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41.
The spatial relaxation of electrons to homogeneous states under the action of space-independent electric fields is investigated
in helium, krypton, and N2 plasmas for various electric field strengths. These investigations are based on a new method recently developed for solving
the one-dimensional inhomogeneous electron Boltzmann equation in weakly ionized, collision-dominated plasmas. Elastic as well
as conservative inelastic collisions of electrons with gas atoms have been included in the kinetic treatment. The spatial
relaxation is caused by an imposed direct disturbance in the velocity distribution of the electrons on a spatial boundary.
A pronounced dependence of the relaxation structure and the resultant relaxation length on the atomic data of the electron
collision processes in different gases has been found. Furthermore the relaxation process sensitively depends on the electric
field strength in the region of medium field values. 相似文献
42.
Fazil O. Gülaar Franois Mermound F. Johann Winkler Armand Vuchs 《Helvetica chimica acta》1984,67(2):488-501
Ammonia chemical ionization (CI) mass spectra of various open-chain, cyclic and unsaturated C5- to C10-alcohols were obtained at source temperatures ranging from 60° to 250°C. The reactivity of the ammonia adduct ion MNH and its fragmentation channels are characteristic for substrate structure. Although strongly temperature-dependent, the spectra give nevertheless information on the OH-group environment as well as on the C-skeleton at any source temperature. Primary, secondary and tertiary alcohols as well as allylic and simple olefinic alcohols can be distinguished by their spectra, which show ammonium adduct ions [MNH4]+, adduct dehydrogenation ions [MNH4-H2], ammonium substitution ions [MNH4-H2O]+ and [M-OH]+-ions as the main characteristic peaks. Moreover, konfigurational assignments of stereoisomeric alcohols are possible for larger substrate-size and source-temperature ranges than with isobutane CI mass spectrometry. Homologous M NH-ions show molecular-size control of fragmentation and linear MNH-ions are less stable than branched isomers due to incomplete energy randomization. 相似文献
43.
In Arbuzov-type reactions CFnCl3?nSCl reacts with ROPCl2 (R = CH3, C2H5) to give CFnCl3?nSP(O)Cl2 (n = 3,2,1,0). The corresponding reaction with CF3SeX (X = Cl, Br) produces CF3SeP(O)Cl2 in good yields only in the presence of catalysts such as SbCl5 or BCl3. Reactions between P4 and the sulfenylchlorides produce (CFnCl3?nS)xPCl3?n (n = 3,2,1 and x = 1,2). On heating CFn′ Cl3?n′ SP(O)Cl2 (n′ = 2,1,0) decompose to P(O)Cl3 and SCFn′ Cl2?n′. During this process fluorination of P(O)Cl3 to P(O)F3 by SCF2 is observed. A Cl/Br exchange between CFnCl3?nSP(O)Cl2 (n = 3,2) and PBr3 was proved 19F? and 31P-NMR-spectroscopically.Chemical and physical properties of the newly synthesized compounds will be discussed. 相似文献
44.
Miller JE Grădinaru C Crane BR Di Bilio AJ Wehbi WA Un S Winkler JR Gray HB 《Journal of the American Chemical Society》2003,125(47):14220-14221
Near-UV irradiation of structurally characterized [Re(I)(CO)3(1,10-phenanthroline)(Q107H)](W48F/Y72F/H83Q/Y108W)AzM(II) [Az = Pseudomonas aeruginosa azurin, M = Cu, Zn]/[Co(NH3)5Cl]Cl2 produces a tryptophan radical (W108*) with unprecedented kinetic stability. After rapid formation (k = 2.8 x 106 s-1), the radical persists for more than 5 h at room temperature in the folded ReAzM(II) structure. The absorption spectrum of ReAz(W108*)M(II) exhibits maxima at 512 and 536 nm. Oxidation of K4[Mo(CN)8] by ReAz(W108*)Zn(II) places the W108*/W108 reduction potential in the protein above 0.8 V vs NHE. 相似文献
45.
[reaction: see text] The stereoselective aldol reaction of 3-silyloxyfurans with aldehydes in the presence of a Lewis acid is described. N-Bromosuccinimide (NBS)-mediated cyclization of the aldol product leads to the formation of the 2,7-dioxa-bicyclo[2.2.1]heptan-3-one ring system, which represents the formal product of hetero Diels-Alder reaction of the furan with the aldehyde. 相似文献
46.
