Reaktion von Diazoniumsalz mit Tyrosin-Resten in Polypeptide

Ohne Zusammenfassung     

Switchable gas permeability of a polypropylene-liquid crystalline composite film

The development of functionalized polyolefins for use as stimuli-responsive commodity polymers has recently received much attention. In this work, a microporous polypropylene (PP) scaffold is used to align and fortify a smectic liquid crystalline network (LCN) which can switch its gas permeability upon pH changes. The LCN is a photopolymerized liquid crystalline mixture of a dimerized benzoic acid derivative monoacrylate and a diacrylate crosslinker. In the hydrogen-bonded state, the composite membrane shows a high-molecular order and a low permeability for He, N₂, and CO₂ gases. By pH switching from the hydrogen-bonded state to the salt form, the molecular order is reduced, and the gas permeability is increased by one order of magnitude. This increase is mainly attributed to a loss in order of the system, increasing the free volume, resulting in an increased diffusibility. By exposing the composite film to basic or acidic environments, reversible switching between low and high gas permeability states is observed, respectively. The physical constraints imposed by the PP scaffold strengthens the membrane while the reversible switching inside the liquid crystalline polymer is maintained. This switching of gas permeation properties is not possible with the fragile freestanding LCN films alone.     

Eine Vorrichtung zur Destillation im Hochvakuum

Ohne Zusammenfassung     

Crystal Structure Refinement of M(NCNH)2 (M = Fe,Co) Based on Combined Neutron and X‐ray Diffraction Data

The crystal structures of Fe(NCNH)₂ and Co(NCNH)₂, isotypical with Ni(NCNH)₂, have been refined by means of combined X‐ray and neutron powder diffraction data (SPODI, FRM II). The lattice parameters are a = 6.6655(7), b = 8.7923(8), c = 3.3304(3) Å for Fe(NCNH)₂ and a = 6.5696(2), b = 8.8058(2), c = 3.2622(1) Å for Co(NCNH)₂ in the orthorhombic system Pnmm (no. 58). The positions of the hydrogen atoms have been clearly resolved.     

Frameshifting in the p6 cDNA phage display system

Phage display is a powerful technique that enables easy identification of targets for any type of ligand. Targets are displayed at the phage surface as a fusion protein to one of the phage coat proteins. By means of a repeated process of affinity selection on a ligand, specific enrichment of displayed targets will occur. In our studies using C-terminal display of cDNA fragments to phage coat protein p6, we noticed the occasional enrichment of targets that do not contain an open reading frame. This event has previously been described in other phage display studies using N-terminal display of targets to phage coat proteins and was due to uncommon translational events like frameshifting. The aim of this study was to examine if C-terminal display of targets to p6 is also subjected to frameshifting. To this end, an enriched target not containing an open reading frame was selected and an E-tag was coupled at the C-terminus in order to measure target display at the surface of the phage. The tagged construct was subsequently expressed in 3 different reading frames and display of both target and E-tag measured to detect the occurrence of frameshifting. As a result, we were able to demonstrate display of the target both in the 0 and in the +1 reading frame indicating that frameshifting can also take place when C-terminal fusion to minor coat protein p6 is applied.     

Bridging the Gap between the Direct and Hydrocarbon Pool Mechanisms of the Methanol‐to‐Hydrocarbons Process

After a prolonged effort over many years, the route for the formation of a direct carbon?carbon (C?C) bond during the methanol‐to‐hydrocarbon (MTH) process has very recently been unveiled. However, the relevance of the “direct mechanism”‐derived molecules (that is, methyl acetate) during MTH, and subsequent transformation routes to the conventional hydrocarbon pool (HCP) species, are yet to be established. This important piece of the MTH chemistry puzzle is not only essential from a fundamental perspective, but is also important to maximize catalytic performance. The MTH process was probed over a commercially relevant H‐SAPO‐34 catalyst, using a combination of advanced solid‐state NMR spectroscopy and operando UV/Vis diffuse reflectance spectroscopy coupled to an on‐line mass spectrometer. Spectroscopic evidence is provided for the formation of (olefinic and aromatic) HCP species, which are indeed derived exclusively from the direct C?C bond‐containing acetyl group of methyl acetate. New mechanistic insights have been obtained from the MTH process, including the identification of hydrocarbon‐based co‐catalytic organic reaction centers.     

Initial Carbon–Carbon Bond Formation during the Early Stages of the Methanol‐to‐Olefin Process Proven by Zeolite‐Trapped Acetate and Methyl Acetate

Methanol‐to‐olefin (MTO) catalysis is a very active field of research because there is a wide variety of sometimes conflicting mechanistic proposals. An example is the ongoing discussion on the initial C?C bond formation from methanol during the induction period of the MTO process. By employing a combination of solid‐state NMR spectroscopy with UV/Vis diffuse reflectance spectroscopy and mass spectrometry on an active H‐SAPO‐34 catalyst, we provide spectroscopic evidence for the formation of surface acetate and methyl acetate, as well as dimethoxymethane during the MTO process. As a consequence, new insights in the formation of the first C?C bond are provided, suggesting a direct mechanism may be operative, at least in the early stages of the MTO reaction.