Synthesis,thermal analysis,and linear and nonlinear optical characterization of substituted polyphosphonates derived from 1,12‐dodecanediol

The syntheses of a series of substituted polyphosphonates of the type [OP(X)(Ar)O(CH₂)₁₂]_n (X = O, S, Se; Ar = phenyl, 2,2′‐bithienyl‐5‐yl) are reported. The s for the polyphosphonates range from 1.1 to 4.6 × 10⁴ Da and are significantly higher than those previously reported for polyphosphonates synthesized via polycondensation reactions. Thermal characterization indicates that all of the polymers are in the rubbery state at room temperature and have thermal stabilities as high as 290 °C. The linear absorption spectra, emission spectra, and emission quantum yields of the 2,2′‐bithenyl‐5‐yl substituted polyphosphonates show distinct trends with respect to the chalcogen attached to the phosphorus. Solutions of these polymers show emission at wavelengths ranging from 380 to 400 nm and, depending on the choice of X, the quantum yields are considerably larger than that of 2,2′‐bithiophene. Nonlinear optical measurements of the polyphosphonates with 2,2′‐bithenyl‐5‐yl substituents show that nonlinear absorbance increases with increasing molecular weight of X. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 3663–3674     

Structural and optical properties of a-Si1−xCx:H films synthesized by dc magnetron sputtering technique

Hydrogenated amorphous SiC films (a-Si_1−xC_x:H) were prepared by dc magnetron sputtering technique on p-type Si(1 0 0) and corning 9075 substrates at low temperature, by using 32 sprigs of silicon carbide (6H-SiC). The deposited a-Si_1−xC_x:H film was realized under a mixture of argon and hydrogen gases. The a-Si_1−xC_x:H films have been investigated by scanning electronic microscopy equipped with an EDS system (SEM-EDS), X-ray diffraction (XRD), secondary ions mass spectrometry (SIMS), Fourier transform infrared spectroscopy (FTIR), UV-vis-IR spectrophotometry, and photoluminescence (PL). XRD results showed that the deposited film was amorphous with a structure as a-Si_0.80C_0.20:H corresponding to 20 at.% carbon. The photoluminescence response of the samples was observed in the visible range at room temperature with two peaks centred at 463 nm (2.68 eV) and 542 nm (2.29 eV). In addition, the dependence of photoluminescence behaviour on film thickness for a certain carbon composition in hydrogenated amorphous SiC films (a-Si_1−xC_x:H) has been investigated.     

Reduction of PAH and soot precursors in benzene flames by addition of ethanol

A one-dimensional premixed flame model (PREMIX) and schemes resulting from the merging of validated kinetic schemes for the oxidation of the components of the present mixtures (benzene and ethanol) were used to investigate the effect of oxygenated additives on aromatic species, which are known to be soot precursors, in fuel-rich benzene combustion. The specific flames were low-pressure (45 mbar), laminar, premixed flames at an equivalence ratio of 2.0. The blended fuels were formed by incrementally adding 4% wt of oxygen (ethanol) to the neat benzene flame and by keeping the inert mole fraction (argon) and the equivalence ratio constants. Special emphasis was directed toward the causes for the concentration-dependent influence of the blends on the amount of polycyclic aromatic hydrocarbons (PAHs) formed. The effects of oxygenate addition to the benzene base flame were seen to result in interesting differences, especially regarding trends to form PAH. The modeling results indicated that the concentration of acetylene and propargyl radicals, the main PAH precursors, as well as the PAH amounts were lower in the flame of the ethanol-benzene fuel mixture than in the pure benzene flame and that all of the formed PAHs were issued from the phenyl radical. Finally, the modeling results provided evidence that the PAH reduction was a result of simply replacing "sooting" benzene with "nonsooting" ethanol without influencing the combustion chemistry of the benzene.     

Effects of ultrasound frequency and acoustic amplitude on the size of sonochemically active bubbles – Theoretical study

Numerical simulation of chemical reactions inside an isolated spherical bubble of oxygen has been performed for various ambient bubble radii at different frequencies and acoustic amplitudes to study the effects of these two parameters on the range of ambient radius for an active bubble in sonochemical reactions. The employed model combines the dynamic of bubble collapse with the chemical kinetics of single cavitation bubble. Results from this model were compared with some experimental results presented in the literature and good apparent trends between them were observed. The numerical calculations of this study showed that there always exists an optimal ambient bubble radius at which the production of oxidizing species at the end of the bubble collapse attained their upper limit. It was shown that the range of ambient radius for an active bubble increased with increasing acoustic amplitude and decreased with increasing ultrasound frequency. The optimal ambient radius decreased with increasing frequency. Analysis of curves showing optimal ambient radius versus acoustic amplitude for different ultrasonic frequencies indicated that for 200 and 300 kHz, the optimal ambient radius increased linearly with increasing acoustic amplitude up to 3 atm. However, slight minima of optimal radius were observed for the curves obtained at 500 and 1000 kHz.     

