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Very Selective (very + selective)
Selected AbstractsElectric field-enhanced transport across phase boundaries and membranes and its potential use in sample pretreatment for bioanalysisELECTROPHORESIS, Issue 5 2010Pavel Kubá Abstract Separation techniques, such as electrodialysis, electroextraction, electro-membrane extraction and extraction across phase interfaces, are reviewed and discussed as methods for sample cleanup and preconcentration. This survey clearly shows that electromigration of ionic species across phase interfaces, especially across supported liquid membranes, may be very selective and is strongly dependent on the chemical composition of these interfaces. Thus, electric field-enhanced transport across chemically tailored liquid membranes may open new perspectives in preparative analytical chemistry. This review offers comprehensive survey of related literature and discussion of the topic, which may stimulate interest of experts and practitioners in bioanalysis. [source] Rapid screening and characterization of drug metabolites using a new quadrupole,linear ion trap mass spectrometerJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 2 2003Gérard Hopfgartner Abstract The application of a new hybrid RF/DC quadrupole,linear ion trap mass spectrometer to support drug metabolism and pharmacokinetic studies is described. The instrument is based on a quadrupole ion path and is capable of conventional tandem mass spectrometry (MS/MS) as well as several high-sensitivity ion trap MS scans using the final quadrupole as a linear ion trap. Several pharmaceutical compounds, including trocade, remikiren and tolcapone, were used to evaluate the capabilities of the system with positive and negative turbo ionspray, using either information-dependent data acquisition (IDA) or targeted analysis for the screening, identification and quantification of metabolites. Owing to the MS/MS in-space configuration, quadrupole-like CID spectra with ion trap sensitivity can be obtained without the classical low mass cutoff of 3D ion traps. The system also has MS3 capability which allows fragmentation cascades to be followed. The combination of constant neutral loss or precursor ion scan with the enhanced product ion scan was found to be very selective for identifying metabolites at the picogram level in very complex matrices. Owing to the very high cycle time and, depending on the mass range, up to eight different MS experiments could be performed simultaneously without compromising chromatographic performance. Targeted product ion analysis was found to be complementary to IDA, in particular for very low concentrations. Comparable sensitivity was found in enhanced product ion scan and selected reaction monitoring modes. The instrument is particularly suitable for both qualitative and quantitative analysis. Copyright © 2003 John Wiley & Sons, Ltd. [source] Analysis of the capsular polysaccharide biosynthesis locus of Porphyromonas gingivalis and development of a K1-specific polymerase chain reaction-based serotyping assayJOURNAL OF PERIODONTAL RESEARCH, Issue 6 2008J. Brunner Background and Objective:,Porphyromonas gingivalis is a gram-negative obligate anaerobe that is strongly associated with severe periodontitis. Previous reports showed an association of P. gingivalis capsular polysaccharide with virulence. The K1 capsular polysaccharide was found to be more immunostimulatory than the other serotypes. Our objective was to explore the genetic background of the capsule biosynthesis (K-antigen) locus in a representative group of K1 serotype strains. Material and Methods:, We used restriction fragment length polymorphism, polymerase chain reaction (PCR) and DNA sequencing to study the capsular polysaccharide locus in P. gingivalis K1 strains. For serotyping by double immunodiffusion and PCR we used 32 strains of P. gingivalis, including strains of all six known K serotypes. Results:, All tested K1 strains showed high conservation of the capsular polysaccharide locus, although a DNA re-arrangement was found in two strains. Based on this information a K1-specific PCR-based serotyping assay was designed. The specificity and sensitivity of this test were confirmed using non-K1 P. gingivalis serotypes. Conclusion:, The capsular polysaccharide