Thermal decomposition of cyclopentane and related compounds

Cyclopentane has been decomposed in comparative-rate single-pulse shock-tube experiments. The pyrolytic mechanism involves isomerization to 1-pentene and also a minor pathway leading to cyclopropane and ethylene. This is followed by the decomposition of 1-pentene and cyclopropane. The rate expressions over the temperature range of 1000°–1200° K are Details of the cyclopentane decomposition processes are considered, and it appears that if the trimethylene radical is an intermediate, then ΔH_f(trimethylene) ≤ 280 kJ/mol at 300°K.     

Tensile properties and partial alignment of polyacetylene, (CH)x,films

The tensile properties of both cis- and trans-polyacetylene, (CH)_x, were investigated in order to determine the variables that influence that ultimate extension ratio (l/l₀) of polyacetylene films. It was found that when cis-films of polyacetylene were extended in an inert (argon) atmosphere, ultimate extension ratios as high as 3.3 were obtained and with subsequent isomerization at 160–200°C under stress, a final l/l₀, of about 4 was obtained. The extension ratio is extremely sensitive to exposure to oxygen and decreases markedly after periods as short as 1 min. It appears as though crosslinking may occur in the polymer when it is exposed to air and this produces brittleness in the specimen. When (CH)_x was isomerized from cis to trans, it became brittle, even in the absence of air.     

Evidence for strongly temperature-dependent A factors in alkane decomposition and high heats of formation for alkyl radicals

The experimental data on alkane decomposition from shock-tube and radical buffer studies and radical combination from very-low-pressure pyrolysis and modulation spectroscopy are shown to be consistent. They lead to experimental A factors which decrease by factors of 10–2000 from 300° to 1100°K. Heats of formation for ethyl, isopropyl, and t-butyl radicals have been found to be 10, 10 and 20 kJ higher than currently accepted numbers from metathesis reactions.     

A simplified approach to kinetic theory of dense fluids

Time correlation functions may be related to the fluctuating force correlation function in the sub-ensemble with fixed initial particle velocity. The latter may be evaluated by following the trajectories of particle pairs in the fluid.     

Low temperature heat capacity of electrotransported scandium

The heat capacity of two scandium samples containing 1.6 and <5 ppm atomic Fe was measured from 1 to 20 K. The weighted values for γ and θ_D are: 10.340 ± 0.018 mJ/g-at. K² and 346.1 ± 0.9 K, respectively. This is the first time anyone has obtained the same heat capacity results on two different scandium samples. The iron impurity concentration appears to be critical.     

Mode conversion and birefringence adjustment by focused-ion-beam etching for slanted rib waveguide walls

We describe how focused-ion-beam (FIB) etching of slanted rib waveguide walls can be used to modify the differential group delay in a waveguide and introduce TE to TM mode conversion in a silicon-on-insulator rib waveguide. We achieved mode conversion by modifying the geometric cross section of a single-mode rib by FIB trimming. Waveguides with different lengths of 45 degrees slant angle rib waveguide walls were fabricated and characterized. We measured the differential group delays and the mode conversion achieved for waveguides with different lengths of a FIB-trimmed slanted rib wall.     

Absolute potassium cation affinities (PCAs) in the gas phase

The potassium cation affinities (PCAs) of 136 ligands (20 classes) in the gas phase were established by hybrid density functional theory calculations (B3-LYP with the 6-311+G(3df,2p) basis set). For these 136 ligands, 70 experimental values are available for comparison. Except for five specific PCA values-those of phenylalanine, cytosine, guanine, adenine (kinetic-method measurement), and Me(2)SO (by high-pressure mass spectrometric equilibrium measurement)-our theoretical estimates and the experimental affinities are in excellent agreement (mean absolute deviation (MAD) of 4.5 kJ mol(-1)). Comparisons with previously reported theoretical PCAs are also made. The effect of substituents on the modes of binding and the PCAs of unsubstituted parent ligands are discussed. Linear relations between Li+/Na+ and K+ affinities suggest that for the wide range of ligands studied here, the nature of binding between the cations and a given ligand is similar, and this allows the estimation of PCAs from known Li+ and/or Na+ affinities. Furthermore, empirical equations relating the PCAs of ligands with their dipole moments, polarizabilities (or molecular weights), and the number of binding sites were established. Such equations offer a simple method for estimating the PCAs of ligands not included in the present study.     

Using biofunctional magnetic nanoparticles to capture gram-negative bacteria at an ultra-low concentration

After conjugation to vancomycin (Van), chemically stable and highly magnetic anisotropic FePt magnetic nanoparticles (approximately 4 nm) become water-soluble and capture E. coli at 15 cfu mL(-1).     

An enantiomerically pure adamantylimido molybdenum alkylidene complex. An effective new catalyst for enantioselective olefin metathesis

An enantiomerically pure Mo-based complex that bears an alkylimido ligand is prepared and characterized through NMR spectroscopy and X-ray analysis. Mo complex 4 is the only reported chiral alkylimido catalyst; all previous chiral complexes are arylimido systems. These studies show that the chiral Mo catalyst exists exclusively as the syn isomer and that it offers unique reactivity and selectivity profiles in asymmetric olefin metathesis.