Effect of frequency sweep direction on motion of excited ions in fourier transform ion cyclotron resonance cells

Ion motion during frequency sweep excitation was computer simulated to study the effect of the direction of frequency sweep on the z motion of ions in a cylindrical Fourier transform ion cyclotron resonance (FT-ICR) cell. It is shown that the z motion is more forcefully excited by upsweep that by downsweep; thus at large amplitudes ions are more easily ejected to the trapping electrodes by upsweep and larger cyclotron orbits can be achieved by downsweep. This effect was confirmed by experiment and the results are favorably compared with the calculations. From these results it is concluded that downward sweeping is advantageous for ion detection and upward sweeping is preferable for ion ejection. The simulations clearly explain the effect of the direction of frequency sweep by visualizing the directions of the forces that ions experience immediately after the excitation of their cyclotron motion. It was demonstrated by experiment that the z ejection can be reduced by applying a phase-adjusted ac potential to the trapping electrodes.     

Hypoxanthine sensor based on an amorphous silicon field-effect transistor

The pH response of an a-ISFET with xanthine oxidase immobilized on a ca. 20-μm thick poly(vinyl butyral) membrane over the gate insulator, is used to detect the uric acid produced by enzyme-catalyzed oxidation of hypoxanthine. The pH sensitivity between pH 5.0 and 10.0 is ca 48 mV/pH at 32°C in 10 mM phosphate buffer. The change in the output gate voltage 1 min after sample injection, is linearly related to the logarithm of the hypoxanthine concentration in the range 0.02–0.1 mM. The optimum buffer pH is 7.5. The system can be used for 2 weeks with 30% loss of enzymatic activity.     

Quantitative determination of bitter principles in specimens of Ganoderma lucidum using high-performance liquid chromatography and its application to the evaluation of ganoderma products

For quantitative determination of 19 triterpene constituents, including six ganoderma alcohols (1-6) and 13 ganoderma acids (7-19), in the products of Ganoderma lucidum, an analytical system was developed using high-performance liquid chromatography with an ODS column. The mobile phase was a linear gradient of 1% AcOH/H(2)O-CH(3)CN and 2% AcOH/H(2)O-CH(3)CN, and the elution profile was monitored at 243 and 250 nm for ganoderma alcohols and acids, respectively. The relative standard deviations of this method were less than 2.35% and 2.18% (n=5) for intraday and interday assays, and the recoveries were 90.9-100.8% and 93.4-103.9% for constituents of alcohol and acid groups, respectively. This system was applied to a quantitative determination of the constituents in 10 different products of G. lucidum: six usual umbrella forms of the fruiting bodies, three antlered forms of the fruiting bodies and spores, and eight specimens from the same G. lucidum strain, which was parasitized on logs from different plants or different fungus beds. The analytical results indicated that the quantity and composition of these triterpenes differed appreciably among various specimens, but the relative ratio of the alcohols and acids was not significantly different when the same strain of G. lucidum was used.     

Harpagometabolins Ⅰ and Ⅱ, Two New Metabolites from Harpagoside by Human Intestinal Bacteria

The dried roots of ScrOPhularia ningpoensl's Hemsl. (radix scrophulariae) have been usedin traditional chinese medicine for replendish the vital essence and relieve pyogenicinflammation'. Iridoids such as a harpagoside are main constitUents of radix scrophulariae2. Until noW, the pharmacological effects of these iridoids were not clearlyunderstood. Biological transformation in the human intestinal tract can induce theconversion of the iridoids to more or less biologically active compounds. …     

Molecular dynamics simulation study on the phase behavior of the Gay-Berne model with a terminal dipole and a flexible tail

To study the effect of the alkyl tail and the terminal dipole on the stability of the liquid crystalline phase of mesogens, we have carried out molecular dynamics simulations for 1CB(4-methyl-4'-cyanobiphenyl) and 5CB(4-n-pentyl-4'-cyanobiphenyl) by using a coarse-grained model. In the coarse-grained model, a 5CB molecule is divided into the rigid part of 1CB moiety, which is represented by an ellipsoid, and the remaining flexible part which is represented by a chain of united atoms. The nonbonded potential between coarse-grained segments is represented by the generalized Gay-Berne (GB) potential and the potential parameters are determined by directly comparing the GB potential with the atomistic potentials averaged over the rotation of the mesogen around its axis. In addition, a dipole moment is placed at one end of the ellipsoid opposite to the flexible tail. The ordered state obtained in the polar 5CB model was assigned as the nematic phase, and the experimental static and dynamical properties were reproduced well by using this coarse-grained model. Both the dipole-dipole interactions and the thermal fluctuation of the flexible tail increase the positional disorder in the director direction, and stabilize the nematic phase. Thus, the nematic phase in the polar 5CB is induced by a cooperative effect of the flexible tail and the terminal dipole. It is noted that a local bilayer structure with head-to-head association is formed in the nematic phase, as experimentally observed by x-ray diffraction measurements.     

