Coordination and Redox Isomerization in the Reduction of a Uranium(III) Monoarene Complex

Synthetic studies on the redox chemistry of trivalent uranium monoarene complexes were undertaken with a complex derived from the chelating tris(aryloxide)arene ligand (^Ad,MeArO)₃mes^3?. Cyclic voltammetry of [{(^Ad,MeArO)₃mes}U^III] ( 1 ) revealed a nearly reversible and chemically accessible reduction at ?2.495 V vs. Fc/Fc⁺—the first electrochemical evidence for a formally divalent uranium complex. Chemical reduction of 1 indicates that reduction induces coordination and redox isomerization to form a uranium(IV) hydride, and addition of a crown ether results in hydride insertion into the coordinated arene to afford uranium(IV) complexes. This stoichiometric reaction sequence provides structural insight into the mechanism of arene functionalization at diuranium inverted sandwich complexes.     

Structural response of different Lewis number premixed flames interacting with a toroidal vortex

Simultaneous measurements of temperature, CH* and OH* chemiluminescent species are carried out to explore the impact of stretch rate and curvature on the structure of premixed flames. The configuration of an initially flat premixed flame interacting with a toroidal vortex is selected for the present study and reasons for this choice are discussed. Lewis number effects are assessed by comparing methane and propane flames. It is emphasized that the flame structure experiences very strong variations. In particular, the flame is shrunk (broadened) in the initial (final) period of the interaction with the vortex where strain rate (curvature) contribution of the stretch rate is predominant. By further analysing independently the thickness of the preheat and reaction zones, it is shown that for propane flames, not only the former but also the latter is significantly altered in zones where the flame curvature is negative. Changes in the reaction zone properties are further emphasized using CH* and OH* radicals. It is demonstrated that higher thermal diffusivity plays a significant role around curved regions, in which the enhanced diffusion of heat leads to a strong increase of CH* compared to OH* intensity. As an overall conclusion, this study suggests that it would be interesting to reassess the internal flame structure at lower and moderate Karlovitz numbers since changes might appear for a moderate vortex intensity with typical size much larger than the flame thickness.     

ESI-MS/MS library of 1,253 compounds for application in forensic and clinical toxicology

An electrospray ionization tandem mass spectrometry (ESI-MS/MS) library which contains over 5,600 spectra of 1,253 compounds relevant in clinical and forensic toxicology has been developed using a hybrid tandem mass spectrometer with a linear ion trap. Pure compound solutions—in some cases solutions made of tablets—were prepared and 1 to 2,000 ng of each compound were injected into the system using standard reversed-phase analytical columns with gradient elution. To obtain maximum mass spectral information enhanced product ion spectra were acquired with positive and/or negative ionization at low, medium, and high collision energies and additionally applying collision energy spread. In this mode, all product ions generated by the different collision energies are trapped in the linear ion trap prior to their detection. The applicability of the library for other types of hybrid tandem mass spectrometers with a linear ion trap of the same manufacturer as well as a standard triple-quadrupole tandem mass spectrometer has been investigated with a selection of compounds. The spectra of the developed library can be used to create methods for target analysis, either screening methods or quantitative procedures by generating transitions for multiple reaction monitoring. For those procedures, suitable transitions and convenient collision energies are selected from the library. It also has been utilized to identify compounds with a multi target screening approach for clinical and forensic toxicology with a standardized and automated system. The novel aspects compared to our former library produced with a standard triple-quadrupole mass spectrometer are the enlargement of the ESI-MS/MS library and the additional acquisition of spectra with collision energy spread.     

Eine Schnellmethode zur Bestimmung von Salz in Butter und Margarine

Ohne Zusammenfassung     

Untersuchung von Fetten

Ohne Zusammenfassung