A Highly Active and Magnetically Recoverable Tris(triazolyl)–CuI Catalyst for Alkyne–Azide Cycloaddition Reactions

Nanoparticle‐supported tris(triazolyl)–CuBr, with a diameter of approximately 25 nm measured by TEM spectroscopy, has been easily prepared, and its catalytic activity was evaluated in the copper‐catalyzed azide–alkyne cycloaddition (CuAAC) reaction. In initial experiments, 0.5 mol % loading successfully promoted the CuAAC reaction between benzyl azide and phenylacetylene, in water at room temperature (25 °C). During this process, the iron oxide nanoparticle‐supported tris(triazolyl)–CuBr displayed good monodispersity, excellent recoverability, and outstanding reusability. Indeed, it was simply collected and separated from the reaction medium by using an external magnet, then used for another five catalytic cycles without significant loss of catalytic activity. Inductively coupled plasma (ICP) analysis for the first cycle revealed that the amount of copper leached from the catalyst into the reaction medium is negligible (1.5 ppm). The substrate scope has been examined, and it was found that the procedure can be successfully extended to various organic azides and alkynes and can also be applied to the one‐pot synthesis of triazoles, through a cascade reaction involving benzyl bromides, alkynes, and sodium azide. In addition, the catalyst was shown to be an efficient CuAAC catalyst for the synthesis of allyl‐ and TEG‐ended (TEG=triethylene glycol) 27‐branch dendrimers.     

Isomeric recognition by ion/molecule reactions: The ionized phenol-cyclohexadienone case

The isomerization process between ionized phenol and ionized cyclohexadienone is studied by performing ion/molecule reactions with several alkyl nitrites in a hexapole collision cell inserted in a six-sector mass spectrometer. The distinction between both isomeric species is readily achieved on the basis of the completely different reactivity patterns observed for them in subsequent reactions. When reacting with alkyl nitrite, ionized phenol undergoes two competitive reactions corresponding to the formal radical substitution of the hydroxylic hydrogen atom by respectively (i) the nitrosyl radical (m/z 123) and (ii) an alkoxyl radical (m/z 138 if alkyl=ethyl). Both reactions were theoretically demonstrated by density functional theory calculations [B3LYP/6-311++G(d,p)+ZPE] to involve hydrogen-bridged radical cations as key intermediates. The ion/molecule reaction products detected starting from ionized cyclohexadienone as the mass-selected ions arise from *OAlkyl, *OH, and NO2* radical additions. The occurrence of a spontaneous ring-opening of cyclohexadienone radical ion into a distonic species is suggested to account for the observed ion/molecule reaction products. We also demonstrated that ionized cyclohexadienone is partly isomerized during a proton-transfer catalysis process into ionized phenol inside the Hcell with ethyl nitrite as the base. The molecular ions of phenol generated in such conditions consecutively undergo reactions producing m/z 123 and 138 radical cations. The proposed mechanism is supported by results of quantum chemical calculations.     

Tandem mass spectrometry of amidated peptides

The behavior of C-terminal amidated and carboxylated peptides upon low-energy collision-induced dissociation (CID) was investigated. Two sets of 76 sequences of variable amino acid compositions and lengths were synthesized as model compounds. In most cases, C-terminal amidated peptides were found to produce, upon CID, an abundant loss of ammonia from the protonated molecules. To validate such MS/MS signatures, the studied peptides contained amino acids that can potentially release ammonia from their side chains, such as asparagine, glutamine, tryptophan, lysine and arginine. Arginine, and to a lesser extent lysine, was shown to induce a competitive fragmentation leading to the loss of ammonia from their side chains, thus interfering with the targeted backbone neutral release. However, when arginine or lysine was located at the C-terminal position mimicking a tryptic digest, losses of ammonia from the arginine side chain and from the peptide backbone were completely suppressed. Such results were discussed in the frame of peptidomic or proteomic studies in an attempt to reveal the presence of C-terminal amidated peptides or proteins.     

Online Resources in Mathematics, Teachers’ Geneses and Didactical Techniques

The study we present here concerns the consequences of integrating online resources into the teaching of mathematics. We focus on the interaction between teachers and specific online resources they draw on: e-exercise bases. We propose a theoretical approach to study the associated phenomena, combining instrumental and anthropological perspectives. For given didactical tasks, we observe teachers’ instrumental geneses, and the didactical techniques they develop. We exemplify our approach with the analysis of a case study of trigonometry in grade 9.

Ordered arrays of epitaxial silicon nanowires produced by nanosphere lithography and chemical vapor deposition

Gold dot arrays on (1 1 1) Si substrates obtained through nanosphere lithography (NSL) combined with sputtering and annealing in Ar at 1000 °C are used to catalyze vapor liquid solid (VLS) epitaxial growth of silicon nanowires (Si NWs) using chemical vapor deposition (CVD) with SiH₄ in Ar. The NWs grow primarily epitaxially on the underlying (1 1 1) Si wafer following the four independent 〈1 1 1〉 directions. The diameter distribution of the wires reflects the diameter distribution of the catalyst gold dot arrays and is therefore predictable. The wire length depends on the size of the gold catalyst for the same CVD parameters. The wire position is foreseeable within the limits of the pattern geometrical quality, but one-to-one growth of NWs to gold dots is not always observed, probably due to (very locally) the remaining presence of silicon oxide. Overall, this inexpensive patterning method for obtaining high-quality crystalline VLS Si NWs by CVD fulfills the requirements of many device applications, where patterning control, quality and reproducibility of the nanostructures are crucial.     

One‐Pot Synthesis of Well‐Defined Amphiphilic and Adaptative Block Copolymers via Versatile Combination of “Click” Chemistry and ATRP

Well‐defined amphiphilic PCL‐b‐PDMAEMA block copolymers were successfully synthesized by a combination of ATRP and “click” chemistry following either a commutative two‐step procedure or a straightforward one‐pot process using CuBr · 3Bpy as the sole catalyst. Compared to the traditional coupling method, combining ATRP and click chemistry even in a “one‐pot” process allows the preparation of PCL‐b‐PDMAEMA diblock copolymers characterized by a narrow molecular weight distribution and quantitative conversion of azides and alkynes into triazole functions. Moreover, the amphiphilic character of these copolymers was demonstrated by surface tension measurements and critical micellization concentration was calculated.

     

Asymptotics for some vibro-impact problems with a linear dissipation term

We consider a mechanical system with a finite number of degrees of freedom submitted to a non smooth potential Φ and a viscous dissipation force. We study the asymptotic behavior of dissipative solutions when the time variable tends to +∞. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)