We describe a simple method for the synthesis of hindered N-aryl diamines. The diastereoselectivity for these processes are relatively low but the diamines can be separated using either chromatography or selective crystallization. Separation of enantiomers can be accomplished using HPLC equipped with a chiral stationary phase. 相似文献
We demonstrate site-specific reporter labeling of proteins within live cells. By accessing the coenzyme A (CoA) metabolic pathway with a cell-permeable pantetheine analogue, we deliver CoA-bound reporter molecules for post-translational protein modification in vivo. These methods may be applied to natural product pathway manipulation as well as applications in conventional molecular and cellular biology. 相似文献
The 70 e V-electron impact mass spectra of the C7–C10n-alkynes have been determined as well as the metastable ion spectra of the molecular ions and the [CS2]+ and [N2O]+ charge exchange mass spectra of the C7-C9n-alkynes. The metastable ion mass spectra provide only a limited opportunity to distinguish between isomers; however, the 70-eV EI mass spectra of isomeric compounds permit a ready distinction between isomers. The [CS2]+ charge exchange mass spectra of isomeric compounds also show substantial differences. The [N2O]+ charge exchange mass spectra do not show the enhancement of β-fission fragments observed in field ionization experiments, despite representing ions of similar internal energy, and it is concluded that field dissociation is responsible for the β-fission fragments in the field ionization experiments. 相似文献
This paper investigates the bifurcation behaviour of a model oxidation reaction in a continuously stirred tank reactor (CSTR). We assume that two gaseous chemical species are pumped separately into the CSTR, at constant total pressure, reacting to produce an inert product. The reaction is assumed to be a single step reaction that is described by Arrhenius kinetics. It is capable of producing oscillatory behaviour as well as steady state multiplicity in certain parameter regions. Bifurcation diagrams in various control parameter spaces are presented. We show that the system always possesses a globally attracting invariant region. The equivalence of a CSTR having n feed streams and the one pipe version, by appropriate rescaling, is also discussed. 相似文献
The tagged particle BBGKY hierarchy is systematically expanded in inverse powers of the square root of the particle mass. In the Brownian limit, for fixed Knudsen number, the hierarchy reduces to the Brownian limit of the repeated ring equation which itself reduces to the Fokker-Planck equation. The friction coefficient of the Fokker-Planck equation is found to be a functional of the solution of Dorfman, van Beijeren, and McClure's extended Boltzmann equation for a fixed object in a flowing gas. As a consequence, the tagged particle diffusion coefficient calculated in the Brownian limit of the repeated ring equation is valid for all particle sizes. 相似文献
Constrained phenylalanine derivatives containing hydrophobic groups and hydrogen bond acceptor and/or donor functionalities were synthesized through a tandem palladium-mediated Heck reaction followed by a rhodium(II)-catalyzed asymmetric hydrogenation. Aryl bromides were found to be better substrates in providing products with higher purity and in good yield. The cesium carbonate-mediated cyclization proceeded smoothly in good yield and optical purity. Aryl iodides reacted selectively over bromides under Jeffery-type conditions (Pd(OAc)2, Bu4NCl, Et3N) providing an opportunity for further metal-mediated functionalization. 相似文献
This paper extends a previous study (Pehrsson and Mercer, submitted to Surf. Sci.) on unheated, hydrogenated, natural diamond (100) surfaces oxidized with thermally activated oxygen (O*2). In this paper, the oxidation is performed at substrate temperatures from Tsub=24 to 670°C. The diamond surface composition and structure were then investigated with high resolution electron energy loss spectroscopy (HREELS), Auger electron spectroscopy (AES), electron loss spectroscopy (ELS) and low energy electron diffraction (LEED).
The oxygen coverage (θ) increased in two stages, as it did during oxidation at T<80°C. However, there are fundamental differences between the oxidation of nominally unheated and heated diamond surfaces. This difference is attributed to simultaneous adsorption and rapid desorption of oxygen species at higher temperatures; the desorption step is much slower without heating. The initial oxidation rates were similar regardless of the substrate temperatures, but the peak coverage (θ) was lower at higher temperatures. For example, θ plateaued at 0.4±0.1 ML at 600°C. The lower saturation coverage is again attributed to oxygen desorption during oxidation. Consistent results were obtained on fully oxidized surfaces, which when heated in vacuum to Tsub=600°C, lost 60% of their adsorbed oxygen. ELS revealed few C=C dimers on the oxidized surfaces, and more graphitization than on unheated surfaces. Oxidation at elevated temperatures also increased the carbonyl to ether ratio, reflecting etching-induced changes in the types of surface sites. The carbonyl and C–H stretch frequencies increased with oxygen dose due to formation of higher oxidation states and/or hydrogen bonding between adjacent groups. The oxygen types did not interconvert when the oxidized surfaces were heated in vacuum. Oxygen desorption generated a much more reactive surface than heating-induced dehydrogenation of the smooth, hydrogenated surface. 相似文献