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901.
Hsu FF Turk J Shi Y Groisman EA 《Journal of the American Society for Mass Spectrometry》2004,15(1):1-11
Acylphosphatidylglycerol (Acyl-PG), a polar lipid class containing three fatty acyl groups, was isolated from Salmonella bacteria and characterized by tandem quadrupole and quadrupole ion-trap mass spectrometric methods with electrospray ionization. The structural characterization of the acyl-PG with various acyl groups (A-B/C-PG, where A not equal B not equal C) is based on the findings that the carboxylate anions (R(x)CO(2)(-)) arising from sn-2 (R(2)CO(2)(-)) is more abundant than that arising from sn-3' (R(3')CO(2)(-)), which is much more abundant than that arising from sn-1 (R(1)CO(2)(-)). This information provides a simple method for determination of the fatty acyl moieties and their positions in the molecule. The structural identification of the molecule can also be achieved by the findings that the fragment ion reflecting the ketene loss at sn-2 is more prominent than that reflecting the acid loss (i.e., [M - H - R'(2)CH=CO](-) > [M - H - R(2)CO(2)H](-)), while the ion arising from acid loss at sn-1 or sn-3' is, respectively, more abundant than the corresponding ketene loss (i.e., [M - H - R(1)CO(2)H](-) > [M - H - R'(1)CH=CO](-); [M - H - R(3')CO(2)H](-) > [M - H -R'(3')CH=CO](-)). The identity of the acyl moiety at sn-3' can be confirmed by an acyl-glycerophosphate anion observed in the product-ion spectrum obtained with a triple-stage quadrupole (TSQ) instrument, but not in that obtained with an ion-trap mass spectrometer (ITMS). However, the MS(2)-spectrum obtained with an ITMS is featured by the ion series that abundances of [M - H - R'(2)CH=CO - R(3)CO(2)H - 74](-) > [M - H - R'(2)CH=CO - R(1)CO(2)H - 74](-) z.Gt; [M - H - R'(1(or 3'))CH=CO - R(3'(or 1))CO(2)H - 74](-). This information also facilitates structural elucidation of the acyl-PG subclass that contains various acyl substituents. Structural identifications of molecular species having two identical fatty acyl substituents at sn-1, sn-2, or sn-3' or consisting of more than one isomeric structures are also demonstrated. The identities of the minor isomeric species in the molecules can be revealed by the aforementioned structural information arising from the various ion series combined. 相似文献
902.
A gold(III)-catalyzed carbon-carbon bond formation reaction between arenes and electron-deficient alkynes or alkenes is described. Electron-rich arenes can be efficiently functionalized with the alkyne or alkene substrates. This reaction can be run with neat reactants at ambient temperature. Under the "solventless" conditions, clean product was obtained from a reaction of equal molar amounts of arene and alkyne substrates. The mild conditions and potential tolerance to different functional groups make this method practical for arene functionalization and for constructing complicated molecules. Efficient preparation of various coumarins from aryl alkynoates was demonstrated. Preliminary mechanistic studies were performed to probe the pathway of this reaction. 相似文献
903.
This paper describes several highly efficient aza-Baylis-Hillman reactions of N-tosylated imines with MVK, acrolein, and phenyl acrylate or alpha-naphthyl acrylate in the presence of a Lewis base. In most cases, the reaction can be completed within 1 h using the appropriate Lewis base catalyst. An efficient method to synthesize beta-amino ketones, aldehydes and esters in high yields and short reaction time has been developed. 相似文献
904.
Acyclic dithiol and cyclic disulfide forms of the peptides Ac-Cys-Pro-Xaa-Cys-NH2 (Xaa = Phe, His, Tyr, Gly, and Thr) and Ac-Cys-Gly-Pro-Cys-NH2 and the peptide Ac-Ala-Gly-Pro-Ala-NH2 were synthesized and characterized by mass spectrometry and NMR spectroscopy. Rate constants kct and ktc for cis-to-trans and trans-to-cis isomerization, respectively, across the Cys-Pro or Gly-Pro peptide bonds were determined by magnetization transfer NMR techniques over a range of temperatures, and activation parameters were derived from the temperature dependence of the rate constants. It was found that constraints imposed by the disulfide bond confer an unexpected rate enhancement for cis/trans isomerization, ranging from a factor of 2 to 13. It is proposed that the rate enhancements are a result of an intramolecular catalysis mechanism in which the NH proton of the Pro-Xaa peptide bond hydrogen bonds to the proline nitrogen in the transition state. The peptides Ac-Cys-Pro-Xaa-Cys-NH2 and Ac-Cys-Gly-Pro-Cys-NH2 are model compounds for proline-containing active sites of the thioredoxin superfamily of oxidoreductase enzymes; the results suggest that the backbones of the active sites of the oxidized form of these enzymes may have unusual conformational flexibility. 相似文献
905.
