Aggregation of 1-dodecyl-3-methylimidazolium nitrate in water and benzene studied by SANS and 1H NMR

Aggregation of imidazolium-based ionic liquid, C(12)mim(+)NO(3)(-), in both polar solvent of water and nonpolar solvent of benzene was elucidated by electrical conductivity, small-angle neutron scattering (SANS), and (1)H NMR measurements. The electrical conductivities of C(12)mim(+)NO(3)(-)-water solutions at 298 K as a function of ionic liquid concentration showed a break point at 8.4 mmol dm(-3) as a cmc. However, those of C(12)mim(+)NO(3)(-)-benzene solutions drastically increase in accordance with a cubic function of concentration, but without a break point. The SANS profiles of both aqueous and benzene solutions obviously differ from each other. The profiles of the aqueous solutions indicated the formation of polydisperse spherical micelles. Those of the benzene solutions revealed Ornstein-Zernike behavior. Thus, C(12)mim(+)NO(3)(-) forms clusters in the benzene solutions, but the shape of clusters is indefinite. On the basis of the (1)H NMR chemical shifts of the aqueous solutions, the effect of nitrate on the formation of micelles was discussed on a microscopic scale. Furthermore, the interactions among C(12)mim(+), NO(3)(-), and benzene molecules in the benzene solutions were considered according to the (1)H NMR data.     

Transport phenomena of aligned ybco polycrystals near vortex-glass transition temperature in weak magnetic field

Abstract

Transport phenomena of aligned polycrystalline Y₁Ba₂Cu₃O_7?δ samples in weak magnetic fields near the vortex-glass transition temperature T_g have been studied. In YBCO polycrystal a fully superconducting state develops via an “intermediate phase”. The non-ohmic dissipation in this “intermediate phase” is examined in terms of both the thermal activated flux-flow (TAFF) model and vortex-glass transition model. Our experimental results in low magnetic fields can better be explained by a vortex glass transition model rather than a TAFF model. We have reinterpreted the non-ohmic dissipative region below T_c , i.e., the so-called “intermediate phase” in terms of a vortex-glass phase.     

High-pressure studies on the coacervation of copoly(<Emphasis Type="Italic">N</Emphasis>-vinylformamide–vinylacetate) and copoly(<Emphasis Type="Italic">N</Emphasis>-vinylacetylamide–vinylacetate)

The effects of pressure on the temperature-induced coacervation of copoly( N-vinylformamide–vinylacetate) and copoly( N-vinylacetylamide–vinylacetate) in aqueous solution were investigated by measuring the apparent light scattering, and the effects of the concentrations of polymer and inert salt were also studied. At lower pressures, the apparent temperature of transition, T _c, increased with an increase in the pressure, but further increases in pressure decreased T _c. In contrast, the apparent pressure of transition, P _c, monotonously increased with decreasing fixed temperature. The T– P diagram was elliptical, but the curvature was not large and extrema were not observed in the low-temperature and high-pressure range. Anions with low lyotropic numbers induced an almost linear decrease in the T _c and P _c, whereas anions with a high number increased the T _c and P _c. In both polymers, the T _c and P _c depended on the concentrations of the polymers, reflecting the association/aggregation mechanism of coacervation. This is in contrast to typical thermoresponsive polymers such as poly( N-isopropylacrylamide) and poly( N-vinylisobutyramide), which show the coil-collapse transition as a single molecular event.     

Toward a structure-activity relationship for apoptolidin: selective functionalization of the hydroxyl group array

[reaction: see text] To investigate the structural basis for the exceptional selectivity and activity of apoptolidin (1), a strategy has been devised that allows for selective functionalization of seven of its eight hydroxyl groups based on progressive silyl protection, derivatization, and deprotection. The syntheses of these derivatives and their ability to inhibit F(0)F(1)-ATPase are reported.     

Temperature dependence of photoluminescence from mono-dispersed Si nanoparticles

The temperature dependence of photoluminescence (PL) from mono-dispersed Si nanoparticles was studied from 4 to 300 K. Si nanoparticles produced by pulsed laser ablation in He background gas were sorted into the 6 nm size range by a differential mobility analyzer (DMA). The spread of the size distribution was narrowed to a geometrical standard deviation _g = 1.05. On decreasing the temperature from 300 to 4 K, the intensity of the PL spectra increased gradually, peaked at about 60 K, and then decreased rapidly. The temperature dependences of the intensity and the full width at half maximum (FWHM) on the PL spectra are discussed in terms of radiative and nonradiative decay rates.     

Squaric acids: a new motif for designing inhibitors of protein tyrosine phosphatases

[structure: see text] Protein tyrosine phosphatases (PTPases) are important targets in medicinal chemistry. These enzymes play a role in a number of human diseases, including type II diabetes and infection by Yersinia pestis, the causative agent of bubonic plague. Derivatives of squaric acids such as 2-aryl-1-hydroxycyclobut-1-ene-3,4-diones represent a new class of monoanionic inhibitors for PTPases.     

Growth of single-walled carbon nanotubes from size-selected catalytic metal particles

Single-walled carbon nanotubes (SWNTs) were synthesized using size-controlled catalyst nanoparticles created by the pulsed laser ablation method. Specifically, the alloy particles (Co/Mo or Co/Pt) were prepared by ablation of the target alloy materials in an inert gas atmosphere. Size selection was performed using a differential mobility analyzer (DMA). The obtained nanoparticles were deposited on a quartz substrate from which SWNTs were grown by the alcohol catalytic CVD (ACCVD) technique that was developed by the authors group. AFM and Raman scattering analysis revealed that SWNTs were successfully synthesized. It seems the Co/Mo alloy catalyst was more effective for the synthesis of SWNTs than the Co/Pt catalyst, though this is a preliminary result to be further investigated. PACS 36.40.-c; 61.46.+w; 65.80.+n; 78.30.Na; 81.07.de