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41.
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Measurements are presented of how polymer surface diffusion at the solid-liquid interface is controlled by surface coverage. The method of measurement was fluorescence correlation spectroscopy (FCS), and the system was poly(ethylene oxide) (PEG) adsorbed onto methyl-terminated self-assembled monolayers in buffered aqueous solution. The translational diffusion coefficient at first increased with increasing surface concentration, presumably because the number of adsorption sites per molecule decreased. Ultimately it slowed by 1 order of magnitude, presumably reflecting jamming by neighboring chains. 相似文献
43.
An ab initio molecular orbital calculation has been carried out for three different conformations of 1,3 propanediol, one of which permits intramolecular H-bond studied by ab initio quantum mechanical methods. The ΔE for H-bonding formation is compated to be 0.9 kcal/mole and the charge redistributions and molecular orbital energy changes are compared to those found in intermolecular H-bonds. 相似文献
44.
John T. Gupton John E. Gall Steve W. Riesinger Stanton Q. Smith Kathy M. Bevirt James A. Sikorski Maria L. Dahl Zdenek Arnold 《Journal of heterocyclic chemistry》1991,28(5):1281-1285
An alternative preparation of a 2-iminovinamidinium salt from phosphonoacetic acids is described along with its application to the synthesis of 5-formylpyrimidines and masked 4-formylpyrazoles. 相似文献
45.
A fundamental difficulty in theoretical physics is the dual and apparently incompatible interpretations of radiation as showing both continuous and extensive wave properties but also those of discrete atomic or smaller individual particles. Some of these contradictions are outlined. The explanation offered is of a quantized nature of time; units to=h/moc2 for a particle at rest, and of similar interval unit so when in relative motion, with conventional relativistic corrections.
For many purposes this form of quantization replaces the need for a wave concept which then appears as a mathematical approach, chosen to avoid the physical concept of an intrinsicc time for any particle, just as we have for its intrinsic mass, spin and electrical charge. to and so are directly related to its frequency, energy and mass. The uncertainty principle and interference relations follow directly from this model, without any physical wave concept. 相似文献
46.
Gaunt AJ May I Helliwell M Richardson S 《Journal of the American Chemical Society》2002,124(45):13350-13351
The reaction between PW9O349- and NpO2+ has yielded the first structurally characterized neptunyl(V) polyoxometalate complex, [Na2(NpO2)2(A-PW9O34)2]14-. This complex is isostructural with the uranyl(VI) analogue, and there is also spectroscopic evidence for its existence in solution. The complex is readily extracted into toluene, and this may have significance in the sequestering and/or separation of the neptunyl ion in terms of nuclear waste management. 相似文献
47.
Shi G Wu JT Li Y Geleziunas R Gallagher K Emm T Olah T Unger S 《Rapid communications in mass spectrometry : RCM》2002,16(11):1092-1099
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49.
Deng Y Wu JT Lloyd TL Chi CL Olah TV Unger SE 《Rapid communications in mass spectrometry : RCM》2002,16(11):1116-1123
In this work, a high-throughput and high-performance bioanalytical system is described that is capable of extracting and analyzing 1152 plasma samples within 10 hours. A Zymark track robot system interfaced with a Tecan Genesis liquid handler was used for simultaneous solid-phase extraction of four 96-well plates in a fully automated fashion. The extracted plasma samples were injected onto four parallel monolithic columns for separation via a four-injector autosampler. The use of monolithic columns allowed for fast and well-resolved separations at a considerably higher flow rate without generating significant column backpressure. This resulted in a total chromatographic run cycle time of 2 min on each 4.6 x 100 mm column using gradient elution. The effluent from the four columns was directed to a triple quadrupole mass spectrometer equipped with an indexed four-probe electrospray ionization source (Micromass MUX interface). Hence, sample extraction, separation, and detection were all performed in a four-channel parallel format that resulted in an overall throughput of about 30 s per sample from plasma. The performance of this system was evaluated by extracting and by analyzing twelve 96-well plates (1152) of human plasma samples spiked with oxazepam at different concentrations. The relative standard deviation (RSD) of analyte sensitivity (slope of calibration curve) across the four channels and across the 12 plates was 5.2 and 6.8%, respectively. An average extraction recovery of 77.6% with a RSD of 7.7% and an average matrix effect of 0.95 with a RSD of 5.2% were achieved using these generic extraction and separation conditions. The good separation efficiency provided by this system allowed for rapid method development of an assay quantifying the drug candidate and its close structural analog metabolite. The method was cross-validated with a conventional liquid chromatography/tandem mass spectrometry (LC/MS/MS) assay. 相似文献
50.