Capillary isoelectric focusing-mass spectrometry for shotgun approach in proteomics

We report on capillary isoelectric focusing-mass spectrometry (CIEF-MS) of complex peptide mixtures in the absence of carrier ampholytes. Furthermore, the use of low concentrations of carrier ampholytes as mere spacers is investigated. Carrier ampholytes are complex mixtures of amphoteric compounds with high buffering capacity. Since all peptides are amphoteric compounds by themselves, the use of carrier ampholytes may be superfluous to establish a stable pH gradient in CIEF analysis of protein digests. Our research showed that when carrier ampholytes are omitted, the analyte ions are not focused at their isoelectric point. The analytes are charged, leading to electrophoretic mobility uncharacteristic for CIEF. The method was tested for a five-protein-mixture at 0.02 mg/mL per protein and 0.05 mg/mL per protein. At the lower concentration, the analytes were stacked during the focusing process in only a limited length of the capillary. Therefore, the higher concentration led to better separation efficiency. It was found that at low concentration (0.20%) the carrier ampholytes could work as spacers. Though it led to sensitivity losses of 15-45%, this was compensated by the higher separation efficiencies seen. The method was evaluated with an eight-protein-mixture, of which all could be identified after performing MS/MS.     

Considerations for proteolytic labeling-optimization of 18O incorporation and prohibition of back-exchange

Proteolytic (18)O labeling is a very powerful tool for differential analysis applied to proteome studies. However, it is a relatively new technique and the optimization of the labeling process still needs some attention. We found that the two-step post-proteolytic labeling should be favored over the conventional digestion of proteins in H(2) (18)O, since the former allows for higher sample concentrations and thus more favorable kinetics. It was demonstrated that the inhibitory effect of urea on (18)O incorporation could be compensated by the use of higher sample concentrations. Furthermore, it was shown that heat-deactivation of trypsin prevents (18)O/(16)O back-exchange. In addition, no non-specific hydrolysis of the peptides could be observed as a result of the heating. Heat inactivation of trypsin opens the way for the use of capillary electrophoresis as a separation technique in proteolytic labeling studies, as it abolishes the need for use of detrimental additives. Analysis of a labeled protein digest by capillary isoelectric focusing/mass spectrometry showed the applicability of the method. No back-exchange was observed across the entire electropherogram.     

Structural similarities and diversity in a series of crystalline solids composed of 2-aminopyridines and glutaric acid

Structural Chemistry - A solvent co-crystallization of three 2-aminopyridine derivatives, 2-aminopyridine (AP), 2-amino-6-methylpyridine (AMP), and 2,6-diaminopyridine (DAP) with the odd-membered...     

Application of Microbeam Techniques in the Steel Industry

 Steel is a very complex material, and nowadays all types of microbeam techniques are used to characterise it. This paper describes how and why microbeam techniques are used in the steel industry, with special emphasis on micro-analysis of precipitates and surface analysis.     

Gamma-ray spectra analyses of molten salts in spent nuclear fuels pyroprocessing facilities for mass measurement

Journal of Radioanalytical and Nuclear Chemistry - To evaluate radioactive tracer dilution and gamma spectroscopy as a safeguards technique for monitoring the mass of liquid salt in molten salt...     

Work Function Measurement of Lanthanum - Boron Compounds

The La-B system was studied between LaB4.24 and LaB29.2, and between 1400 and 2100 K to determine the phase relationship, the chemical activity of the components, the vaporization rate and the vapor composition. A blue colored phase near LaB9 was found to exist between purple colored LaB6 and elemental boron. Diffusion is so much slower than vaporization that large composition differences can exist between the surface and the interior which, nevertheless, produce a steady state loss rate from freely vaporizing material. The flux at 1700 K is 6 × 10-10 g/cm2-sec for LaB4 + LaB6 and 7 × 10-11 g/cm2-sec for LaB6 + LaB9. There is an activation energy which lowers the vaporization rate of boron from LaB6. Freely vaporizing material will have a steady state surface composition between LaB6.04 and LaB6.07, depending on temperaure, purity and interior composition. The free energy of formation of LaB6 is (0.071T-351) kJ/mole between 1700 K and 2100 K.