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The effect of chain conformation change on the self-assembly behavior of poly(gamma-benzyl- l-glutamate)-block-poly(ethylene glycol) (PBLG-b-PEG) was studied both experimentally by transmission electron microscopy, laser light scattering, and circular dichroism and computationally using molecular dynamics (MD) simulation. It was found that, by introducing trifluoroacetic acid to the PBLG-b-PEG solution, the conformation of the PBLG chain transforms from alpha-helix to random coil, which results in a change of the micelle structures formed by PBLG-b-PEG from rod to sphere. Meanwhile, the MD simulations were performed by using Brownian dynamics on the self-assembly behavior of model AB-type diblock copolymers with various chain rigidities of the A-block. The results show that, by decreasing the fraction of rigid chain conformation of the A-block, which corresponds to the helix-coil transition in the PBLG-b-PEG sample, the aggregate structure transforms from rod to sphere. The MD simulations also provide chain packing information in the micelles. On the basis of both experimental and MD simulation results, the mechanism regarding the effect of the conformation change of the polypeptide block copolymer on its self-association behavior is suggested.

International audienceThis paper is concerned with the existence and qualitative properties of pulsating fronts for spatially periodic reaction-diffusion equations with bistable nonlinearities. We focus especially on the influence of the spatial period and, under various assumptions on the reaction terms and by using different types of arguments, we show several existence results when the spatial period is small or large. We also establish some properties of the set of periods for which there exist non-stationary fronts. Furthermore, we prove the existence of stationary fronts or non-stationary partial fronts at any period which is on the boundary of this set. Lastly, we characterize the sign of the front speeds and we show the global exponential stability of the non-stationary fronts for various classes of initial conditions

Ethylene, an important plant hormone, is of utmost importance during many developmental processes of plants. However, the efficient enrichment and analysis of trace ethylene still remains a challenge. A simple and mild multilayer interparticle linking strategy was proposed to fabricate a novel hybrid MOF-199 enrichment coating. Strong chemical interparticle linkages throughout the coating improved the durability and reproducibility of hybrid MOF-199 coating dramatically. This coating performed a significant extraction superiority of ethylene over commonly used commercial coatings, attributed to the multiple interactions including "molecular sieving effect", hydrogen bonding, open metal site interaction, and π-π affinity. The hybridization of multiwalled carbon nanotubes (MWCNTs) with MOF-199 further improved the enrichment capability and also acted as a hydrophobic "shield" to prevent the open metal sites of MOF-199 from being occupied by water molecules, which effectively improved the moisture-resistant property of MOF-199/CNTs coating. Finally, this novel enrichment method was successfully applied for the noninvasive analysis of trace ethylene, methanol, and ethanol from fruit samples with relatively high humidity. The low detection limit was 0.016 μg/L for ethylene. It was satisfactory that trace ethylene could be actually detected from fruit samples by this noninvasive method. Good recoveries of spiked grape, wampee, blueberry, and durian husk samples were obtained in the range of 90.0-114%, 79.4-88.6%, 78.5-86.8%, and 85.2-105% with the corresponding relative standard deviations of 4.8-9.8%, 6.9-8.9%, 3.8-8.1%, and 9.3-10.5% (n = 3), respectively.

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