Polymerization of higher α‐olefins using a Cs‐symmetry hafnium metallocene catalyst. Kinetics of the polymerization and microstructural analysis

The C_s‐symmetry hafnium metallocene [(p‐Et₃Si)C₆H₄]₂C(2,7‐di‐tert‐BuFlu)(C₅H₄)Hf(CH₃)₂ and tetrakis(pentafluorophenyl) borate dimethylanilinium salt ([B(C₆F₅)₄]^?[Me₂NHPh]⁺) were used as the catalytic system for the polymerization of higher α‐olefins (from hexene‐1 to hexadecene‐1) in toluene at 0 °C. The evolution of the polymerization was studied regarding the variation of the molecular weight, molecular weight distribution and yield with time. The effect of the monomer structure on the polymerization kinetics was established. The role of trioctylaluminum in accelerating the polymerization was investigated. ¹³C NMR spectroscopy was used to study the microstructure of the poly(α‐olefins) by the determination of the pentad monomer sequences. The thermal properties of the polymers were obtained by differential scanning calorimetry, DSC. The results were discussed in connection with the polymer microstructure. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4314–4325, 2009     

Electrochemical Impedance Spectroscopy and Cyclic Voltammetry of <Emphasis Type="Italic">cis</Emphasis>-[Cr(bipy)<Subscript>2</Subscript>(SCN)<Subscript>2</Subscript>]I (where bipy: 2,2′-Bipyridine) in Polar Solvents

Cyclic voltammetric studies (CV) on the complex cis-bis(2,2′-bipyridine)bis(thiocyanate)chromium(III) iodide [Cr(bipy)₂(SCN)₂]I (where bipy: 2,2′-bipyridine, C₁₀H₈N₂) were recorded on platinum (Pt) and glassy carbon (GC) electrodes in either acetonitrile (ACN) or acetone (ACE) solvent media including n-tetrabutylammonium hexafluorophosphate (NBu₄PF₆) as supporting electrolyte, at scan rates (v) ranging from 0.05 to 0.12 V⋅s⁻¹. In addition, electrochemical impedance spectroscopic (EIS) measurements in the frequency (f) range from 0.1 Hz to 50 kHz were carried out on GC and Pt electrodes. The half-wave potential (E _1/2) of the redox couple Cr(III)/Cr(II) was determined as −0.84 V and −0.79 V (versus Ag/AgCl) in ACN and ACE, respectively. The heterogeneous electron transfer rate constant (k _s) corresponding to the couple Cr(III)/Cr(II) was found to be greater on GC compared to the Pt electrode. The nature of the solvent medium also affects the kinetics of the investigated couple, to be exact, k _s increases remarkably upon replacement of ACE by ACN. The EIS results indicate that the GC electrode is a better capacitor and provides the smaller charge transfer resistance in ACN.     

Thin film pyrolytic carbon electrodes: A new class of carbon electrode for electroanalytical sensing applications

This communication describes the electrochemical properties of thin pyrolytic carbon (PyC) films created using a reliable, non-catalytic chemical vapour deposition (CVD) process. After deposition, the electron transfer characteristics of the films are optimised using a simple oxygen plasma treatment. The redox probes Ru(NH₃)₆^3+/2+, Fe(CN)₆^3?/4? and Fe^3+/2+ are employed to demonstrate that the resulting material is endowed with a large electrochemical surface area and outstanding electron transfer properties. Atomic force microscopy (AFM), Raman and X-ray photoelectron spectroscopy (XPS) are used to elucidate the morphology and chemical composition of the electrode surfaces. This material represents a new class of carbon electrode, and its large densities of edge-plane sites and oxygenated functionalities make it an ideal candidate for electrochemical sensor applications.     

Bioconjugated quantum dots as fluorescent probes for bioanalytical applications

Quantum dots (QDs) are inorganic semiconductor nanocrystals that have unique optoelectronic properties responsible for bringing together multidisciplinary research to impel their potential bioanalytical applications. In recent years, the many remarkable optical properties of QDs have been combined with the ability to make them increasingly biocompatible and specific to the target. With this great development, QDs hold particular promise as the next generation of fluorescent probes. This review describes the developments in functionalizing QDs making use of different bioconjugation and capping approaches. The progress offered by QDs is evidenced by examples on QD-based biosensing, biolabeling, and delivery of therapeutic agents. In the near future, QD technology still faces some challenges towards the envisioned broad bioanalytical purposes.      

Dielectric breakdown and avalanches at nonequilibrium metal-insulator transitions

Motivated by recent experiments on the finite temperature Mott transition in VO(2) films, we propose a classical coarse-grained dielectric breakdown model where each degree of freedom represents a nanograin which transitions from insulator to metal with increasing temperature and voltage at random thresholds due to quenched disorder. We describe the properties of the resulting nonequilibrium metal-insulator transition and explain the universal characteristics of the resistance jump distribution. We predict that by tuning voltage, another critical point is approached, which separates a phase of boltlike avalanches from percolationlike ones.     

Generalized Landau-Lifshitz models on the interval

We study the classical generalized gln Landau-Lifshitz (L-L) model with special boundary conditions that preserve integrability. We explicitly derive the first non-trivial local integral of motion, which corresponds to the boundary Hamiltonian for the sl₂ L-L model. Novel expressions of the modified Lax pairs associated to the integrals of motion are also extracted. The relevant equations of motion with the corresponding boundary conditions are determined. Dynamical integrable boundary conditions are also examined within this spirit. Then the generalized isotropic and anisotropic gln Landau-Lifshitz models are considered, and novel expressions of the boundary Hamiltonians and the relevant equations of motion and boundary conditions are derived.     

Asymptotics for Hessenberg Matrices for the Bergman Shift Operator on Jordan Regions

Let $G$ be a bounded Jordan domain in the complex plane. The Bergman polynomials $\{p_n\}_{n=0}^\infty $ of $G$ are the orthonormal polynomials with respect to the area measure over $G$ . They are uniquely defined by the entries of an infinite upper Hessenberg matrix $M$ . This matrix represents the Bergman shift operator of $G$ . The main purpose of the paper is to describe and analyze a close relation between $M$ and the Toeplitz matrix with symbol the normalized conformal map of the exterior of the unit circle onto the complement of $\overline{G}$ . Our results are based on the strong asymptotics of $p_n$ . As an application, we describe and analyze an algorithm for recovering the shape of $G$ from its area moments.