Aminolysis of 5-Phenyl-2-tetrazolylacetic Acid Ethyl Ester

It was shown using 5-phenyl-2-tetrazolylacetic acid ethyl ester as an example that aminolysis is a competitive method of synthesizing primary amides. The efficiency of aminolysis by primary amines is linked to the basicity of the initial amine. Highly basic amines display more high reactivity independent of the spatial structure of the substituent. Reaction of the investigated ester with secondary amines occurs ambiguously.     

Electron capture dissociation of gaseous multiply charged ions by Fourier-transform ion cyclotron resonance

Fourier-transform ion cyclotron resonance instrumentation is uniquely applicable to an unusual new ion chemistry, electron capture dissociation (ECD). This causes nonergodic dissociation of far larger molecules (42 kDa) than previously observed (<1 kDa), with the resulting unimolecular ion chemistry also unique because it involves radical site reactions for similarly larger ions. ECD is highly complementary to the well known energetic methods for multiply charged ion dissociation, providing much more extensive protein sequence information, including the direct identification of N- versus C-terminal fragment ions. Because ECD only excites the molecule near the cleavage site, accompanying rearrangements are minimized. Counterintuitively, cleavage of backbone covalent bonds of protein ions is favored over that of noncovalent bonds; larger (>10 kDa) ions give far more extensive ECD if they are first thermally activated. This high specificity for covalent bond cleavage also makes ECD promising for studying the secondary and tertiary structure of gaseous protein ions caused by noncovalent bonding.     

Improved low-energy electron injection systems for high rate electron capture dissociation in Fourier transform ion cyclotron resonance mass spectrometry

New low-energy electron injection systems based on indirectly heated dispenser cathodes facilitate electron capture dissociation (ECD) in Fourier transform ion cyclotron resonance (FTICR) mass spectrometry. In this joint report, details are presented of the design and performance of these systems on two commercial FTICR instruments, 9.4 T Bruker BioAPEX in Uppsala and 4.7 T IonSpec Ultima in Odense. New results include obtaining meaningful one-scan MS/MS data for isolated precursor ions with millisecond irradiation times. The ECD rate improvement is not only due to the larger total electron current, but the larger emitting area as well.     

Transition radiation of modulated electron beam in strongly inhomogeneous plasma

A formula for the transition radiation of a modulated electron bean in a strongly inhomogeneous plasma is derived in a given-current approximation. Nonmonotonic variation of the transition-radiation power is detected when the inhomogeneity parameter for the beam emerging from the plasma is varied. The analytic results are confirmed by numerical calculations.Kiev State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 37, No. 2, pp. 194–199, February, 1994.     

A direct comparison of protein structure in the gas and solution phase: the Trp-cage

Molecular dynamics simulations of zwitterions of the Trp-cage protein in the gas phase show that the most stable ion in vacuo has preserved the charge locations acquired in solution. A direct comparison of the gas and solution-phase structures reveals that, despite the similarity in charge location, there is significant difference in the structures, with a substantial increase in hydrogen bonds and exposure of hydrophobic parts in the gas phase. The structure of the salt bridge in the gas phase is also much more stable than in the (experimental) solution structure.     

Fluorination of aromatic compounds with xenon difluoride in the presence of boron trifluoride etherate

Fluorination of benzene with the XeF₂—BF₃?Et₂O system in acetonitrile at low temperatures affords fluorobenzene in 18% yield, the conversion of benzene being 92%. The rest products are di-, tri-, tetra-, and polyphenyls with different fluorination pattern. Toluene and chloro- and bromobenzenes are fluorinated predominantly at the ortho and para positions. Fluorination of 4-nitroanisole affords 2-fluoro-4-nitroanisole in 73% yield.     

A portable X-ray source for testing of TRD/ALICE radiators and chambers

Portable X-ray sources were designed and produced for experimental study of radiator absorption uniformity and mapping of large-scale drift chamber gain. The tests are performed on-line with creation of the Transition Radiation Detector (TRD) for the ALICE experiment at CERN. The source is a key element of automatic scanner, and it produces X-ray photons in the energy range up to 10 keV with required intensity. The design and characteristics of the source are described. The article is published in the original.