Enantioselectivity of 6-O-alkyldimethylsilyl-2,3-di-O-methyl-β-cyclodextrins as chiral stationary phases in capillary GC

Summary Clenbuterol has been determined in urine by solidphase extraction on a C₁₈ cartridge, diazotization of the eluate with nitrite, coupling of the diazonium ion with 1-(naphthyl)ethylenediamine, and separation of the azo dye formed by HPLC with a C₁₈ column and a micellar mobile phase containing 0.1 M sodium dodecyl sulphate, 12%n-butanol and 0.05 M citrate buffer, pH 3. Recoveries higher than 90% were obtained by mixing the samples with a 20% 0.2 M NaOH before extraction. Limits of detection of 51 and 6.7 ng L⁻¹ were obtained with spectrophotometric and thermal lens spectrometric detection, respectively; respective repeatabilities were 3.1% (5 μg mL⁻¹) and 5.6% (0.16 μg mL⁻¹).     

Rigorous information-theoretic derivation of quantum-statistical thermodynamics. II

Part I of the present work outlined the rigorous application of information theory to a quantum mechanical system in a thermodynamic equilibrium state. The general formula developed there for the best-guess density operator \(\hat \rho\) was indeterminate because it involved in an essential way an unspecified prior probability distribution over the continuumD _H of strong equilibrium density operators. In Part II mathematical evaluation of \(\hat \rho\) is completed after an epistemological analysis which leads first to the discretization ofD _H and then to the adoption of a suitable indifference axiom to delimit the set of admissible prior distributions. Finally, quantal formulas for information-theoretic and thermodynamic entropies are contrasted, and the entire work is summarized.     

Tuning chirality of single-wall carbon nanotubes by selective etching with carbon dioxide

CO2 molecule chemisorbs selectively on the zigzag tube edge without an activation barrier, whereas it physisorbs on the armchair edge of nanotubes. In addition, carbon nanotubes can be etched by an adsorbed oxygen atom of CO2 molecule. From our results, we suggest a selective etching mechanism for tuning the chirality of the mass-produced carbon nanotubes.     

A series of long-chain lamellar hydrated copper(II) alkylsulfonates with different chain molecular assemblies

Reaction of copper(II) salts with n-alkylsulfonate anions yields light blue lamellar Cu(C(n)H(2n + 1)SO3)2 x zH2O displaying distinct (mono/bi-layer) chain packing with increasing alkyl chain lengths. This may be attributed to the amphiphilic nature of the surfactants, i.e., the hydrophilic sulfonate head groups, mediating the coordination, and H-bonding interactions, and the hydrophobic alkyl chains.     

Studies on polymers and composites from lignin and fiber derived from sugar cane

Sugarcane fiber (i.e. bagasse) lignin has a larger fraction of aromatics unsubstitution in the ortho position than hardwood or softwood lignin and hence has the greater ability to be derivatized. Furthermore, organosolv lignin has a higher purity than sulfonated and kraft lignins. This work examines the purification of organosolv lignin derived from bagasse and the physico‐chemical properties of the lignin and lignin‐phenol formaldehyde (PF) resin coatings, and composites. The wetability tests have shown that lignin and lignin‐PF resin films are effective water barrier coatings, though the contact angles of lignin‐PF resin films were considerably less than the wax films. The overall mechanical properties (i.e. peak stress, peak strain and modulus) of the bagasse fiber composites were lower than the values obtained with the composites without the inclusion of bagasse fiber. Copyright © 2007 John Wiley & Sons, Ltd.     

Analysis of an ancient bronze statue by external beam pixe

A quantitative analysis of an ancient Buddha statue was performed by external beam Proton Induced X-ray Emission for the purpose of identifying its originality. It is shown how the PIXE method can be applied for archeological study. The elemental composition of the statue is compared with that of several samples with definite ages. The experiment was performed by extracting 2.4 MeV proton beam through a 2 mm diameter collimator and 7.6 m kapton foil to the He atmosphere. X-rays were measured by a Si(Li) detector. The analysed elements were Fe, Cu, Ag, Au and Hg for gold coating and Fe, Ni, Cu, Zn, As, Ag, Sn, Au, Pb and Bi for bronze body.     

Stacking sequence effect of aramid–UHMPE hybrid composites by flexural test method: MATERIAL PROPERTIES

Aramid fibre–ultra-high modulus polyethylene (UHMPE) fibre interply hybrid composites were fabricated with changes in the stacking sequence. The flexural strength and modulus of hybrid composites were measured in order to investigate the effect of stacking sequence. Scanning electron microscopy (SEM) was used to examine the fracture surface of interply hybrid composites. When aramid fibre was at the compressive side and dispersion extent of fibers was small, the higher flexural strength and positive hybrid effect were observed. In addition, the different stacking sequence resulted in a change in flexural failure mechanism which had an effect on the flexural strength. As the dispersion extent of fibers decreased, the introduction of cohesive failure in aramid–aramid interface and PE–PE interface improved the flexural strength of hybrid composites.     

DNA-templated self-assembly of protein and nanoparticle linear arrays

Self-assembling DNA tiling lattices represent a versatile system for nanoscale construction. Self-assembled DNA arrays provide an excellent template for spatially positioning other molecules with increased relative precision and programmability. Here we report an experiment using a linear array of DNA triple crossover tiles to controllably template the self-assembly of single-layer or double-layer linear arrays of streptavidin molecules and streptavidin-conjugated nanogold particles through biotin-streptavidin interaction. The organization of streptavidin and its conjugated gold nanoparticles into periodic arrays was visualized by atomic force microscopy and scanning electron microscopy.     

Imidazole-based excited-state intramolecular proton-transfer materials: synthesis and amplified spontaneous emission from a large single crystal

We have synthesized a novel class of imidazole-based excited-state intramolecular proton-transfer (ESIPT) materials, i.e., hydroxy-substituted tetraphenylimidazole (HPI) and its derivative HPI-Ac, which formed large single crystals exhibiting intense blue fluorescence and amplified spontaneous emission (ASE). Transparent, clear, and well-defined fluorescent single crystals of HPI-Ac as large as 20 mm x 25 mm x 5 mm were easily grown from its dilute solution. From the X-ray crystallographic analysis and semiempirical molecular orbital calculation, it was deduced that the four phenyl groups substituted into the imidazole ring of HPI and HPI-Ac allowed the crystals free from concentration quenching of fluorescence by limiting the excessive tight-stacking responsible for intermolecular vibrational coupling and relevant nonradiative relaxation. Fluorescence spectral narrowing and efficient ASE were observed in the HPI-Ac single crystal even at low excitation levels attributed to the intrinsic four-level ESIPT photocycle.