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.     

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.     

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.     

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.     

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.     

Deprotometalation-Iodolysis and Direct Iodination of 1-Arylated 7-Azaindoles: Reactivity Studies and Molecule Properties

Five protocols were first compared for the copper-catalyzed C-N bond formation between 7-azaindole and aryl/heteroaryl iodides/bromides. The 1-arylated 7-azaindoles thus obtained were subjected to deprotometalation-iodolysis sequences using lithium 2,2,6,6-tetramethylpiperidide as the base and the corresponding zinc diamide as an in situ trap. The reactivity of the substrate was discussed in light of the calculated atomic charges and the pK_a values. The behavior of the 1-arylated 7-azaindoles in direct iodination was then studied, and the results explained by considering the HOMO orbital coefficients and the atomic charges. Finally, some of the iodides generated, generally original, were involved in the N-arylation of indole. While crystallographic data were collected for fifteen of the synthesized compounds, biological properties (antimicrobial, antifungal and antioxidant activity) were evaluated for others.     

Mesoporous PtCu Alloy Nanoparticles with Tunable Compositions and Particles Sizes Using Diblock Copolymer Micelle Templates

A simple, scalable route for the generation of mesoporous Rh particles by chemical reduction on self-assembled block-copolymer micelle templates was reported recently (Nat. Commun. 2017 , 8, 15581). Here, this concept is extended to generate mesoporous PtCu alloy nanoparticles through the same approach. The PtCu alloy particles possess high-surface-area nanoporous architectures and good chemical stability for applications in catalysis. Both the composition and diameter of the bimetallic PtCu nanoparticles can be controlled by adjusting the amount of precursor in the reaction, which affects the electrochemical properties of the material. The combination of the mesoporous structure with the synergistic bimetallic electronic effects of PtCu gives rise to enhanced activity for the catalytic oxidation of methanol compared with commercial Pt black.     

On a solvable system of p difference equations of higher order

Periodica Mathematica Hungarica - In this paper we present the well-defined solution of the following system of higher-order rational difference equations: $$\begin{aligned}...     

Finite-Size Left-Passage Probability in Percolation

We obtain an exact finite-size expression for the probability that a percolation hull will touch the boundary, on a strip of finite width. In terms of clusters, this corresponds to the one-arm probability. Our calculation is based on the q-deformed Knizhnik–Zamolodchikov approach, and the results are expressed in terms of symplectic characters. In the large size limit, we recover the scaling behaviour predicted by Schramm’s left-passage formula. We also derive a general relation between the left-passage probability in the Fortuin–Kasteleyn cluster model and the magnetisation profile in the open XXZ chain with diagonal, complex boundary terms.