BaIr0,67Be0,33O3: Eine stabilisierte kubische Form von BaIrO3

Inhaltsübersicht. Es ist gelungen, ein durch BeO stabilisiertes Bariumoxoiridat der Zusammensetzung BaIr_0,67Be_0,33O₃ in der Kristallform eines kubischen Perowskits mit kleiner Elementarzelle erstmals darzustellen. Raumgruppe O¹_h–Pm3m, a = 4,1009 Å, Z = 1. Ir⁵⁺ und Be² + besetzen die Oktaederposition des Perowskits statistisch. BaIr_0,67Be_0,33O₃: A Stabilized Cubic Form of BaIrO₃ For the first time it was possible to prepare a new barium-oxoiridate of the formula BaIr_0,67Be_0,33O₃, stabilized by BeO. It crystallizes in a small cubic unit cell of the perovskite type. Space group O¹_h–Pm3m; a = 4.1009 Å; Z = 1. Ir⁵⁺ and Be²⁺ occupy the octahedra positions of the perovskite structure statistically.     

On the loss of a benzyl radical from the molecular ion of α,ω -dibenzyloxyalkanes : Evidence for a benzyl cation transfer in an SNi-type reaction,revealed by a simultaneous D- and 18O-labelling

The molecular ions of the title compounds appear to lose a benzyl radical, which must be due to the presence of two benzyloxy groups, as benzylalkyl ethers do not exhibit such an expulsion upon electron impact. The results of the partition of the labels deuterium and ¹⁸O in the ions m/e 107 (protonated benzaldehyde) and [M-benzyl-benzaldehyde]⁺ put forward evidence that this process is initiated by a successive migration of a benzylic H atom to the opposite ether function and transfer of the benzyl cation from this protonated O atom to the uncharged O atom in an S_Ni-type reaction (cf Scheme 5).     

Thermozymes and their applications

Enzymes from thermophilic microorganisms, thermozymes, have unique characteristics such as temperature, chemical, and pH stability. They can be used in several industrial processes, in which they replace mesophilic enzymes or chemicals. Thermozymes are often used when the enzymatic process is compatible with existing (high-temperature) process conditions. The main advantages of performing processes at higher temperatures are reduced risk of microbial contamination, lower viscosity, improved transfer rates, and improved solubility of substrates. However, cofactors, substrates, or products might be unstable or other side reactions may occur. Recent developments show that thermophiles are a good source of novel catalysts that are of great industrial interest. Thermostable polymer-degrading enzymes such as amylases, pullulanases, xylanases, proteases, and cellulases are expected to play an important role in food, chemical, pharmaceutical, paper, pulp, and waste-treatment industries. Considerable research efforts have been made to better understand the stability of thermozymes. There are no major conformational differences with mesophilic enzymes, and a small number of extra salt bridges, hydrophobic interactions, or hydrogen bounds seem to confer the extra degree of stabilization. Currently, overexpression of thermozymes in standard Escherichia coli allows the production of much larger quantities of enzymes, which are easy to purify by heat treatment. With wider availability and lower cost, thermophilic enzymes will see more application in industry.     

Characterization of typical chemical background interferences in atmospheric pressure ionization liquid chromatography-mass spectrometry

The structures and origins of typical chemical background noise ions in positive atmospheric pressure ionization liquid chromatography/mass spectrometry (API LC/MS) are investigated and summarized in this study. This was done by classifying chemical background ions using precursor and product ion scans on most abundant background ions to draw a family tree of the commonly occurring chemical background ions. The possible structures and the origins of the major chemical background noise are clearly revealed in the family trees. In agreement with some suggestions in the literature, the chemical background ions studied so far can be classified mainly as either ions of contaminants (or their degradation fragments) or cluster-related ones. A significant contribution from the contaminants (airborne, from tubing and/or solvents) from plasticizer additives (phthalates, phenyl phosphates, sebacates and adipates, etc.) and silicones is concluded. These ions of contaminants can also serve as nuclei for the clustering of HPLC solvent or additives, such as water and acetic acid, thereby leading to a second family of background ions. This study explains the persistence of some chemical background noise even under fairly strong declustering conditions in API LC/MS. One of the other interesting conclusions is that there is a clear difference in structures between the chemical background ions and the protonated analytes generated under atmospheric pressure ionization. This conclusion will contribute to the on-going research efforts to exclusively remove or reduce the interference of chemical background noise in API LC/MS.     

The response surface of an amperometric flow cell detector based on a rotating disk electrode for h.p.l.c.and continuous flow analysis

The amperometric detector flow cell based on a rotating disk electrode can be used in conjunction with continuous flow analysis as well as with h.p.l.c. The response surface of the detector as a function of flow rate, electrode rotation speed and concentration of electroactive species (hexacyanoferrate(II)) is measured in combination with continuous flow analysis. When the electrode is stationary, the detector behaves as a wall-jet detector. Rotating the electrode results in a completely different hydrodynamic flow pattern in the flow cell. The response becomes independent of the flow rate and is linearly related to the electrode rotation speed. The influence of nozzle height in the flow cell on the detector response in combination with h.p.l.c. is described. With certain combinations of nozzle height and rotation speeds, a favourable flow pattern appears to be created in the cell and the sensitivity is increased considerably.     

In vitro mimicry of metabolic oxidation reactions by electrochemistry/mass spectrometry

The aim of these studies was to investigate the scope and limitations of electrochemistry on-line with mass spectrometry as a quick and convenient way to mimic phase I oxidative reactions in drug metabolism. A compound with previously reported in vitro and in vivo metabolism, the dopamine agonist 2-(N-propyl-N-2-thienylethylamino)-5-hydroxytetralin, was examined in an electrochemistry/mass spectrometry (EC/MS) system. The previously reported N-dealkylation was mimicked by the electrochemical cell while the oxidation of the phenol function was not fully mimicked by the EC/MS system, since the catechol and p-hydroquinone formed were immediately oxidized to the corresponding quinones. Since cytochrome P450 isoenzymes are the most important enzymes in phase I oxidative metabolism, two standard substrates used for the characterization of those enzymes, lidocaine and 7-ethoxycoumarin, were tested in the EC/MS system. The electrochemical cell was capable of mimicking the N-dealkylation of lidocaine but, under the conditions used in our experiments, the O-deethylation of 7-ethoxycoumarin could not be simulated in the electrochemical cell.     

Comparison of thermospray and ion spray mass spectrometry in an atmospheric pressure ion source

Ion spray is an approach to liquid chromatography, mass spectrometry which includes features common to the electrospray and ion evaporation interfaces. Thermospray is a liquid chromatographic/mass spectrometric technique which utilizes heat and electrolytes in the mobile phase to generate sample ions. In this paper the operation of these two techniques at atmospheric pressure are compared with respect to the effects of solvent composition and electrolyte ion concentration for the production of ions from compounds that are ionized in solution (safranin orange, acid black 1 and testosterone sulfate) and un-ionized in solution (methyl red, adenosine and diethylstilbestrol). The results indicate that at atmospheric pressure ion spray produces ions by the ion evaporation mechanism while thermospray produces ions by both gas-phase chemical ionization and ion evaporation processes.