Attomole catechins determination by capillary liquid chromatography with electrochemical detection.

Attomole quantities of catechins were determined by a capillary liquid chromatography system with electrochemical detection (CLC-ECD) and the system is applied to the determination of catechins in human plasma. The eight catechins: catechin (C), epicatechin (EC), gallocatechin (GC), epigallocatechin (EGC), catechin gallate (Cg), epicatechin gallate (ECg), gallocatechin gallate (GCg), and epigallocatechin gallate (EGCg), were separated within 10 min using a capillary column (0.2 mm i.d.) and a mobile phase of phosphoric acid (85%)-methanol-water (0.5:27.5:72.5, v/v/v), and were detected at +0.85 V vs. Ag/AgCl. Peak heights were found to be linearly related to the amount of catechins injected, from 200 amol to 500 fmol (r > 0.998). The detection limits of the catechins were 61 amol for EGC, 75 amol for EC, 54 amol for GC, 61 amol for C, 67 amol for GCg, 75 amol for EGCg, 75 amol for ECg and 89 amol for Cg (S/N = 3). Because the present method is highly sensitive and allows facile pretreatment for plasma sample, the time courses of concentrations of catechins (GCg, EC, EGCg, ECg, and Cg) and their conjugates in human plasma obtained from a 10 microl plasma sample after ingestion of green tea could be determined.     

Construction of quaternary carbon centers by a base-catalyzed enantioselective aldol reaction and related reactions of trimethoxysilyl enol ethers

The aldol reactions of trimethoxysilyl enol ethers catalyzed by lithium binaphtholate were found to be powerful tools for the construction of quaternary asymmetric carbon centers. The stereoselectivities were greatly affected by the presence of water. Trimethoxysilyl enol ether derived from a cyclic ketone, such as cyclohexanone, was used as a substrate to obtain the anti-adduct preferentially under anhydrous conditions; by contrast, the syn-adduct was preferentially obtained under aqueous conditions with high stereoselectivity. The aldol-Tishchenko reaction of a trimethoxysilyl enol ether derived from acyclic ketones proceeded to give monoacyl 1,3-diol derivatives in high enantioselectivities.     

Effects of digital processing on repeatability assessment of a multiple reaction monitoring liquid chromatography–tandem mass spectrometry system by ISO 11843-7

ISO 11843 part 7 (ISO 11843-7) can provide a standard deviation (SD) of area measurements of a target peak through the stochastic behaviors of instrumental noises. The purpose of this study is to demonstrate that ISO 11843-7 can be applied to assess repeatability in an isocratic liquid chromatography–tandem mass spectrometry (LC–MS/MS) system without repetitive measurements. The relative standard deviation (RSD) of the peak area of ergosterol picolinyl ester, which was used as an example, on a multiple reaction monitoring (MRM) chromatogram was determined by ISO 11843-7. The RSD by ISO 11843-7 (N = 1) was within a 95% confidence band of the RSD by repetitive measurements (N = 6). Moreover, the effects of digital smoothing, such as moving average, were also examined on the repeatability assessment in LC–MS/MS by ISO 11843-7. From the results of the comparisons of the RSDs obtained by ISO 11843-7 and the repetitive measurements, it was shown that suitable RSDs of the peak area were obtained from the smoothed MRM chromatograms by the moving average for narrow data point windows (e.g., one-sixth of the peak width). In conclusion, the utility of repeatability assessment based on ISO 11843-7 has been expanded for the validation of an LC–MS/MS system.     

X-ray magnetic circular dichroism at rare-earth L23 absorption edges in various compounds and alloys

