Liquid crystalline banana‐shaped monomers derived from 2,7‐naphthalene: synthesis and properties

Three banana‐shaped monomers, i.e. 2,7‐naphthalene bis[4‐(4‐allyloxyphenylazo)‐benzoate], 2,7‐naphthalene bis[4‐(4‐allyloxy‐3‐fluorophenylazo)benzoate] and 2,7‐naphthalene bis{4‐[4‐(10‐undecenyloxy)phenylazo]benzoate}, containing azobenzene as side arms, 2,7‐dihydroxynaphthalene as central units and terminal double bonds as polymerisable functional groups, were synthesised and their mesophase behaviour investigated. Polarizing optical microscopy and DSC measurements reveal that all compounds exhibit nematic mesophases. The absorption spectrum of the trans‐azobenzene groups displays a high‐intensity π–π* transition at about 365 nm and a low‐intensity n–π* transition at around 450 nm for all compounds. Hence, photochromism can be achieved by the introduction of the azo linkage to banana‐shaped liquid crystals molecules.     

A Practical One‐Pot Synthesis of New S‐Glycosyl Amino Acid Building Blocks for Combinatorial Neoglycopeptide Synthesis

S‐Glycosyl L‐aspartic acid building blocks were synthesized starting from 1‐thiosugars by reaction with 5‐aminopentanol and suitably protected L‐aspartic acid pentafluorophenyl ester in a one‐pot procedure under Mitsunobu conditions using 1,1′‐azodicarbonyl dipiperidine and trimethyl phosphine. The method allowed for the preparation of S‐glycosyl amino acid building blocks in one step without protection of the amino function for the Mitsunobu condensation. Alternatively, the title compounds were prepared by a stepwise approach via 5‐aminopentyl 1‐thioglycosides.     

Quantum‐Chemical and Electrochemical Investigation of the Electrochemical Windows of Halogenated Carborate Anions

The range of electrochemical stability of a series of weakly coordinating halogenated (Hal=F, Cl, Br, I) 1‐carba‐closo‐dodecaborate anions, [1‐R‐CB₁₁X₅Y₆]^? (R=H, Me; X=H, Hal, Me; Y=Hal), has been established by using quantum chemical calculations and electrochemical methods. The structures of the neutral and dianionic radicals, as well as the anions, have been optimized by using DFT calculations at the PBE0/def2‐TZVPP level. The calculated structures are in good agreement with existing experimental data and with previous calculations. Their gas‐phase ionization energies and electron affinities were calculated based on their optimized structures and were compared with experimental (cyclic and square‐wave) voltammetry data. Electrochemical oxidation was performed in MeCN at room temperature and in liquid sulfur dioxide at lower temperatures. All of the anions show a very high resistance to the onset of oxidation (2.15–2.85 V versus Fc^0/+), with only a minor dependence of the oxidation potential on the different halogen substituents. In contrast, the reduction potentials in MeCN are strongly substituent dependent (?1.93 to ?3.32 V versus Fc^0/+). The calculated ionization energies and electron affinities correlate well with the experimental redox potentials, which provide important verification of the thermodynamic validity of the mostly irreversible redox processes that are observed for this series. The large electrochemical windows that are afforded by these anions indicate their suitability for electrochemical applications, for example, as supporting electrolytes.     

Mechanistic Insights into Copper‐Catalyzed Sonogashira–Hagihara‐Type Cross‐Coupling Reactions: Sub‐Mol % Catalyst Loadings and Ligand Effects

An efficient catalytic system for Sonogashira–Hagihara‐type reactions displaying ligand acceleration in the copper‐catalyzed formation of C(sp²)? C(sp) bonds is described. The structure of the ligand plays a key role for the coupling efficiency. Various copper sources show excellent catalytic activity, even in sub‐mol % quantities. A wide variety of substituents is tolerated in the substrates. Mechanistic details have been revealed by kinetic measurements and DFT calculations.     

Facile,efficient and eco-friendly synthesis of 5-sulfenyl tetrazole derivatives of indoles and pyrroles

A concise, two-step eco-friendly approach towards the synthesis of 5-sulfenyl tetrazole derivatives of indoles and pyrroles, is reported. The synthesis comprises the oxone-mediated thiocyanation of the starting heterocycles towards intermediate 3-thiocyanato indoles and 2-thiocyanato pyrroles, and their subsequent treatment with sodium azide in 2-propanol/water under zinc bromide promotion.     

