Methionine radical cation: structural studies as a function of pH using X- and Q-band time-resolved electron paramagnetic resonance spectroscopy

A comprehensive high resolution electron paramagnetic resonance (EPR) characterization of the l-methionine radical cation and its N-acetyl derivative in liquid solution at room temperature is presented. The cations were generated photochemically in high yield by excimer laser excitation of a water soluble dye, anthraquinone sulfonate sodium salt, the excited triplet state of which is quenched by electron transfer from the side chain sulfur atom of methionine or N-acetylmethionine. The radicals were detected by continuous wave (CW) time-resolved electron paramagnetic resonance (TREPR) spectroscopy at X-band (9.5 GHz) and Q-band (35 GHz) microwave frequencies. At pH values well below the pK(a) of the protonated amine nitrogen, the cation forms a dimer with another ground-state methionine molecule through a S-S three-electron bond. In basic solution, the lone pair on the nitrogen of the amino acid is available to make an intramolecular S-N three-electron bond with the side chain sulfur atom, leading to a five-membered ring structure for the cation. When the amino acid nitrogen is unsubstituted (methionine itself), rapid deprotonation to an aminyl radical takes place at high pH values. If the nitrogen is substituted (N-acetylmethionine), the cyclic structure is observed within its electron spin relaxation time at about 1 micros. Spectral simulation provides chemical shifts (g-factors) and hyperfine coupling constants for all structures, and isotopic labeling experiments strongly support the assignments.     

High spin level structure of 63 143 Eu80

The level scheme of ¹⁴³ Eu has been extended to I=75/2 in an experiment with the NORDBALL Compton-suppressed Ge detector array and the ¹¹⁰ Pd(³⁷ Cl, 4n) reaction. Most of the scheme shows irregular structure of multiparticle excitations. A strongly populated straight cascade of more than 10 stretched E2 transitions suggests the onset of collectivity.     

Die Bestimmung der Verbrennungsw?rmen organischer Substanzen

Ohne Zusammenfassung     

The solid fuel-cell future

The third generation of fuel cells, which is expected to provide clean, quiet power for customers and electric utilities alike, is discussed. The principle of the fuel cell is explained. Three basic designs of solid oxide fuel cells that are being developed-planar, monolithic, and tubular-are described. Commercialization of the technology is considered     

Validation of high gradient magnetic field based drug delivery to magnetizable implants under flow.

The drug-eluting stent's increasingly frequent occurrence late stage thrombosis have created a need for new strategies for intervention in coronary artery disease. This paper demonstrates further development of our minimally invasive, targeted drug delivery system that uses induced magnetism to administer repeatable and patient specific dosages of therapeutic agents to specific sites in the human body. Our first aim is the use of magnetizable stents for the prevention and treatment of coronary restenosis; however, future applications include the targeting of tumors, vascular defects, and other localized pathologies. Future doses can be administered to the same site by intravenous injection. This implant-based drug delivery system functions by placement of a weakly magnetizable stent or implant at precise locations in the cardiovascular system, followed by the delivery of magnetically susceptible drug carriers. The stents are capable of applying high local magnetic field gradients within the body, while only exposing the body to a modest external field. The local gradients created within the blood vessel create the forces needed to attract and hold drug-containing magnetic nanoparticles at the implant site. Once these particles are captured, they are capable of delivering therapeutic agents such as antineoplastics, radioactivity, or biological cells.     

Standardisation and codification of analytical methods

1. The necessity of standardising an analytical method nationally or internationally depends on the nature of the method. Research methods will hardly be suitable for standardisation, but routine methods especially those of an empirical nature (not general chemical and physical methods) demand international agreement. 2. If analytical methods are published they should be printed in a standard format to facilitate comparison and standardisation and as a safeguard against the lack of details important to the execution of the method.     

Thermal cook-off of an HMX based explosive: Pressure gauge experiments and modeling

Safety issues related to thermal cook-off are important for handling and storing explosive devices. Violence of an event as a function of confinement is important for prediction of collateral events. There are major issues which require an understanding of the following events: (1) transit to detonation of a pressure wave from a cook-off event, (2) sensitivity of changes in HMX-based explosives with thermally induced phase transitions, and (3) the potential danger of neighboring explosive devices being affected by a cook-off reaction. Results of cook-off events of known size, confinement, and thermal history allow for development and/or calibration of computer models for calculating events that are difficult to measure experimentally. The text was submitted by the authors in English.