Modification of a spectrophotofluorometric method of analyzing serotonin, norepinephrine, and dopamine in one brain sample

A method is presented for analyzing 5-HT, NE, and DA in a single brain sample. The method utilizes slightly larger, more easily handled volumes that can be used in standard size cuvets. Although the method may be slightly more time consuming than other reported methods, separation and good recovery of all three amines can be attained.     

Biorthogonalentwicklungen analytischer Funktionen nach Eigenlösungen linearer Differentialgleichungen

Ohne Zusammenfassung     

Untersuchungen der Reaktionsprodukte von Isocyanaten mit Hydroxylamin

Investigations of the Products of Isocyanates with Hydroxylamine The reactions of isocyanates with hydroxylamine give rise to several compounds according to the different conditions involved when starting with the primary reaction products, the hydroxy-ureas. The pure compounds have been isolated. An interesting reaction of N-phenyl-N′-phenylcarbamoyloxyurea with sodium hydroxide has been observed. This compound is converted to 3-hydroxy-1, 5-diphenylbiuret under conditions described.     

Mechanism and kinetics of the catalytic CO-H2 reaction: An approach by chemical transients and surface relaxation spectroscopy

The aim of this paper is to demonstrate the importance of providing time-resolved information in catalysis research. Two truly in situ methods will be presented and compared for their merits and drawbacks: chemical transient kinetics (CTK) and pulsed field desorption mass spectrometry (PFDMS). The presentation will be given by way of example choosing the syngas (CO/H2) reaction over cobalt-based catalysts as a catalytic process. Despite numerous efforts in the past, the mechanism of this reaction is still under debate. In CTK the reaction is studied on a metal-supported catalyst under flow conditions in a pressure range extending from atmospheric pressure down to 100 Pa. Sudden changes in the partial pressures of the reactants then allow following the relaxation to either steady-state conditions ("transients") or cleanoff ("back transients"). In PFDMS short field pulses of several volts per nanometer are applied to a model catalyst which resembles a single metal particle grain (a "tip"). These pulses intervene during the ongoing reaction under flow conditions at pressures ranging from 10(-1) to 10(-5) Pa and cause field desorption of adsorbed species. This method is particularly suited to detect reaction intermediates in a time-dependent manner since the repetition frequency of the pulses can be systematically varied. It is shown that both methods lead to complementary results. While CTK allows conclusions on the mechanism of CO hydrogenation by following the time-dependent formation of hydrocarbon species, PFDMS provides insight into the initial steps leading to adsorbed CxHy species. A quantitative assessment of the CTK data allows the demonstration that the catalyst under working conditions is in an oxidized rather than metallic state. The initial steps to oxidation are also traced by PFDMS. Most importantly, however, CTK results allow formulation of a reaction mechanism that is common for both hydrocarbon and oxygenate formation and is based on the occurrence of a formate-type species as the most abundant surface intermediate.     

Exponential decay lifetimes of excitons in individual single-walled carbon nanotubes

The dynamics of excitons in individual semiconducting single-walled carbon nanotubes was studied using time-resolved photoluminescence (PL) spectroscopy. The PL decay from tubes of the same (n,m) type was found to be monoexponential, however, with lifetimes varying between less than 20 and 200 ps from tube to tube. Competition of nonradiative decay of excitons is facilitated by a thermally activated process, most likely a transition to a low-lying optically inactive trap state that is promoted by a low-frequency phonon mode.     

Productive chloroarene C-cl bond activation: palladium/phosphine-catalyzed methods for oxidation of alcohols and hydrodechlorination of chloroarenes

The palladium/phosphine-catalyzed productive chloroarene C-Cl bond activation provides general, efficient, and functional group friendly methods for the selective oxidation of alcohols and the hydrodechlorination of chloroarenes.     

Bromine catalyzed conversion of S-tert-butyl groups into versatile and, for self-assembly processes accessible, acetyl-protected thiols

The facile and efficient conversion of a tert-butyl protecting group to an acetyl protecting group for thiols by catalytic amounts of bromine in acetyl chloride and the presence of acetic acid has been developed. The fairly mild reaction conditions are of particular interest for new protecting group strategies for sulfur functionalised target structures.     

Widely tunable sub-30-fs pulses from a compact erbium-doped fiber source

Coupling femtosecond light pulses from an all-fiber Er:laser system into a dispersion-shifted and highly non-linear fiber, we generate output spectra exhibiting two broadband and mutually coherent maxima. Depending on the chirp of the input pulse, the spectral separation is easily tunable over a wide range up to values exceeding 100 THz. In this way, the source provides access to an ultrabroadband wavelength interval from 1130 to 1950 nm. Because of soliton effects, the long-wave component exhibits a transform-limited pulse width of 40 fs directly after the nonlinear element. The high-frequency part propagating in the dispersive regime is recompressed to pulse durations as short as 24 fs with an optimized prism sequence.     

A high-throughput NMR-based ee-assay using chemical shift imaging

The throughput of a previously described NMR-based -assay has been increased by a factor of at least 4 as a consequence of adapting the system to chemical shift imaging; by using a 19-capillary system the enantiomeric purity of 5600 samples can be measured per day.