Novel adsorbents which can concentrate Th(IV) in aqueous solution were prepared by immobilizingMyrica rubra tannin and larch tannin onto collagen fibre matrices. The adsorption capacities of the immobilized tannins to Th(IV) are
related to temperature and pH value of the adsorption process. For example, when the initial concentration of Th(IV) was 116.0
mg·l-1 and the immobilized tannin was 100 mg, the adsorption capacities of immobilized Myrica rubra tannin and larch tannin were 55.98 mg Th(IV)·g-1 and 13.19 mg Th(IV)·g-1, respectively at 303 K, and 73.67 mg Th(IV)·g-1 and 18.19 mg Th(IV)·g-1 at 323 K. It was also found that the higher adsorption capacity was obtained at higher pH value. The adsorption equilibrium
data of the immobilized tannins for Th(IV) can be well fitted by the Langmuir model and the mechanism of the adsorption was
found to be a chemical adsorption. In general, the adsorption capacity of immobilized Myrica rubra tannin to Th(IV) is significantly higher than that of immobilized larch tannin, probably due to the fact that the B ring
of Myrica rubra tannin has a pyrogallol structure which has higher reaction activity with metal ions. The breakthrough point of the adsorption
column of immobilized Myrica rubra tannin was at 33 bed volumes for the experimental system. The mass transfer coefficient of adsorption column determined by
Adams-Bohart equation was 1.61·10-4 l·mg-1.min-1. The adsorption column can be easily regenerated by 0.1 mol·l-1 HNO3 solution, showing outstanding ability of concentrating Th(IV).
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
906.
Lanying Yang Yi Zhang Qingqi Chen Jin Shi Ma 《Monatshefte für Chemie / Chemical Monthly》2004,417(3):223-229
1-(Dipyrrin-2-yl)-1-(dipyrrin-3-yl)methane, the N-confused analog of biladiene-ac, is prepared by condensation of 2,3-dipyrromethane with two molecules of 2-formylpyrrole in dichloromethane in the presence of hydrogen bromide. Self-assembly of the ligand with Zn(II) in dichloromethane and methanol offers a dinuclear dimeric complex with a ligand:metal ratio of 2:2. X-Ray crystal structure analysis reveals two ligands bound through a head-to-tail pattern to two zinc centers to form a severely distorted helical conformation, which has the shape of a rectangle. 相似文献
907.
908.
制备条件对Au/TiO2催化CO氧化性能的影响 总被引:6,自引:0,他引:6
采用沉积沉淀法和化学沉积法,分别制备了Au/TiO2催化剂,比较详尽地探讨了制备方法及制备条件对其催化CO氧化性能的影响,并对催化剂进行XRD表征,优化了制备条件,结果显示,控制沉积-沉淀反应液的pH值范围为6.5-7.0,浓度为40mL水/g载体,温度70℃,还原温度85℃,时间60min,以沉积-沉淀法制备的3%Au/TiO2催化剂可于-35℃将CO完全转化,经还原预处理比经焙烧得到的催化剂的活性更高,用光化学沉积法制备的Au/TiO2催化剂的活性欠佳。 相似文献
909.
910.
Hui‐Bo Zhou Wen Dong Mao Liang Dai‐Zheng Liao Zong‐Hui Jiang Shi‐Ping Yan Peng Cheng 《无机化学与普通化学杂志》2004,630(4):498-500
A three‐dimensional cyano‐bridged copper(II) complex, [Cu(dien)Ag(CN)2]2[Ag2(CN)3][Ag(CN)2] ( 1 ) (dien = diethylenetriamine), has been prepared and characterized by X‐ray crystallography. Complex 1 crystallized in the monoclinic space group P21/n with a = 6.988(2), b = 17.615(6), c = 12.564(4) Å, β = 90.790(5)°. The crystal consists of cis‐[Cu(dien)]2+ units bridged by [Ag(CN)2]— to form a zig‐zag chain. The Ag atoms of the free and bridging [Ag(CN)2]— link together to form additional infinite zig‐zag chains with short Ag···Ag distances. The presence of Ag···Ag interactions effectively increases the dimensionality from a 1‐D chain to a 3‐D coordination polymer. 相似文献