Bis(diethylamino)carbene and the mechanism of dimerisation for simple diaminocarbenes

Bis(diethylamino)carbene is kinetically stable to dimerization in THF at ambient temperature; dimer formed during carbene generation arises from reaction of the carbene with the precursor formamidinium ion; this is probably the commonest route to tetraaminoethene dimers, and in a related case the intermediate protonated tetraaminoethene can be observed by NMR.     

Electrochemical impedance probing of DNA hybridisation on oligonucleotide-functionalised polypyrrole

We report a new approach for detecting DNA hybridisation using non faradaic electrochemical impedance spectroscopy. The technique was applied to a system of DNA probes bearing amine groups that are immobilized by covalent grafting on a supporting polypyrrole matrix functionalised with activated ester groups.The kinetics of the attachment of the ss-DNA probe was monitored using the temporal evolution of the open circuit potential (OCP). This measurement allows the determination of the time necessary for the chemical reaction of ss-DNA probe into the polypyrrole backbone.The hybridisation reactions with the DNA complementary target and non complementary target were investigated by non faradaic electrochemical impedance spectroscopy. Results show a significant modification in the Nyquist plot upon addition of the complementary target whereas, in presence of the non complementary target, the Nyquist plot is not modified. The spectra, in the form of Nyquist plot, were analysed with the Randles circuit. The transfer charge resistance R₂ shows a linear variation versus the complementary target concentration. Sensitivity and detection limit (0.2 nM) were determined and detection limit was lower of one order of magnitude than that obtained with the same system and measuring variation of the oxidation current at constant potential.     

Synthesis,structural characterization,Hirshfeld surface analysis,spectroscopic and ferroelectric properties studies of 4-methylbenzylammonium sulfate

Single crystals of 4-methylbenzylammonium sulfate were grown in an aqueous solution at room temperature. The grown compound is characterized by spectroscopic, thermal, and dielectric studies and its structure was determined by single-crystal X-ray diffraction analysis. Its crystal structure is described as a three-dimensional network where the sulfate anions (HSO₄^?) are interconnected through H-bonds to form anionic layers between which the 4-methylbenzylammonium cations are located. The hydrogen bonding network connecting the different components is given. Hirshfeld surface analysis was performed to visualize, explore and quantify intermolecular interactions in the crystal lattice. This analysis revealed the presence of H…C/H…C, C…O/O…C intermolecular interactions and O…O, H…H short contacts in the crystal. X-ray, structural and electrical results are correlated. The kind of the observed conduction is protonic by translocation. Differential scanning calorimetry (DSC) shows that this material presents a reversible phase transition at 390 K, confirmed by the dielectric permittivity study.     

Drying Study of Siloxane-PPG Nanocomposites

This is a study of the structural transformations occurring in hybrid siloxane-polypropyleneglycol (PPG) nanocomposites, with different PPG molecular weight, along the drying process. The starting materials are wet gels obtained by the sol-gel procedure using as precursor the 3-(trietoxysilyl)propylisocyanate (IsoTrEOS) and polypropylenglycol bis(2-amino-propyl-ether) (NH₂-PPG-NH₂). The shrinkage and mass loss measurements were performed using a temperature-controlled chamber at 50°C. The nanostructural evolution of samples during drying was studied in situ by small angle x-ray scattering (SAXS). The experimental results demonstrate that the drying process is highly dependent on the molecular weight of polymer. After the initial drying stage, the progressive emptying of pores leads to the formation of a irregular drying front in gels prepared from PPG of high molecular weight, like 4000 g/mol. As a consequence, an increase of the SAXS intensity due to the increase of electronic density contrast between siloxane clusters and polymeric matrix is observed. For hybrids containing PPG of low molecular weight, the pore emptying process is fast, leading to a regular drying front, without isolated nanopockets of solvents. SAXS intensity curves exhibit a maximum, which was associated to the existence of spatial correlation of the silica clusters embedded in the polymeric matrix. The spatial correlation is preserved during drying. These results also reveal that the structural transformation during drying is governed by capillary forces and depends on the entanglement of polymer chains.     

