Search PubMed⌕ Search

Biomedical subjects

Yehia Mechref

Publications and source records attributed to Yehia Mechref.

25 records · Page 2Linked to original sources
PubMed2003

Development of high-sensitivity ion trap ion mobility spectrometry time-of-flight techniques: a high-throughput nano-LC-IMS-TOF separation of peptides arising from a Drosophila protein extract.

A linear octopole trap interface for an ion mobility time-of-flight mass spectrometer has been developed for focusing and accumulating continuous beams of ions produced by electrospray ionization. The interface improves experimental efficiencies by factors of approximately 50-200 compared with an analogous configuration that utilizes a three-dimensional Paul geometry trap (Hoaglund-Hyzer, C. S.; Lee, Y. J.; Counterman, A. E.; Clemmer, D. E. Anal. Chem. 2002, 74, 992-1006). With these improvements, it is possible to record nested drift (flight) time distributions for complex mixtures in fractions of a second. We demonstrate the approach for several well-defined peptide mixtures and an assessment of the detection limits is given. Additionally, we demonstrate the utility of the approach in the field of proteomics by an on-line, three-dimensional nano-LC-ion mobility-TOF separation of tryptic peptides from the Drosophila proteome.

Animals↗
PubMed2003

Structural characterization of oligosaccharides using MALDI-TOF/TOF tandem mass spectrometry.

Extensive cross-ring fragmentation ions, which are very informative of the linkages of the monosaccharide residues constituting these molecules, were readily observed in the MALDI-TOF/TOF/MS/MS spectra of oligosaccharides. These ions, in some cases, were more intense than the commonly observed Y and B ions. The A-type ions observed for the simple oligosaccharides allowed the distinction between alpha(1-4)- and alpha(1-6)-linked isobaric structures. The distinction was based not merely on the differences in the type of ions formed, but also on the ion intensities. For example, both alpha(1-4)- and alpha(1-6)-linked isobaric structures produce ions resulting from the loss of approximately 120 m/z units, but with different intensities, as a result of the fact that they correspond to two different ions (i.e., 0,4A- and 2,4A-ions), requiring different energies to be formed. Abundant A- and X-type ions were also observed for high-mannose N-glycans, allowing the determination of linkages. In addition, the high resolution furnished by MALDI-TOF/TOF allowed determination of certain ions that were commonly overlooked by MALDI-TOF or MALDI-magnetic sector instruments as a result of their lower resolution. Moreover, as a result of the fact that MS/MS spectra for parent ions and all fragment ions are acquired under the same experimental conditions, accurate determination of the molar ratios of isomeric glycans in a mixture analyzed simultaneously by MALDI-TOF/TOF tandem MS becomes possible.

Carbohydrate Conformation↗
PubMed2003

Coupling capillary electrochromatography with electrospray Fourier transform mass spectrometry for characterizing complex oligosaccharide pools.

To deal with the complexity of the glycan mixtures released from glycoproteins, an efficient form of micro-column separations, capillary electrochromatography, has been combined with high-performance mass spectrometry (Fourier transform ion cyclotron resonance). Contour plots have been generated from the mixtures of O-linked oligosaccharides originated from bovine mucin and bile salt-stimulated lipase, a large glycoprotein enzyme.

Animals↗
PubMed2003

Complexation trends and binding constants between dextrin oligomers and small molecules as measured through affinity capillary electrophoresis.

Quantitative aspects of a previously reported pre-equilibration affinity/capillary electrophoretic methodology (Hong, M., et al., Anal. Chem. 1998, 70, 3590-3597) were studied using fluorescently labeled oligosaccharides and analgesic drugs. Frontal analysis capillary electrophoresis (FA-CE) was investigated for these interaction systems. In order to fulfill certain FA requirements, the analysis conditions of the sugar-drug combinations had to be adjusted individually. Only after the establishment of these conditions, acceptable binding data (association constants) could be obtained. The constants are in the range of weak hydrogen bonding and are comparable to the constants that were independently obtained through 1H nuclear magnetic resonance (NMR) spectroscopy.

Analgesics↗
PubMed2002

Determination of trace isoflavone phytoestrogens in biological materials by capillary electrochromatography.

Capillary electrochromatography using a specialty monolithic matrix was utilized in developing a rapid and highly efficient separation of isoflavones in biological materials. Without a preconcentration technique, it is relatively easy to reach ppm-ppb concentrations of these compounds in soy-based foods and verify them structurally using a photodiode array detector. With on-column preconcentration, we were able to measure low-ppb levels in human serum. Using blood samples from human volunteers, whose diet was supplemented by a soy-based product, the method has been validated for high-throughput screening of isoflavones in clinical studies.

Chromatography, Micellar Electrokinetic Capillary↗
PubMed2002

Matrix-assisted laser desorption/ionization mass spectrometry compatible beta-elimination of O-linked oligosaccharides.

A new beta-elimination procedure has been introduced to cleave O-linked oligosaccharides from low- to sub-microgram amounts of glycoproteins prior to analysis by mass spectrometry. Borane-ammonia complex in aqueous ammonia is used as a cleaving solution alternative to the sodium borohydride/sodium hydroxide medium conventionally used in beta-elimination. The procedure results in minimum sample purification, leading to minimal sample loss and consequently an overall enhancement in sensitivity. It was applied successfully in the analysis of bovine fetuin and submaxillary mucin, as well as to a complex bile-salt-stimulated lipase glycoprotein isolated from human milk.

Ammonia↗