Microscale preconcentration by liquid-liquid extraction of cadmium in indium and nickel

Microscale preconcentration techniques using 1 to 10 milligrams of samples and microliter volumes of aqueous solutions and organic solvents are described for the determination of cadmium at the sub-ppm level in indium and nickel by graphite-furnace atomic absorption spectrometry. Several simple apparatus are devised to overcome operational difficulties resulting from the miniaturization and ensure the precision and accuracy of analytical results. Cadmium in the metals is heterogeneously distributed.     

Group Transfer Carbonylations: Photoinduced Alkylative Carbonylation of Alkenes Accompanied by Phenylselenenyl Transfer

The photolysis of methyl alpha-(phenylseleno)acetate (1b) and related compounds in the presence of an alkene and CO leads to acyl selenides 2 via group transfer carbonylation. The mechanism of this three-component coupling reaction involves the addition of a (methoxycarbonyl)methyl radical to an alkene, the trapping of the produced alkyl free radical by CO, and termination of the reaction by a phenylselenenyl group transfer from the starting material.     

Total synthesis of mycalamide A

This communication describes a concise and efficient total synthesis of mycalamide A by the convergent coupling of pederic acid unit with the mycalamine unit. The left-half, (+)-7-benzoylpederic acid, was synthesized from (2R,3R)-3-methylpent-4-en-2-ol in seven steps and 34.6% overall yield through a route that features a one-step Pd(II)-catalyzed tandem Wacker/Heck cyclization reaction to prepare the tetrahydropyran ring system. The right-half, the mycalamine unit, was synthesized in 21 steps and 10.5% overall yield from diethyl d-tartrate. Effective, stereoselective methods were developed for the assembly of the two parts to yield either mycalamide A or C(10)-epi-mycalamide A.     

Orientation of fluorinated cholesterol in lipid bilayers analyzed by 19F tensor calculation and solid-state NMR

6-F-cholesterol was reported to exhibit biological and interfacial properties similar to unmodified cholesterol. We have also found that 6-F-cholesterol mimicked the cholesterol activity observed in the systems of amphotericin B and lipid rafts. However, to use 6-F-cholesterol as a molecular probe to explore molecular recognition in membranes, it is indispensable to have detailed knowledge of the dynamic and orientation properties of the molecule in membrane environments. In this paper, we present the molecular orientation of 6-F-cholesterol (30 mol %) in dimyristoylphosphatidylcholine (DMPC) bilayers revealed by combined use of 19F chemical shift anisotropy (CSA), 2H NMR, and C-F rotational echo double resonance (REDOR) experiments. The axis of rotation of 6-F-cholesterol was shown to be in a similar direction to that of cholesterol in DMPC bilayers, which is almost parallel to the long axis of the molecular frame. The molecular order parameter of 6-F-cholesterol was determined to be ca. 0.85, which is within the range of reported values of cholesterol. These findings suggest that the dynamic properties of 6-F-cholesterol in DMPC are quite similar to those of unmodified cholesterol; therefore, the introduction of a fluorine atom at C6 has virtually no effect on cholesterol dynamics in membranes. In addition, this study demonstrates the practical utility of theoretical calculations for determining the 19F CSA principal axes, which would be extremely difficult to obtain experimentally. The combined use of quantum calculations and solid-state 19F NMR will make it possible to apply the orientation information of 19F CSA tensors to membrane systems.     

Vinyl polymerization. 416. Polymerization of vinyl monomer initiated by polyethyleneglycol

The polymerization of vinyl monomer initiated by polyethyleneglycol (PEG) in aqueous solution was carried out at 85°C with shaking. Acrylonitrile (AN), methyl methacrylate (MMA), and methacrylic acid were polymerized by PEG–300 (M?_n = 300), whereas styrene was not. The effects of the amounts of monomer and PEG, the molecular weight of PEG, and the hydrophobic group at the end of PEG molecule on the polymerization were studied. The selectivity of vinyl monomer and the effect of the hydrophobic group are discussed according to “the concept of hard and soft hydrophobic areas and monomers.” The kinetics of the polymerization was investigated. The overall activation energy in the polymerization of AN was estimated as 37.9 kJ mol^?1. The polymerization was effected by a radical mechanism.     

Physical properties of sol-gel derived poly(Vinylidene Fluoride)/Silica hybrid

Poly(vinylidene fluoride) (PVDF) was incorporated in situ with silica by a sol-gel process involving tetraethoxysilane. The mechanical properties of these in situ hybrids were compared with those of PVDF composites mechanically blended with 14-nm diameter fumed silica particles. The ultimate strength of the in situ hybrids was higher than that of the blend composites, since fumed silica particles aggregate and act as mechanically weak points. The thermal analysis, dynamic viscoelastic properties, and dielectric properties were compared. The β-relaxation of PVDF caused by the glass transition was observed at around −40°C in the differential scanning calorimetry (DSC) and the mechanical tan δ curves and at −30°C in the dielectric loss factor (ϵ”) curve. The αc-relaxation due to the molecular motion in the crystalline phase occurred at 61°C in DSC curve, at 100°C in the tan δ curve, and at 80°C in the ϵ” curve. The peak positions of these relaxations did not change, but the peak intensities were decreased with the increase in silica content for both the in situ hybrids and blend composites. The activation energies for PVDF were calculated as 136 kJ/mol for the β-relaxation and 96 kJ/mol for the αc-relaxation. The result that these activation energies did not depend on silica content may indicate the weak interaction between PVDF and silica.