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排序方式: 共有87条查询结果,搜索用时 15 毫秒
21.
DC Muddiman AP Null JC Hannis 《Rapid communications in mass spectrometry : RCM》1999,13(12):1201-1204
Electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICRMS) has been used to determine the mass of a double-stranded 500 base-pair (bp) polymerase chain reaction (PCR) product with an average theoretical mass of the blunt-ended (i.e. unadenylated) species of 308 859.35 Da. The PCR product was generated from the linearized bacteriophage Lambda genome which is a double-stranded template. Utilization of ethanol precipitation in tandem with a rapid microdialysis step to purify and desalt the PCR product was crucial to obtain a precise mass measurement. The PCR product (0.8 pmol/μL) was electrosprayed from a solution containing 75% acetonitrile, 25 mM piperidine, and 25 mM imidazole and was infused at a rate of 200 nL/min. The average molecular mass and the corresponding precision were determined using the charge-states ranging from 172 to 235 net negative charges. The experimental mass and corresponding precision (reported as the 95% confidence interval of the mean) was 309 406 +/- 27 Da (87 ppm). The mass accuracy was compromised due to the fact that the PCR generates multiple products when using Taq polymerase due to the non-template directed 3'-adenylation. This results in a mixture of three PCR products with nearly identical mass (i.e. blunt-ended, mono-adenylated and di-adenylated) with unknown relative abundances that were not resolved in the spectrum. Thus, the experimental mass will be a weighted average of the three species which, under our experimental conditions, reflects a nearly equal concentration of the mono- and di-adenylated species. This report demonstrates that precise mass measurements of PCR products up to 309 kDa (500 bp) can be routinely obtained by ESI-FTICR requiring low femtomole amounts. Copyright 1999 John Wiley & Sons, Ltd. 相似文献
22.
DC Bassett 《Macromolecular Symposia》1997,114(1):121-126
Molecular cilia, the uncrystallized portions of chains already partly attached to polymer crystals, exert a profound influence on the course of polymeric crystallization with ultimate responsibility for the divergence of adjacent lamellae which leads to spherulitic growth. Their effective size and pressure have been measured, in α-polypropylene, from electron microscopic measurements of the separation and maximum curvature of lamellae in row structures. That cilia exist and extend the effective region occupied by a lamella beyond the geometrical confines of its fold surfaces is important for crystallization theory and may well have implications for the connection of lamellae into networks and for gelation. 相似文献
23.
Marchesan S Easton CD Kushkaki F Waddington L Hartley PG 《Chemical communications (Cambridge, England)》2012,48(16):2195-2197
Change of chirality of the first N-terminal amino acid of tripeptides VFF and FFV from l to d results in self-assembled hydrogels at physiological pH from non-assembling l-analogues. Interestingly, changing the chirality of F yields very different nanostructures; nanotapes are observed for (D)VFF, twisted fibers for (D)FFV. 相似文献
24.
Simon Waddington 《Communications in Mathematical Physics》1996,176(2):273-305
We derive various asymptotic formulae for the numbers of closed orbits in the Lorenz and Horseshoe templates with given knot invariants, (for example braid index and genus). We indicate how these estimates can be applied to more complicated flows by giving a bound for the genus of knotted periodic orbits in the figure of eight template. 相似文献
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26.
概述了碳碳双键在气相中无催化环氧化反应研究方法、反应机理、测定了2-甲基丙烯醛与过氧化乙酰基在393K和413K时环氧化反应的速率,实验结果表明,不同结构烯烃的环氧化反应速率主要取决于双键所连取代基的性质,取代基的给电子能力越强环氧化反应速率越快。 相似文献
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28.
Gd‐DTPA‐Dopamine‐Bisphytanyl Amphiphile: Synthesis,Characterisation and Relaxation Parameters of the Nanoassemblies and Their Potential as MRI Contrast Agents 下载免费PDF全文
Abhishek Gupta Dr. Scott A. Willis Lynne J. Waddington Dr. Tim Stait‐Gardner Dr. Liliana de Campo Prof. Dennis W. Hwang Dr. Nigel Kirby Prof. William S. Price Dr. Minoo J. Moghaddam 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(40):13950-13960
Here, a new amphiphilic magnetic resonance imaging (MRI) contrast agent, a GdIII‐chelated diethylenetriaminepentaacetic acid conjugated to two branched alkyl chains via a dopamine spacer, Gd‐DTPA‐dopamine‐bisphytanyl (Gd‐DTPA‐Dop‐Phy), which is readily capable of self‐assembling into liposomal nanoassemblies upon dispersion in an aqueous solution, is reported. In vitro relaxivities of the dispersions were found to be much higher than Magnevist, a commercially available contrast agent, at 0.47 T but comparable at 9.40 T. Analysis of variable temperature 17O NMR transverse relaxation measurements revealed the water exchange of the nanoassemblies to be faster than that previously reported for paramagnetic liposomes. Molecular reorientation dynamics were probed by 1H NMRD profiles using a classical inner and outer sphere relaxation model and a Lipari–Szabo “model‐free” approach. High payloads of GdIII ions in the liposomal nanoassemblies made solely from the Gd‐DTPA‐Dop‐Phy amphiphiles, in combination with slow molecular reorientation and fast water exchange makes this novel amphiphile a suitable candidate to be investigated as an advanced MRI contrast agent. 相似文献
29.
R. W. Woittiez A. Lagerwaard K. J. Volkers M. DC. Tangonan 《Journal of Radioanalytical and Nuclear Chemistry》1993,169(1):229-237
The use of ion chromatography with continuous UV detection for radiochemical separation of Cr with simultaneous yield determination is presented. The RNAA method consists of sample destruction in HNO3+HClO4, extraction of Cr(VI) with tribenzylamine in CHCl3, backextraction in NaOH and chromatography of chromate. From radiotracer experiments, the ratio of signals for51Cr and Cr spike was found to be constant for a chromium mass range of 15 to 100 g. Application of the RNAA method to Cr determination in biological reference materials showed a reasonable agreement with the reference values. A relative standard deviation of 3% on the 100 g/kg level for homogeneous material was achieved.IAEA-fellow, on leave from the Philippine Nuclear Research Institute Philippine 相似文献
30.
Flibotte S Andrews HR Ball GC Beausang CW Beck FA Belier G Byrski T Curien D Dagnall PJ de France G Disdier D Duchêne G Finck C Haas B Hackman G Haslip DS Janzen VP Kharraja B Lisle JC Merdinger JC Mullins SM Nazarewicz W Radford DC Rauch V Savajols H Styczen J Theisen C Twin PJ Vivien JP Waddington JC Ward D Zuber K Åberg S 《Physical review letters》1993,71(26):4299-4302