locus of P. gingivalis is conserved but may vary slightly among K1 strains. The new K1 serotyping assay presented here is much faster than double immunodiffusion and can detect K1 strains in a very selective and sensitive way. This method may therefore be clinically relevant in the detection of the virulent P. gingivalis K1 serotype. [source] Plasticity of the phonotactic selectiveness of four species of chirping crickets (Gryllidae): Implications for call recognitionPHYSIOLOGICAL ENTOMOLOGY, Issue 2 2010JOHN STOUT Earlier studies of phonotaxis by female crickets describe this selective behavioural response as being important in the females' choices of conspecific males, leading to reproduction. In the present study, moderate (30+) to very large data sets of phonotactic behaviour by female Acheta domesticus L., Gryllus bimaculatus DeGeer, Gryllus pennsylvanicus Burmeister and Gryllus veletis Alexander demonstrate substantially greater plasticity in the behavioural choices, as made by females of each species, for the syllable periods (SP) of model calling songs (CS) than has been previously described. Phonotactic choices by each species range from the very selective (i.e. responding to only one or two SPs) to very unselective (i.e. responding to all SPs presented). Some females that do not respond to all SPs prefer a range that includes either the longest or shortest SP tested, which fall outside the range of SPs produced by conspecific males. Old female A. domesticus and G. pennsylvanicus are more likely to be unselective for SPs than are young females. Each species includes females that do not respond to a particular SP when responding to CSs with longer and shorter SPs. The results suggest that the plasticity of phonotactic behaviour collectively exhibited by the females of each species does not ensure that choices of a male's CS effectively focus the female's phonotactic responses on CSs that represent the conspecific male. The phonotactic behaviour collectively exhibited by females of each species does not readily fit any of the models for selective processing by central auditory neurones that have been proposed to underlie phonotactic choice. [source] Plasmabromination , the Selective Way to Monotype Functionalized Polymer SurfacesPLASMA PROCESSES AND POLYMERS, Issue 9 2007Sascha Wettmarshausen Abstract In contrast to other plasma modification processes of polymer surfaces, the bromination is very selective and shows a high yield in CBr groups. The most convenient bromination process was found using bromoform, which was thus preferred to elemental bromine, allyl bromide, vinyl bromide or tert -butylbromide. The bromoform process give yields in CBr up to 40 CBr or more, with only 2,3% co-introduction of O-functionalities whereas allyl bromide results in yields of about 20 CBr and more, but in more than 10% oxygen-containing by-products. CBr groups serve as anchoring points for grafting of molecules, oligomers and pre-polymers of diole or diamine character. [source] RDC-assisted modeling of symmetric protein homo-oligomersPROTEIN SCIENCE, Issue 5 2008Xu Wang Abstract Protein oligomerization serves an important function in biological processes, yet solving structures of protein oligomers has always been a challenge. For solution NMR, the challenge arises both from the increased size of these systems and, in the case of homo-oligomers, from ambiguities in assignment of intra- as opposed to intersubunit NOEs. In this study, we present a residual dipolar coupling (RDC)-assisted method for constructing models of homo-oligomers with purely rotational symmetry. Utilizing the fact that one of the principal axes of the tensor describing the alignment needed for RDC measurement is always parallel to the oligomer symmetry axis, it is possible to greatly restrict possible models for the oligomer. Here, it is shown that, if the monomer structure is known, all allowed dimer models can be constructed using a grid search algorithm and evaluated based on RDC simulations and the quality of the interface between the subunits. Using the Bacillus subtilis protein YkuJ as an example, it is shown that the evaluation criteria based on just two sets of NH RDCs are very selective and can unambiguously produce a model in good agreement with an existing X-ray structure of YkuJ. [source] Direction