including nucleoside phosphates, every dual stacking of an unbuffered sample exhibited an additional enhancement up to 86% larger than that of usual transient isotachophoresis of the corresponding buffered sample without loss of separation efficiency and reproducibility. Therefore, it would be useful to skip over buffering in sample preparation for TITP, contrary to the general recommendation. [source] Activity-dependent modulation of GABAergic synapses in developing rat spinal networks in vitroEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 11 2002Marcelo Rosato-Siri Abstract The role of activity-dependent plasticity in modulating inhibitory synapses was investigated in embryonic rat spinal cord slice cultures, by chronic exposure to non-NMDA receptor blockers. GABAergic synaptic efficacy in control and chronic-treated cultures was investigated by patch-recordings from visually identified spinal interneurons. In both culture groups proximal stimulation induced the appearance of postsynaptic currents (PSCs), which were fully antagonized by 20 µM bicuculline application and reverse polarity at potential values close to those reported for spontaneous GABAergic PSCs. In chronically treated cells GABAergic evoked PSCs displayed a larger failure rate and a smaller coefficient of variation of mean PSC amplitude, when compared to controls. As opposed to controls, chronic GABAergic evoked PSCs did not facilitate upon paired-pulse stimulation. Facilitation at chronic synapses was observed when extracellular calcium levels were decreased below physiological values (< 2 mM). Kainate was used to disclose any functional differences between control and treated slices. In accordance with the presynaptic action of kainate, the application of this drug along with GYKI, an AMPA receptor selective antagonist, changed, with analogous potency, short-term plasticity of GABAergic synapses from control and treated cultures. Nevertheless, in chronic cultures, the downstream effects of such activation unmasked short-term depression. Ultrastructural analysis of synapses in chronically treated cultures showed a reduction both in symmetric synapses and in the number of vesicles at symmetric terminals. Thus, based on electrophysiological and ultrastructural data, it could be suggested that during the development of spinal circuits, GABAergic synapses are modulated by glutamatergic transmission, and thus implying that excitatory transmission regulates the strength of GABAergic synapses. [source] Tectonic and environmental evolution of Quaternary intramontane basins in Southern Apennines (Italy): insights from palaeomagnetic and rock magnetic investigationsGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2010M. Porreca SUMMARY Southern Apennines is characterized by active extensional tectonics with NE,SW stretching direction. The seismicity of the region is very well understood and continuously monitored. In contrast, the onset of extensional tectonics is chronologically poorly constrained. The aim of this study is that to give important constraints on the development of extensional regime and the onset of the continental deposition during Quaternary in Southern Apennines. We report the results of palaeomagnetic and rock magnetic analyses from four Quaternary small intramontane basins in the Picentini Mountains (Southern Apennines). The sedimentary sequences are located at different altitudes, from 600 to 1200 m a.s.l., and were deposited in fluvial-lacustrine environments. We sampled 29 sites in clays and lacustrine limestones from Tizzano, Piano del Gaudo and Acerno basins and in red palaeosoils and matrix-supported conglomerates from the Iumaiano basins. In the clay and limestones samples magnetite, titano-magnetite, hematite and iron-sulphide have been recognized as the main magnetic carriers, whereas magnetite and hematite characterize the Iumaiano conglomerates and red soils. Palaeomagnetic results have been integrated with published radiometric data in order to constrain the age of each sedimentary basins. Sites from the Iumaiano basin, which represents the substrate of the Tizzano and Piano del Gaudo basins, show a reverse polarity and therefore have been attributed to the lower Matuyama chron. In contrast, palaeomagnetic data from Tizzano basin show a transition from reversed to normal polarity along the exposed section, which has been interpreted as the Matuyama/Brunhes transition. Sites from Acerno and Piano del Gaudo basins show a normal polarity, which, according to radiometric and pollen data, have been correlated to the Brunhes epoch. On the base of such results we discuss the tectono-stratigraphic evolution of the basins and the role of extensional tectonics in this portion of the Southern Apennine during the Quaternary. [source] Method for enantiomeric purity of a quinuclidine candidate drug by capillary electrophoresisJOURNAL OF SEPARATION SCIENCE, JSS, Issue 13 2006Tore Ramstad Abstract A chiral procedure based on EKC was developed and validated for determination of the enantiomeric purity of PHA-543613, a drug candidate that was under development for treatment of the cognitive deficits of Alzheimer's disease and schizophrenia. Separation of enantiomers is accomplished via differential, enantiospecific complexation with a single-isomer, precisely sulfated beta-CD and heptakis-6-sulfato-,-CD (HpS-,-CD). Both neutral and sulfated CDs were screened before selecting HpS-,-CD as the chiral selector. The separation is conducted in a 61 cm×50 ,m uncoated fused silica capillary with 25 mM HpS-,-CD in pH 2.50, 25 mM lithium phosphate as the separation buffer with detection at 220 nm. Application of reverse polarity at ,30 kV results in an elution time of about 12 min for PHA-543613 and 13 min for the undesired S -enantiomer. Quantification is versus an authentic reference S -enantiomer as an external standard in combination with an internal standard. The procedure was validated over the range 0.1,2.0% w/w. The detection limit is 0.01,0.02%. The amount of distomer intrinsic to the drug substance is about 0.1% or less. The developed method was used to generate stability data on multiple lots: in one case for up to 3 years. [source] Atomic structure of pyramidal defects in GaN:Mg: Influence of annealingPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 7 2006Z. Liliental-Weber Abstract The atomic structure of the characteristic defects (Mg-rich hexagonal pyramids) in p-doped bulk and MOCVD GaN:Mg thin films grown with Ga polarity was determined at atomic resolution by direct reconstruction of the scattered electron wave in a transmission electron microscope. Small cavities were present inside the defects, confirmed also with positron annihilation. The inside walls of the cavities were covered by GaN of reverse polarity compared to the matrix. Annealing of the MOCVD layers lead to slight increase of the defect size and an increase of the room temperature photoluminescence intensity. Positron annihilation confirms presence of vacancy clusters of different sizes triggered by the Mg doping in as-grown samples and decrease of their concentration upon annealing at 900 and 1000 °C. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||