A model of electron emission from a wedge in the space-charge-limited current regime

The process of electron emission from a wedge-shaped cathode in the space-charge-limited current regime has been theoretically studied. The field distribution in the interelectrode gap is described using a simple analytical model, which is based on the matching of self-similar solutions for electron flows at the vertex region and at the periphery. The dependence of the perveance on the wedge angle in the wedge cathode-flat anode system is determined.     

Distinguishing of Ile/Leu amino acid residues in the PP3 protein by (hot) electron capture dissociation in Fourier transform ion cyclotron resonance mass spectrometry

In hot electron capture dissociation (HECD), multiply protonated polypeptides fragment upon capturing approximately 11-eV electrons. The excess of energy upon the primary c, z* cleavage induces secondary fragmentation in z* fragments. The resultant w ions allow one to distinguish between the isomeric Ile and Leu residues. The analytical utility of HECD is evaluated using tryptic peptides from the bovine milk protein PP3 containing totally 135 amino acid residues. Using a formal procedure for Ile/Leu (Xle) residue assignment, the identities of 20 out of 25 Xle residues (80%) were determined. The identity of an additional two residues could be correctly guessed from the absence of the alternative w ions, and only two residues, for which neither expected nor alternative w ions were observed, remained unassigned. Reinspection of conventional ECD spectra also revealed the presence of Xle w ions, although at lower abundances, with 44% of all Xle residues distinguished. Using a dispenser cathode as an electron source, identification of four out of five Xle residues in a 2.7-kDa peptide was possible with one acquisition 2 s long, with identification of all five residues by averaging of five such acquisitions. Unlike the case of high-energy collision-induced dissociation, no d ions were observed in the HECD of tryptic peptides.     

The non-newtonian hydromechanics of suspensions

Because of internal diffusion effects, the rheological equation of state of a suspension of elastic particles has a dispersive form. The characteristic time of the dispersive effect can fall in the range from a fraction of a second to tens of minutes.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 59, No. 1, pp. 41–47, July, 1990.     

Distinguishing and quantifying peptides and proteins containing D-amino acids by tandem mass spectrometry

Tandem mass spectrometry (MS/MS) utilizing both electron capture dissociation (ECD) and collisionally activated dissociation (CAD) was used to develop a qualitative and quantitative analytical method for chiral analysis of individual amino acid residues in polypeptides. ECD produced a more distinct chiral recognition than CAD, which is attributed to the smaller degree of vibrational excitation in ECD. Several peptide and protein model systems were used in this study, including the smallest known protein, tryptophan cage, a lactoferrin peptide, and the biologically relevant opioid peptide, dermorphin. An adaptation of the kinetic method was used to quantify the degree of separation between fragmentation patterns of stereoisomeric peptides as a function of fragment ion abundances. The obtained calibration scale for relative abundances of d-amino acids in diastereomeric peptide mixtures was accurate to 1% for ECD and to 3-5% for CAD. It was found that separation and quantification of stereoisomers could be advantageously performed by nanoflow reversed-phase liquid chromatography, with the objective of on-line MS/MS limited to stereoisomer identification. This technique shows promise for the analysis of chiral substitution in peptides and proteins, broadening the application area for tandem mass spectrometry.