Ring opening of 2-acylaziridines by acid chlorides

Good nucleophilicity of the ring nitrogen in chiral (2R,1′R)-2-acyl-(1′-phenylethyl)aziridines initiated the reaction with various acid chlorides to form the corresponding acylaziridinium ion intermediates whose rings were opened by the chloride anion to yield the β-amino-α-chlorocarbonyl compounds. The subsequent displacement of the chloride with the internal oxygen nucleophile originated from methylchloroformate, acetyl chloride, and methyl chlorooxoacetate yielded oxazolidin-2-ones, β-amino-α-acetyloxypropionates, and morpholin-2,3-diones, respectively.     

Fluorescence enhancement of N2O2-type dipyrrin ligand in two step responding to zinc(II) ion

Fluorescence imaging is well-suited for the live imaging of biological Zn(II), which has no facile spectroscopic or magnetic signature. The successful application of this methodology requires the development of robust Zn(II) imaging agents that display high sensitivity, selectivity and temporal fidelity. In this study, a N₂O₂-type dipyrrin based bimolecular zinc(II) complex was produced and shown to have sharper, blue-shifted and more enhanced fluorescence emission. An approximate three-fold fluorescence enhancement was achieved within the micromolar concentration range, which is an important parameter for Zn(II) detection in vivo. The increase in emission intensity was due to the dominant role of aryl-ring rotation in governing the excited state dynamics and fluorescence properties of the dipyrrin dye. Fluorescence titration showed that the ligand complex exhibited very strong zinc(II) binding affinity when compared to that in the binuclear chloro complex. The fluorescence emission changes in the dipyrrin dye to zinc(II) ion could be observed not only using instruments but also by the naked-eye (violet→sky blue).     

Composition operators induced by smooth self-maps of the real or complex unit balls

In this paper, we study the composition operator CΦ with a smooth but not necessarily holomorphic symbol Φ. A necessary and sufficient condition on Φ for CΦ to be bounded on holomorphic (respectively harmonic) weighted Bergman spaces of the unit ball in Cn (respectively Rn) is given. The condition is a real version of Wogen's condition for the holomorphic spaces, and a non-vanishing boundary Jacobian condition for the harmonic spaces. We also show certain jump phenomena on the weights for the target spaces for both the holomorphic and harmonic spaces.     

Benzylic C(sp3)–C(sp2) cross-coupling of indoles enabled by oxidative radical generation and nickel catalysis

A mechanistically unique functionalization strategy for a benzylic C(sp³)–H bond has been developed based on the facile oxidation event of indole substrates. This novel pathway was initiated by efficient radical generation at the benzylic position of the substrate, with subsequent transition metal catalysis to complete the overall transformation. Ultimately, an aryl or an acyl group could be effectively delivered from an aryl (pseudo)halide or an acid anhydride coupling partner, respectively. The developed method utilizes mild conditions and exhibits a wide substrate scope for both substituted indoles and C(sp²)-based reaction counterparts. Mechanistic studies have shown that competitive hydrogen atom transfer (HAT) processes, which are frequently encountered in conventional methods, are not involved in the product formation process of the developed strategy.

A mechanistically distinct Ni-catalysed benzylic functionalization of indoles is developed by the facile oxidation of arenes. The method exhibits a wide substrate scope and pronounced chemoselectivity that cannot be accessed via known protocols.     

Sharp adaptation for spherical inverse problems with applications to medical imaging

This paper examines the estimation of an indirect signal embedded in white noise for the spherical case. It is found that the sharp minimax bound is determined by the degree to which the indirect signal is embedded in the linear operator. Thus, when the linear operator has polynomial decay, recovery of the signal is polynomial, whereas if the linear operator has exponential decay, recovery of the signal is logarithmic. The constants are determined for these classes as well. Adaptive sharp estimation is also carried out. In the polynomial case a blockwise shrinkage estimator is needed while in the exponential case, a straight projection estimator will suffice. The framework of this paper include applications to medical imaging, in particular, to cone beam image reconstruction and to diffusion magnetic resonance imaging. Discussion of these applications are included.     

The application of PCMMcs and SiC by commercially direct dual-complex coating on textile polymer

To enhance the thermal insulation effect, waterproof/breathable fabrics were directly top dual-coated by the dry coating method with ceramic materials (silicon carbide, SiC). The fabric was base coated by the wet coating method with 5 wt% phase-change material microcapsules (PCMMcs) and tested for the emission of far-infrared (FIR) radiation. With increasing SiC content, the fabric altered some of the physical properties by increasing the FIR emissivity, emission power, water vapor transmission rate (WVTR) and heat release capacity. Scanning electron microscopy (SEM) analysis revealed the presence of the PCMMcs and SiC particles at the cross-section and surface of the coating, respectively, which exhibited a rugged and blocky shape. The results indicated that SiC addition did not affect the water entry pressure (WEP) in the fabric structure, but did alter the following physical properties: WVTR, interactions between the macromolecule chains and the susceptibility to humidity.     

