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排序方式: 共有87条查询结果,搜索用时 140 毫秒
1.
Harrison KA Davies SS Marathe GK McIntyre T Prescott S Reddy KM Falck JR Murphy RC 《Journal of mass spectrometry : JMS》2000,35(2):224-236
Oxidized low-density lipoprotein (LDL) is thought to play an important role in atherogenesis and cardiovascular disease in humans. Oxidized LDL is a complex mixture of many oxidized species, including numerous oxidized glycerophospholipids. Electrospray ionization and tandem mass spectrometry as well as microchemical derivatization of high-performance liquid chromatographically purified fractions derived from oxidized LDL were investigated as means to determine the structure of individual components present in oxidized LDL. One major oxidized phosphocholine lipid had an [M + H](+) ion at m/z 650. Derivatization to the trimethylsilyl ether and methoxime caused shifts in mass which, along with negative ion collision-induced dissociation mass spectra, were consistent with the presence of three species, 1-palmitoyl-2-(9-oxononanoyl)glycerophosphocholine and two isomeric 1-octadecanoyl-2-(hydroxyheptenoyl)glycerophosphocholines. These species were chemically synthesized. Trimethylsilylation of free hydroxyl groups increased the mass of the phospholipid acyl chains containing hydroxyl groups by 72 u. Conversion of carbonyl groups to the methoxylamine derivative increased the mass by 29 u. Ozonolysis of those products which contained double bonds proved to be a facile technique to determine the position and number of double bonds present. The use of these techniques was illustrated in the structural characterization of one major component (m/z 650, positive ions) in oxidized LDL as 1-octadecanoyl-2-(7-hydroxyhepta-5-enoyl)glycerophosphocholi ne. A possible mechanism for the formation of this unique chain-shortened glycerophospholipid is proposed. 相似文献
2.
Abe K Akagi T Anthony PL Antonov R Arnold RG Averett T Band HR Bauer JM Borel H Bosted PE Breton V Button-Shafer J Chen JP Chupp TE Clendenin J Comptour C Coulter KP Court G Crabb D Daoudi M Day D Dietrich FS Dunne J Dutz H Erbacher R Fellbaum J Feltham A Fonvieille H Frlez E Garvey D Gearhart R Gomez J Grenier P Griffioen KA Hoibraten S Hughes EW Hyde-Wright C Johnson JR Kawall D Klein A Kuhn SE Kuriki M Lindgren R Liu TJ Lombard-Nelsen RM Marroncle J Maruyama T Maruyama XK McCarthy J Meyer W 《Physical review letters》1995,74(3):346-350
3.
Balest R Cho K Ford WT Lohner M Park H Rankin P Smith JG Alexander JP Bebek C Berger BE Berkelman K Bloom K Browder TE Cassel DG Cho HA Coffman DM Crowcroft DS Dickson M Drell PS Dumas DJ Ehrlich R Elia R Gaidarev P Garcia-Sciveres M Gittelman B Gray SW Hartill DL Heltsley BK Henderson S Jones CD Jones SL Kandaswamy J Katayama N Kim PC Kreinick DL Lee T Liu Y Ludwig GS Masui J Mevissen J Mistry NB Ng CR Nordberg E Patterson JR Peterson D Riley D Soffer A Avery P Freyberger A Lingel K Prescott C 《Physical review letters》1995,75(21):3809-3813
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5.
W.B. Atwood E.D. Bloom R.L.A. Cottrell H. DeStaebler M. Mestayer C.Y. Prescott L.S. Rochester S. Stein R.E. Taylor D. Trines 《Physics letters. [Part B]》1976,64(4):479-482
Inelastic electron scattering cross sections have been measured for four-momentum transfers between 4.1 GeV2 and 30.5 GeV2. At the large scattering angles of this experiment, the dominant contribution to the cross section comes from the W1 structure function. In the conventional scaling variables, x and x′, this structure function does not exhibit scaling behavior, and at fixed x or x′ it is found to decrease with increasing four-momentum transfer. 相似文献
6.