Self-selective recovery of photoluminescence in amphiphilic polymer encapsulated PbS quantum dots

Self-selected recovery of the photoluminescence (PL) of amphiphilic polymer encapsulated PbS quantum dots (QDs) was observed in water for the first time and possible mechanisms were proposed based on investigations by means of transmission electron microscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction and fluorescence spectroscopy. Water-soluble PbS QDs were synthesized by transferring monodispersed QDs capped with hydrophobic ligands of oleylamine from an organic solvent into water via amphiphilic polymers poly(maleic anhydride-alt-1-octadecene-co-poly(ethylene glycol)). The water transfer process leads to a double size distribution (5.6 ± 0.9 nm and 2.7 ± 0.4 nm), attributed to ligand etching together with Ostwald ripening, as well as the fast decay of PL. The automatic recovery of the PL in PbS QDs stored in water in the dark for 3 months was only observed for the subset of smaller QDs and is largely due to the removal of surface defects with aging, as evidenced by the decreased percentage of unpassivated surface atoms from XPS studies. In contrast, the PL of the subset of larger QDs in the same sample does not self-recover in water and can only be slightly recovered by transferring them into environments with less external quenches. The results strongly suggest that it is the surface defect in the larger QDs themselves, introduced during Ostwald ripening, that is primarily responsible for their non-emitting status or rather low PL intensity under different conditions. The increase of unpassivated Pb atoms in larger PbS QDs after the 3 month aging has been confirmed by XPS, which explains their non-recovery behavior in water. The PL-recovered QD sample in water is very stable and shows comparable photostability to the initial QDs dispersed in an organic phase.     

Laser-induced fluorescence detection of lead atoms in a laser-induced plasma: An experimental analytical optimization study

The combination of the laser-induced breakdown spectroscopy (LIBS) and laser-induced fluorescence (LIF) techniques was investigated to improve the limit of detection (LoD) of trace elements in solid matrices. The influence of the main experimental parameters on the LIF signal, namely the ablation fluence, the excitation energy, and the inter-pulse delay, was studied experimentally and a discussion of the results was presented. For illustrative purpose we considered detection of lead in brass samples. The plasma was produced by a Q-switched Nd:YAG laser and then re-excited by a nanosecond Optical Parametric Oscillator (OPO) laser. The experiments were performed in air at atmospheric pressure. We found out that the optimal conditions were obtained for our experimental set-up using relatively weak ablation fluence of 2–3 J/cm² and an inter-pulse delay of about 5–10 μs. Also, a few tens of microjoules was typically required to maximize the LIF signal. Using the LIBS–LIFS technique, a single-shot LoD for lead of about 1.5 part per million (ppm) was obtained while a value of 0.2 ppm was obtained after accumulating over 100 shots. These values represent an improvement of about two orders of magnitude with respect to LIBS.     

Comparison of MALDI‐TOF mass spectra with microsatellite length polymorphisms in Candida albicans

Candida albicans is the most frequent yeast involved in human infections. Its population structure can be divided into several genetic clades, some of which have been associated with antifungal susceptibility. Therefore, detecting and monitoring fungal clones in a routine laboratory setting would be a major epidemiological advance. Matrix‐assisted laser desorption/ionization time‐of‐flight (MALDI‐TOF) mass spectra results are now widely used as bar codes to identify microorganisms in clinical microbiology laboratories. This study aimed at testing MALDI‐TOF mass spectra bar codes to identify clades among a set of C. albicans isolates. Accordingly, 102 clinical strains were genotyped using 10 microsatellite markers and analyzed via MALDI‐TOF mass spectrometry. The mass spectra were compared with a reference spectral library including 33 well‐characterized collection strains, using a Microflex^TM system and Biotyper^TM software, to test the capacity of the spectrum of a given isolate to match with the reference mass spectrum of an isolate from the same genetic clade. Despite high confidence species identification, the spectra failed to significantly match with the corresponding clade (p = 0.74). This was confirmed with the MALDI‐TOF spectra similarity dendrogram, in which the strains were dispersed irrespective of their genetic clade. Various attempts to improve intra‐clade spectra recognition were unsuccessful. In conclusion, MALDI‐TOF mass spectra bar code analysis failed to reliably recognize genetically related C. albicans isolates. Further studies are warranted to develop alternative MALDI‐TOF mass spectra analytical approaches to identify and monitor C. albicans clades in the routine clinical laboratory. Copyright © 2015 John Wiley & Sons, Ltd.     

