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31.
The reaction of a racemic perhydroisoquinolene derivative 9 with the homochiral lithium amide basse 3 in the presence of Me3SiCl in an regiodivergent fashion to give the two non-racemic regioisomeric enol silanes 10 and 11. Conversion of 10 into enone 15, an intermediate useful in the synthesis of the alkaloid (+)-yohimbine, was also possible. 相似文献
32.
New derivatization method for determination of 3-chloro-4(dichloromethyl)-5-hydroxy-2(5H)-furanone in water 总被引:3,自引:0,他引:3
Jacek Nawrocki Przemysaw Andrzejewski Leif Kronberg Henryk Jele
《Journal of chromatography. A》1997,790(1-2):242-247
An extremely potent mutagen, 3-chloro-4(dichloromethyl)-5-hydroxy-2(5H)-furanone (MX) is commonly present in chlorinated drinking water. Due to its high mutagenic activity and according to World Health Organization guidelines its concentration should be controlled in drinking waters. Determination of MX is difficult due to ppt levels at which the compound usually exists in drinking waters. Derivatization of MX with 2-propanol is presented as a method which significantly lowers the GC–MS detection level compared to other alcohol derivatization agents. 相似文献
33.
PERFORMANCE IMPROVEMENT OF POLYMERS BY THE ADDITION OF GRAFTED NANO-INORGANIC PARTICLES 总被引:1,自引:0,他引:1
An irradiation grafting method was applied for the modification of nanoparticles so that the latter can be added topolymeric materials for improving their mechanical performance using existing compounding techniques. The followingitems are discussed in this paper: (a) chemical interaction between the grafting monomers and the nanoparticles duringirradiation, (b) properties including modulus, yield strength, impact strength and fracture toughness of the resultantcomposites, and (c) possible morphological changes induced by the addition of nanoparticles. Though irradiation graftingpolymerization, nanoparticle agglomerates turn into a nano-composite microstructure (comprised of the nanoparticles and thegrafted, homopolymerized secondary polymer), which in turn builds up a strong interfacial interaction with the surrounding,primary polymeric matrix during the subsequent mixing procedure. Due to the fact that different grafting polymers broughtabout different nanoparticle/matrix interfacial features, microstructures and properties of the ultimate composites could thusbe tailored. It was found that the reinforcing and toughening effects of the nanoparticles on the polymer matrix can be fullybrought into play at a rather low filler loading in comparison to conventional particulate filled composites. 相似文献
34.
The mercuration of a series of aryliminomethylferrocenes occurred predominantly in an ortho-position of the substituted ferrocenyl ring to yield 2-mercurated ferrocenylimines. The regiospecificity of this reaction suggests that the mercury is directed into the ortho-position by coordination of the mercury to imino nitrogen with subsequent electrophilic substitution. The chromatographic and spectral properties of the 2-mercurated products show the presence of an intramolecular N → Hg coordination via the five-membered ring in these molecules, which was further confirmed by the single-crystal structure analysis of 2-chloromercuro-1-[(4-methoxyphenylimino)methyl]ferrocene. 相似文献
35.
Kapurimycin A3 (kap A3, 1 ), an antitumour antibiotic, alkylates N7 of guanine2 (G2) and G4 of d(C1G2C3G4)2 to produce their covalent adducts 2 (64 %) and 3 (7.0 %), respectively. Heating at 90 °C for 5 min degraded both adducts to kap A3 - G adduct (5) with the concurrent release of their respective abasic-site containing oligomers 4 and 6. 相似文献
36.