Cp2TiCl2-catalyzed grignard exchange reactions with 1,3-dienes or styrenes. Preparation of allylic and α-arylethyl grignard reagents by a convenient and quantitative method

The addition of a catalytic amount of Cp₂TiCl₂ to an ether solution of propylmagnesium bromide and 1,3-dienes brings about an exchange reaction forming allylic Grignard reagents.Styrene also undergoes the exchange reaction under the same conditions affording α-phenethylmagnesium bromide.     

Studies on tacticity of polyacrylonitrile. II. High-resolution nuclear magnetic resonance spectra of 2,4-dicyanopentanes

The NMR spectra of 2,4-DCNP were measured in CCl₄, NaCNS–D₂O, DMSO-d₆, and other solutions. The spectra of the meso form show no significant change with the solvent, but the racemic form shows two kinds of spectra, one of which is observed in a solvent for PAN and the other in a nonsolvent. In the solution, the meso 2,4-DCNP is considered to have two equivalent conformations, TG and G'T, which are the mirror images with each other. The racemic 2,4-DCNP, however, might have predominantly either the TT or GG conformation in CCl₄, pyridine, and benzene, while it has the two conformers with almost equal probability in NaCNS–D₂O and DMSO-d₆. The results obtained from the calculation assuming appropriate constants are in fairly good agreements with the observed spectra of the 2,4-DCNP isomers. The values of chemical shifts and coupling constants used in the calculation correspond to those of PAN which were obtained previously from the analysis of the NMR spectra.     

Topical application of a novel, water-soluble gamma-tocopherol derivative prevents UV-induced skin damage in mice

We investigated whether the topical application of a novel, water-soluble gamma-tocopherol (gamma-Toc) derivative, gamma-tocopherol-N,N-dimethylglycinate hydrochloride (gamma-TDMG), could protect against UV-induced skin damage in hairless mice. Topical pre- or post-application of a 5% (93 mM) gamma-TDMG solution in water/propylene glycol/ethanol (2:1:2) significantly prevented sunburn cell formation, lipid peroxidation and edema/inflammation that were induced by exposure to a single dose of UV irradiation of 5 kJ/m2 (290-380 nm, maximum 312 nm). This effect was greater than that seen with two alpha-Toc derivatives, alpha-tocopherol acetate (alpha-TA) and alpha-tocopherol-N,N-dimethylglycinate (alpha-TDMG). When a 5% solution of gamma-TDMG was applied to mouse skin for 1 h, cutaneous gamma-Toc increased by 25-fold after 24 h; levels of cutaneous alpha-Toc increased by only two- and eight-fold in alpha-TDMG and alpha-TA treated skins, respectively. These findings indicated that gamma-TDMG immediately converted to gamma-Toc in the skin and suggest that ability of gamma-TDMG to protect the skin from the damaging effects of irradiation was due to its conversion to gamma-Toc. When a 5% solution of gamma-Toc was applied to mouse skin for 1 h, cutaneous gamma-Toc rapidly increased by 25-fold, but fell to baseline levels by 24 h. In contrast, the concentration of gamma-Toc in skin that was treated with gamma-TDMG similarly increased, but these high levels were maintained after 24 h. These results suggest that gamma-TDMG may be a more effective source of gamma-Toc in skin. Thus, the topical application of gamma-TDMG may be efficacious for the prevention of UV-B-induced skin damage.     

Mechanism of decomposition of α,α-dimethylbenzyl hydroperoxide producing acetophenone and α,α-dimethylbenzyl alcohol in a constant proportion of 2 to 1

In the decomposition of ,-dimethylbenzyl hydroperoxide (1) by use of copper(II) chlorocomplexes, the novel fact was found that the product ratio of acetophenone (2) to ,-dimethylbenzyl alcohol (3) is 2 to 1. The kinetics of this result was investigated and a mechanism consistent with the experimental result is proposed.

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Mechanismus der Zersetzung von ,-Dimethylbenzylhydroperoxid unter Bildung von Acetophenon und ,-Dimethylbenzylakohol in einem konstanten Verhältnis von 2:1

Zusammenfassung Bei der Zersetzung von ,-Dimethylbenzylhydroperoxid (1) unter Verwendung eines Kupfer(II)chlorkomplexes wurde die neue Feststellung gemacht, daß das Produktverhältnis Acetophenon (2): ,-Dimethylbenzylalkohol (3) stets 2:1 ist. Die Kinetik der Reaktion wurde untersucht und ein Mechanismus vorgeschlagen, der mit dem experimentellen Resultat konsistent ist.