Osmium(II) Phthalocyanines: Preparation and Properties of Di(acido)phthalocyaninatoosmates(II) “H[Os(X)2Pc2?]” (X = Br, Cl) reacts in basic medium or in the melt with (nBu4N)X forming less stable, diamagnetic, darkgreen (nBu4N)2[Os(X)2Pc2?]. Similar dicyano and diimidazolido(Im) complexes are formed by the reaction of “H[Os(Cl)2Pc2?]” with excess ligand in the presence of [BH4]?. The cyclic voltammograms show up to three quasireversible redoxprocesses: E1/2(I) = 0.13 V (X = CN), ?0.03 V (Im), ?0.13 V (Br) resp. ?0.18 V (Cl) is metal directed (OsII/III), E1/2(II) = 0.69 V (Cl), 0.71 V (Br), 0.83 V (CN), 1.02 V (Im) is ligand directed (Pc2?/?) and E1/2(III) = 1.17 V (Cl) resp. 1.23 V (Br) is again metal directed (OsIII/IV). Between the typical “B” (~16.2 kK) and “Q” (~29.4 kK), “N regions” (~34.1 kK) up to seven strong “extra bands” of the phthalocyanine dianion (Pc2?) are observed in the uv-vis spectrum. Within the row CN > Im > Br > Cl, most of the bands are shifted slightly, the “extra bands” considerably more to lower energy in correlation with E1/2(I). The vibrational spectra are typical for the Pc2? ligand with D4h symmetry. M.i.r. bands at 514, 909, 1 173 and 1 331 cm?1 are specific for hexa-coordinated low spin OsII phthalocyanines. In the resonance Raman (r.r.) spectra polarized, depolarized or anomalously polarized deformation and stretching vibrations of the Pc2? ligand will be selectively enhanced, if the excitation frequency coincides with “extra bands”. With excitation at ~19.5 kK the intensity of the symmetrical Os? X stretching vibration at 295 cm?1 (X = Cl), 252 cm?1 (X = Im) and 181 cm?1 (X = Br) is r.r. enhanced, too. The asymmetrical Os? X stretching vibration is observed in the f.i.r. spectrum at 345 cm?1 (X = CN), 274 cm?1 (X = Cl), 261 cm?1 (X = Im) and 200 cm?1 (X = Br). 相似文献
47.
Krauth-Siegel RL Bauer H Schirmer RH 《Angewandte Chemie (International ed. in English)》2005,44(5):690-715
Parasitic diseases such as sleeping sickness, Chagas' heart disease, and malaria are major health problems in poverty-stricken areas. Antiparasitic drugs that are not only active but also affordable and readily available are urgently required. One approach to finding new drugs and rediscovering old ones is based on enzyme inhibitors that paralyze antioxidant systems in the pathogens. These antioxidant ensembles are essential to the parasites as they are attacked in the human host by strong oxidants such as peroxynitrite, hypochlorite, and H2O2. The pathogen-protecting system consists of some 20 thiol and dithiol proteins, which buffer the intraparasitic redox milieu at a potential of -250 mV. In trypanosomes and leishmania the network is centered around the unique dithiol trypanothione (N1,N8-bis(glutathionyl)spermidine). In contrast, malaria parasites have a more conservative dual antioxidative system based on glutathione and thioredoxin. Inhibitors of antioxidant enzymes such as trypanothione reductase are, indeed, parasiticidal but they can also delay or prevent resistance against a number of other antiparasitic drugs. 相似文献
48.
Zusammenfassung Es werden eine einfache Apparatur für nichtisotherme kinetische Messungen und Auswertungsverfahren mit Hilfe eines elektronischen Digitalrechners beschrieben. Die Meßmethode wurde an Diels-Alder-Reaktionen mit Nitrosoverbindungen erprobt; sie eignet sich gut zur raschen Ermittlung von Reaktionskonstanten nach Hammett.
Herrn H. Ebert sei für die Hilfe beim Aufbau der Apparatur vielmals gedankt, der Deutschen Forschungsgemeinschaft für die großzügige Unterstützung durch Sachund Geldmittel, dem Leibniz-Rechenzentrum der Bayrischen Akademie der Wissenschaften für die Rechenerlaubnis am Digitalrechner TR 4. 相似文献
Summary A simple apparatus is described for non-isothermal kinetic measurements, together with methods for interpreting the data using a digital computer. The method is tested for Diels-Alder reactions with nitroso compounds; it is useful for rapidty determining values of Hammett's reaction constants.
Herrn H. Ebert sei für die Hilfe beim Aufbau der Apparatur vielmals gedankt, der Deutschen Forschungsgemeinschaft für die großzügige Unterstützung durch Sachund Geldmittel, dem Leibniz-Rechenzentrum der Bayrischen Akademie der Wissenschaften für die Rechenerlaubnis am Digitalrechner TR 4. 相似文献
49.
Charles J. Colbourn Dean G. Hoffman Kevin T. Phelps Vojtěch Rödl Peter M. Winkler 《Combinatorica》1991,11(3):207-218
We prove that the number oft-wise balanced designs of ordern is asymptotically
, provided that blocks of sizet are permitted. In the process, we prove that the number oft-profiles (multisets of block sizes) is bounded below by
and above by
for constants c2>c1>0. 相似文献
50.
Rhodium-Katalysierte Isomerisierungen von 2-Methylidenglutarsäureestern zu Methylglutaconsäureestern
The Rhodium(III)-catalyzed thermal isomerization of 2-methylidenglutaric acid esters affords predominantly mixtures of cis/trans-2-methylglutaconic acid esters ( 2, 3 ) which upon slow distillation isomerize completely into the cis-esters ( 2 ). Saponification of 2 yields trans-2-methylglutaconic acid ( 5 ). Attempts to prepare the acid chloride of 5 produces 6-chloro-5-methylpyrone-2 ( 9 ) or 6-chloro-3-methylpyrone-2 ( 10 ) which react with anilines to N-substituted derivatives of trans-4-methylglutaconic acid amides ( 11 ). The thermal isomerizations of the respective esters are discussed in terms of 1,5-hydrogen shifts in their ester enol structures. 相似文献