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941.
Martens-Lobenhoffer J Krug O Bode-Böger SM 《Journal of mass spectrometry : JMS》2004,39(11):1287-1294
Arginine (ARG) is a substrate for endogenous nitric oxide (NO) production whereas its metabolite, asymmetric dimethylarginine (ADMA), acts as an inhibitor. Sufficient NO production is essential for cardiovascular key functions, thus elevated concentration levels of ADMA are related to a range of cardiovascular diseases. Owing to the lack of reliable methods for the measurement of ARG and ADMA in human plasma, concentration values determined with these methods can differ considerably. We present here a simple and very robust liquid chromatographic/mass spectrometric method for the determination of ARG and ADMA utilizing isotope-labeled internal standards. Sample preparation requires only protein precipitation; the analytes were derivatized with o-phthalaldehyde-mercaptoethanol and separated on a reversed-phase C(18) column with gradient elution. The analytes were detected with an electrospray ionization ion trap instrument working in the full-scan single mass spectrometry mode. Concentration values obtained with this method for healthy controls were ARG = 63.9 +/- 23.9 microM and ADMA = 0.355 +/- 0.066 microM, with a normal range for ADMA from 0.225 to 0.485 microM. The corresponding values for end-stage chronic renal failure patients are ARG = 48.1 +/- 18.5 microM, p < 0.01 and ADMA = 0.673 +/- 0.134 M, p < 0.001. 相似文献
942.
Dr. Md Mokhlesur Rahman Irin Sultana Dr. Tianyu Yang Dr. Zhiqiang Chen Dr. Neeraj Sharma Dr. Alexey M. Glushenkov Prof. Ying Chen 《Angewandte Chemie (International ed. in English)》2016,55(52):16059-16063
A simple, cost‐effective, and easily scalable molten salt method for the preparation of Li2GeO3 as a new type of high‐performance anode for lithium‐ion batteries is reported. The Li2GeO3 exhibits a unique porous architecture consisting of micrometer‐sized clusters (secondary particles) composed of numerous nanoparticles (primary particles) and can be used directly without further carbon coating which is a common exercise for most electrode materials. The new anode displays superior cycling stability with a retained charge capacity of 725 mAh g?1 after 300 cycles at 50 mA g?1. The electrode also offers excellent rate capability with a capacity recovery of 810 mAh g?1 (94 % retention) after 35 cycles of ascending steps of current in the range of 25–800 mA g?1 and finally back to 25 mA g?1. This work emphasizes the importance of exploring new electrode materials without carbon coating as carbon‐coated materials demonstrate several drawbacks in full devices. Therefore, this study provides a method and a new type of anode with high reversibility and long cycle stability. 相似文献
943.
Masao Kishida Chihiro Mio Kiyoshi Imamura Akira Kondo Akikazu Kaga Manohar Lal Shrestha 《International journal of environmental analytical chemistry》2013,93(2):67-82
The concentrations of polycyclic aromatic hydrocarbons (PAHs) in particulate matter (PM) with a diameter <10 µm (PM10, 50% cut off) were investigated in the Kathmandu Valley, Nepal, during 2003. In order to understand the dynamics of atmospheric PAHs in winter, the PAH concentrations in total PM and in the gaseous phase were investigated in the valley in December 2005. Total of 45 PAH compounds (∑45PAHs) were analysed by high-resolution gas chromatography/high-resolution mass spectrometry (HRGC/HRMS). In 2003, the ∑45PAH concentrations in PM10 ranged between 4.3 and 89 ng m?3 (annual average; 27 ± 24 ng m?3). The average concentrations of ∑45PAHs in December 2005 were 210 ± 33 ng m?3 in total PM and 430 ± 90 ng m?3 in the gaseous phase. The ∑45PAH concentration in PM accounted for more than 30% of the sum of their particulate and gaseous forms. Phenanthrene (Ph) was the most predominant compound in the gaseous phase, whereas four- to seven-ring PAHs were predominant in total PM. The highest values of ∑45PAHs occurred in the winter and spring. Estimates of emission sources based on diagnostic molecular ratios showed that atmospheric PAHs in the Kathmandu Valley mainly originated from the exhaust gas of diesel engine. In the winter and spring, PAH pollution would be accelerated by the operations of brick kilns and the frequent formation of an atmospherically stable layer in the valley. 相似文献
944.
Yoshitaka Saito Hidetoshi Matsumoto Tomoya Higashihara Mitsuru Ueda 《Journal of polymer science. Part A, Polymer chemistry》2013,51(18):3950-3955
Transparent and thermally stable polycyanurates, whose solubility can be changed by thermal rearrangement, have been synthesized as functional films used in the multilayer coating process. Before the synthesis of polycyanurates, the model compound, 2,6‐bis(4‐methoxyphenyl)?6‐methoxy‐1,3,5‐triazine as a cyanurate is prepared and rearranged to an isocyanurate, 1,3‐bis(4‐methoxyphenyl)?5‐methyl‐1,3,5‐triazinane‐2,4,6‐trione in an excellent yield by thermal treatment. Based on this result, polycyanurates are prepared by the phase‐transfer‐catalyzed polycondensation of 2,4‐dichloro‐6‐methoxy‐1,3,5‐triazine with bisphenol monomers in the presence of quaternary ammonium salts. The polycyanurate obtained from 9,9‐bis(hydroxyphenyl)fluorene exhibits a high glass transition temperature at 251 °C. The solubility of polycyanurate films containing 1 wt % of tetrabutylammonium bromide can be changed by thermal rearrangement. The partially rearranged films keep high transparency and low birefringence. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 3950–3955 相似文献
945.
