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991.
Yang L Lin G Liu D Dria KJ Telser J Li L 《Journal of the American Chemical Society》2011,133(27):10434-10447
5-Thyminyl-5,6-dihydrothymine (commonly called spore photoproduct or SP) is the exclusive DNA photodamage product in bacterial endospores. It is generated in the bacterial sporulation phase and repaired by a radical SAM enzyme, spore photoproduct lyase (SPL), at the early germination phase. SPL utilizes a special [4Fe-4S] cluster to reductively cleave S-adenosylmethionine (SAM) to generate a reactive 5'-dA radical. The 5'-dA radical is proposed to abstract one of the two H-atoms at the C6 carbon of SP to initiate the repair process. Via organic synthesis and DNA photochemistry, we selectively labeled the 6-H(proS) or 6-H(proR) position with a deuterium in a dinucleotide SP TpT substrate. Monitoring the deuterium migration in enzyme catalysis (employing Bacillus subtilis SPL) revealed that it is the 6-H(proR) atom of SP that is abstracted by the 5'-dA radical. Surprisingly, the abstracted deuterium was not returned to the resulting TpT after enzymatic catalysis; an H-atom from the aqueous buffer was incorporated into TpT instead. This result questions the currently hypothesized SPL mechanism which excludes the involvement of protein residue(s) in SPL reaction, suggesting that some protein residue(s), which is capable of exchanging a proton with the aqueous buffer, is involved in the enzyme catalysis. Moreover, evidence has been obtained for a possible SAM regeneration after each catalytic cycle; however, such a regeneration process is more complex than currently thought, with one or even more protein residues involved as well. These observations have enabled us to propose a modified reaction mechanism for this intriguing DNA repair enzyme. 相似文献
992.
Fang J Kelarakis A Lin YW Kang CY Yang MH Cheng CL Wang Y Giannelis EP Tsai LD 《Physical chemistry chemical physics : PCCP》2011,13(32):14457-14461
We report a simple, scalable approach to improve the interfacial characteristics and, thereby, the performance of commonly used polyolefin based battery separators. The nanoparticle-coated separators are synthesized by first plasma treating the membrane in oxygen to create surface anchoring groups followed by immersion into a dispersion of positively charged SiO(2) nanoparticles. The process leads to nanoparticles electrostatically adsorbed not only onto the exterior of the surface but also inside the pores of the membrane. The thickness and depth of the coatings can be fine-tuned by controlling the ζ-potential of the nanoparticles. The membranes show improved wetting to common battery electrolytes such as propylene carbonate. Cells based on the nanoparticle-coated membranes are operable even in a simple mixture of EC/PC. In contrast, an identical cell based on the pristine, untreated membrane fails to be charged even after addition of a surfactant to improve electrolyte wetting. When evaluated in a Li-ion cell using an EC/PC/DEC/VC electrolyte mixture, the nanoparticle-coated separator retains 92% of its charge capacity after 100 cycles compared to 80 and 77% for the plasma only treated and pristine membrane, respectively. 相似文献
993.
Two new triterpene glycosides with monomethyl malonate groups from the rhizome of Cimifuga foetida L
Two new 9,19-cycloartane triterpene glycosides 1-2, together with four known compounds--26-deoxyactein (3), actein (4), 7,8-didehydro-26-deoxyactein (5) and cimiaceroside B (6)--were isolated from the rhizome of Cimicifuga foetida. The new triterpene glycosides were identified as 23-O-methyl-24-deoxy-2'-O-(3'-methylmalonyl)-cimiaceroside B (1) and 2'-O-(3'-methylmalonyl)actein (2) based on analysis of their spectral data and chemical reactions. 相似文献
994.
The iron-catalyzed heterocyclizations from 2-nitroanilines and benzylic alcohols to form benzimidazoles using hydrogen transfer reaction were investigated in this study. In the presence of dppf in toluene at 150 °C, various benzimidazoles were obtained in moderate to good yields within 24 h. The reaction was proposed to proceed via a cascade of alcohol oxidation, nitro reduction, condensation, and dehydrogenation. 相似文献
995.