Fabrication and characterization of iron oxide nanoparticles filled polypyrrole nanocomposites

The effect of iron oxide nanoparticle addition on the physicochemical properties of the polypyrrole (PPy) was investigated. In the presence of iron oxide nanoparticles, PPy was observed in the form of discrete nanoparticles, not the usual network structure. PPy showed crystalline structure in the nanocomposites and pure PPy formed without iron oxide nanoparticles. PPy exhibited amorphous structure and nanoparticles were completely etched away in the nanocomposites formed with mechanical stirring over a 7-h reaction. The thermal stability of the PPy in the nanocomposites was enhanced under the thermo-gravimetric analysis (TGA). The electrical conductivity of the nanocomposites increased greatly upon the initial addition (20 wt%) of iron oxide nanoparticles. However, a higher nanoparticle loading (50 wt%) decreased the conductivity as a result of the dominance of the insulating iron oxide nanoparticles. Standard four-probe measurements indicated a three-dimensional variable-range-hopping conductivity mechanism. The magnetic properties of the fabricated nanocomposites were dependent on the particle loading. Ultrasonic stirring was observed to have a favorable effect on the protection of iron oxide nanoparticles from dissolution in acid. A tight polymer structure surrounds the magnetic nanoparticles, as compared to a complete loss of the magnetic iron oxide nanoparticles during conventional mechanical stirring for the micron-sized iron oxide particles filled PPy composite fabrication.     

Accuracy evaluation of blood flow distribution in the Fontan circulation: effects of resolution and velocity noise

Journal of Visualization - This study analyzes the accuracy of the Fontan circulation using four-dimensional (4D) flow magnetic resonance imaging (MRI) for a variety of spatial resolution and noise...     

Performance of a Two-Bed Pressure Swing Adsorption Process with Incomplete Pressure Equalization

Incomplete pressure equalization (PE) is practiced in a commercial oxygen concentrator for medical use by adopting simultaneous PE and feed-pressurization for pressurizing an adsorption bed. In such a cycle configuration, extent of equalization during PE affects process performance. In order to assess the effect, performance of pressure swing adsorption (PSA) process with incomplete PE was determined by both simulations and experiments. In simulations, an equilibrium model was used with the assumptions of multicomponent Langmuir isotherms, isothermal operation, and no pressure drop through a bed. The required parameters for simulations were measured in separate experiments. PSA experiments were performed for a two-bed cycle with PE. Two kinds of pressurization, feed and product, were examined. Effects of purge amount and extent of equalization on process performance were assessed in view of productivity and light-component recovery. From the obtained results performance contours were constructed. 95 oxygen mole percent production from air with zeolite 13× was considered as a case study. In both pressurizations, an optimal specific purge and an extent of equalization for the productivity and recovery were observed, but with a different level of equalization. For a maximum productivity feed-pressurization favored incomplete PE, while a maximum recovery occurred at complete PE for both pressurizations. The simulations depicted well existence of optimum conditions, though they showed quantitative disagreement with experiments.     

Spin dimer analysis of the magnetic structures of Ba3Cr2O8, Ba3Mn2O8, Na4FeO4, and Ba2CoO4 with a three-dimensional network of isolated MO4 (M = Cr, Mn, Fe, Co) tetrahedra

The spin exchange interactions of the magnetic oxides Ba3Cr2O8, Ba3Mn2O8, Na4FeO4, and Ba2CoO4 with a three-dimensional network of isolated MO4 (M = Cr, Mn, Fe, Co) tetrahedra were examined by performing spin dimer analysis on the basis of tight-binding electronic structure calculations. Although the shortest O...O distances between adjacent MO4 tetrahedra are longer than the van der Waals distance, our analysis shows that the super-superexchange interactions between adjacent MO4 tetrahedra are substantial and determine the magnetic structures of these oxides. In agreement with experiment, our analysis predicts a weakly interacting isolated AFM dimer model for both Ba3Cr2O8 and Ba3Mn2O8, the (0.0, 0.5, 0.0) magnetic superstructure for Na4FeO4, the (0.5, 0.0, 0.5) magnetic superstructure for Ba2CoO4, and the presence of magnetic frustration in Ba2CoO4. The comparison of the intra- and interdimer spin exchange interactions of Ba3Cr2O8 and Ba3Mn2O8 indicates that orbital ordering should be present in Ba3Cr2O8.