946.
采用紧束缚分子动力学模拟硅团簇的结构,通过比较它们的结合能来确定基态结构,最后描绘出不同尺寸所对应的径向分布函数、角分布函数.模拟表明硅团簇在n=27处发生结构转变,从结构图上看,是由扁长结构向近球形结构转变.从径向分布函数图像、键角分布函数图像上也可以得到团簇结构在n=27处发生了变化,结构变得越来越紧密.关键词：硅团簇紧束缚分子动力学模拟退火基态结构 相似文献
947.
Stable aqueous dispersive colloidal Ag nanoparticles were prepared by reducing silver nitrate with sodium borohydride in the presence of 3-mercaptopropionic acid. The formation process of the Ag nanoparticles was investigated by UV-Visible spectroscopy and transmission electron microscopy. The results show that the spherical and rodlike particles and aggregates are formed in the initial stage of the reaction， then the rodlike particles and aggregates are gradually decomposed into small spherical particles， and the final obtained Ag nanoparticles with an average size of 8 nm are in uniform shapes and narrow size distribution， and the colloid remains stable for more than one month， which makes it convenient for use in practice. The presence of capping agent plays an extra role over nanoparticles stabilization and morphology. The presence of capping agent on the surface of Ag nanoparticle is confirmed by the X-ray photoelectron spectroscopy. It is found that Ag nanoparticles are negatively charged in alkaline condition， whereas they are positively charged in acid condition. Electrosteric effect is responsible for their long-term stability. 相似文献
948.
合金纳米粒子展示出单金属粒子所不具有的多功能性能, 而其稳定结构的研究对于进一步了解其催化性能具有重要的意义. 本文采用改进的遗传算法和量子修正Sutton-Chen型多体势对二十四面体Au-Cu-Pt三元合金纳米粒子的稳态结构进行了系统的研究. 针对不同尺寸、不同组成比例的合金纳米粒子, 探讨了遗传算法的收敛性及初始构型对稳态结构的影响. 计算的结果表明: 初始结构的选取并不影响最终的稳定结构, 并且改进的遗传算法具有较好的稳定性; Au和Cu形成表面偏聚, 而Pt则倾向于分布在内层; 当Au或Cu比例较小时, Au和Cu表现出表面最大偏聚; 当Au与Cu原子数之和大于表面原子数时, 二者表现出竞争偏聚, 且Cu的偏聚效应较强; 随着Au, Cu原子数继续增长至大于表面和次表面原子数之和时, Au的偏聚性能增强. 此外, Cu在占据表面后, 会越过次外层, 与Pt在内层形成混合相结构. 相似文献
949.
Pt-Pd合金纳米粒子相对于Pt及Pd单晶纳米粒子均具有更好的催化活性和选择性, 研究它的稳定结构对进一步了解催化性能具有重要意义. 本文采用粒子群算法和量子修正Sutton-Chen多体势对不同尺寸、 不同组成比例的二十四面体Pt-Pd合金纳米粒子的结构稳定性进行研究. 结果表明: Pt-Pd合金纳米粒子中Pt原子趋向于分布在纳米粒子内层, 而Pd原子趋向于分布在纳米粒子外层, 且Pt, Pd原子的分布越对称有序, 其能量越低, 结构越稳定; 随着Pt原子比例的增加, 三种不同尺寸的合金纳米粒子的Warren-Cowley化学短程有序值都逐渐升高, 即纳米粒子更趋向于偏聚分布状态; 在相同比例下, 小尺寸纳米粒子的偏聚程度比大尺 寸纳米粒子的大.关键词：合金纳米粒子粒子群算法稳态结构 相似文献
950.
报道了一种基于全啁啾镜腔内色散补偿的、可长期稳定运行的亚8 fs钛宝石激光器.在4 W绿光抽运下, 可获得300 mW、86 MHz脉冲输出.腔内用于色散补偿的两对啁啾镜是国内自主设计自行镀膜的, 其对色散的精确控制可以在腔内不加尖劈对的情况下获得半宽超过150 nm超宽带输出.利用腔外色散补偿, 脉冲宽度被压缩至7.9 fs, 这是目前采用国产啁啾镜获得的最短脉宽, 也是无尖劈对谐振腔获得的最短脉宽.同时, 利用电路系统提供实时反馈调节, 可保证钛宝石激光器长期稳定运行, 24 h内功率抖动约0.6%. 相似文献