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991.
The cerium‐containing MCM‐41 (Ce‐MCM‐41) has been synthesized by direct hydrothermal method. The low‐angle XRD patterns revealed the typical five major peaks of MCM‐41 type hexagonal structures. The interplanar spacing d100 = 38.4 Å was obtained that can be indexed on a hexagonal unit cell parameter with ao = 44.3 Å which was larger than that of pure siliceous MCM‐41 (Si‐MCM‐41). Transmission electron micrograph shows the regular hexagonal array of uniform channel characteristics of MCM‐41. The BET surface area of Ce‐MCM‐41 was 840 m2/g, which is much reduced as compared to that of Si‐MCM‐41, with the pore size of 26.9 Å and mesopore volume of 0.78 cm3/g were measured by nitrogen adsorption‐desorption isotherm at 77 K. Along with the results, the synthesized Ce‐MCM‐41 exhibited a well‐ordered MCM‐41‐type mesoporous structure with the incorporation of cerium. Using Ce‐MCM‐41 as a support, the Rh (0.5 wt%) catalyst exhibited very high activity for the NO/CO reactions. 相似文献
992.
Zhen‐Yu Li Ping Chen Hong‐Gui Xu Shu‐Ying Peng Yi‐Ming Yang Zhong‐Zhen Zhao Yue‐Wei Guo 《Helvetica chimica acta》2007,90(7):1353-1359
Five new polycyclic Daphniphyllum alkaloids, macropodumines F ( 1 ) and G ( 2 ), 17‐oxoyuzurimine ( 3 ), and macropodumines H ( 4 ) and I ( 5 ), were isolated from the leaves of D. macropodum Miq ., collected in Sichuan Province, China. The structures and relative configurations of the new compounds – as well as of four known, related alkaloids – were elucidated on the basis of in‐depth spectroscopic and mass‐spectrometric analyses, by chemical derivatization, and by comparison of spectroscopic data with those of known compounds. 相似文献
993.
Shushi Chen 《中国化学会会志》2003,50(6):1177-1182
The phenyl isothiocyanate, an electrophilic reagent for peptide chain sequencing, is used to pre‐column derivatize a variety of α‐amino acids in alkaline medium before their enantioresolution on a vancomycin bonded chiral phase using the acetonitrile‐based mobile phase. The observed resolution is believed to be due to the re‐location of the hydrogen receptor site from sulfur to nitrogen on the isothiocyanyl fragment of derivatizing reagent, which in turn changes the enantioselectivity. Under the same chromatographic conditions, the resolution for N‐benzoylated, 3,5‐dinitrobenzoylated and N‐carbobenzyloxylated amino acids is either not found or unsatisfactory. Also, no resolution is obtained in the reversed‐ or normal phase mode for all phenyl isothiocyanated amino acids examined in this study. 相似文献
994.
To investigate the disposition of unbound cocaine in the rat blood, brain and bile, we demonstrate an in vivo multiple sampling microdialysis system coupled with liquid chromatography for cocaine assay and verified by tandem mass spectrometry. Three microdialysis probes were concurrently inserted into the jugular vein, bile duct and brain striatum of each anesthetized rat. After a period of 2 h post-surgical stabilization, cocaine (10 mg kg(-1)) was administered through the femoral vein. Separation of unbound cocaine from various biological fluids was applied to a reversed-phase C(18) column (250 x 4.6 mm I.D., 5 microm). The mobile phase consisted of acetonitrile--10 mm potassium dihydrogen phosphate buffer (25:75, v/v, pH 4.0) and 0.8% diethylamine at a flow rate of 1 mL min(-1). The UV detector wavelength was set at 235 nm. The results indicate that cocaine penetrates the blood--brain barrier with a rapid distribution. However, unbound cocaine in the bile dialysate was not detectable in the UV detection. We therefore use LC--tandem mass spectrometry to detect the bile fluid after cocaine administration (3 mg kg(-1), i.v.). The results indicate that cocaine goes through hepatobiliary excretion. 相似文献
995.
Investigation of the root extract of Antidesma pentandrum var. barbatum led to the isolation of seven new compounds, antidesmol ( 1 ), antidesmanins E ( 2 ) and F ( 3 ), antidesnone ( 4 ), antidesnol ( 5 ), barbatumols A ( 6 ) and B ( 7 ), together with 14 known compounds including sodium aristolochate‐I ( 10 ) and aristolochic acid‐I methyl ester ( 11 ). 相似文献
996.