J AliaMatysik C Soede-Huijbregts M Baldus J Raap J Lugtenburg P Gast H J van Gorkom A J Hoff H J de Groot 《Journal of the American Chemical Society》2001,123(20):4803-4809
Low-temperature 15N and 13C CP/MAS (cross-polarization/magic angle spinning) NMR has been used to analyze BChl-histidine interactions and the electronic structure of histidine residues in the light-harvesting complex II (LH2) of Rhodopseudomonas acidophila. The histidines were selectively labeled at both or one of the two nitrogen sites of the imidazole ring. The resonances of histidine nitrogens that are interacting with B850 BChl a have been assigned. Specific 15N labeling confirmed that it is the tau-nitrogen of histidines which is ligated to Mg2+ of B850 BChl molecules (beta-His30, alpha-His31). The pi-nitrogens of these Mg2+-bound histidines were found to be protonated and may be involved in hydrogen bond interactions. Comparison of the 2-D MAS NMR homonuclear (13C-13C) dipolar correlation spectrum of [13C6,15N3]-histidines in the LH2 complex with model systems in the solid state reveals two different classes of electronic structures from the histidines in the LH2. In terms of the 13C isotropic shifts, one corresponds to the neutral form of histidine and the other resembles a positively charged histidine species. 15N-13C double-CP/MAS NMR data provide evidence that the electronic structure of the histidines in the neutral BChl a/His complexes resembles the positive charge character form. While the Mg...15N isotropic shift confirms a partial positive charge transfer, its anisotropy is essentially of the lone pair type. This provides evidence that the hybridization structure corresponding to the neutral form of the imidazole is capable of "buffering" a significant amount of positive charge. 相似文献
37.
D. J. Newman
M. M. Curtis
《Journal of Physics and Chemistry of Solids》1969,30(12):2731-2737Crystal field parameters have been calculated, using ab initio LCAO-MO theory, for the ion pair Pr3+—F− at five metal ligand distances appropriate to Pr3+:LaF3. The parameters are found to be twice as large as in PrCl3, but with only half the distance dependence. In the absence of precise Pr3+:LaF3 experimental parameters only qualitative agreement with experiment can be recorded. However, very good numerical agreement is obtained with the experimental covalency parameters for Yb3+:CaF2, which provides a check on the methods adopted for calculating energy denominators. 相似文献
38.
Larry I. Amstutz Horst Meyer Samuel M. Myers
Robert L. Mills
《Journal of Physics and Chemistry of Solids》1969,30(12):2693-2697Measurements of T1 in the hep phase of H2, over the temperature range 2°–12°K and the ortho concentration range between 0.5 and 0.97 are presented. At temperatures below 10°K, the thermally activated self-diffusion is negligible and the mechanism for nuclear relaxation is that attributed by Moryia and Motizuki and by Harris to intramolecular dipolar interaction, modulated by intennolecular electric quadrupole-quadrupole (EQQ) interaction. The gaussian approximation for the correlation function was used by these authors to predict T1. From the comparison between experiment and theory, we determine the EQQ parameter Γ/kB to be 0.67°K. Above 10°K the effect of diffusion influences T1, and the experimental results for an 88 per cent ortho H2 sample up to the melting point suggest that the relaxation mechanisms resulting from EQQ interaction and diffusion are not independent of one another. 相似文献
39.
Selective flow-injection determination of methanol in the presence of ethanol based on a multi-enzyme system with chemiluminescence detection 总被引:2,自引:0,他引:2
Yoshiie Sekine
Masayasu Suzuki
Toshifumi Takeuchi Eiichi Tamiya Isao Karube 《Analytica chimica acta》1993,280(2):179-184A highly selective flow-injection system was developed for the determination of methanol. The system consisted of three immobilized enzymes with luminol chemiluminescence detection. First, methanol was oxidized in the presence of alcohol oxidase to yield formaldehyde and hydrogen peroxide. The hydrogen peroxide produced was then destroyed by catalase. The formaldehyde formed in the first stage was further oxidized by NAD+-formaldehyde dehydrogenase. The NADH formed was oxidized by 1-methoxy-5-methylphenazinium methylsulphate (1-MPMS), and finally the reduced 1-MPMS was spontaneously oxidized and hydrogen peroxide was produced. The concentration of the hydrogen peroxide produced, which was proportional to the initial concentration of methanol, was determined by luminol chemiluminescence. The determination range was from 0.1 to 100 mg l−1 and the response time was less than 2 min per sample with a relative standard deviation of less than 3%. The system showed good selectivity for methanol; the response was ca. 50 times higher than for ethanol. 相似文献
40.
The present state of knowledge of the biosynthesis of cholesterol is summarised. An experiment is described wherein a special application of the carbon isotope 13C permits a decision between possible modes of rearrangement during the enzymic cyclisation of squalene. 相似文献