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991.
Shyh‐Jong Chen Cheng Chen Yaw‐Shun Hong 《International journal of quantum chemistry》2005,103(2):198-214
This investigation conducted reaction channels of weakly bound complexes CO2…HF, CO2…HF…NH3, CO2…HF…NH2CH3, CO2…HF…NH(CH3)2, and CO2…HF…N(CH3)3 systems, using the Gaussian 98 package at the B3LYP/6‐311++G(3df,2pd) level. The syn‐fluoroformic acid or syn‐fluoroformic acid plus NH3 or amine conformers are more stable than the related anti‐fluoroformic acid or anti‐fluoroformic acid plus NH3 or amine conformers. However, the above‐mentioned weakly bound complexes are more stable than both the related syn‐ and anti‐type fluoroformic acid or acid plus NH3 or amine conformers and their related decomposed into CO2 + HF or CO2 + NHR3F (R?H, CH3) combined molecular systems. Five reaction channels of the weakly bound complexes exist. Each channel includes weakly bound complexes and their related above‐mentioned systems. Moreover, each reaction channel contains two transition states. The transition state between the weakly bound complex and anti‐fluoroformic acid type structure (T13) is significantly higher than that of internal rotation (T23) between syn‐ and anti‐FCO2H (or FCO2H…NR3) structures. However, the above‐mentioned T13 can significantly decrease its energy by adding the third molecule NH3 or NR3 (R?H or CH3). The more CH3 that is substituted in NR3 of the reaction channel, the lower the activation energy of the transition state in the system is affected. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005 相似文献
992.
Morikawa T Sun B Matsuda H Wu LJ Harima S Yoshikawa M 《Chemical & pharmaceutical bulletin》2004,52(10):1194-1199
A new beta-carboline-type alkaloidal glycoside, glucodichotomine B, four new neolignan glycosides, dichotomosides A, B, C, and D, and a new phenylpropanoid glycoside, dichotomoside E, were isolated from a Chinese natural medicine, the roots of Stellaria dichotoma L. var. lanceolata. The structures of the new glycosides were determined on the basis of chemical and physicochemical evidence. Among them, dichotomoside D inhibited the release of beta-hexosaminidase (IC(50)=64 microM) as well as tumor necrosis factor-alpha and interleukin-4 (IC(50)=16, 34 microM) in RBL-2H3 cells. These findings suggest that dichotomoside D is more effective against the late-phase reactions in type I allergy than in the immediate phase. 相似文献
993.
A sample of 10 mM tolmetin in methanol was photo-irradiated with a Hanovia 200 W high-pressure quartz Hg lamp for four days. In total, eight photoproducts were observed from the HPLC chromatogram. Three major photoproducts were separated, and their structures were elucidated by spectroscopic methods. The structures of all photoproducts were further determined by LC-ESI-MS. A reaction scheme of tolmetin was proposed. 相似文献
994.
The structures of two new dimeric acridone alkaloids, glycobismine-D (1) and -E (2), having a novel linkage as binary acridones, three monomeric acridones, glycocitrine-IV (3), -V (4), and -VI (5), and three quinolone alkaloids, glycocitlone-A (6), -B (7), and -C (8) from Glycosmis citrifolia (Willd.) Lindl. (Rutaceae) have been elucidated by spectrometric studies. 相似文献
995.
996.
997.
Xing Yong Wang Jing Nan Cui Wei Min Ren Feng Li Chun Liang Lu Xu Hong Qian State Key Laboratory of Fine Chemicals Dalian University of Technology Dalian China School of Chemical Engineering Technology China University of Mining & Technology Xuzhou China Shanghai Key Laboratory of Chemical Biology East China University of Science Technology Shanghai China 《中国化学快报》2007,18(6):681-684
Baker's yeast mediated reduction of acenaphthenequinone within 4-10 h afforded mono-hydroxyacenaphthenone mainly with low enantioselectivity, the substrate and mono-hydroxyacenaphthenone product almost converted to dihydroxyacenaphthene after 48 h. By control of the reaction time and in the presence of DMF as co-solvent, the reduction of 6-substituted acenaphthenequinones under vigorous agitation afforded the corresponding 2-hydroxyacenaphthenones in 24-84% yields with 10-93% ee. 相似文献
998.
Antonio Doménech María Teresa Doménech‐Carbó Howell G. M. Edwards 《Electroanalysis》2007,19(18):1890-1900
Multivariate chemometric methods are applied for identifying earth pigments from square‐wave voltammetric measurements performed at pigment‐modified paraffin‐impregnated graphite electrodes allowing for a separation between hematite‐based earths, French ochres, Spanish ochres, siennas, umbers and green earths. This methodology is applied to the identification of the pigments in samples from the ceiling frescoes of Antonio Palomino (dated 1707) in the vaulted nave of the Sant Joan del Mercat church in Valencia (Spain). These frescoes suffered considerable damage by fire during the Spanish Civil War in 1936, resulting in severe chemical and chromatic alterations. Electrochemical data, supported by scanning electron microscopy/energy dispersive X‐ray microanalysis and Raman spectroscopy, indicate that thermal stress induced the transformation of goethite‐based yellow ochres into hematite and magnetite. 相似文献
999.
Intracellular delivery of enzymes is essential for protein-based diagnostic and therapeutic applications. Protein-spherical nucleic acids (ProSNAs) defined by protein core and dense shell of oligonucleotides have been demonstrated as a promising vehicle-free enzyme delivery platform. In this work, we reported a crosslinking strategy to vastly improve both delivery efficiency and intracellular sensor performance of ProSNA. By assembling individual ProSNA with lactate oxidase (LOX) core into a nanoscale particle, termed as crosslinked SNA (X-SNA), the enzyme delivery efficiency increased up to 5–6 times higher. The LOX X-SNA was later demonstrated as a ratiometric probe for quantitative detection of lactate in living cells. More importantly, X-SNA probe showed significantly improved sensor performance with signal-to-noise ratio 4 times as high as ProSNA when detecting intracellular lactate.By crosslinking protein spherical nucleic acid (SNA) into a supramolecular architecture X-SNA, the intracellular enzyme delivery efficiency was significantly enhanced, showing 3–4 times higher signal-to-noise ratio in detecting intracellular lactate. 相似文献
1000.
Capillary electrophoresis with end-column amperometric detection of urinary 8-hydroxy-2'-deoxyguanosine 总被引:1,自引:0,他引:1
Urinary 8-hydroxy-2'-deoxyguanosine (8OHdG) is an excellent marker of oxidative DNA damage. Until now, urinary 8OHdG has been measured by high-performance liquid chromatography with electrochemical detection. A simple and sensitive method for the analysis of urinary 8OHdG by capillary electrophoresis with end-column amperometric detection has been developed in our laboratory. A single-step solid-phase extraction procedure was optimized and used for extracting 8OHdG from human urine. To improve the sensitivity of this method, a new focusing technique based on a dynamic pH junction was used. The limit of detection was 20 nM (signal-to-noise ratio S/N = 3), the linear range was 50 nM-10 microM, and the correlation coefficient was better than 0.999. The relative standard deviation (RSD) was found to be 0.57% for migration time, and 4.79% for peak current. To show the usefulness of the method, the urinary concentration of 8OHdG in nine healthy persons and ten cancer patients was determined. The urinary concentration of 8OHdG in cancer patients was significantly higher than that in healthy persons. 相似文献