Rong Chen Yu-Hui Cheng Lei Liu Xiao-Song Li Qing-Xiang Guo 《Research on Chemical Intermediates》2002,28(1):41-48
MP2/6-31+G* calculations were performed on the cation- complexes of ethylene, cyclobutadiene and benzene with a number of atomic cations. It was found that except B+ all the atomic cations form -type cation- complexes with ethylene. On the other hand, with cyclobutadiene Li+, N+, Na+, P+ and K+ form -type complexes, whereas H+, F+, and Cl+ form covalent -type complexes. With benzene Li+, B+, Na+, Al+, and K+ form -type complexes whereas H+, F+, and Cl+ form -type complexes. It was concluded that the driving force to form the -type complex is chemical bonding, and that for metal cations to form -type complexes is non-covalent interaction. 相似文献
997.
998.
Damage Threshold of Normal Rat Brain in Photodynamic Therapy 总被引:4,自引:0,他引:4
Q. Chen M. Chopp L. Madigan M. O. Dereski F. W. Hetzel 《Photochemistry and photobiology》1996,64(1):163-167
Normal brain tissue response to photodynamic therapy (PDT) must be quantified in order to implement PDT as a treatment of brain neoplasm. We therefore calculated the threshold for PDT-induced tissue necrosis in normal brain using Photofrin (porfimer sodium, Quadralogic Technologies Inc., Vancouver, BC) as the photosensitizer. The absolute light fluence-rate distribution for superficial irradiation and effective attenuation depth were measured in vivo using an invasive optical probe. Photosensitizer uptake in cerebral cortex was measured with chemical extraction and fluorometric analysis. Photodynamic therapy-induced lesion depths at various drug dose levels were measured as a biological end point. The PDT threshold for normal brain necrosis was calculated as in the magnitude of 1016 photons/cm3. Thus normal rat brain is extremely vulnerable to PDT damage. This suggests that extra precautions must be exercised when PDT is used in brain. 相似文献
999.
The nitrosyl-hemoglobin (HbNO) is the carrier of nitric oxide (NO) which is the important messenger molecule displaying multiple physiologic and pathophysiologic roles. However it is still not clear for the fate of HbNO molecules during the venous-arterial transit. In this letter, the HbNO transition in vitro was studied by using the electron paramagnetic resonance (EPR) spectra. It was found that HbNO molecules were stable when oxygen did not exist in the system but not stable in aerobic conditions. The absorption spectra further revealed that the methemoglobin (metHb) was the product of HbNO in aerobic environment, showing that the HbNO changed to metHb when there were enough oxygen molecules in the system. 相似文献
1000.
Alexandra Tsybizova Christopher Brenig Christoph Kieninger Bernhard Kräutler Peter Chen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(25):7252-7264
Aryl-cobalamins are a new class of organometallic structural mimics of vitamin B12 designed as potential ‘antivitamins B12’. Here, the first cationic aryl-cobinamides are described, which were synthesized using the newly developed diaryl-iodonium method. The aryl-cobinamides were obtained as pairs of organometallic coordination isomers, the stereo-structure of which was unambiguously assigned based on homo- and heteronuclear NMR spectra. The availability of isomers with axial attachment of the aryl group, either at the ‘beta’ or at the ‘alpha’ face of the cobalt-center allowed for an unprecedented comparison of the organometallic reactivity of such pairs. The homolytic gas-phase bond dissociation energies (BDEs) of the coordination-isomeric phenyl- and 4-ethylphenyl-cobinamides were determined by ESI-MS threshold CID experiments, furnishing (Co−C )-BDEs of 38.4 and 40.6 kcal mol−1, respectively, for the two β-isomers, and the larger BDEs of 46.6 and 43.8 kcal mol−1 for the corresponding α-isomers. Surprisingly, the observed (Co−C )-BDEs of the Coβ-aryl-cobinamides were smaller than the (Co−C )-BDE of Coβ-methyl-cobinamide. DFT studies and the magnitudes of the experimental (Co−C )-BDEs revealed relevant contributions of non-bonded interactions in aryl-cobinamides, notably steric strain between the aryl and the cobalt-corrin moieties and non-bonded interactions with and among the peripheral sidechains. 相似文献