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271.
Investigation of Capparis spinosa of Jordanian origin lead to isolation of two new compounds beta-sitosterylglucoside-6'-octadecanoate (1) and 3-methyl-2-butenyl-beta-glucoside (2). Linked Scan MS measurements were used to propose a mass fragmentation pattern for the alkaloid Cadabicine isolated here for the second time from nature. 相似文献
272.
Separation of peptides with an aqueous mobile phase by temperature-responsive chromatographic column 总被引:1,自引:0,他引:1
Liu Z Liang Y Geng F Ge C Ullah K Lv F Dai R Zhang Y Deng Y 《Journal of separation science》2012,35(16):2069-2074
Peptide separation technology is significant and is still an analytical challenge in proteomic studies. We report a simple preparation method for poly(N-isopropylacrylamide) grafted silica through the copolymerization of N-isopropylacrylamide with acetyl moieties immobilized on the silica surfaces. Differential scanning calorimetry results indicated that the prepared silica exhibited a sharp phase transition at 35.03°C. Silica grafted with poly(N-isopropylacrylamide) was evaluated as a temperature-responsive chromatography medium for the separation of peptides using 0.2 M NaCl solution as a mobile phase. Results indicated that at 10°C, the peptides were not resolved, but baseline separation with prolonged retention time at 50°C was attained. Particularly, a mixture of four peptides was efficiently separated within 8 min. The theoretical plate number of every peptide was more than 2500, and the resolutions were more than 3.40. The increased selectivity of the temperature-responsive column resulted from the temperature-modulated hydrophobic interaction with peptides. The retention times of these peptides were related to their hydrophobicities. This protocol provided a reliable set of chromatographic tool usable across all research and development applications that required isolation and analysis of peptides. It may represent a step forward in the complex analysis of hydrophobic and other proteins. 相似文献
273.
A.Camilo P. Alves J.Michael Hollas Hamdan Musa Trevor Ridley 《Journal of Molecular Spectroscopy》1985,109(1):99-122
Single vibronic level fluorescence (SVLF) spectra of tropolone from vibronic levels in the electronic state, in combination with recently reported supersonic jet spectra, have enabled the assigning of many absorption bands in the region of 000 which had previously been impossible. Some of the complexity in these bands has been shown to be due to a large Duschinsky effect involving the two lowest b1 vibrations, ν25 and ν26. It has been shown that these vibrations have wavenumbers of 176 and 110 cm?1, respectively, in the state, and 172 and 39 cm?1 in the state. This last value shows how unresistent the molecule is in the state to out-of-plane bending in the region of the five-membered ring. Other aspects of the vibrational complexity are due to the effect of ν′26 in increasing the barrier to tunnelling of the hydrogen-bonding proton in the state contrasting with very little effect of ν″26 in the state. 相似文献
274.
275.
Ibrahim Garib Mamedov Uwe Eichhoff Abel Mammadali Maharramov Musa Rza Bayramov Yegana Vagif Mamedova 《Magnetic resonance in chemistry : MRC》2010,48(9):671-677
The formation of hydrogen bonds and molecular dynamics for the molecules cis‐1‐(2‐hydroxy‐5‐methylphenyl)ethanone oxime ( I ) and N‐(2‐hydroxy‐4‐methylphenyl)acetamide ( II ) have been investigated in solution using NMR. The results confirm the formation of O? H···O, O? H···N and O···H? N type inter‐ and intramolecular hydrogen bonds. Spin‐lattice relaxation times (T1), activation energy of molecular dynamics and energy of intramolecular hydrogen bonds have been determined. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
276.
K. Kaleem F. Chertok S. Erhan 《Journal of polymer science. Part A, Polymer chemistry》1989,27(3):865-872
A novel oligomeric compound has been synthesized by reacting 1,3 bis-(3-aminophenoxy)-benzene (APB) with p-benzoquinone. A dark reddish brown product has been characterized using UV, IR, and NMR spectra, and elemental analysis. It, too, adheres to metals, as does another polyetheramine-p-benzoquinone polymer synthesized in Part I [Prog. Org. Coating, 15 , 63 (1987)], and becomes nonwettable after heat curing. However, its moisture adsorption is only 0.1% by weight, as against 3% for the latter product. This makes it a likely candidate for insulating electronic components from moisture. 相似文献
277.
A new type of discharge in pure metal vapors like copper or titanium is described. A stable discharge is produced between a heated cathode and the anode which has a melted spot on its surface due to the electron bombardment. The spectral characteristics prove that the discharge take place in the vapors of the anode material continuously evaporated from the melted spot on the anode. The discharge has a similar behaviour as the low voltage arc. 相似文献
278.
Gallocynin immobilized in chitosan membrane has been studied as a sensor element of an optical sensor for lead using a flowing system. By using this set up, lead in solution has been determined in the concentration range from 1.0x10(-1) to 1.0x10(3) ppm with a detection limit of 0.075 ppm. The standard deviation of the method for the repeatability of lead detection at a concentration of 100 ppm was found to be 2.10%. The response of the sensor was reproducible and can be regenerated by using acidified saturated KNO(3) solution. Interference from foreign ions was also studied at 1:1 mole ratio of Pb(II):foreign ions. 相似文献
279.
Reactions of the intermediate W(CO)5THF, generated photochemically from W(CO)6 in THF, with Ph2P(CH2)
n
PPh2 [ = PP; n = 2 (dppe), 4 (dppb), 6 (dpph), 10 (dppd)] at room temperature in THF solutions gave exclusively bimetallic complexes of the (CO)5WPPW(CO)5 type. In addition, complexes bridged by diphosphine ligands of the (CO)4(pip)MPPM(pip)(CO)4 type (pip = piperidine; M = Mo, W) were prepared by stirring the (CO)4M(pip)2 complexes with bis(diphenylphosphino)alkanes in CH2Cl2 solution at ambient temperatures. These new bis(diphenylphosphino)alkane-bridged complexes were characterized by i.r., 1H- and 31P-n.m.r. spectroscopies, as well as by elemental analysis. 相似文献
280.
Optical resolution of (±)-tetrahydrojatrorrhizine using (-)-O,O-di--toluoyl--tartaric acid gave rise to (+)-tetrahydrojatrorrhizine ( of high optical purity and of known absolute configuration. Oxidation of this enantiomer with lead tetraacetate, followed by acid hydrolysis, furnished alcohols and in a 2:1 ratio, whose relative stereochemistry was established from their nmr spectra. Iodine oxidation of the major alcohol led to protoberberinium salt which was found to be dextrorotatory. Since berberastine () and thalidastine () are also dextrorotatory, they must possess the same absolute configuration as . 相似文献