Palladium‐catalysed P?C bond forming reactions between diphenylphosphine and ortho‐substituted aryl bromides

The use of palladium catalysts derived from 1,1′‐bis‐diisopropylphosphino‐ferrocene and a microwave heating source allows the coupling of a range of ortho‐substituted aryl bromides to diphenylphosphine derivatives to proceed in good yield in under 30 min. Optimization studies reveal that the combination of diphenylphosphine and DABCO is superior to more basic phosphide nucleophiles such as Ph₂PK or Ph₂PMgBr. High yields are only observed when moderately bulky electron rich diphosphines are used as ligands. The differences between P? C coupling and other cross‐coupling reactions are discussed in the light of the reactivity observed. Studies aimed at producing industrially important 1,2‐bis‐phosphino‐benzene ligands are also described. Copyright © 2009 John Wiley & Sons, Ltd.     

Synthesis,self‐assembly and adsorption of PEO–PLA block copolymers onto colloidal polystyrene

A series of amphiphilic block copolymers composed of poly(ethylene oxide) and poly(lactide) were synthesized and their solution properties studied using static and dynamic light scattering. These materials self‐assemble in aqueous media with the hydrodynamic radius increasing with increasing hydrophobic fraction in the copolymer. To ascertain the potential for use of these materials as degradable coatings in delivery applications, block copolymers of varying compositions were adsorbed onto a series of colloidal polystyrene particles with varying radii, and the thickness of the adsorbed layer was determined from changes in the hydrodynamic size. The adlayer thicknesses ranged from 3 to 14 nm with varying block copolymer compositions, and colloid radii. The trends fit well with theoretical models for adlayer thickness, with the exception of the smallest colloids. In these systems, we propose that the colloids may become encapsulated into the block copolymer assembly. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 244–252, 2008     

Spectroscopic investigations on polypropylene‐carbon nanofiber composites. I. Raman and electron spin resonance spectroscopy

Isotactic polypropylene‐vapor grown carbon nanofiber composites containing various fractions of carbon nanofibers, ranging from 0 to 20 wt %, have been prepared. Raman spectroscopy was used to analyze the effect of the dispersion of carbon nanofibers within polypropylene and the interactions between carbon nanofibers and macromolecular chains. The as‐recorded Raman spectra have been successfully fitted by a linear convolution of Lorentzian lines. Changes of the Raman lines parameters (position, intensity, width, and area) of polypropylene and carbon nanofibers were analyzed in detail. The Raman spectra of the polymeric matrix—at low concentrations of nanofibers—show important modifications that indicate strong interactions between carbon nanofibers and the polymeric matrix reflecting by vibrational dephasing of macromolecular chains. The Raman spectrum of carbon nanofibers is sensitive to the loading with carbon nanofibers, showing changes of the resonance frequencies, amplitudes, and width for both D‐ and G‐bands. Raman data reveals the increase of the disorder, as the concentration of carbon nanofibers is increased. The presence of the typical ESR line assigned to conducting electrons delocalized over carbon nanofibers is confirmed and the presence of a spurious magnetic line due to catalyst's residues is reported. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1644–1652, 2009     

Structural Stability for Ill-Posed Problems in Banach Space

We prove Holder-continuous dependence results for the difference between solutions of certain ill-posed and approximate well-posed problems in both Hilbert and Banach spaces. We use operator-theoretic methods, including C-semigroups, to treat the abstract Cauchy problem $\frac{du}{dt} = Au, u(0) = \chi, 0 \leq t < T,$ where the operator $-A$ is the infinitesimal generator of a holomorphic semigroup.     

Isolation of lanthanides from spent nuclear fuel by means of high performance ion chromatography (HPIC) prior to mass spectrometric analysis

Pure and complete fractions of neodymium, samarium, europium, gadolinium and dysprosium were isolated by means of high performance ion chromatography, using a cation exchange column and gradient elution with alpha-hydroxyisobutyric acid solutions (α-HIBA). Intermediate precision and robustness of the isolation method was investigated, identifying eluent pH as the most important parameter. Investigation of the elution behaviour of the most important fission and activation products and actinides indicated that preventing the accumulation of cesium on the cation exchange column required further isocratic elution with a higher concentrated α-HIBA solution after elution of the lanthanides. A sample matrix free of carbon was achieved by means of acid digestion, followed by UV photo-oxidation, resulting in samples suitable for mass spectrometric analysis.

     

Study on cyanobiphenyl nematic doped by silver nanoparticles

We study the effects of doped (1%wt and 2%wt) silver nanoparticles on material properties of nematic liquid crystal: 4-pentyl-4′-cyanobiphenyl. Using differential scanning calorimetry, electrical and dielectric measurements methods, we show that the doped NPs do not affect the nematic’s phase clearing point, lower the dielectric anisotropy, viscosity, switching-off time, and increase the threshold voltage and elasticity of the nematic. We report that the doped materials temperature behaviour of Frederick’s transition threshold voltage and switching-off time, deviates from the expected behaviour for pristine nematics. To explain this anomalous behaviour, we perform data analysis of the governing Frederick’s transition material parameters of studied samples. We show that the elastic parameter of doped samples is not following the predictions of Maier–Saupe theory, which is valid for conventional nematics. We report that the doped samples temperature behaviour of the elastic parameter follows the predictions of the Gelbart and Ben-Shaul theory.     

Ultrathin Carbon Film Electrodes from Vacuum‐Carbonised Cellulose Nanofibril Composite

A novel way to produce ultrathin transparent carbon layers on tin‐doped indium oxide (ITO) substrates is developed. The ITO surface is coated with cellulose nanofibrils (from sisal) via layer‐by‐layer electrostatic binding with poly(diallyldimethylammonium chloride) or PDDAC acting as the binder. The cellulose nanofibril‐PDDAC composite film is then vacuum‐carbonised at 500 °C. The resulting carbon films are characterised by atomic force microscopy (AFM), small angle X‐ray scattering (SAXS), wide‐angle X‐ray scattering (WAXS), and Raman methods. Smooth carbon films with good adhesion to the ITO substrate are formed. The electrochemical characterisation of the carbon films is based on the oxidation of hydroquinone and the reduction of benzoquinone in aqueous phosphate buffer media. A modest effect of the cellulose nanofibril‐PDDAC film on the rate of electron transfer is observed. The effect of the film on the rate of electron transfer after carbonisation is more dramatic. For a 40‐layer cellulose nanofibril‐PDDAC film after carbonisation a two‐order of magnitude change in the rate of electron transfer occurs presumably due to a better interaction of the hydroquinone/benzoquinone system with the electrode surface.     

Preparation and characterization of standard reference material 1849 infant/adult nutritional formula

Standard Reference Material (SRM) 1849 Infant/Adult Nutritional Formula has been issued by the National Institute of Standards and Technology (NIST) as a replacement for SRM 1846 Infant Formula, issued in 1996. Extraction characteristics of SRM 1846 have changed over time, as have NIST's analytical capabilities. While certified mass fraction values were provided for five constituents in SRM 1846 (four vitamins plus iodine), certified mass fraction values for 43 constituents are provided in SRM 1849 (fatty acids, elements, and vitamins) and reference mass fraction values are provided for an additional 43 constituents including amino acids and nucleotides, making it the most extensively characterized food-matrix SRM available from NIST.