Pd nanoparticles immobilized on PNIPAM–halloysite: highly active and reusable catalyst for Suzuki–Miyaura coupling reactions in water

Poly(N‐isopropylacrylamide)–halloysite (PNIPAM‐HNT) nanocomposites exhibited inverse temperature solubility with a lower critical solution temperature (LCST) in water. Palladium (Pd) nanoparticles were anchored on PNIPAM‐HNT nanocomposites with various amounts of HNT from 5 to 30 wt%. These Pd catalysts exhibited excellent reactivities for Suzuki–Miyaura coupling reactions at 50–70 °C in water. In particular, Pd anchored PNIPAM/HNT (95:5 w/w ratio) nanocomposites showed excellent recyclability up to 10 times in 96% average yield by simple filtration. Copyright © 2014 John Wiley & Sons, Ltd.     

Switched exponential state estimation of neural networks based on passivity theory

In this paper, a new exponential state estimation method is proposed for switched Hopfield neural networks based on passivity theory. Through available output measurements, the main purpose is to estimate the neuron states such that the estimation error system is exponentially stable and passive from the control input to the output error. Based on augmented Lyapunov–Krasovskii functional, Jensen’s inequality, and linear matrix inequality (LMI), a new delay-dependent state estimator for switched Hopfield neural networks can be achieved by solving LMIs, which can be easily facilitated by using some standard numerical packages. The unknown gain matrix is determined by solving delay-dependent LMIs. Finally, a numerical example is provided to demonstrate the effectiveness of the proposed method.     

Ag/Ni Metallization Bilayer: A Functional Layer for Highly Efficient Polycrystalline SnSe Thermoelectric Modules

The structural and electrical characteristics of Ag/Ni bilayer metallization on polycrystalline thermoelectric SnSe were investigated. Two difficulties with thermoelectric SnSe metallization were identified for Ag and Ni single layers: Sn diffusion into the Ag metallization layer and unexpected cracks in the Ni metallization layer. The proposed Ag/Ni bilayer was prepared by hot-pressing, demonstrating successful metallization on the SnSe surface without interfacial cracks or elemental penetration into the metallization layer. Structural analysis revealed that the Ni layer reacts with SnSe, forming several crystalline phases during metallization that are beneficial for reducing contact resistance. Detailed investigation of the Ni/SnSe interface layer confirms columnar Ni-Sn intermetallic phases [(Ni₃Sn and Ni₃Sn₂) and Ni_5.63SnSe₂] that suppress Sn diffusion into the Ag layer. Electrical specific-contact resistivity (5.32 × 10^?4 Ω cm²) of the Ag/Ni bilayer requires further modification for development of high-efficiency polycrystalline SnSe thermoelectric modules.     

Micromorphology of epicuticular wax structures of the garden strawberry leaves by electron microscopy: Syntopism and polymorphism

Ultrastructural aspects of leaf epicuticular wax structures were investigated in the garden strawberry Fragaria × ananassa by scanning and transmission electron microscopy. Both the adaxial and abaxial surfaces of two cultivars (Maehyang and Red Pearl) were collected and subjected to surface observations and ultrathin sections. The most prominent leaf epicuticular wax structures included membraneous platelets and angular rodlets. Most wax platelets were membraneous, and appeared to protrude from the surface at an acute angle. Angular rodlets were usually bent and had rather distinct facets in the abaxial surface of the two cultivars. Membraneous platelets were predominant on the adaxial surface of Maehyang, whereas the adaxial surface of Red Pearl was characterized by angular rodlets. However, both cultivars possessed angular rodlets on the abaxial surface, simultaneously. The combination of air-drying without vacuum and in-lens imaging of secondary electron signals with a field emission gun could impart the superb resolution at low electron dose with minimal specimen shrinkage. In vertical profiles of the leaf epidermis, epicuticular waxes were observed above the cuticle layer, and measured approximately as 50 nm in thickness. The natural epicuticular waxes were seemingly mixtures of electron-dense microfibrils, and heterogeneous in shape on ultrathin sections. Distinct crystal-like strata could be hardly discernable in the wax structures. These results suggest that the garden strawberry has the nature of syntopism within one plant and polymorphism within the same species in the formation and occurrence of leaf epicuticular waxes.     

ε‐Branched Flexible Side Chain Substituted Diketopyrrolopyrrole‐Containing Polymers Designed for High Hole and Electron Mobilities

Based on the integrated consideration and engineering of both conjugated backbones and flexible side chains, solution‐processable polymeric semiconductors consisting of a diketopyrrolopyrrole (DPP) backbone and a finely modulated branching side chain (ε‐branched chain) are reported. The subtle change in the branching point from the backbone alters the π?π stacking and the lamellar distances between polymer backbones, which has a significant influence on the charge‐transport properties and in turn the performances of field‐effect transistors (FETs). In addition to their excellent electron mobilities (up to 2.25 cm² V^?1 s^?1), ultra‐high hole mobilities (up to 12.25 cm² V^?1 s^?1) with an on/off ratio (I_on/I_off) of at least 10⁶ are achieved in the FETs fabricated using the polymers. The developed polymers exhibit extraordinarily high electrical performance with both hole and electron mobilities superior to that of unipolar amorphous silicon.     

Rates of Sulfonation of Bead Copolymers of Styrene Cross - Linked with Mixtures of m- and p-Divinylbenzene

Abstract

The rate of sulfonation of bead copolymers of styrene cross-linked with 8 mole % divinylbenzene (mixed isomers) is remarkably sensitive to the isomeric (para/meta) composition of the mixture of divinylbenzenes. The rate is enhanced by a factor of 4 for compositions containing 20–40% para isomer.     

Palladium-Catalyzed Arylation and Vinylation of 2,3-Dihydrofuran with Hypervalent Iodonium Salts

The palladium-catalyzed arylation and vinylation of 2,3-dihydrofuran with aryl and alkenyl iodonium salts afforded 2-phenyl- or 2-alkenyl-2,5-dihydrofurans at room temperature in an aqueous medium.     

5′-O-TBDMS-3′-O--(1H-Imidazole-1-Thiocarbonyl)thymidine: A Novel Intermediate for the Synthesis of 2,3′-Anhydrothymidine

Thermal or base-promoted conversion of 5′-O-TBDMS-3′-O-(1H-imidazole-1-thiocarbonyl)thymidine (1) afforded 5′-O-TBDMS-2,3′-anhydro-thymidine (2), a pivotal intermediate for the transformation of the 3′-hydroxy group of 2′-deoxyribonucleosides, in high yield.     

Synthesis and characterisation of photopolymerisable liquid crystals based on the π-extended fluorene core and their corresponding non-reactive analogues

We have synthesised a series of new reactive mesogens with photopolymerisable di-acrylates and their corresponding non-reactive analogues based on the π-conjugated aromatic core, fluorene (F)-di-[thiophene (T)-benzene (B)], using the Stille and Suzuki coupling reaction. The effect of lateral alkyl chains on the 9-position of the central fluorene moiety as well as α, ω- side alkyl chains attached to the π-conjugated aromatic core on the mesomorphism was investigated by utilising differential scanning calorimetry (DSC) and polarising optical microscopy (POM). A wide angle X-ray scattering (WAXS) study at the various temperatures was also carried out to reveal phase structures. Photopolymerisable di-acrylates connected directly to the rigid aromatic core showed higher phase transition temperatures, probably due to the induced dipole moment in comparison with those of a non-reactive methyl–ether counterpart.