White-Light-Emitting Self-Assembled NanoFibers and Their Evidence by Microspectroscopy of Individual Objects

The self-assembly of a blue-emitting light-harvesting organogelator and specifically designed highly fluorescent tetracenes yields nanofibers with tunable emissive properties. In particular, under near-UV excitation, white light emission is achieved in organogels and dry films of nanofibers. Confocal fluorescence microspectroscopy demonstrates that each individual nanofiber emits white light. A kinetic study shows that an energy transfer (ET) occurs between the blue-emitting anthracene derivative and the green- and red-emitting tetracenes, while inter-tetracene ETs also take place. Moreover, microscopy unravels that the nanofibers emit polarized emission in the blue spectral region, while at wavelengths higher than 500 nm the emission is not significantly polarized.     

Sustainable and green microextraction of organophosphorus flame retardants by a novel phosphonium‐based deep eutectic solvent

Based on the solidification of a hydrophobic deep eutectic solvent in air‐assisted liquid phase microextraction combined with gas chromatography and mass spectrometry, a green and sustainable microextraction technique was developed for extracting, separating, and detecting organophosphorus flame retardants in aqueous samples. In this study, some strategies were considered for overcoming or improving the challenges of conventional solvent microextraction procedures. In addition, a hydrophobic deep eutectic solvent with a freezing point near the ambient temperature was employed as an extraction phase, the dispersive solvent was substituted by the syringe pump process, and the centrifugation step was omitted by using salting‐out phenomenon. Further, the effect of the main independent variables was evaluated by using the chemometric methods in order to maximize the extraction efficiency of the procedure. Under optimal conditions, the calibration model was linear in the range of 0.01–25.0 µg/L. Limits of detection and quantitation were assessed at the concentration levels of 2–23 and 9–65 ng/L, respectively. The precision involving repeatability and reproducibility was evaluated by estimating the relative standard deviation, the levels of which were <6.6 and <8.7%, respectively. The applicability of the method was successfully evaluated by analyzing the target analytes in real aqueous samples, which illustrated satisfactory recoveries (95–104.61%).     

A reformulation of the nonsmooth approaches of M. Frémond and J.J. Moreau for rigid body dynamics

This paper deals with the nonsmooth dynamics of a rigid bodies system. The proposed theory is inspired by the formalism of J.J. Moreau and that of M. Frémond and relies on the notion of percussion which is the integral of the contact force during the duration of the collision. Contrary to classical discrete element models, it is here assumed that percussions can be expressed as a function of only the velocity before the impact. This assumption is checked for the usual mechanical constitutive laws for collisions derived from a pseudopotential of dissipation or the Coulomb friction law. Motion equations are then reformulated taking into account simultaneous collisions of solids. A mathematical study of the new model is presented: the existence and uniqueness of the solution are discussed according to the regularity of both the forces (Lebesgue‐density occurring during the regular evolution of the system) and the percussions (Dirac‐density describing the collision). In the light of the principles of thermodynamics, a condition on the internal percussion assuring that the collision is thermodynamically admissible, is established. Finally, an application of this new model to the motion of a system of rigid disks, including simultaneous collisions is presented.     

Covariant Wigner function approach to the relativistic quantum electron gas in a strong magnetic field

This paper is concerned with a unified approach to some equilibrium properties of the relativistic quantum electron plasma embedded in a strong external magnetic field. This unified approach rests on the systematic use of a covariant Wigner function. The equilibrium Wigner function of the noninteracting gas is derived and its main properties are studied. In particular, it satisfies equations that are the complete analog of the usual Liouville equation and thus can be termed “relativistic quantum Liouville equation” whose properties are considered. The equations of state are rederived in this formalism and the results obtained earlier by Canuto and Chiu are found anew. Also, the covariant Wigner funetion of the magnetized vacuum is derived: it is needed, in this formalism, in order to obtain, e.g., the vacuum polarization tensor. Since we are also interested in the plasma modes, the fluctuations of one-particle quantities—and their spectrum—(in particular, of the four current) are calculated in view of their use in the fluctuation-dissipation theorem. We also outline a microscopic proof of this theorem, on the basis of a BBGKY hierarchy for the covariant Wigner functions, and point out the existence of an effective plasma frequency.     

Expression of Recombinant Human Epidermal Growth Factor in Escherichia coli and Characterization of its Biological Activity

Recombinant human epidermal growth factor (EGF) was successfully expressed as a fusion protein in Escherichia coli system. This system was used OmpA signal sequence to produce soluble protein into the periplasm of E. coli. Human EGF (hEGF) synthesized in bacterial cell was found to be similar in size with the original protein and molecular weight approximately at 6.8 kDa. Cell proliferation assay was conducted to characterize the biological activity of hEGF on human dermal fibroblasts. The synthesized hEGF was found to be functional as compared with authentic hEGF in stimulating cell proliferation and promoting growth of cell. In comparison of biological activity between synthesized and commercial hEGF on cell proliferation, the results showed there was no significant different. This finding indicates the synthesized hEGF in E. coli system is fully bioactive in vitro.     

