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951.
Ma Y Lu Y Zeng H Ron D Mo W Neubert TA 《Rapid communications in mass spectrometry : RCM》2001,15(18):1693-1700
A two-step mass spectrometric method for characterization of phosphopeptides from peptide mixtures is presented. In the first step, phosphopeptide candidates were identified by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) based on their higher relative intensities in negative ion MALDI spectra than in positive ion MALDI spectra. The detection limit for this step was found to be 18 femtomoles or lower in the case of unfractionated in-solution digests of a model phosphoprotein, beta-casein. In the second step, nanoelectrospray tandem mass (nES-MS/MS) spectra of doubly or triply charged precursor ions of these candidate phosphopeptides were obtained using a quadrupole time-of-flight (Q-TOF) mass spectrometer. This step provided information about the phosphorylated residues, and ruled out nonphosphorylated candidates, for these peptides. After [(32)P] labeling and reverse-phase high-performance liquid chromatography (RP-HPLC) to simplify the mixtures and to monitor the efficiency of phosphopeptide identification, we used this method to identify multiple autophosphorylation sites on the PKR-like endoplasmic reticulum kinase (PERK), a recently discovered mammalian stress-response protein. 相似文献
952.
Pd(OAc)(2) combined with nitrogen-containing ligands (e.g., 2,2'-bipyridine) catalyzed the cyclization of (Z)-4'-acetoxy-2'-butenyl 2-alkynoates (1) in acetic acid to afford the alpha-(Z)-acetoxyalkylidene-beta-vinyl-gamma-butyrolactones (2) with high efficiency and high stereoselectivity. The nitrogen-containing ligands, like halides, served to favor beta-heteroatom elimination over beta-hydride elimination in Pd(II)-mediated reactions. The generality of this ligand effect was probed in both stoichiometric and catalytic reactions. With these results in hand, the catalytic asymmetric protocol was achieved with high enantioselectivity (up to 92% ee) when pymox (pyridyl monooxazoline) or bisoxazoline was used. The absolute configuration of the products and the synthetic utility of this asymmetric transformation were established through the convenient synthesis of (3S)-(+)-A-factor. 相似文献
953.
近来,有关 C60的研究主要集中在有关晶格动力学 [1]、电子结构 [2~ 4]和 MxC60( M代表碱金属或碱土金属)的超导电性研究 [5].但由于 MxC60在大气中不能稳定存在,制约了 MxC60的深入研究和实际应用 .最近, Masterov等人报导了他们对 Cu/C60的超导特性研究 [6~ 7],认为其转变温度 Tc在 80~ 120 K之间,这个转变温度比现有的 MxC60的转变温度( Tc~ 40 K)要高得多 .但有关更进一步的研究未见报导 .因此,我们拟对 CuxC60体系作较为详尽的研究,这对于进一步研究其超导机理是有必要的 .本工作是在成功地制备了 CuxC60薄膜的… 相似文献
954.
A new analytical method for the determination of ascorbic acid by the perturbation caused by different amounts of ascorbic acid on the BZ oscillating chemical system involving the Ce(IV)-catalyzed reaction between potassium bromate and malonic acid in a acidic medium is proposed. The method relies on the linear relationship between the change in the oscillation amplitude of the chemical system and the concentration of ascorbic acid, which is in this work exposed for the first time. The calibration curve is linearly proportional to the concentration of ascorbic acid over the range 3.5x10(-6)-4.7x10(-4) M, with the regression coefficient is 0.9975. Two different methodologies were used to address the determination. Some aspects of the potential mechanism of action of ascorbic acid on the BZ oscillating chemical system are discussed in detail. 相似文献
955.
Six novel diorganotin(IV) complexes have been synthesized in good yields by the reaction of R2SnCl2 (R= methyl, phenyl) with the Schiff base derived from salicylaldehyde and substituted thiosemicarbazide. The complexes were characterized by elemental analysis, IR, 1H NMR and MS spectra. The structure of 2f was confirmed by single crystal X‐ray diffraction. The crystal of 2f is triclinic, space group P‐1 with a = 0.84996(12), b = 1.1204(2), c = 1.27597(12) nm, β = 81.908(9)°, V=1.0904(2) nm3, Z = 2, Dc= 1.551 g/cm3. The final discrepancy factors are R = 0.0211 and Rw = 0.0536 for 3710 independent reflections. Tests of antitumor activities in vitro showed that the obtained complexes had relative inhibition interaction to the KB, HCT‐8 and BEL‐7402 tumor cell lines. 相似文献
956.
Qingli Hao Hoong‐Kun Fun Suchada Chantrapromma Ibrahim Abdul Razak Fangfang Jian Xujie Yang Lude Lu Xin Wang 《Acta Crystallographica. Section C, Structural Chemistry》2001,57(6):717-718
The title coordination complex, [Ni(C14H14O2PS2)2(C12H8N2)] or [Ni(pMePh‐dtp)2(phen)] (phen is 1,10‐phenanthroline; dtp is diaryldithiophosphate), has a non‐crystallographic twofold axis of symmetry through the Ni atom and the phen moiety. Two O,O‐di‐p‐tolyldithiophosphate (dtp) ions act as bidentate ligands. The central metal atom is coordinated by four S atoms from two dtp groups and two N atoms from the phen ligand. The title compound displays distorted octahedral geometry around the central Ni atom. 相似文献
957.
958.
959.
Lin Yan Wengang Chai Guanghui Wang Guanli Wu Kaijuan Lu Yue Luo 《Journal of mass spectrometry : JMS》1987,22(5):279-282
During a comparison study of the fast atom bombardment (FAB) and electron impact mass spectra of 1-organyl-2,9,10-trioxa-6-aza-1-silatricyclo[4.3.3.01,6]dodecanes, an unusual ion peak at m/z 164 was noticed in the FAB spectra. Accurate mass measurement indicated that m/z 164 corresponds to protonated 1-[N,N-bis(2-hydroxyethyl)amino]-1-propanol (BHAP), which is produced by a ring-rupture reaction. Further experiment showed that the intensity of the [BHAP + H]+ ion peak increased markedly as the 7keV Ar0 bombardment proceeded, suggesting a FAB-induced reaction. The possible mechanism is also discussed. 相似文献
960.
利用Rhcovibron DDV-II-EA型动态粘弹谱仪测试了PET平纹布在不同温度热定型后的布样及其经、纬纱的动态力学性质。发现布及其纱的动态力学-温度谱与原纤维的截然不同。在[Ε]-T 曲线上出现[Ε]峰,[Ε]_max值随织物热定型温度的增高呈指数下降,峰位向高温移动。同时在Ε’’-T曲线上出现双损耗模量峰,相应的松弛转变活化能相差半个数量级。初步分析认为,与织布过程及随后的织物热定型有关。 相似文献