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101.
102.
103.
Hao Wang Robert M. Straubinger John M. Aletta Jin Cao Xiaotao Duan Haoying Yu Jun Qu 《Journal of the American Society for Mass Spectrometry》2009,20(3):507-519
Protein arginine (Arg) methylation serves an important functional role in eucaryotic cells, and typically occurs in domains
consisting of multiple Arg in close proximity. Localization of methylarginine (MA) within Arg-rich domains poses a challenge
for mass spectrometry (MS)-based methods; the peptides are highly charged under electrospray ionization (ESI), which limits
the number of sequence-informative products produced by collision induced dissociation (CID), and loss of the labile methylation
moieties during CID precludes effective fragmentation of the peptide backbone. Here the fragmentation behavior of Arg-rich
peptides was investigated comprehensively using electron-transfer dissociation (ETD) and CID for both methylated and unmodified
glycine-/Arg-rich peptides (GAR), derived from residues 679–695 of human nucleolin, which contains methylation motifs that
are widely-represented in biological systems. ETD produced abundant information for sequencing and MA localization, whereas
CID failed to provide credible identification for any available charge state (z=2–4). Nevertheless, CID produced characteristic
neutral losses that can be employed to distinguish among different types of MA, as suggested by previous works and confirmed
here with product ion scans of high accuracy/resolution by an LTQ/Orbitrap. To analyze MA-peptides in relatively complex mixtures,
a method was developed that employs nano-LC coupled to alternating CID/ETD for peptide sequencing and MA localization/characterization,
and an Orbitrap for accurate precursor measurement and relative quantification of MA-peptide stoichiometries. As proof of
concept, GAR-peptides methylated in vitro by protein arginine N-methyltransferases PRMT1 and PRMT7 were analyzed. It was observed that PRMT1 generated a number of monomethylated (MMA) and
asymmetric-dimethylated peptides, while PRMT7 produced predominantly MMA peptides and some symmetric-dimethylated peptides.
This approach and the results may advance understanding of the actions of PRMTs and the functional significance of Arg methylation
patterns. 相似文献
104.
Zhang J Tao D Duan J Liang Z Zhang W Zhang L Huo Y Zhang Y 《Analytical and bioanalytical chemistry》2006,386(3):586-593
A comprehensive two-dimensional liquid chromatographic (2D-LC) separation system based on the combination of a CN column and
a Merck Chromolith Flash reversed-phase column was developed for the separation of components in Adinandra nitida, one type of traditional Chinese medicine (TCM). The two dimensions were connected by a ten-port, dual-position valve controlled
automatically by software written in-house. The effluents were detected by both ultraviolet and atmospheric pressure chemical
ionization source ion trap tandem mass spectrometry (MS). The calculated peak capacity of the 2D-LC–MS/MS system was above
1240. More than 57 components were resolved in the methanol extract from Adinandra nitida leaves, and five of these were identified based on their relative retention times, molecular weights and MS/MS spectra. 相似文献
105.
建立了基质固相分散萃取-高效液相色谱-串联质谱法(MSPD-HPLC-MS/MS)同时测定拟南芥中3种赤霉素GA1, GA3和GA4的分析方法。将拟南芥样品与C18填料混合研磨制成MSPD柱,并采用80%冷甲醇洗脱。采用反相C18色谱柱进行分离,以0.05%甲酸水溶液和乙腈为流动相进行梯度洗脱,采用电喷雾离子源负离子模式(ESI~)电离,多反应监测模式检测。对样品前处理条件、色谱分离条件和质谱检测条件进行了优化,结果表明,在最优条件下,3种赤霉素在10~300 ng/g范围内均呈良好线性关系,相关系数(r2)均大于0.98,检出限在1.1~4.1 ng/g之间。在10~50 ng/g添加水平下,平均回收率范围为54.7%~102.6%,相对标准偏差(RSD,n=3)为3.2%~12.8%。该方法操作简单、灵敏度高、选择性好、回收率高,适合拟南芥中GA1、GA3、GA4含量的测定。 相似文献
106.
Meili Duan Takeyasu Tasaka Hiroaki Okamoto Vladimir F. Petrov Shunsuke Takenaka 《Liquid crystals》2013,40(9):1195-1205
This paper describes the effect of substituent and ester linkage on smectic properties for some derivatives of 4-R -phenyl 4-(4-octyloxybenzoyloxy)benzoates (1), 4-octyloxyphenyl 4-(4-R-benzyloxy)benzoates (2), 4-(4-octyloxybenzoyloxy)phenyl 4- R -benzoates (3), and 4-R-phenyl 4-octyloxyphenyl terephthalates (4) where R = OCH3, CH3, OC8H17, C8H17, halogens, CF3, OCF3, CN, NO2, etc. The thermal properties are discussed in terms of the electrostatic nature of the substituents and the relative orientation of the ester groups with respect to both terminal substituents. The substituent effect on the layer structure of the smectic A phase is also examined by means of a small angle X-ray analysis. 相似文献
107.
