Strain control in germanium nanowires: the use of a silicon nitride shell

The core–shell geometry is a strong tool for inducing and controlling strains in nano‐objects in order to tune their optoelectronic properties. We synthesized and characterized core–shell nanostructures by depositing a non‐epitaxial silicon nitride shell around germanium nanowires. Scanning electron microscopy as well as energy dispersive X‐ray spectroscopy confirms the structural integrity of the heterostructures, and grazing incidence X‐ray diffraction measurements reveal the presence of a radial tensile strain in the Ge nanowires. A control of this strain is then demonstrated up to 0.3% by adjusting the SiN_x shell thickness versus Ge nanowire diameter. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Hypercyclic subspaces and weighted shifts

We first generalize the results of León-Saavedra and Müller (2006) [10] on hypercyclic subspaces to sequences of operators on Fréchet spaces with a continuous norm. Then we study the particular case of iterates of an operator T   and show a simple criterion for having no hypercyclic subspace. Finally we deduce from this criterion a characterization of weighted shifts with hypercyclic subspaces on the spaces l^p$l^p$ or _c0$c_0$, on the space of entire functions and on certain Köthe sequence spaces. We also prove that if P is a non-constant polynomial and D   is the differentiation operator on the space of entire functions then P(D)$P(D)$ possesses a hypercyclic subspace.     

Vacuum Ultraviolet Action Spectroscopy of Polysaccharides

We studied the optical properties of gas-phase polysaccharides (maltose, maltotetraose, and maltohexaose) ions by action spectroscopy using the coupling between a quadrupole ion trap and a vacuum ultraviolet (VUV) beamline at the SOLEIL synchrotron radiation facility (France) in the 7 to 18 eV range. The spectra provide unique benchmarks for evaluation of theoretical data on electronic transitions of model carbohydrates in the VUV range. The effects of the nature of the charge held by polysaccharide ions on the relaxation processes were also explored. Finally the effect of isomerization of polysaccharides (with melezitose and raffinose) on their photofragmentation with VUV photons is presented.

Kinetic studies of drug-protein interactions by using peak profiling and high-performance affinity chromatography: examination of multi-site interactions of drugs with human serum albumin columns

Carbamazepine and imipramine are drugs that have significant binding to human serum albumin (HSA), the most abundant serum protein in blood and a common transport protein for many drugs in the body. Information on the kinetics of these drug interactions with HSA would be valuable in understanding the pharmacokinetic behavior of these drugs and could provide data that might lead to the creation of improved assays for these analytes in biological samples. In this report, an approach based on peak profiling was used with high-performance affinity chromatography to measure the dissociation rate constants for carbamazepine and imipramine with HSA. This approach compared the elution profiles for each drug and a non-retained species on an HSA column and control column over a board range of flow rates. Various approaches for the corrections of non-specific binding between these drugs and the support were considered and compared in this process. Dissociation rate constants of 1.7 (±0.2) s(-1) and 0.67 (±0.04) s(-1) at pH 7.4 and 37°C were estimated by this approach for HSA in its interactions with carbamazepine and imipramine, respectively. These results gave good agreement with rate constants that have determined by other methods or for similar solute interactions with HSA. The approach described in this report for kinetic studies is not limited to these particular drugs or HSA but can also be extended to other drugs and proteins.     

Photo-SRM: laser-induced dissociation improves detection selectivity of Selected Reaction Monitoring mode

Selected Reaction Monitoring (SRM) carried out on triple‐quadrupole mass spectrometers coupled to liquid chromatography has been a reference method to develop quantitative analysis of small molecules in biological or environmental matrices for years and is currently emerging as a promising tool in clinical proteomic. However, sensitive assays in complex matrices are often hampered by the presence of co‐eluted compounds that share redundant transitions with the target species. On‐the‐fly better selection of the precursor ion by high‐field asymmetric waveform ion mobility spectrometry (FAIMS) or increased quadrupole resolution is one way to escape from interferences. In the present work we document the potential interest of substituting classical gas‐collision activation mode by laser‐induced dissociation in the visible wavelength range to improve the specificity of the fragmentation step. Optimization of the laser beam pathway across the different quadrupoles to ensure high photo‐dissociation yield in Q2 without detectable fragmentation in Q1 was assessed with sucrose tagged with a push‐pull chromophore. Next, the proof of concept that photo‐SRM ensures more specific detection than does conventional collision‐induced dissociation (CID)‐based SRM was carried out with oxytocin peptide. Oxytocin was derivatized by the thiol‐reactive QSY® 7 C₅‐maleimide quencher on cysteine residues to shift its absorption property into the visible range. Photo‐SRM chromatograms of tagged oxytocin spiked in whole human plasma digest showed better detection specificity and sensitivity than CID, that resulted in extended calibration curve linearity. We anticipate that photo‐SRM might significantly improve the limit of quantification of classical SRM‐based assays targeting cysteine‐containing peptides. Copyright © 2011 John Wiley & Sons, Ltd.     

Glyphosate–Exonuclease Interactions: Reduced Enzymatic Activity as a Route to Glyphosate Biosensing

N-phosphonomethyle-glycine (glyphosate) is the most widely used pesticide worldwide due to its effectiveness in killing weeds at a moderate cost, bringing significant economic benefits. However, owing to its massive use, glyphosate and its residues contaminate surface waters. On site, fast monitoring of contamination is therefore urgently needed to alert local authorities and raise population awareness. Here the hindrance of the activity of two enzymes, the exonuclease I (Exo I) and the T5 exonuclease (T5 Exo) by glyphosate, is reported. These two enzymes digest oligonucleotides into shorter sequences, down to single nucleotides. The presence of glyphosate in the reaction medium hampers the activity of both enzymes, slowing down enzymatic digestion. It is shown by fluorescence spectroscopy that the inhibition of ExoI enzymatic activity is specific to glyphosate, paving the way for the development of a biosensor to detect this pollutant in drinking water at suitable detection limits, i.e., 0.6 nm .     

Nickel-Photoredox-Catalyzed Synthesis of sp2−sp3 Fragments and the Impact of Bicycloalkane Isosteric Replacement on Their Physical-Chemical Properties

Bicycloalkanes are well-known isosteres of alkynes and aromatic rings and their use in the field of medicinal chemistry and drug discovery has been on the rise in the past ten years. Herein, we report the modular and practical synthesis of bicycloalkane-containing fragments using nickel-photoredox catalysis. The comparison of their relevant physical-chemical properties with their aromatic counterparts shows a substantial improvement in LogP and aqueous solubility for bicyclo[1.1.1]pentane derivatives, but not for bicyclo[2.2.2]octane derivatives.     

Lithium Promotes Acetylide Formation on MgO During Methane Coupling Under Non-Oxidative Conditions

A prototypical material for the oxidative coupling of methane (OCM) is Li/MgO, for which Li is known to be essential as a dopant to obtain high C₂ selectivities. Herein, Li/MgO is demonstrated to be an effective catalyst for non-oxidative coupling of methane (NOCM). Moreover, the presence of Li is shown to favor the formation of magnesium acetylide (MgC₂), while pure MgO promotes coke formation as evidenced by solid-state ¹³C NMR, thus indicating that Li promotes C−C bond formation. Metadynamic simulations of the carbon mobility in MgC₂ and Li₂C₂ at the density functional theory (DFT) level show that carbon easily diffuses as a C₂ unit at 1000 °C. These insights suggest that the enhanced C₂ selectivity for Li-doped MgO is related to the formation of Li and Mg acetylides.