Nickel A Maruyama T Tang H Murphy PD Greene B Yusuff N Wood JL 《Journal of the American Chemical Society》2004,126(50):16300-16301
A total synthesis of the biologically important diterpene ingenol has been completed. Ring-closing olefin metathesis was used to construct the strained "inside-outside" tetracyclic skeleton, and a series of diastereoselective reactions were employed to complete the synthesis. Another naturally occurring ingenane, 20-deoxyingenol, has also been prepared. 相似文献
7.
R P Evershed M C Prescott M Kabbouh H H Rees 《Rapid communications in mass spectrometry : RCM》1989,3(10):352-355
Metastable ions arising from pseudomolecular [M-H]- ions produced by fast-atom bombardment negative-ion mass spectrometry of a range of free ecdysteroids, ecdysteroid conjugates and polar metabolites were investigated by means of linked scanning at constant B/E. Free ecdysteroids displayed daughter-ion spectra which allow 20-hydroxyecdysteroids and ecdysteroids lacking C-20 hydroxylation to be readily distinguished. The ejection of acetic acid from acetylated ecdysteroids was also readily detectable. Characteristic metastable-ion decomposition of ecdysteroid acids was not observed, presumably as a result of charge localization. High-mass daughter ions were also lacking in the case of phosphate conjugates. 相似文献
8.
Alexander S Cosgrove T Prescott SW Castle TC 《Langmuir : the ACS journal of surfaces and colloids》2011,27(13):8054-8060
Pulsed-field gradient stimulated-echo nuclear magnetic resonance (NMR) and surface tension measurements have been used to study the effect of drug addition on the micellization behavior of pluronic triblock copolymers (P103, P123, and L43). The addition of 0.6 wt% flurbiprofen to Pluronic P123 and P103 solutions reduced their cmc and promoted micellization. Also, a substantial increase in the hydrodynamic radius of Pluronic P103 from 5 to 10 nm was observed, along with an increased fraction of polymer micellized, demonstrating that the polymers solubilize this nonsteroidal anti-inflammatory drug. 相似文献
9.
Sediment dating by luminescence: a review 总被引:17,自引:0,他引:17
In the present article we review applications of luminescence methods for the determination of the age of sediments for Quaternary Earth science. “Sediment” is taken to include any mineral particles transported by wind, water and/or ice and subsequently deposited. Methodology is not discussed per se but appears in context. The emphasis is on recent work and is illustrative rather than exhaustive. Applications in archaeology are mentioned only briefly. Successful dating requires that the luminescence signal has been zeroed by sunlight at the time the sediment was laid down. Dune sands and loess transported in full daylight usually satisfy this condition and have been dated by both traditional thermoluminescence and by optical methods. Optical dating is advantageous for less well-bleached sediments, such as are found in colder climates and those laid down by fluvial and glacial processes, although the prospects for dating the latter are shown to be poor. Among less common contexts are volcanic eruptions, earthquake faults and tsunami deposits. The dating of very young sediments, less than 2 ka, is demonstrated and the factors limiting the dating of very old sediments, 500 ka to 1 Ma, are discussed. Validation of any dating method by comparison with other methods is necessary; luminescence ages have been successfully compared with ages obtained by, for example, 14C, U–Th series and δ18O isotope ratios. The most difficult problems encountered in dating quartz, feldspars and undifferentiated fine grain mixtures include: anomalous fading (which leads to underestimates of age), incomplete zeroing (which gives overestimates) and sample inhomogeneity. Methods devised to minimise these effects include preheating regimes, selection of observing wavelengths and of stimulating wavelengths for optical dating, the use of single aliquot and single grain measurements. The use of appropriate data analysis procedures is also important. Advice on current best practice on procedures for obtaining reliable ages is offered and, in all applications, there are suggestions as to where further research might be directed. 相似文献
10.
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