Selective preconcentration of amino acids and peptides using single drop microextraction in-line coupled with capillary electrophoresis

Single drop microextraction (SDME) can be in-line coupled with capillary electrophoresis by attaching a drop to the tip of a capillary. With a 2-layer drop comprised of an aqueous basic acceptor phase covered with a thin organic layer, acidic analytes in an aqueous acidic donor phase can be extracted into the organic layer and then back-extracted into the acceptor phase. However, preconcentration of amino acids and peptides by SDME is difficult since their zwitterionic properties prevent them from being partitioned in the middle organic phase. When amino acids were derivatized with 4-fluoro-7-nitro-2,1,3-benzoxadiazole (NBD-F), amino acids without a charged side chain were converted to carboxylic acids. In the acidic donor phase, those NBD-amino acids were predominantly neutral and they were successfully concentrated into the basic acceptor phase. In the meantime, amino acids with a charged side chain after NBD-F derivatization were not concentrated via SDME. With this selective SDME, we were able to extract acidic and neutral amino acids obtaining several hundred-fold enrichments within 5 min at 25 °C, while leaving basic amino acids—Arg, Lys, and His—in the acidic donor phase. Furthermore, detection sensitivity was enhanced by employing laser-induced fluorescence detection. We then applied this technique to the selective concentration of peptides.     

Accurate mass measurement by matrix‐assisted laser desorption/ionisation time‐of‐flight mass spectrometry. I. Measurement of positive radical ions using porphyrin standard reference materials

A method for the accurate mass measurement of positive radical ions by matrix‐assisted laser desorption/ionisation time‐of‐flight mass spectrometry (MALDI‐TOFMS) is described. Initial use of a conjugated oligomeric calibration material was rejected in favour of a series of meso‐tetraalkyl/tetraalkylaryl‐functionalised porphyrins, from which the two calibrants required for a particular accurate mass measurement were chosen. While all measurements of monoisotopic species were within ±5 ppm, and the method was rigorously validated using chemometrics, mean values of five measurements were used for extra confidence in the generation of potential elemental formulae. Potential difficulties encountered when measuring compounds containing multi‐isotopic elements are discussed, where the monoisotopic peak is no longer the lowest mass peak, and a simple mass‐correction solution can be applied. The method requires no significant expertise to implement, but care and attention is required to obtain valid measurements. The method is operationally simple and will prove useful to the analytical chemistry community. Copyright © 2010 John Wiley & Sons, Ltd.     

Integrable spin chain for the SL(2,R)/U(1) black hole sigma model

We introduce a spin chain based on finite-dimensional spin-1/2 SU(2) representations but with a non-Hermitian "Hamiltonian" and show, using mostly analytical techniques, that it is described at low energies by the SL(2,R)/U(1) Euclidian black hole conformal field theory. This identification goes beyond the appearance of a noncompact spectrum; we are also able to determine the density of states, and show that it agrees with the formulas in [J. Maldacena, H. Ooguri, and J. Son, J. Math. Phys. (N.Y.) 42, 2961 (2001)] and [A. Hanany, N. Prezas, and J. Troost, J. High Energy Phys. 04 (2002) 014], hence providing a direct "physical measurement" of the associated reflection amplitude.     

CdSe/ZnS quantum dot-Cytochrome c bioconjugates for selective intracellular O2˙⁻ sensing

We demonstrate that the coupling system of negatively capped CdSe/ZnS QDs with an oxidized Cytochrome c (Cyt c) is capable of the fluorescent imaging of a superoxide radical (O(2)˙?) with high sensitivity and specificity in living cells, without interference from other Reactive Oxygen Species (ROS) or relevant intracellular components.     

Tyrosine phosphorylation of Munc18c on residue 521 abrogates binding to Syntaxin 4

Background  

Insulin stimulates exocytosis of GLUT4 from an intracellular store to the cell surface of fat and muscle cells. Fusion of GLUT4-containing vesicles with the plasma membrane requires the SNARE proteins Syntaxin 4, VAMP2 and the regulatory Sec1/Munc18 protein, Munc18c. Syntaxin 4 and Munc18c form a complex that is disrupted upon insulin treatment of adipocytes. Munc18c is tyrosine phosphorylated in response to insulin in these cells. Here, we directly test the hypothesis that tyrosine phosphorylation of Munc18c is responsible for the observed insulin-dependent abrogation of binding between Munc18c and Syntaxin 4.