Multilevel hybrid split-step implicit tau-leap

In biochemically reactive systems with small copy numbers of one or more reactant molecules, the dynamics is dominated by stochastic effects. To approximate those systems, discrete state-space and stochastic simulation approaches have been shown to be more relevant than continuous state-space and deterministic ones. In systems characterized by having simultaneously fast and slow timescales, existing discrete space-state stochastic path simulation methods, such as the stochastic simulation algorithm (SSA) and the explicit tau-leap (explicit-TL) method, can be very slow. Implicit approximations have been developed to improve numerical stability and provide efficient simulation algorithms for those systems. Here, we propose an efficient Multilevel Monte Carlo (MLMC) method in the spirit of the work by Anderson and Higham (SIAM Multiscal Model. Simul. 10(1), 2012). This method uses split-step implicit tau-leap (SSI-TL) at levels where the explicit-TL method is not applicable due to numerical stability issues. We present numerical examples that illustrate the performance of the proposed method.     

Local regularity for nonlocal equations with variable exponents

In this paper, we study local regularity properties of minimizers of nonlocal variational functionals with variable exponents and weak solutions to the corresponding Euler–Lagrange equations. We show that weak solutions are locally bounded when the variable exponent p is only assumed to be continuous and bounded. Furthermore, we prove that bounded weak solutions are locally Hölder continuous under some additional assumptions on p. On the one hand, the class of admissible exponents is assumed to satisfy a log-Hölder–type condition inside the domain, which is essential even in the case of local equations. On the other hand, since we are concerned with nonlocal problems, we need an additional assumption on p outside the domain.     

Bruguiera gymnorhiza (L.) Lam. at the Forefront of Pharma to Confront Zika Virus and Microbial Infections—An In Vitro and In Silico Perspective

The recent emergence of Zika virus (ZIKV) in Brazil and the increasing resistance developed by pathogenic bacteria to nearly all existing antibiotics should be taken as a wakeup call for the international authority as this represents a risk for global public health. The lack of antiviral drugs and effective antibiotics on the market triggers the need to search for safe therapeutics from medicinal plants to fight viral and microbial infections. In the present study, we investigated whether a mangrove plant, Bruguiera gymnorhiza (L.) Lam. (B. gymnorhiza) collected in Mauritius, possesses antimicrobial and antibiotic potentiating abilities and exerts anti-ZIKV activity at non-cytotoxic doses. Microorganisms Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853, Klebsiella pneumoniae ATCC 70603, methicillin-resistant Staphylococcus aureus ATCC 43300 (MRSA), Salmonella enteritidis ATCC 13076, Sarcina lutea ATCC 9341, Proteus mirabilis ATCC 25933, Bacillus cereus ATCC 11778 and Candida albicans ATCC 26555 were used to evaluate the antimicrobial properties. Ciprofloxacin, chloramphenicol and streptomycin antibiotics were used for assessing antibiotic potentiating activity. ZIKV^MC-MR766NIID (ZIKV^GFP) was used for assessing anti-ZIKV activity. In silico docking (Autodock 4) and ADME (SwissADME) analyses were performed on collected data. Antimicrobial results revealed that Bruguiera twig ethyl acetate (BTE) was the most potent extract inhibiting the growth of all nine microbes tested, with minimum inhibitory concentrations ranging from 0.19–0.39 mg/mL. BTE showed partial synergy effects against MRSA and Pseudomonas aeruginosa when applied in combination with streptomycin and ciprofloxacin, respectively. By using a recombinant ZIKV-expressing reporter GFP protein, we identified both Bruguiera root aqueous and Bruguiera fruit aqueous extracts as potent inhibitors of ZIKV infection in human epithelial A549 cells. The mechanisms by which such extracts prevented ZIKV infection are linked to the inability of the virus to bind to the host cell surface. In silico docking showed that ZIKV E protein, which is involved in cell receptor binding, could be a target for cryptochlorogenic acid, a chemical compound identified in B. gymnorhiza. From ADME results, cryptochlorogenic acid is predicted to be not orally bioavailable because it is too polar. Scientific data collected in this present work can open a new avenue for the development of potential inhibitors from B. gymnorhiza to fight ZIKV and microbial infections in the future.