Heavy Chains: Synthesis,Reactivity and Decomposition of Interpnictogen Chains with Terminal Diaryl Bismuth Fragments

In this work, we report the preparation of multiple interpnictogen chain compounds with three consecutive pnictogen atoms and terminal Ar₂Bi fragments (Ar=Ph, Mes). Symmetrical compounds of the form Ar₂Bi−E(tBu)−Bi₂Ar ( 1 : Ar=Ph, E=P; 2 : Ar=Ph, Mes, E=As) as well as ternary interpnictogen compounds of the form Ar₂Bi−E¹(tBu)−E²tBu₂ (Ar=Ph, Mes; 4 : E¹=P, E²=As; 5 : E¹=P, E²=Sb; 6 : E¹=As, E²=P) were prepared. The decomposition in solution at room temperature and under the influence of light was studied for compounds 1 – 6 . The reactivity of 1_Ph and 2_Ph with the small N-heterocyclic carbene 1,3,4,5-tetramethylimidazol-2-ylidene (Me₂IMe) was also studied. In the case of 1_Ph , the formation and consecutive decomposition of Me₂IMe=PtBu ( 8 ) was observed in solution. Hence, it was shown that 1_Ph can react as a “masked phosphinidene”. In the case of 2_Ph , no reaction with Me₂IMe was observed. All isolated compounds were analysed by NMR and IR spectroscopy, mass spectrometry, elemental analysis and single-crystal X-ray diffraction.     

Cooperative Chemotaxis of Magnesium Microswimmers for Corrosion Spotting

Numerous artificial micro- and nanomotors, as well as various swimmers have been inspired by living organisms that are able to move in a coordinated manner. Their cooperation has also gained a lot of attention because the resulting clusters are able to adapt to changes in their environment and to perform complex tasks. However, mimicking such a collective behavior remains a challenge. In the present work, magnesium microparticles are used as chemotactic swimmers with pronounced collective features, allowing the gradual formation of macroscopic agglomerates. The formed clusters act like a single swimmer able to follow pH gradients. This dynamic behavior can be used to spot localized corrosion events in a straightforward way. The autonomous docking of the swimmers to the corrosion site leads to the formation of a local protection layer, thus increasing corrosion resistance and triggering partial self-healing.     

Monolithic 160 Gbit/s optical time-division multiplexer

We present the design and experimental characterization of a monolithic optical time-division multiplexer (MUX) for 160 Gbit/s operation based on periodically poled lithium niobate (PPLN) waveguides. Its key figures of merit agree well with theoretical predictions and meet or exceed those of a previously demonstrated PPLN-planar-light-wave-circuit hybrid MUX. The monolithic design has a simpler layout and higher efficiency while keeping the cross talk low.     

Unexpected dimerization of 1,3‐dimethyl‐5‐methylenebarbituric acid revealed by a combined experimental and computational study

A comparison of experimental and calculated ¹³C‐nuclear magnetic resonance chemical shifts reveals the molecular structure of a dimer that was obtained by an unexpected dimerization of 1,3‐dimethyl‐5‐methylenebarbituric acid. Furthermore, the puckering angle of the cyclobutane unit linking the six‐membered rings is discussed in detail. The influence of substituents on 1,3‐position of the cyclobutane ring on the puckering angle is demonstrated based on 1,1,3,3‐tetramethylcyclobutane. Copyright © 2015 John Wiley & Sons, Ltd.     

Tailoring Chimeric Ligands for Studying and Biasing ErbB Receptor Family Interactions

Described is the development and application of a versatile semisynthetic strategy, based on a combination of sortase‐mediated coupling and tetrazine ligation chemistry, which can be exploited for the efficient incorporation of tunable functionality into chimeric recombinant proteins. To demonstrate the scope of the method, the assembly of a set of bivalent ligands, which integrate members of the epidermal growth factor (EGF) ligand family, is described. By using a series of bivalent EGFs with variable intraligand spacing, the differences in structure were correlated with the ability to bias signaling in the ErbB receptor family in a cell motility assay. Biasing away from EGFR‐HER2 dimerization with a bivalent EGF was observed to reduce cell motility in an intraligand distance‐dependent fashion, thus demonstrating the utility of the approach for acutely perturbing receptor‐mediated cell signaling pathways.