Study of (cyclic peptide)-polymer conjugate assemblies by small-angle neutron scattering

We present a fundamental study into the self-assembly of (cyclic peptide)–polymer conjugates as a versatile supramolecular motif to engineer nanotubes with defined structure and dimensions, as characterised in solution using small-angle neutron scattering (SANS). This work demonstrates the ability of the grafted polymer to stabilise and/or promote the formation of unaggregated nanotubes by the direct comparison to the unconjugated cyclic peptide precursor. This ideal case permitted a further study into the growth mechanism of self-assembling cyclic peptides, allowing an estimation of the cooperativity. Furthermore, we show the dependency of the nanostructure on the polymer and peptide chemical functionality in solvent mixtures that vary in the ability to compete with the intermolecular associations between cyclic peptides and ability to solvate the polymer shell

Enzymatic Chemoselective Aldehyde-Ketone Cross-Couplings through the Polarity Reversal of Methylacetoin

The thiamine diphosphate (ThDP) dependent enzyme acetoin:dichlorophenolindophenol oxidoreductase (Ao:DCPIP OR) from Bacillus licheniformis was cloned and overexpressed in Escherichia coli. The recombinant enzyme shared close similarities with the acetylacetoin synthase (AAS) partially purified from Bacillus licheniformis suggesting that they could be the same enzyme. The product scope of the recombinant Ao:DCPIP OR was expanded to chiral tertiary α-hydroxy ketones through the rare aldehyde-ketone cross-carboligation reaction. Unprecedented is the use of methylacetoin as the acetyl anion donor in combination with a range of strongly to weakly activated ketones. In some cases, Ao:DCPIP OR produced the desired tertiary alcohols with stereochemistry opposite to that obtained with other ThDP-dependent enzymes. The combination of methylacetoin as acyl anion synthon and novel ThDP-dependent enzymes considerably expands the available range of C-C bond formations in asymmetric synthesis

Accoustic thin layer shear wave resonators for weighing of small masses and processing

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Electron-Beam processed SAW devices for sensor applications

International audienceIn this paper, electron-beam (e-beam) lithography for processing of surface acoustic wave devices is investigated, and its suitability for large-scale processing discussed. Electron-beam lithography is used for exposure of surface acoustic wave (SAW) resonator patterns on polymethyl methacrylate (PMMA) coated piezoelectric substrates. Electron-beam lithography can be used for high frequency SAW designs, due to a minimal finger width of 100 nm to 400 nm. Such SAW devices can be used for high-frequency sensor applications. This contribution will consider processing, on-wafer characterization, and characterization of sensor effects in instrumentation applications

High-Overtone Bulk Acoustic Wave Resonator on Galliumnitride

International audienceIn our previous research we already demonstrated micro acoustic devices, such as membrane based thin film bulk acoustic shear wave resonators and surface acoustic shear wave resonators, based on Metal-Organic-Vapour-Phase-Epitaxial (MOVPE) grown highly oriented a-plane piezoelectric material. Although MOVPE is a well established process for compound semiconductor layer growth especially of III-V semiconductors as InP, GaAs, and the nitrides GaN or AlN as also design and simulation of micro acoustic devices is nowadays a well established knowledge, the linkage between both is quite a technological challenge. Using an adapted MOVPE growth process for a-plane GaN on r-plane sapphire with a process linked improved surface quality; the challenge to build up high-overtone bulk acoustic wave resonators (HBAR) with a shear polarization of the acoustic wave was risen within this research. Different designs of MEMS-based prototypes of HBARs were processed on a-plane GaN after intensive simulations, their acoustic electrical behaviour analyzed and the temperature coefficient of frequency determined

Oligopeptide-based amide functional initiators for ATRP

Polymer–peptide conjugates are receiving significant interest. Here, we show that, under the appropriate conditions, a small family of oligopeptide-based initiators can be used successfully to initiate the polymerization of methacrylic monomers by atom transfer radical polymerization (ATRP), generating new examples of such materials. However, the use of the peptidic amide-based initiators results in polymers which have a higher molecular weight than expected and a significantly higher polydispersity than those prepared from ester-based initiators. In many cases significant initiator remains, suggesting that either not all peptides successfully initiate polymerization or that significant termination reactions occur early in the reaction. This low initiator efficiency agrees with other reports for amino acid-based initiators. It therefore appears that such amide-based initiators can be used successfully, but have a significantly lower applicability than the more commonly used ester-based initiators