996.
Liu Q Lu W Ma A Tang J Lin J Fang J 《Journal of the American Chemical Society》2005,127(15):5276-5277
In this communication, we report a successful synthesis of quasi-monodisperse In2O3 nanocrystals with high crystallinity in a high-temperature organic solution. The average size of nanocrystals can be tuned using a dynamic injection technique. TEM and XRD investigations indicate that each nanocrystal is a single crystal. The optical determination implies that the photoluminescence behavior of these In2O3 nanocrystals is different from that of the bulk, probably due to the combination of weak quantum-confinement-effects and the nature of high crystallinity in nanocrystals. 相似文献
997.
A new enzymatic process is reported, in which penicillin G acylase from Escherichia coli displays a promiscuous activity in catalyzing the Markovnikov addition of allopurinol to vinyl ester. 相似文献
998.
Determination of bisphenol A based on chemiluminescence from gold(III)-peroxymonocarbonate 总被引:1,自引:0,他引:1
Peroxymonocarbonate (HCO4−) was produced by the online reaction of bicarbonate with hydrogen peroxide. A strong chemiluminescence (CL) was observed when HCO4− reacted with AuCl4− without any special CL reagent. When bisphenol A (BPA) was added to AuCl4−-HCO4− CL system, the CL emission was inhibited significantly. This new CL system was developed as a flow-injection method for the determination of BPA. Under the optimum experimental conditions, the inhibited CL intensity was linearly related to the concentration of BPA from 0.3 to 80 μM (R = 0.9958). The detection limit of BPA was 0.08 μM. The relative standard deviation for 12 repeated measurements of 1.0 μM BPA was 2.9%. The interferences of some cationic ions can be removed by an online cation-exchange column. The applicability of the present CL system was demonstrated for the sensitive and selective determination of BPA in real samples (mineral water bottle, baby bottle, beverage bottle and polycarbonate container). Based on the CL spectrum, UV-visible adsorption spectra, and the quenching effect of reactive oxygen species scavengers, a possible CL mechanism was proposed. 相似文献
999.
Rui Gao Bai-Wang Sun Jun Lin Xiao-Li Gao 《Journal of Thermal Analysis and Calorimetry》2014,117(2):731-739
Studies of active drug-excipient compatibility represent an important phase in the preformulation stage of the development of all dosage forms. For the development of conjugation estrogens and medroxyprogesterone acetate (MPA) double-layer tablets, techniques of thermal, isothermal stress testing (IST), and molecular vibrational spectroscopy analysis were performed to access the compatibility. Differential scanning calorimetry (DSC) studies were used as an important and complementary tool during preformulation to determine drug-excipient compatibility. On the basis of DSC results, MPA was found to be compatible with polyethylene glycol 6000. However, the results of Raman and IST studies showed that all the excipients defined in the prototype formula were found to be compatible with MPA. Overall, the compatibility of selected excipients with MPA was successfully evaluated using a combination of thermal and IST methods, and the formulations developed using the compatible excipients were found to be stable. 相似文献
1000.
Reactions of dimethyl ether (DME) over γ-Al2O3 at 250°C have been investigated in a flow catalytic reactor. The main products of the interaction between DME and alumina are methanol and water. Heat evolution is observed as DME is passed over alumina, and replacing DME with nitrogen gives way to heat absorption. Calcination of alumina before the reaction considerably strengthens the exotherm, which is due to DME adsorption, while the endotherm is due to the desorption of weakly bound DME. The role of the hydroxyl groups of γ-Al2O3 in methanol and water formation has been elucidated. Treating alumina with water vapor after bringing it into contact with DME completely restores the hydroxyl cover and replaces strongly adsorbed DME with hydroxyl groups. 相似文献