selectivity in V1 of alert monkeys: evidence for parallel pathways for motion processingTHE JOURNAL OF PHYSIOLOGY, Issue 2 2007Moshe Gur In primary visual cortex (V1) of macaque monkeys, motion selective cells form three parallel pathways. Two sets of direction selective cells, one in layer 4B, and the other in layer 6, send parallel direct outputs to area MT in the dorsal cortical stream. We show that these two outputs carry different types of spatial information. Direction selective cells in layer 4B have smaller receptive fields than those in layer 6, and layer 4B cells are more selective for orientation. We present evidence for a third direction selective pathway that flows through V1 layers 4Cm (the middle tier of layer 4C) to layer 3. Cells in layer 3 are very selective for orientation, have the smallest receptive fields in V1, and send direct outputs to area V2. Layer 3 neurons are well suited to contribute to detection and recognition of small objects by the ventral cortical stream, as well as to sense subtle motions within objects, such as changes in facial expressions. [source] Chaperone Activity of Bicyclic Nojirimycin Analogues for Gaucher Mutations in Comparison with N -(n -nonyl)DeoxynojirimycinCHEMBIOCHEM, Issue 17 2009Zhuo Luan Abstract Gaucher disease (GD), the most prevalent lysosomal storage disorder, is caused by mutations of lysosomal ,-glucosidase (acid ,-Glu, ,-glucocerebrosidase); these mutations result in protein misfolding. Some inhibitors of this enzyme, such as the iminosugar glucomimetic N -(n -nonyl)-1-deoxynojirimycin (NN-DNJ), are known to bind to the active site and stabilize the proper folding for the catalytic form, acting as "chemical chaperones" that facilitate transport and maturation of acid ,-Glu. Recently, bicyclic nojirimycin (NJ) analogues with structure of sp2 iminosugars were found to behave as very selective, competitive inhibitors of the lysosomal ,-Glu. We have now evaluated the glycosidase inhibitory profile of a series of six compounds within this family, namely 5- N,6- O -(N, -octyliminomethylidene-NJ (NOI-NJ), the 6-thio and 6-amino-6-deoxy derivatives (6S-NOI-NJ and 6N-NOI-NJ) and the corresponding galactonojirimycin (GNJ) counterparts (NOI-GNJ, 6S-NOI-GNJ and 6N-NOI-GNJ), against commercial as well as lysosomal glycosidases. The chaperone effects of four selected candidates (NOI-NJ, 6S-NOI-NJ, 6N-NOI-NJ, and 6S-NOI-GNJ) were further evaluated in GD fibroblasts with various acid ,-Glu mutations. The compounds showed enzyme enhancement on human fibroblasts with N188S, G202R, F213I or N370S mutations. The chaperone effects of the sp2 iminosugar were generally stronger than those observed for NN-DNJ; this suggests that these compounds are promising candidates for clinical treatment of GD patients with a broad range of ,-Glu mutations, especially for neuronopathic forms of Gaucher disease. [source] Behaviour of [PdH(dppe)2]X (X=CF3SO3,, SbF6,, BF4,) as Proton or Hydride Donor: Relevance to CatalysisCHEMISTRY - A EUROPEAN JOURNAL, Issue 15 2004Michele Aresta Prof. Abstract The synthesis, characterization and properties of [PdH(dppe)2]+CF3SO3,,0.125,THF (1; dppe=1,2-bis(diphenylphosphanyl)ethane) and its SbF6, (1,) and BF4, (1,,) analogues, the missing members of the [MH(dppe)2]+X, (M=Ni, Pd, Pt) family, are described. The Pd hydrides are not stable in solution and can react as proton or hydride donors with formation of dihydrogen, [Pd(dppe)2]2+ and [Pd(dppe)2]. Complexes 1,1,, react with carbocations and carbanions by transferring a hydride and a proton, respectively. Such H, or H+ transfer occurs also towards unsaturated compounds, for example, hydrogenation of a CC double bond. Accordingly, 1 can hydrogenate methyl acrylate to methyl propionate. Complex 1,, is an effective (hourly turnover frequency=16) and very selective (100,%) catalyst for the hydrogenation of cyclohexen-2-one to cyclohexanone with dihydrogen under mild conditions. Density functional calculations coupled with a dielectric continuum model were carried out to compute the energetics of the hydride/proton transfer reactions, which were used to rationalize some of the experimental findings. Theory provides strong support for the thermodynamic and kinetic viability of a tetracoordinate Pd complex as an intermediate in the reactions. [source] | |||||||||||||