Xiao‐Hui Duan Jian‐Feng Li Wen‐Jun Zhu 《International journal of quantum chemistry》2011,111(14):3873-3880
A molecular dynamics study is performed to determine the dynamics and transport properties of the ions on the molten interface between anode metal Li and electrolyte KCl. Radial distribution function of the ionic pair and the behavior of the mean‐square displacement (MSD) as a function of time (t) indicate that KCl and metal Li are in the molten state at 2,200 K in the canonical ensemble. The dynamics of the ionic transport are characterized by studying MSD for the centers of mass of the ions at different temperatures. Diffusion coefficient is evaluated from the linear slope of the MSD (t) function in the range of 0–500 ps. The MSD and diffusion coefficient of the Li+ ions are much larger than those of the Cl? and K+ ions due to the difference in ionic characteristic. The transport process has been dominated by the Li+ ions on the molten interface and the Li+ ions are main charge carriers. The energy barrier of the Li+ ions transporting into the molten KCl is fitted to be 5.28 kcal/mol in the light of the activation model. The electrical conductivity of the Li+ ions transporting into the molten KCl are calculated from the Nernst–Einstein formula to be in the range of 0.2–0.3 S cm?1. The current density resulted from the Li+ ions through the interface are estimated to be an order of 106 A cm?2, which may be the value corresponding to a larger concentration gradient of the Li+ ions. Simulated results at different temperatures show that the diffusion coefficient, conductivity and current density have increased with the temperature. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011 相似文献
108.
Yueqiang Cao Hao Zhang Shufang Ji Zhijun Sui Zheng Jiang Dingsheng Wang Francisco Zaera Xinggui Zhou Xuezhi Duan Yadong Li 《Angewandte Chemie (International ed. in English)》2020,59(28):11647-11652
Atomic regulation of metal catalysts has emerged as an intriguing yet challenging strategy to boost product selectivity. Here, we report a density functional theory‐guided atomic design strategy for the fabrication of a NiGa intermetallic catalyst with completely isolated Ni sites to optimize acetylene semi‐hydrogenation processes. Such Ni sites show not only preferential acetylene π‐adsorption, but also enhanced ethylene desorption. The characteristics of the Ni sites are confirmed by multiple characterization techniques, including aberration‐corrected high‐resolution scanning transmission electron microscopy and X‐ray absorption spectrometry measurements. The superior performance is also confirmed experimentally against a Ni5Ga3 intermetallic catalyst with partially isolated Ni sites and against a Ni catalyst with multi‐atomic ensemble Ni sites. Accordingly, the NiGa intermetallic catalyst with the completely isolated Ni sites shows significantly enhanced selectivity to ethylene and suppressed coke formation. 相似文献
109.
Zexi Liu Jing Ai Prashant Kumar Enming You Xiong Zhou Xi Liu Zhongqun Tian Petr Bou Yingying Duan Lu Han Nicholas A. Kotov Songyuan Ding Shunai Che 《Angewandte Chemie (International ed. in English)》2020,59(35):15226-15231
A surface‐enhanced Raman scattering‐chiral anisotropy (SERS‐ChA) effect is reported that combines chiral discrimination and surface Raman scattering enhancement on chiral nanostructured Au films (CNAFs) equipped in the normal Raman scattering Spectrometer. The CNAFs provided remarkably higher enhancement factors of Raman scattering (EFs) for particular enantiomers, and the SERS intensity was proportional to the enantiomeric excesses (ee) values. Except for molecules with mesomeric species, all of the tested enantiomers exhibited high SERS‐ChA asymmetry factors (g), ranging between 1.34 and 1.99 regardless of polarities, sizes, chromophores, concentrations and ee. The effect might be attributed to selective resonance coupling between the induced electric and magnetic dipoles associated with enantiomers and chiral plasmonic modes of CNAFs. 相似文献
110.
Catecholamines play important roles in biology but their structural similarity makes it challenging to construct synthetic receptors with selective binding. A combination of covalent and noncovalent binding groups in the hydrophobic core of water‐soluble nanoparticles enabled them to recognize dopamine and epinephrine with an association constant (Ka) of 3–4×104 M?1 in water, an order of magnitude higher than those of previously reported synthetic hosts. In addition, minute structural changes among analogues were detected including the addition or removal of a single hydroxyl or methyl group. 相似文献