Gold(I)‐Catalyzed Highly Diastereo‐ and Enantioselective Cyclization–[4+3] Annulation Cascades between 2‐(1‐Alkynyl)‐2‐alken‐1‐ones and Anthranils

This work reports gold‐catalyzed [4+3]‐annulations of 2‐(1‐alkynyl)‐2‐alken‐1‐ones with anthranils to yield epoxybenzoazepine products with excellent exo‐diastereoselectivity (dr>25:1). The utility of this new gold catalysis is manifested by applicable substrates over a broad scope. More importantly, the enantioselective versions of these [4+3]‐cycloadditions have been developed satisfactorily with chiral gold catalysts under ambient conditions (DCM, 0 °C); the ee levels range from 88.0–99.9 %. With DFT calculations, we postulate a stepwise pathway to rationalize the preferable exo‐stereoselection.     

Effect of the premelting temperature and sample thickness on the polymorphic behavior of syndiotactic polystyrene/clay nanocomposites

X‐ray diffraction methods and differential scanning calorimetry thermal analysis have been used to investigate the structural changes of syndiotactic polystyrene (sPS)/clay nanocomposites. sPS/clay nanocomposites have been prepared by the mixing of sPS polymer solutions with organically modified montmorillonite. X‐ray diffraction data and differential scanning calorimetry results indicate that the dominating crystal forms and their relative fractions in sPS and sPS/clay nanocomposites are different for various premelting temperatures (T_max's). Higher T_max's favor the formation of the thermodynamically more stable β‐crystalline form, and its relative fraction has been obtained from the X‐ray diffraction data in the range of 11.5–13°. The intensity of the X‐ray diffraction data in the range of 11.5–13° decreases as the thickness of sPS/clay nanocomposites decreases from 150 to 20 μm. At the same time, the intensity of the X‐ray data in the range of 6–7° becomes sharper as the thickness of sPS/clay nanocomposites decreases. The calculation ratio based on the peak intensities at 6.2 and 6.8° for sPS/clay nanocomposites of equal thickness and crystallinity in the pure β and α forms has also been determined in this study. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1730–1738, 2003     

Polymorphic behavior in syndiotactic polystyrene/clay nanocomposites

X‐ray diffraction methods were used in an investigation of the structural changes in syndiotactic polystyrene (sPS)/clay nanocomposites. sPS/clay was prepared by the intercalation of sPS polymer into layered montmorillonite. Both X‐ray diffraction data and transmission electron microscopy micrographs of sPS/clay nanocomposites indicated that most of the swellable silicate layers were exfoliated and randomly dispersed in the sPS matrix. The X‐ray diffraction data also showed the presence of polymorphism in the sPS/clay nanocomposites. This polymorphic behavior was strongly dependent on the thermal history of the sPS/clay nanocomposites from the melt and on the content of clay in the sPS/clay nanocomposites. Quenching from the melt induced crystallization into the α‐crystalline form, and the addition of montmorillonite probably increased heterophase nucleation of the α‐crystalline form. The effect of the melt crystallization of sPS and sPS/clay nanocomposites at different temperatures on the crystalline phases was also examined. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 736–746, 2002     

Investigation of Flavonoid Glycosides from Neolitsea Sericea var. Aurata via the General Method and HPLC‐SPE‐NMR

Six flavonoid rhamnosides ( 1‐2, 4‐7 ) were separated from the water‐soluble non‐alkaloidal portion of the EtOH extract of the leaves of Neolitsea sericea var. aurata using various chromatographic techniques including Sephadex LH‐20, centrifugal partition chromatography, and RP‐18 Lobar. One additional compound ( 3 ) besides these six was identified by application of HPLC‐SPE‐NMR in a flavonoid rich fraction. The latter approach consumed only 1.5 mg of samples, theoretically equivalent to 0.2 g of dry leaves. This study demonstrates that HPLC‐SPE‐NMR has great advantage over the general methods on the aspects of manpower, research time, amounts of plant materials, and consumables in separation and characterization of natural products.     

Evaluation of the pH- and thermal stability of the recombinant green fluorescent protein (GFP) in the presence of sodium chloride

The thermal stability of recombinant green fluorescent protein (GFP) in sodium chloride (NaCl) solutions at different concentrations, pH, and temperatures was evaluated by assaying the loss of fluorescence intensity as a measure of denaturation. GFP, extracted from Escherichia coli cells by the three-phase partitioning method and purified through a butyl hydrophobic interaction chromatography (HIC) column, was diluted in water for injection (WFI) (pH 6.0-7.0) and in 10 mM buffer solutions (acetate, pH 5.0; phosphate, pH 7.0; and Tris-EDTA, pH 8.0) with 0.9-30% NaCl or without and incubated at 80-95 degrees C. The extent of protein denaturation was expressed as a percentage of the calculated decimal reduction time (D-value). In acetate buffer (pH 4.84+/-0.12), the mean D-values for 90% reduction in GFP fluorescence ranged from 2.3 to 3.6 min, independent of NaCl concentration and temperature. GFP thermal stability diluted in WFI (pH 5.94+/-0.60) was half that observed in phosphate buffer (pH 6.08+/-0.60); but in both systems, D-values decreased linearly with increasing NaCl concentration, with D-values (at 80 degrees C) ranging from 3.44, min (WFI) to 6.1 min (phosphate buffer), both with 30% NaCl. However, D-values in Tris-EDTA (pH 7.65+/-0.17) were directly dependent on the NaCl concentration and 5-10 times higher than D-values for GFP in WFI at 80 degrees C. GFP pH- and thermal stability can be easily monitored by the convenient measure of fluorescence intensity and potentially be used as an indicator to monitor that processing times and temperatures were attained.     

