Ab initio study of the inversion barrier in NF3+

Ab initio Hartree–Fock, Møller–Plesset perturbation theory (MP 2), and quadratic configuration interaction, using single and double substitutions (QCISD ), calculations were carried out for the NF₃⁺ ion. Optimized structures were examined at the various levels of theory. Calculation of the inversion barrier height shows the importance of optimizing the geometry at the post-Hartree–Fock level and the inclusion of polarization functions. The best calculated inversion barrier was 13.3 kcal/mol, compared to an experimental value of 17.3 kcal/mol. The dissociation transition state was computed to determine the well depth of the NF₃⁺ ion and its stability toward dissociation. The computed well depth was 28 and 48 kcal/mol at the SCF and MP 2 levels, respectively. © 1994 John Wiley & Sons, Inc.     

Post-source decay in the analysis of polystyrene by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Various secondary series are observed in matrix-assisted laser desorption/ionization (MALDI) time-of-flight mass spectra of polystyrene. The number and positions of the series depend on the choice of matrix and added cation. For a given treatment, series observed in linear mode are not necessarily observed in reflectron mode, and vice versa. Post-source decay analysis was used to determine that the secondary series arise at least in part from formation and decay of adducts of polystyrene with matrix species. There is some treatment-to-treatment variation, but adduct formation and decay were observed for all tested treatments. The multiplicity of secondary series makes it unclear whether post-source decay occurs for the main series (polystyrene + cation)⁺ ions under the conditions normally used for polystyrene analysis. Such ions do undergo post-source decay at laser fluences greater than normally used. Although only polystyrene was investigated in this work, other polymers may also produce adduct and decay series in MALDI analysis. Their presence can mask the presence of minor components in a sample, but at least as observed here, do not have a strong influence on molecular mass determinations.     

Eine einfache chromatographische Methode zur Charakterisierung bitumin?ser Stoffe

Zusammenfassung Die Methode der Ringpapierchromatographie unter Anwendung von UV-Licht als einfachem Hilfsmittel zur Unterscheidung organischen Materials wurde hinsichtlich der Möglichkeit überprüft, zahlenmäßig greifbare Ergebnisse zu erhalten, die eine sichere Klassifizierung und Unterscheidung bituminöser Stoffe ermöglichen. Es wurde gefunden, daß für eine gute Reproduzierbarkeit der Ergebnisse die gleichmäßige Aufgabe der Lösung auf das Papier wesentlich ist. Ein äußerst gleichmäßiger Zufluß, der mit der Sauggeschwindigkeit des Papieres korrespondiert, konnte mit Hilfe eines Mikrodosiergerätes, das von einem Motor gleichmäßig angetrieben wurde, erzielt werden. Die erhaltenen Flächen für die verschiedenen Substanzgruppen stellen ein relatives, gut reproduzierbares Maß für die Zusammensetzung der untersuchten Proben dar.Herrn Prof. Dr. W. Fischer zum 60. Geburtstag gewidmet.     

Direct immobilization of native yeast iso-1 cytochrome C on bare gold: fast electron relay to redox enzymes and zeptomole protein-film voltammetry

Cyclic voltammetry shows that yeast iso-1-cytochrome c (YCC), chemisorbed on a bare gold electrode via Cys102, exhibits fast, reversible interfacial electron transfer (k(0) = 1.8 x 10(3) s(-1)) and retains its native functionality. Vectorially immobilized YCC relays electrons to yeast cytochrome c peroxidase, and to both cytochrome cd(1) nitrite reductase (NIR) and nitric oxide reductase from Paracoccus denitrificans, thereby revealing the mechanistic properties of these enzymes. On a microelectrode, we measured nitrite turnover by approximately 80 zmol (49 000 molecules) of NIR, coadsorbed on 0.65 amol (390 000 molecules) of YCC.     

Computation of Entropy Production in Stratified Flames Based on Chemistry Tabulation and an Eulerian Transported Probability Density Function Approach

This contribution presents a straightforward strategy to investigate the entropy production in stratified premixed flames. The modeling approach is grounded on a chemistry tabulation strategy, large eddy simulation, and the Eulerian stochastic field method. This enables a combination of a detailed representation of the chemistry with an advanced model for the turbulence chemistry interaction, which is crucial to compute the various sources of exergy losses in combustion systems. First, using detailed reaction kinetic reference simulations in a simplified laminar stratified premixed flame, it is demonstrated that the tabulated chemistry is a suitable approach to compute the various sources of irreversibilities. Thereafter, the effects of the operating conditions on the entropy production are investigated. For this purpose, two operating conditions of the Darmstadt stratified burner with varying levels of shear have been considered. The investigations reveal that the contribution to the entropy production through mixing emerging from the chemical reaction is much larger than the one caused by the stratification. Moreover, it is shown that a stronger shear, realized through a larger Reynolds number, yields higher entropy production through heat, mixing and viscous dissipation and reduces the share by chemical reaction to the total entropy generated.     

Fortschritte in der Auswertung von Markierungsversuchen an dynamischen Systemen

In einem dynamischen System vollziehen sich kontinuierlich ablaufende Stoffwandlungen, deren Ausgangsstoffe dem System ständig zufließen und deren Folgeprodukte das System kontinuierlich verlassen. Es wird das Verhalten eines solchen Systems mit drei Pools bei Markierungsexperimenten untersucht. Die Ergebnisse dieser mathematischen Untersuchungen werden auf die Erforschung des Stickstoffstoffwechsels laktierender Rinder mit Hilfe des stabilen Isotops ¹⁵N angewandt. In diesem Fall enthält das dynamische System zwei kleine stoffwechselaktive Pools und einen großen, niclit intensiv am Stoffwechsel beteiligten Körpereiweiβ-Pool.