Method development for the determination of 24S‐hydroxycholesterol in human plasma without derivatization by high‐performance liquid chromatography with tandem mass spectrometry in atmospheric pressure chemical ionization mode

We developed a highly sensitive and specific high‐performance liquid chromatography with tandem mass spectrometry method with an atmospheric pressure chemical ionization interface to determine 24S‐hydroxycholesterol, a major metabolite of cholesterol formed by cytochrome P450 family 46A1, in human plasma without any derivatization step. Phosphate buffered saline including 1% Tween 80 was used as the surrogate matrix for preparation of calibration curves and quality control samples. The saponification process to convert esterified 24S‐hydroxycholesterol to free sterols was optimized, followed by liquid–liquid extraction using hexane. Chromatographic separation of 24S‐hydroxycholesterol from other isobaric endogenous oxysterols was successfully achieved with gradient mobile phase comprised of 0.1% propionic acid and acetonitrile using L‐column2 ODS (2 μm, 2.1 mm id × 150 mm). This assay was capable of determining 24S‐hydroxycholesterol in human plasma (200 μL) ranging from 1 to 100 ng/mL with acceptable intra‐ and inter‐day precision and accuracy. The potential risk of in vitro formation of 24S‐hydroxycholesterol by oxidation from endogenous cholesterol in human plasma was found to be negligible. The stability of 24S‐hydroxycholesterol in relevant solvents and human plasma was confirmed. This method was successfully applied to quantify the plasma concentrations of 24S‐hydroxycholesterol in male and female volunteers.     

Electrical Properties of Polycrystalline Lithium Chloroboracite Prepared by the Sol-Gel Method

The electrical properties of polycrystalline lithium chloroboracite, Li4B7O12Cl, prepared by the sol-gel method were investigated in connection with their structure. Li4B7O12Cl pellets were prepared with different amounts of hydrochloric acid or ammonium chloride. The kind and amount of the chlorine source affected the formation of by-products (Li2B4O7, LiCl, a glass phase) and the morphology of the Li4B7O12Cl pellets. Thus their conductivity, which is dominated by grain boundary response owing to the high porosity of the materials, was also affected. The formation of Li2B4O7 as a by-product led to a higher activation energy and lower conductivity. In those pellets in which Li2B4O7 did form, an increase of the amount of glass phase led to higher conductivities.     

Synthesis and characterization of titanium and zirconium complexes with silicone-bridged phenoxycyclopentadienyl ligands

Dimethylsilyl(2,3,4,5-tetramethylcyclopentadienyl)(3-tert-butyl-5-methyl-2-phenoxy)titanium dichloride (1a), a useful catalyst precursor for olefin copolymerization, was synthesized at high yield starting from allyl-protected phenolic ligand 3a,which was first treated with 2 equiv. of n-BuLi to selectively give the dilithium salt of 3a along with 1-heptene, a coupling product of a protected allyl ether moiety and butyl anion. Addition of TiCl₄ to the resulting dilithium salt of 3a in toluene afforded 1a in 50% isolated yield. This methodology could be applied to the preparation of related titanium and zirconoium complexes 1b-1d, 8 with silicone-bridged Cp-phenoxy ligands, whereas the reaction starting from methyl-protected precursor 2a did not produce the zirconium complex 8. Copolymerization of ethylene and 1-hexene with the newly prepared complexes was also investigated.     

Diisobutylaluminum hydride-promoted cyclization of silylated 1,3-dien-5-ynes: Application to total synthesis of a 20-norabietane derivative

The diisobutylaluminum hydride (DIBAL-H)-promoted benzocyclization, recently developed by this group, was adopted for the synthesis of a natural product containing a 9,10-dihydrophenanthrene skeleton to demonstrate its synthetic utility. One of the extracts from the roots of Salvia hydrangea DC. ex Bentham (Lamiaceae), a 20-norabietane derivative, was selected as the target molecule. The key step forming the 9,10-dihydrophenanthrene skeleton was achieved by the DIBAL-H-promoted cyclization of a silylated 1,3-dien-5-yne easily accessible from a substituted α-tetralone.     

Projector Monte Carlo method based on Slater determinants: a new sampling method for singlet state calculations

A new sampling method is proposed for projector Monte Carlo (PMC) calculations based on Slater determinants (SD) in singlet states. Using the symmetry of the ?? and ?? electron determinants, the number of configurations to be considered can be about one-half of the original sampling. We applied the new sampling to the PMC-SD calculations of the H₂O molecule in the ground state. The results were always improved by the new sampling method both for the equilibrium and for bond-stretched structures.     

Uniaxially aligned carbon nanofibers derived from electrospun precursor yarns

Unlike conventional electrospun polymer fibers deposited on a target electrode as a randomly oriented mesh, poly(p‐xylenetetrahydrothiophenium chloride) was electrospun into centimeters‐long yarns vertically on the surface of the electrode but parallel to the electric field. The diameter of the yarn was strongly affected by the concentration, spinning rate, and viscosity of the polymer solution, but less dependent on the applied voltage. The subsequent carbonization of thus‐electrospun yarns at 600–1000 °C resulted in uniaxially aligned carbon nanofibers with average diameters of 127–184 nm. On the basis of Raman spectra, the graphitic crystallite size and the molar fraction of graphite were estimated to be 1.2–1.4 and 0.21–0.24 nm, respectively. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 305–310, 2008     

Improvement in superconductivity of TlBa2CaCu2Oy system by introduction of oxygen loss

The T_c and oxygen content of TlBa₂CaCu₂O_y have been investigated by quenching experiments, in which the heat-treated samples were dropped into liquid nitrogen. The oxygen loss, v, of TlBa₂CaCu₂O_{yo − v} was determined by thermogravimetry in a nitrogen atmosphere using an oxygen-annealed specimen of TlBa₂CaCu₂O_yo and also by measurements of the weight differences before and after quenching. T_c increased from 80 K of the oxygen-annealed specimen up to about 110 K with increasing oxygen loss up to v = 0.035 by annealing at 500°C in a nitrogen atmosphere. Judging from the high T_c above 110 K achieved by a small oxygen loss about v = 0.035, the as-sintered oxygen-annealed TlBa₂CaCu₂O_yo specimen was in the over-doping state and probably has an oxygen vacancy of 7 − y_o0.