Alpha-phenyl-N-tert-butylnitrone-type derivatives bound to beta-cyclodextrins: syntheses, thermokinetics of self-inclusion and application to superoxide spin-trapping

alpha-Phenyl-N-tert-butylnitrone (PBN) derivatives bound to beta-cyclodextrin derivatives have been synthesized. Inclusion of the PBN group into the beta-cyclodextrin moiety is host- and temperature-dependent. In the case of the nitrone linked to permethylated cyclodextrin (Me3CD-PBN), the thermokinetic parameters are in favour of a slow chemical exchange between a tight and a loose complex. In contrast, 2,6-di-O-Me-beta-cyclodextrin-grafted PBN (Me2CD-PBN) exists either in a fast exchange or as a strongly self-associated complex. The covalent cyclodextrin-PBN compounds have been used to trap carbon and oxygen-centred free radicals. The self-associated forms of the beta-CD-spin-traps are compatible with effective spin-trapping, affording spin-adducts with enhanced EPR signal intensities relative to noncovalent CD-nitrone systems or the nitrone alone. This kind of cyclodextrin-bound nitrone is the first type of covalent supramolecular spin-trap and should open new possibilities for the study of biological free radicals in vivo.     

Synthesis of novel chitosan resin derivatized with serine diacetic acid moiety and its application to on-line collection/concentration of trace elements and their determination using inductively coupled plasma-atomic emission spectrometry

A novel chelating resin functionalized with serine diacetic acid moiety was synthesized by using chitosan as base material, and applied to the collection/concentration of trace elements in environmental water samples, followed by the determination using inductively coupled plasma-atomic emission spectrometer (ICP-AES). The synthesized resin, crosslinked chitosan serine diacetic acid (CCTS-SDA), showed good adsorption behavior toward trace amounts of Cd, Pb, Cu, Ni, V, Ga, Sc, In, and Th in a wide pH range. Additionally, rare earth elements also can be retained on the resin at neutral pH region. The adsorbed elements can be easily eluted with 1 mol L⁻¹ of nitric acid, and their recoveries were found to be 90-100%. The CCTS-SDA was packed in a mini-column, which was then installed in a computer-controlled auto-pretreatment system (Auto-Pret System) for on-line trace elements collection and determination with ICP-AES. Experimental parameters which related to the improvement of sensitivity and reproducibility were optimized. The limits of detection (LOD) for 13 elements were found to be in sub-ppb level. The proposed method with CCTS-SDA resin was successfully applied to the determination of trace elements in river water samples. The method was validated by determining a certified reference material of river water, SLRS-4.     

Does phenomenological kinetics provide an adequate description of heterogeneous catalytic reactions?

Phenomenological kinetics (PK) is widely used in the study of the reaction rates in heterogeneous catalysis, and it is an important aid in reactor design. PK makes simplifying assumptions: It neglects the role of fluctuations, assumes that there is no correlation between the locations of the reactants on the surface, and considers the reacting mixture to be an ideal solution. In this article we test to what extent these assumptions damage the theory. In practice the PK rate equations are used by adjusting the rate constants to fit the results of the experiments. However, there are numerous examples where a mechanism fitted the data and was shown later to be erroneous or where two mutually exclusive mechanisms fitted well the same set of data. Because of this, we compare the PK equations to "computer experiments" that use kinetic Monte Carlo (kMC) simulations. Unlike in real experiments, in kMC the structure of the surface, the reaction mechanism, and the rate constants are known. Therefore, any discrepancy between PK and kMC must be attributed to an intrinsic failure of PK. We find that the results obtained by solving the PK equations and those obtained from kMC, while using the same rate constants and the same reactions, do not agree. Moreover, when we vary the rate constants in the PK model to fit the turnover frequencies produced by kMC, we find that the fit is not adequate and that the rate constants that give the best fit are very different from the rate constants used in kMC. The discrepancy between PK and kMC for the model of CO oxidation used here is surprising since the kMC model contains no lateral interactions that would make the coverage of the reactants spatially inhomogeneous. Nevertheless, such inhomogeneities are created by the interplay between the rate of adsorption, of desorption, and of vacancy creation by the chemical reactions.     

多相CeO2催化剂上氧化吲哚与醛的选择性C3烯基化反应

本文报道了将市售CeO2作为一种高活性和可重复使用的催化剂用于无溶剂条件下氧化吲哚与醛的C3选择性烷基化反应.这种催化方法一般适用于不同的芳香族和脂肪族醛,得到3-烷基二烯-辛醇,产率高(87%–99%),立体选择性高(79%–93%为E-异构体).这是从氧化吲哚与各种脂肪族醛催化合成3-烯基氧化吲哚的首例.采用原位红外光谱研究了CeO2上Lewis酸位点与苯甲醛之间的Lewis酸-碱相互作用.不同粒径CeO2催化剂的构效关系研究表明,无缺陷CeO2表面是该反应的活性中心.