Coadsorption of oxygen and carbon monoxide on tungsten: Desorption spectra,electron stimulated desorption and field emission microscopy

CO/W desorption spectra are characterized by an α state and multiple β states; using electron stimulated desorption (ESD) the α state was shown to comprise two sub-states, α₁ and α₂. In this paper the consecutive interactions of O₂ and CO on W are investigated using ESD, flash desorption and field emission microscopy (FEM).Desorption spectra show that the α-CO state is displaced by O₂, in two stages. The ESD probe provides an identification of the first stage with the removal of the α₁-CO state, and energy analysis of ESD ions reveals a large energy shift (～ ? 1.5 eV) during O₂ coadsorption which can be attributed to an incresae in the α₁-CO WC bond length of ～ 0.15 Å. During this O₂-induced displacement, the two β peaks converge into a single peak at the β₁ position; this is ascribed to adatom interactions in the mixed O and C adlayer. Isotope exchange experiments with ²⁸CO and ³⁶O₂ reveal (i) no exchange in the α-CO states, and (ii) complete exchange in the β-CO states, which is consistent with dissociative adsorption in the latter. The amount of coadsorbed O₂ is estimated from these results, and from FEM data: a full monolayer of O adatoms can be coadsorbed on CO-saturated W, but CO pre-adsorption inhibits the formation of W oxides. The β₁-O₂ (ESD active) state also forms on the CO-covered surface: this state is identical in population, ESD cross section and ion energy distribution to β₁-O₂ on clean W, and retains its identity in the mixed layer (it does not undergo isotopic exchange). CO₂ desorption spectra from the mixed layer were also characterised, complete isotopic scrambling being observed.Pre-exposure of tungsten to O₂ inhibits CO adsorption: a monolayer of O₂ is sufficient to prevent CO adsorption, and at low O₂ coverages, every O₂ molecule preadsorbed prevents one CO molecule from adsorbing. Isotopic exchange is again complete in the β states, and a lateral interaction model for desorption kinetics, based on dissociative adsorption in the β-CO state, quantitatively describes the CO desorption spectra.     

Generalization of simulation results practicality of statistical methods

The major purpose of this paper is to evaluate the practical use of statistical techniques in both the generalization or analysis of simulation results, and the design of simulation experiments. This problem is investigated with the help of a real-life system, namely the container terminus of ECT in Rotterdam. This system is modeled by a simulation program. The relationship between the simulation response and its input variables is modeled by a linear regression model: metamodel or auxiliary model. The paper summarizes regression analysis including generalized least squares which might be used for simulation responses with non-constant variances. The validity of the postulated regression metamodel is tested statistically: F- and t-statistics. The selection of the situations to be simulated, is done through experimental design methodology, permitting both quantitative and qualitative factors. The statistical techniques apply not only to simulation but also to real-life experiments.     

Intramolecular Allylations of Carbonions

In the general centaxt of examining a variety of organic, reactions which probably proceed via cyclic transition stares, we predicted scme years ago² that the aniens (II) produced by the action of appropriate bases on allylic esters(I) would undergo intramolecular rearrangement to form the iscmeric carboxylate anions (III).     

Effective synthesis of cyclic peptide yunnanin C and analogues via Ser/Thr ligation (STL)-mediated peptide cyclization

Cyclic peptide yunnanin C isolated from the root of Stellaria yunnanensis was efficiently synthesized in which the linear peptide was prepared by Boc-SPPS and the cyclization was realized by serine/threonine ligation (STL)-mediated cyclization. In addition, nine yunnanin C analogues, including mutations of Tyr7Gly, Tyr7Val, Tyr7Pro, Tyr7Phe, Ser1Thr, Pro2Val, Gly5Pro, Phe6Ala and Ile4Ala, were prepared in the same fashion. Here, we demonstrated that STL-mediated peptide cyclization could be an effective approach to construct cyclic peptides. Except that proline at the C-terminus could retard the cyclization process, cyclization of yunnanin C analogues with various C-terminal amino acids proceeded with fast cyclization rate (<4 h) and only trace amount of dimers (<5%) at a working concentration of 5 mM.     

Targeting choroid plexus epithelia and ventricular ependyma for drug delivery to the central nervous system

Background  

Because the choroid plexus (CP) is uniquely suited to control the composition of cerebrospinal fluid (CSF), there may be therapeutic benefits to increasing the levels of biologically active proteins in CSF to modulate central nervous system (CNS) functions. To this end, we sought to identify peptides capable of ligand-mediated targeting to CP epithelial cells reasoning that they could be exploited to deliver drugs, biotherapeutics and genes to the CNS.     

Stative

Ohne Zusammenfassung     

Hager's Methode der quantitativen Bestimmung von China-Alkalo?den

Ohne ZusammenfassungAus dem Holländischen übersetzt von der Redaction.