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Wulff WD Korthals KA Martínez-Alvarez R Gómez-Gallego M Fernández I Sierra MA 《The Journal of organic chemistry》2005,70(13):5269-5277
By means of deuterium-labeling experiments, we have carried out a systematic ESI-MS study to determine the mechanism of ESI ionization of alkenyl and alkynyl group 6 Fischer carbene complexes. These compounds can be ionized under ESI conditions only in the presence of additives such as hydroquinone (HQ) or tetrathiafulvalene (TTF). Our results demonstrate that in the ESI source an anion-radical is formed after the initial HQ- or TTF-mediated electron transfer to the metallic carbene complex. For alkenyl carbene complexes, this species evolves by extrusion of a hydrogen radical to form an allenylchromium anion that is detected as the [M - H](-) ion in the mass spectrum. The preference for this mechanistic pathway could be rationalized by DFT calculations. In the case of alkynyl carbene complexes, experiments combining deuterated substrate, additive, and solvent demonstrate that the previously proposed allene-anion carbene complex is not formed. Instead, the H transfer from the ethoxy group in the anion radical, followed by extrusion of a hydrogen radical, leads to an allenyl anion that is detected in the ESI-MS as [M - H - CO](-). 相似文献
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A simple method is described for the simultaneous determination of vanilmandelic acid (VMA), 3,4-dihydroxyphenylacetic acid (DOPAC), 5-hydroxyindole-3-acetic acid (5-HIAA) and homovanillic acid (HVA) in urine. The compounds are isolated by a one-step sample clean-up on Sephadex G-10, separated by ion-pair reversed-phase liquid chromatography and detected electrochemically. A single analysis is completed within 65 min. Sample clean-up did not cause losses of the compounds of interest. The detection limits in urine were 0.4, 0.8, 1.0 and 1.6 mumol/l for VMA, DOPAC, 5-HIAA and HVA, respectively. 3,4-Dihydroxymandelic acid and vanillic acid (VA) were also detectable, but, under the chromatographic conditions used, they were not resolved from interfering components. VA and 5-HIAA could be analysed separately in the Sephadex G-10 eluate if more restrictive sampling conditions were used. Ingestion of bananas caused an increase of VMA, DOPAC, 5-HIAA and HVA in 24-h urine. After ingestion of vanilla an increased excretion of VA was observed, while the excretion of VMA, DOPAC and HVA was unaffected. 相似文献
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DETECTION OF DNA-PSORALEN PHOTOADDUCTS in situ 总被引:1,自引:0,他引:1
ZOFIA ZAREBSKA† MARIA JARZABEK-CHORZELSKA ‡ GENOWEFA RZSA WIESLAW GLISKI MARIA PAWIKA TADEUSZ CHORZELSKI STEFANIA JABLOKA 《Photochemistry and photobiology》1984,39(3):307-312
Abstract— An immunological method, with the use of specific immune serum, has been developed for detection of 8-methoxypsoralen (8-MOP) photoadducts to DNA, formed in situ in cell nuclei, after combined treatment with 8MOP and UV-A irradiation (Zarçbska et al. , 1978). Lymphocytes fixed on slides or in suspension, and cryostat sections of different mammalian tissues, served as antigenic substrate, after treatment with 8-MOP and UV-A in vitro. Specific fluorescence in these substrates was detected in the nuclei after treatment with 30 ˜ 140 kJ/m2 UV-A in the presence of 0.1-0.3 μg/cm2 8-MOP. PHA-stimulated-lymphocytes appeared to be the most sensitive substrate.
However, hairless mice treated with high doses of UV-A in vivo , 70 ˜ 360 kJ/m2 did not reveal a specific fluorescence of epidermal nuclei, unless a high local concentration of 8-MOP was attained.
The apparent discrepancy in the level of photoadduct detection between the in vitro and in vivo treated specimens was explained by the low number of DNA-8-MOP-photoadducts formed in vivo under these experimental conditions. The relevance of these findings to the role of DNA-8-MOP-photoadducts formed during PUVA photochemotherapy is discussed. 相似文献
However, hairless mice treated with high doses of UV-A in vivo , 70 ˜ 360 kJ/m
The apparent discrepancy in the level of photoadduct detection between the in vitro and in vivo treated specimens was explained by the low number of DNA-8-MOP-photoadducts formed in vivo under these experimental conditions. The relevance of these findings to the role of DNA-8-MOP-photoadducts formed during PUVA photochemotherapy is discussed. 相似文献
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We compute the zero-momentum finite-size effects in non-abelian gauge theories. In some cases, these effects are to lowest-order identical for lattice and continuum theories and are of the order of a few percent for an SU(3) gauge theory in four dimensions. 相似文献
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ABSTRACT. Let G be the group ?[t, t ?1] x ?. By studying the action of the braid group Bn on the set Gn , we obtain representations of Bn into a wreath product of the symmetric group and the general linear group over ?[t, t ?1]. This in particular recovers the Burau representation of the braid group. Furthermore, some quotients of the braid group are obtained by using the representations found. 相似文献
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Göttker-Schnetmann I Korthals B Mecking S 《Journal of the American Chemical Society》2006,128(24):7708-7709
Water-soluble single-component (kappa2-N,O)-salicylaldiminato nickel-methyl complexes 1-4-L (L = TPPTS, TPPDS, H2N-PEG-OMe) allow for the catalytic polymerization of ethylene under organic solvent-free aqueous conditions producing high molecular weight polyethylene with particle sizes below 10 nm. Amphiphilic TPPDS- and H2N-PEG-OMe complexes exhibit a polymerization activity in water higher than that in toluene. A solvation-favored activation of precatalysts 1-4-L by equilibrium dissociation of L in aqueous solution likely accounts for this enhanced polymerization activity. The observed generation of a given particle by a single active site is an unprecedented mechanism for formation of aqueous particle dispersions. 相似文献
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A form of the correction for a two-dimensional system described by the mixed fundamental-adjoint action is discussed. An exact result for the U(N) gauge group is derived. The form of correction in SU(N) is also discussed and the difference between the two groups is pointed out. The form of correction in two dimensions can be generalized for any number of dimensions if corrections to the plaquette free energy are to be calculated. 相似文献