Factors affecting the NQR line width in nitramine explosives

A number of factors associated with crystal quality contribute to the nuclear quadrupole resonance (NQR) line width. Imperfections such as dislocations, voids, strain and impurities can be electrical sources that distort the electric field gradient at nearby quadrupolar nuclei and broaden the observed NQR line. We measured the¹⁴N NQR line widths in powdered samples of the nitramine explosives hexahydro-1,3,5-trinitro-s-triazine (RDX), octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) and 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane and show correlations with sample purity, particle size distribution and density. Cast plastic-bonded explosives containing either RDX or HMX were also studied and their line widths compared with those of the powdered samples.     

Copper and iron interactions with angiotensin-converting enzyme inhibitors. A study by fast-atom bombardment tandem mass spectrometry

Fast atom bombardment, combined with high-energy collision-induced tandem mass spectrometry, has been used to investigate gas-phase metal-ion interactions with captopril, enalaprilat and lisinopril, all angiotensin-converting enzyme inhibitors.Suggestions for the location of metal-binding sites are presented. For captopril, metal binding occurs most likely at both the sulphur and the nitrogen atom. For enalaprilat and lisinopril, binding preferably occurs at the amine nitrogen. Copyright 1999 John Wiley & Sons, Ltd.     

ESI‐MS/MS of expanded porphyrins: a look into their structure and aromaticity

Electrospray mass spectrometry/mass spectrometry was used to investigate the gas‐phase properties of protonated expanded porphyrins, in order to correlate those with their structure and conformation. We have selected five expanded meso‐pentafluorophenyl porphyrins, respectively, a pair of oxidized/reduced fused pentaphyrins (22 and 24 π electrons), a pair of oxidized/reduced regular hexaphyrins (26 and 28 π electrons) and a regular doubly N‐fused hexaphyrin (28 π electrons). The gas‐phase behavior of the protonated species of oxidized and reduced expanded porphyrins is different. The oxidized species (aromatic Hückel systems) fragment more extensively, mainly by the loss of two HF molecules. The reduced species (Möbius aromatic or Möbius‐like aromatic systems) fragment less than their oxidized counterparts because of their increased flexibility. The protonated regular doubly fused hexaphyrin (non‐aromatic Hückel system) shows the least fragmentation even at higher collision energies. In general, cyclization through losses of HF molecules decreases from the aromatic Hückel systems to Möbius aromatic or Möbius‐like aromatic systems to non‐aromatic Hückel systems and is related to an increase in conformational distortion. Copyright © 2016 John Wiley & Sons, Ltd.     

CHOLESTERYL DELTA-AMINOBUTYL SULFIDES FROM CYCLIC SULFONIUM SALTS

Abstract

In the course of studies with cholesterol sulfur derivatives, cholesteryl 3β-sulfonium salts were observed to act as alkylating agents toward amines.¹ 3β-Dimethyl-sulfonio-5-cholestene salts and aniline gave N-methyl-aniline, and not N-cholesterylaniline. Thus, the reaction seemed to be controlled more by steric requirements than by stabilizing factors involved in incipient formation of the homoallylic carbonium ion.     

Preparation and mass spectra of 2,5-diaryl-1,4-dithiins

2 Seven5-diaryl-1,4-dithiins were prepared from phenacyl halides via the corresponding Bunte salts. The mass spectra showed a number of similarities within this series of compounds. Various dipositive ions were observed in all cases while the unsubstituted and p-methyl derivatives formed tripositive ions. Ir, nmr, and chemical analysis were also completed and reported.     

14N NQR study of some local anesthetics

Nitrogen-14 nuclear quadrupole resonance (NQR) spectra for eleven local anesthetics in the solid state are reported and analyzed using the Townes and Dailey approach. The changes in the electron distributions at various nitrogen sites, produced by protonating the tertiary amino nitrogen, are discussed and shown to be in general agreement with expectations based on the increased electrophilic character of the protonated amino group.     

Time resolved magnetization dynamics of ultrathin Fe(001) films: spin-pumping and two-magnon scattering

The time-resolved magnetic response of ultrathin epitaxial Fe(001) films grown on GaAs(001) and covered by Au, Pd, and Cr capping layers was investigated by time and spatially resolved Kerr effect measurements. The magnetization was excited by an in-plane magnetic field pulse using the transient internal field generated at a Schottky barrier while the wavelength of the excitation (resonant mode) was roughly 4 microm. Each of the three cap layers affected the spin relaxation in a unique way. Au cap layers resulted in the bulk Gilbert damping of the Fe film. Pd cap layers caused an additional Gilbert damping due to spin-pump or spin-sink effects. Cr cap layers lead to a strong extrinsic damping which can be described by two-magnon scattering. In this case the strength of the extrinsic damping can be controlled by a field induced shift of the spin wave manifold with respect to the excited k vector.     

Micromagnetic dissipation, dispersion, and mode conversion in thin permalloy platelets

Micron-sized ferromagnetic Permalloy disks exhibiting an in-plane ferromagnetic vortex structure are excited by a fast rise time perpendicular magnetic field pulse and their modal structure is analyzed. We find azimuthal and axial modes. By a Fourier filtering technique we can separate and analyze the time dependence of individual modes. Analysis of the experimental data demonstrates that the azimuthal modes damp more quickly than the axial modes. We interpret these results as mode conversion from low-frequency azimuthal modes to the fundamental mode which is higher in frequency, i.e., mode-mode coupling in a system with a single Landau-Lifshitz-Gilbert phenomenological damping constant alpha.