Theoretical interpretations of X-ray magnetic circular dichroism (XMCD) at rare-earth (called R hereafter) L₂₃ absorption edges are reviewed using differing models, depending on the material under investigation. In the first chapter, we present an overview of recent developments for XMCD in XAS with a few general remarks, especially at R atom absorption edges. In Section 2, we first describe basic mechanism of XMCD at L₂₃ edges of R systems, and then we essentially discuss two examples of XMCD spectra in: (i) R₂Fe₁₄B metallic compounds, with the help of a cluster model, and (ii) RFe₂ Laves-phase compounds, using a tight-binding approximation for R 5d and Fe 3d conducting states. A good agreement between theory and experiment for R₂Fe₁₄B suggests that a cluster model provides a valuable method to quantitatively calculate XMCD spectra of R systems, even with quite complicated atomic arrangements. For RFe₂ systems the XMCD spectral shape, especially for the L₂ edge of heavy R elements, is more complicated than those of R₂Fe₁₄B systems, and this is explained by the competition of some different XMCD mechanisms. In Section 3, we focus on special series of Ce systems, related to XAS and XMCD studies at the Ce L₂₃ edges. Two clearly differing cases are interpreted: (i) A well localized 4f¹ system, i.e. CeRu₂Ge₂; (ii) A less localized 4f¹ system, i.e. CeFe₂, with a 3d partner. Then, from a more experimental point of view, we investigate the influence of substitution on the low temperature properties of CePd₃ compounds, i.e. Ce(_Pd1-xMnx)3$\mathrm{Ce}({\mathrm{Pd}}_{1-x}{\mathrm{Mn}}_x{)}_3$ alloys where x   is about 0.03, giving rise to (_CePd3)8Mn$({\mathrm{CePd}}_3{)}_8\mathrm{Mn}$ ordered structure. We give another example: Ce(_Pd1-xNix)3$\mathrm{Ce}({\mathrm{Pd}}_{1-x}{\mathrm{Ni}}_x{)}_3$ alloys with x taken up to about 0.25. Also the Ce L₂₃ XMCD signal measured in pure CePd₃ demonstrates that in the Ce based dense Kondo materials, only the 4f¹ channel yields a magnetic response.     

A Central Limit Theorem for Magnetic Transition Operators on a Crystal Lattice

A central limit theorem for a generalized Harper operator ona crystal lattice is obtained. As the limit, the continuoussemigroup of a uniform magnetic Schrödinger operator iscaptured on a vector space equipped with a special Euclideanstructure. The standard realization of the crystal lattice isa key to the Euclidean structure and a linear vector potentialon the Euclidean space from combinatorial data of the generalizedHarper operator.     

Thermal behavior of ground mixtures of heptakis (2,6-di-O-methyl)-β-cyclodextrin and benzoic acid

Characterization of an inclusion complex prepared from amorphous ground mixtures of heptakis (2,6-di-O-methyl)--cyclodextrin (DMCD) and benzoic acid was carried out by a sealed heating method. The formation of the crystalline inclusion complex and the variation in physicochemical properties of the ground mixture were investigated as a function of heating temperature. On the basis of X-ray diffractometry and Fourier transform infrared spectroscopy, the crystallization of the ground mixture was confirmed to take place at about 135°C. The crystallization temperature was shifted to lower temperatures and the bound molar ratio of benzoic acid to DMCD increased as the mixing molar ratio of benzoic acid to DMCD was raised.Tsumura & Co., 3586 Yoshiwara, Amimachi, Inashikigun, Ibaraki 300-11, Japan.     

Solid-state fluorescence study of naphthalene adsorption on porous material

Naphthalene adsorption profile on porous materials was studied using solid-state fluorescence spectroscopy. When naphthalene crystals were simply mixed with porous crystalline cellulose (PCC), excimer emission of naphthalene was observed after 1 min of mixing, suggesting a drastic change in the naphthalene molecular environment during the mixing procedure. For the naphthalene-octadesyl silane (ODS)-80A or naphthalene-ODS-2 systems, the changes in adsorption profiles and fluorescence spectral pattern of naphthalene were similar to those of the naphthalene-PCC system. The final amounts of naphthalene adsorbed to ODS-80A and ODS-2 were 0.05 and 0.024 g/g adsorbent, respectively, even though the two materials had comparable values of specific surface area. The relative emission intensity (I(excimer)/I(monomer)) in the ODS-80A system was higher than that in the ODS-2 system when compared at the same amount of naphthalene adsorbed. It was concluded that the pore size of porous materials affected the naphthalene excimer formation on the surface.     

Hydrosilylation of carbonyl compounds using a PhSeSiMe(3)/Bu(3)SnH/AIBN system

[reaction: see text] When carbonyl compounds were allowed to react with phenyl trimethylsilyl selenide and tributylstannyl hydride in the presence of a catalytic amount of AIBN as a radical initiator, the hydrosilylation of the carbonyl compounds efficiently proceeded to give the corresponding silyl ethers in moderate to good yields.     

Preparation and properties of electron donor acceptor complexes of the compounds having capto-dative substituents

In order to examine the “capto-dative” substitution-effect on the electrical conductivity, five compounds which have capto-dative substituents were prepared. Electron withdrawing (capto) group was nitro- or cyano-substituted phenyl and electron donating (dative) one was 5-methyl-5,10-dihydrophenazinyl moiety. The character of intramolecular electron donor acceptor complex of the five compounds were demonstrated by their uv spectra. Electron donor acceptor complexes of them with tetracyanoquinodimethane were prepared and their electrical resistivities were measured.