Repurposing the Pummerer Rearrangement: Determination of Methionine Sulfoxides in Peptides

The reversible oxidation of methionine residues in proteins has emerged as a biologically important post-translational modification. However, detection and quantitation of methionine sulfoxide in proteins is difficult. Our aim is to develop a method for specifically derivatizing methionine sulfoxide residues. We report a Pummerer rearrangement of methionine sulfoxide treated sequentially with trimethylsilyl chloride and then 2-mercaptoimidazole or pyridine-2-thiol to produce a dithioacetal product. This derivative is stable to standard mass spectrometry conditions, and its formation identified oxidized methionine residues. The scope and requirements of dithioacetal formation are reported for methionine sulfoxide and model substrates. The reaction intermediates have been investigated by computational techniques and by ¹³C NMR spectroscopy. These provide evidence for an α-chlorinated intermediate. The derivatization allows for detection and quantitation of methionine sulfoxide in proteins by mass spectrometry and potentially by immunochemical methods.     

Instabilities in coaxial rotating jets

IntroductionIn this paper, we present the fundamentalexperimental stUdy of the instabilities present in swirlingjets for the Reynolds number range from 1000 tO 3000.The originality of this flow is the coexistence andinteraction between shear and centrifugal instabilities.Furthermore, the confinement effects existing in theclassical plane mixing 1byers are absent from theaxisynunetrical jet cases. The presence of a centrifugalforce, the axial and radial pressure gradients, theenhanced "dxing …     

Influence of degree of deformation in rolling on anneal hardening effect of a cast copper alloy

This paper reports results of investigations carried out on a cast copper alloy containing 8 at.% Al. The alloy, and pure copper for the sake of comparison, were subjected to cold rolling with a final reduction of 30, 50 or 70%. The cold rolled copper and copper alloy samples were isochronally and isothermally annealed up to the recrystallization temperature. The hardness, strength and electrical conductivity were measured and X-ray and DSC analyses performed. Anneal hardening effect was observed in the alloy in the temperature range 180–300°C, followed by an increase in the electrical conductivity. The amount of strengthening increases with increasing degree of prior cold work. The X-ray analysis shows a change in the lattice parameter during annealing when anneal hardening effect was observed. The DSC analysis shows the exothermic character of this effect.     

Thin films in biosensors

Thin films are used in every domain of biosensor systems as for sample handling, biological recognition and amplification, transduction and electronic signal processing. Several planar microelectrochemical chips with thin-film electrodes of different shapes and arrangements on Si or glass substrates have been developed and utilized in voltammetric and potentiometric sensors. Bilayer lipid membranes (BLMs) are very ‘‘adaptive’’ thin-film materials applicable in biosensors. Forming of BLMs on planar chip with thin-film electrodes has opened up new possibilities for the development of miniaturized biosensors as well as for basic research on electrical and mechanical properties of biological membranes.