Phosphoprotein Analysis by MALDI-TOF Mass Spectrometry using On-Probe Tandem Proteolysis and Dephosphorylation

In this investigation, methods based on on-probe enzymatic cleavage matrix-assisted laser desorption/ionization time-of-flight mass spectrometric (MALDI-TOF-MS) analyses have been developed, allowing the rapid assignment of phosphorylation sites within phosphoproteins. The procedures involved robotic sample deposition of a phosphoprotein, such as intact bovine β-casein, on stainless steel or gold MALDI plates, on-probe proteolysis with trypsin for 10–180?s at 37°C, on-probe dephosphorylation for 1–10?min at 37°C with alkaline phosphatase, followed by differential mass spectrometry with peptide mass mapping. The dephosphorylation conditions were initially optimized using in-solution tryptic digestion of the phosphoprotein performed in the presence of MS-compatible anionic surfactant sodium 3-[(2-methyl-2-undecyl-1,3-dioxolan-4-yl)methoxy]-1-propanesulfonate. Two methods of trypsin deactivation were investigated, cooling and quenching by acidification, which resulted in the surfactant either staying intact or becoming cleaved, respectively. Since the surfactant had no detrimental effects on dephosphorylation of phosphopeptides, the acidification and neutralization steps were not included in the final analytical method. A protocol, comprising on-probe tandem, surfactant-aided proteolysis for 3?min followed by on-probe dephosphorylation for 10?min was thus established, allowing the rapid identification of location and sequence of phosphopeptides within a phosphoprotein by these procedures.     

Photoelectron spectroscopy of methyl,ethyl and isopropyl alcohol adsorbed on the (110) surface of Cu

Methyl, ethyl and isopropyl alcohol were allowed to adsorb on a clean (110) face of a copper crystal at room temperature, and photoelectron spectra were obtained using He(I) (21.2 eV) radiation. The spectra of the adsorbed species differed sufficiently from those of the free molecules to indicate a chemical change on adsorption. In accordance with studies in the literature using flash-desorption and energy-loss spectroscopy, it is suggested that the observed spectra are those of the corresponding alkoxy radicals formed as a result of dehydrogenation. In the case of the methoxy radical, calculations were carried out for a cluster of nine copper atoms and the results shown to be consistent with the experimental data. Results were also obtained on the rates of adsorption and desorption and on the dependence of the spectra on the polar angle between the normal to the surface and the photoelectron direction. Finally, results were obtained on the extent of adsorption by means of X-ray photoelectron spectroscopy.     

Controlled convergence theorems for Henstock-Kurzweil-Pettis integral on m-dimensional compact intervals

In this paper we use a generalized version of absolute continuity defined by J. Kurzweil, J. Jarník, Equiintegrability and controlled convergence of Perron-type integrable functions, Real Anal. Exch. 17 (1992), 110–139. By applying uniformly this generalized version of absolute continuity to the primitives of the Henstock-Kurzweil-Pettis integrable functions, we obtain controlled convergence theorems for the Henstock-Kurzweil-Pettis integral. First, we present a controlled convergence theorem for Henstock-Kurzweil-Pettis integral of functions defined on m-dimensional compact intervals of ℝ ^m and taking values in a Banach space. Then, we extend this theorem to complete locally convex topological vector spaces.     

Photoelectron spectroscopy of sulfur heterocycles adsorbed onto a Cu(110) surface

Photoelectron spectra of Cu(110) after exposure to thiacyclobutane, thiacyclopentane, and thiacyclohexane, as well as of the clean Cu(110) surface, have been obtained using He(I) radiation. Comparison of the spectra of the absorbates with gas-phase spectra suggests a strong sulfur-to-copper dative bond. Sulfur lone-pair orbital stabilization energies were obtained for thiacyclobutane (1.4 eV), thiacyclopentane (1.1 eV), and thiacyclohexane (0.6 eV), and these stabilization energies are correlated with the dative sulfur-to-surface bond energies. Ring-strain changes are suggested as the reason for additional small shifts of absorbate-bond energies in the thiacyclobutane spectrum. Relaxation energies were found to decrease in the order 4- > 5- > 6-membered ring. An empirical linear relation was found between relaxation shifts and lone-pair orbital stabilization energies for monoheteroatom heterocycles bonded to Cu(110) by a lone-pair dative bond. All adsorbates studied showed marked angular dependence, suggesting nonrandom orientation on the surface. Al Kα X-ray data were used to calculate percentage surface coverages. Other sulfur-containing adsorbates are discussed, including thiophene, allyl mercaptan, and thiacyclopropane. Thiacyclopropane was found to decompose upon exposure to copper.     

Focused scattering of low energy Li+ from Mo(001): Experimental and computer simulation results

The azimuthal dependence of the energy distribution of Li⁺, specularly scattered from Mo(001), has been obtained for several incident energies E_i. The energy distributions exhibit one or two peaks, which always lie below the kinematical single scattering energy and which have intensity and energy that depend upon the azimuth. Due to trajectory focusing, the intensity is strongly peaked along the [100] azimuth for E_i ? 500 eV, but at higher E_i the intensity enhancement is shifted toward the [310] azimuth. Results of computer simulation give reasonable agreement with experimental observations. Analysis of the simulated trajectories allows identification of the scattering mechanisms which contribute to each portion of the spectrum.     

IR-Untersuchungen über die Wassersorption an polymorphen ZrO2-Produkten

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