Crystal structures of high-valent transition-metal chalcogenide fluorides

The structures of high-valent transition-metal chalcogenide fluorides are of interest since it is not clear whether they will be related to those of their oxide-fluoride analogues or to those of the transition-metal chalcogenide chlorides and bromides. This will depend on the extent to which substitution of fluorine for chlorine or bromine or sulphur, or selenium for oxygen has the more significant effect.The first single-crystal structure on a compound of this class, WSF₄, shows that it consists of octahedrally coordinated tungsten atoms linked by cis-bridged fluorine atoms into polymeric chains. This, together with work on the structure of ReSF₄, suggests that the tendency is to follow oxide-fluoride and fluoride structures.     

The mechanism of reaction of tetraalkyltins with mercuric carboxylates in methanol

In the reaction of mercuric carboxylates with tetraalkyltins in methanol, rate constrants for attack of the species (RCO₂)₂ Hg increase along the series R = t-Bu < Et < Me < Ph < ClCH₂CH₂ < MeOCH₂ < ClCH₂ which suggests an open transition state for these S_E2 substitutions.     

Thermal desorption of hydrogen from carbon nanosheets

Carbon nanosheets are a unique nanostructure that, at their thinnest configuration, approach a single freestanding graphene sheet. Temperature desorption spectroscopy (TDS) has shown that the hydrogen adsorption and incorporation during growth of the nanosheets by radio frequency plasma-enhanced chemical vapor deposition are significant. A numerical peak fitting to the desorption spectra (300-1273 K) via the Polanyi-Wigner equation showed that desorption followed a second order process, presumably by the Langmuir-Hinshelwood mechanism. Six peaks provide the best fit to the TDS spectra. Surface desorption activation energies were determined to be 0.59, 0.63, and 0.65 eV for the external graphite surface layers and 0.85, 1.15, and 1.73 eV for desorption and diffusion from the bulk. In contrast to TDS data from previously studied a-C:H films [Schenk et al. J. Appl. Phys. 77, 2462 (1995)], a greater amount of hydrogen bound as sp(2) hybridized carbon was observed. A previous x-ray diffraction study of these films has shown a significant graphitic character with a crystallite dimension of L(a)=10.7 nm. This result is consistent with experimental results by Raman spectroscopy that show as-grown carbon nanosheets to be crystalline as commercial graphite with a crystallite size of L(a)=11 nm. Following TDS, Raman data indicate that the average crystallite increased in size to L(a)=15 nm.     

The enthalpy of formation of tungsten thiotetrafluoride

The enthalpy of hydrolysis of solid tungsten thiotetrafluoride, WF(in4)S, in aqueous sodium hydroxide solution is -528.2 kJ mo1^-1. Hence its standard enthalpy of formation has been calculated to be -1150.5 kJ mo1^-1.     

On the lamb solution and Rayleigh-wave-induced cracking

This paper examines the extension of surface microcracks induced by a surface or Rayleigh wave (R-wave). This problem is examined both theoretically and experimentally. The theoretical approach involves a full-field reappraisal of the Lamb solution for a surface wave propagating in a homogeneous, isotropic, elastic, two-dimensional material for the cases of plane strain and plane stress. Using the Griffith-Irwin energy-release-rate fracture criterion for cracks under combined Mode I and Mode II loading, a prediction is made of the path and final length of the surface microcrack extension produced by the R-wave. Predictions of the crack-extension direction are also obtained using the maximum normal-stress fracture criterion. The experimental approach uses dynamic photoelasticity to observe the isochromatic patterns associated with an R-wave propagating along the narrow edge of a transparent birefringent plate, examining in detail the process of crack extension. When the theoretically and experimentally obtained results are compared, reasonable agreement is obtained.     

Synthesis of water-dispersible fluorescent, radio-opaque, and paramagnetic CdS:Mn/ZnS quantum dots: a multifunctional probe for bioimaging

Ultra-small (3.1 nm) multifunctional CdS:Mn/ZnS core-shell semiconductor quantum dots (Qdots), which possess fluorescent, radio-opacity, and paramagnetic properties, have been shown here. To demonstrate in vivo bioimaging capability, a rat was administered endovascularly with Qdots conjugated with a TAT peptide. The labeling efficacy of these Qdots was demonstrated on the basis of the histological analysis of the microtome sliced brain tissue, clearly showing that TAT-conjugated Qdots stained brain blood vessels.     

Delayed onset of intermolecular bonding in the water adlayer on Ru(001) due to the presence of preadsorbed oxygen

Infrared reflection absorption spectroscopy has been employed to study adsorption of water on Ru(001) at liquid nitrogen temperatures. For even the lowest H₂O coverages a broad absorption band at ≈3400 cm^?1 is observed on the clean surface, indicating formation of hydrogen-bonded clusters Small amounts of preadsorbed oxygen delay the clustering process.     

New Antibacterial Diterpenes from Pseudopterogorgia elisabethae

From the MeOH extract of Pseudopterogorgia elisabethae, collected from the Bahamas, four new diterpenes, elisabethin E ( 1 ), elisabethin F ( 2 ), pseudopterosin P ( 3 ), and pseudopterosin Q ( 4 ), were isolated and their structures established with the aid of extensive spectroscopic studies. Compounds 3 and 4 showed antibacterial activity selectively against the Gram‐positive bacteria Streptococcus pyogenes, Staphylococcus aureus, and Enterococcus faecalis.     

Synthesis and characterization of colloidal ternary ZnCdSe semiconductor nanorods

For the synthesis of colloidal ternary ZnCdSe nanorods, CdSe nanorods were first prepared under a mixture of tetradecylphosphonic acid/trioctylphosphine oxide surfactants at 250 degrees C, and then ZnSe shell layer was grown onto CdSe nanorods at 180 degrees C, forming CdSeZnSe core/shell nanorods. Green-yellow emitting ternary ZnCdSe nanorods were obtained by a subsequent alloying process at 270 degrees C for 1-3 h through the diffusion of Zn ions into CdSe nanorods. The photoluminescence quantum yield (QY) of ZnCdSe nanorods was 5%-10%, which is higher than that from pristine CdSe nanorods (0.6%). The QY of these alloy nanorods depends on the alloying time and is discussed in terms of compositional disorders and defects produced by the alloying process. The Raman and time resolved photoluminescence spectroscopies were used to understand the detailed alloying process from CdSeZnSe core/shell to ZnCdSe alloy nanorods.