Proof Pearl: The KeY to Correct and Stable Sorting

We discuss a proof of the correctness of two sorting algorithms: Counting sort and Radix sort. The semi-automated proof is formalized in the state-of-the-art theorem prover KeY.     

Coordination‐Assisted Bioorthogonal Chemistry: Orthogonal Tetrazine Ligation with Vinylboronic Acid and a Strained Alkene

Bioorthogonal chemistry can be used for the selective modification of biomolecules without interfering with any other functionality that might be present. Recent developments in the field include orthogonal bioorthogonal reactions to modify multiple biomolecules simultaneously. During our research, we observed that the reaction rates for the bioorthogonal inverse‐electron‐demand Diels–Alder (iEDDA) reactions between nonstrained vinylboronic acids (VBAs) and dipyridyl‐s‐tetrazines were exceptionally higher than those between VBAs and tetrazines bearing a methyl or phenyl substituent. As VBAs are mild Lewis acids, we hypothesised that coordination of the pyridyl nitrogen atom to the boronic acid promoted tetrazine ligation. Herein, we explore the molecular basis and scope of VBA–tetrazine ligation in more detail and benefit from its unique reactivity in the simultaneous orthogonal tetrazine labelling of two proteins modified with VBA and norbornene, a widely used strained alkene. We further show that the two orthogonal iEDDA reactions can be performed in living cells by labelling the proteasome by using a nonselective probe equipped with a VBA and a subunit‐selective VBA bearing a norbornene moiety.     

Fungal Infection Reduces Herbivore-Induced Plant Volatiles of Maize but does not Affect Naïve Parasitoids

Plants attacked by insects release volatile compounds that attract the herbivores' natural enemies. This so-called indirect defense is plastic and may be affected by an array of biotic and abiotic factors. We investigated the effect of fungal infection as a biotic stress agent on the emission of herbivore-induced volatiles and the possible consequences for the attraction of two parasitoid species. Maize seedlings that were simultaneously attacked by the fungus Setosphaeria turcica and larvae of Spodoptera littoralis emitted a blend of volatiles that was qualitatively similar to the blend emitted by maize that was damaged by only the herbivore, but there was a clear quantitative difference. When simultaneously challenged by fungus and herbivore, the maize plants emitted in total 47% less of the volatiles. Emissions of green leaf volatiles were unaffected. In a six-arm olfactometer, the parasitoids Cotesia marginiventris and Microplitis rufiventris responded equally well to odors of herbivore-damaged and fungus- and herbivore-damaged maize plants. Healthy and fungus-infected plants were not attractive. An additional experiment showed that the performance of S. littoralis caterpillars was not affected by the presence of the pathogen, nor was there an effect on larvae of M. rufiventris developing inside the caterpillars. Our results confirm previous indications that naïve wasps may respond primarily to the green leaf volatiles.     

银河桥 荷兰皮尔墨伦德

正荷兰Melkweg大桥,俗称"银河桥",横跨Noord-hollandsch运河,连接皮尔默伦德市历史中心区与西南地区不断发展的Weidevenne区。银河桥的建造是运河及其周边地区总体发展规划的第一阶段。"设计团队旨在打造一个具有特定标志的新区,以作为新旧两个中心城区之间的连系纽带。"银河桥,由NEXT建筑事务所设计建造。最引人注目的部分是一个巨大的拱形桥,水平面之上高达12米,与Melkweg路连绵延伸为一     

Combinatorial Design of Copper‐Based Mixed Nanoclusters: New Catalysts for Suzuki Cross‐Coupling

Quantum dots (2–5 nm) of copper and copper/palladium mixtures are found to be good catalysts for Suzuki cross‐coupling. The catalysts are applicable to a wide range of iodo‐ and bromoaryl substrates, and give moderate yields using chloroaryl substrates. Cluster activity and stability is found to depend strongly on the preparation method and the reaction conditions. The mechanism of cluster deactivation and the sensitivity of the cluster‐catalysed reaction to substituent effects are studied and discussed.     

Microcontact Printing with Heavyweight Inks

Thioether derivatives with 1–4 thioether moieties were used as inks in microcontact printing on gold for the reproduction of patterns as they combine good monolayer quality with synthetic versatility, and high molecular weights. Self‐assembled monolayers (SAMs) on gold of compounds 1 and 2 had a quality comparable to SAMs of decanethiol, both regarding monolayer order and etch resistance. Etch resistances of SAMs of 3 and 4 were lower. Resulting structures after etching of patterned SAMs using 1 , 2 , and 3 were of good quality for patterns with feature sizes on the same stamp ranging from 1–200 μm. Patterns of 4 were not reproduced. Overall, compounds 1 and 2 are good candidates for low‐diffusion inks.     

Atomic force microscopy of the morphology and mechanical behaviour of barnacle cyprid footprint proteins at the nanoscale

Barnacles are a major biofouler of man-made underwater structures. Prior to settlement, cypris larvae explore surfaces by reversible attachment effected by a ‘temporary adhesive’. During this exploratory behaviour, cyprids deposit proteinaceous ‘footprints’ of a putatively adhesive material. In this study, footprints deposited by Balanus amphitrite cyprids were probed by atomic force microscopy (AFM) in artificial sea water (ASW) on silane-modified glass surfaces. AFM images obtained in air yielded better resolution than in ASW and revealed the fibrillar nature of the secretion, suggesting that the deposits were composed of single proteinaceous nanofibrils, or bundles of fibrils. The force curves generated in pull-off force experiments in sea water consisted of regions of gradually increasing force, separated by sharp drops in extension force manifesting a characteristic saw-tooth appearance. Following the relaxation of fibrils stretched to high strains, force–distance curves in reverse stretching experiments could be described by the entropic elasticity model of a polymer chain. When subjected to relaxation exceeding 500 ms, extended footprint proteins refolded, and again showed saw-tooth unfolding peaks in subsequent force cycles. Observed rupture and hysteresis behaviour were explained by the ‘sacrificial bond’ model. Longer durations of relaxation (>5 s) allowed more sacrificial bond reformation and contributed to enhanced energy dissipation (higher toughness). The persistence length for the protein chains (L_P) was obtained. At high elongation, following repeated stretching up to increasing upper strain limits, footprint proteins detached at total stretched length of 10 µm.     

Apple extract induces increased epithelial resistance and claudin 4 expression in Caco-2 cells

BACKGROUND: The small intestinal epithelium functions both to absorb nutrients, and to provide a barrier between the outside, luminal, world and the human body. One of the passageways across the intestinal epithelium is paracellular diffusion, which is controlled by the properties of tight junction complexes. We used a differentiated Caco‐2 monolayer as a model for small intestinal epithelium to study the effect of crude apple extracts on paracellular permeability. RESULTS: Exposure of crude apple homogenate to the differentiated Caco‐2 cells increased the paracellular resistance, determined as trans‐epithelial electrical resistance (TEER). This increase was linearly related to the concentration of apple present. The TEER‐enhancing effect of apple extract was due to factors mainly present in the cortex, and the induction was not inhibited by protein kinase inhibitors. Apple‐induced resistance was accompanied by increased expression of several tight junction related genes, including claudin 4 (CLDN4). CONCLUSION: Crude apple extract induces a higher paracellular resistance in differentiated Caco‐2 cells. Future research will determine whether these results can be extrapolated to human small intestinal epithelia. Copyright © 2011 Society of Chemical Industry