VCSEL based Faraday rotation spectroscopy with a modulated and static magnetic field for trace molecular oxygen detection

Faraday Rotation Spectroscopy (FRS) is a useful technique for quantification of paramagnetic trace gases with significantly higher sensitivity when compared to direct absorption techniques. Our prototype system based on the openPHOTONS sensor core measures the concentration of molecular oxygen (O₂) in the A band using a 763-nm vertical cavity surface emitting laser. We provide detailed analysis of two measurement methods based on FRS using the same sensor configuration: one with a modulated magnetic field, and one with a static magnetic field in combination with wavelength modulation. Our spectra signal-to-noise ratios agree well with our simulations via modeling of the FRS signal. For alternating magnetic field, we achieve an equivalent minimum detectable absorption (MDA) of 8.86×10^-7/Hz^\frac128.86\times 10^{-7}/\mathrm{Hz}^{\frac{1}{2}} resulting in a minimum detection limit of 30 ppmv⋅m/ Hz^\frac12\mathrm{Hz}^{\frac{1}{2}} of O₂, limited by detector noise and laser noise. For the same system configuration in the static field case, parasitic etalon fringes limited the MDA to 4.8×10^-6/Hz^\frac124.8\times 10^{-6}/\mathrm{Hz}^{\frac{1}{2}}. In both cases, we describe methods to improve signal-to-noise ratio based on our data and models.     

Growth of nano Co encapsulated in carbon-shell

Nanostructured cobalt is one of the key elements in catalysis and therapeutic drug delivery. To design and prepare nanosize-controllable cobalt, a better understanding of its growth mechanism is essential. Growth of Co nanoparticles encapsulated in carbon-shell (Co@C) during temperature-programmed carbonization of the Co²⁺-β-cyclodextrin (CD) complex at 363–573 K was, therefore, studied by in situ synchrotron small-angel X-ray scattering and X-ray absorption near edge structure spectroscopy. The carbon-shell having a thickness of about 2 nm can prevent the core Co from being aggregated and oxidized. A relatively slow reduction of Co(II) to Co is observed at 393–423 K (stage I) prior to a particle growth transition-state possessing Co of 2.2 nm in diameter at 423–483 K. At 483–513 K (stage II), an increasing Co(II) reduction rate coupled with a rapid fusion and coalescence of Co nanoparticles is found. The average growth rates of Co at stages I and II are about 27 and 98 atoms/min, respectively. The most-probable particle diameter of the ripened Co is 5.9 nm. The carbon-shell can be removed by steam reforming to yield the Co nanoparticles. This work also exemplifies the possible temperature-controllable growth of Co@C, especially in the Co size range of 2–6 nm in diameter.     

Numerical Methods for Constrained Equations of Motion in Mechanical System Dynamics

ABSTRACT

ABSTRACT A new class of numerical methods for solving equations of motion of constrained mechanical systems is presented, the framework of which is based on manifold theoretic methods. Rewriting the system of differential-algebraic equations (DAEs) that describe constrained motion is ordinary differentia] equations (ODEs) on a constraint manifold, the theoretical framework for solving equations of motion is constructed, using a local     

The mechanism of the recrystallization process in epitaxial GaN under dynamic stress field: atomistic origin of planar defect formation

The mechanism of the recrystallization in epitaxial (0001) GaN film, introduced by the indentation technique, is probed by lattice dynamic studies using Raman spectroscopy. The recrystallized region is identified by micro‐Raman area mapping. ‘Pop‐in’ bursts in loading lines indicate nucleation of dislocations and climb of dislocations. These processes set in plastic motion of lattice atoms under stress field at the center of indentation for the initiation of the recrystallization process. A planar defect migration mechanism is evolved. A pivotal role of vacancy migration is noted, for the first time, as the rate‐limiting factor for the dislocation dynamics initiating the recrystallization process in GaN. Copyright © 2009 John Wiley & Sons, Ltd.     

Improvement of field emission of graphite flakes using hydrogen thermal processing

In order to improve the field electron emission properties of the graphite, the carbon nanoparticles (CNPs) are synthesized on the micrographite flakes by hydrogen thermal processing. We spin the graphite solution on the silicon wafer and desiccate it, then produce the CNPs on the graphite flakes using hydrogen thermal processing in the furnace. The processing parameters such as the processing temperature, hydrogen flow rate and processing time, were varied to find the optimal conditions for the improvement of the field emission properties of the graphite flakes. The experimental results show that the field emission properties of the graphite flakes have glaring improvement after heat treatment owing to the increase of the defect density and the CNPs on above. The turn-on field was decreased from 7.7 of the untreated sample to 4.3 V/μm of the treated sample at the optimal processing conditions.