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31.
We report on a novel method for the quantitation of proteins specifically bound on a ligand-presenting biochip by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry (MS). The bound protein was digested by trypsin, and the resulting peptide fragments were analyzed by MALDI-TOF MS in the presence of an isotope-labeled internal standard (IS). The IS has the same sequence as a reference peptide (RP) of the target protein digest, but a different molecular weight. The absolute amount of the specifically bound protein on a biochip is then quantitated by comparison of mass intensities between the RP and the IS. Because they have the same molecular milieu, the mass intensities of these two analytes represent the real amounts of analytes on the chip. As a model system, we tested glutathione s-transferase (GST) and a GST-fusion protein, which were captured on glutathione-presenting biochips. We observed that the glutathione densities on biochips showed a good correlation with the absolute quantity of the proteins. We believe that our method will provide an alternative to currently existing tools for the absolute quantitation of surface-bound proteins. 相似文献
32.
A highly regioselective synthesis of branched vinylsilanes through silicon-copper additions to terminal alkynes catalyzed by copper(I) was developed using methanol as additive. The corresponding vinylsilanes were obtained with excellent branched to linear selectivity of up to 99/1 in good yields. 相似文献
33.
Determination of hexavalent chromium (Cr(VI)) in plastics using organic-assisted alkaline extraction
An organic-assisted alkaline extraction method was developed for the determination of hexavalent chromium (Cr(VI)) in plastics. The solubilization of polymer as a pre-step of the alkaline extraction provided good extraction efficiency of Cr(VI) from the sample. The optimization of the experimental conditions affecting the extraction and UV–vis spectrophotometric analysis was accomplished by evaluating the recovery rate of Cr(VI) through the analysis of Cr(VI) in in-house polymer reference materials (RMs). With the proposed method, most of the Cr(VI) in polymers was released within a short extraction time of 30 min and the Cr(III)-DPCO complex can be kept stable for 24 h. The heating for the extraction of the Cr(VI) was not necessary. The optimal pH of the final solution was fixed at 2.0. The proposed extraction method was applied successfully for the determination of Cr(III) and Cr(VI) in spiked samples. The practical applicability of this new method was evaluated through the analysis of Cr(VI) in in-house polymer RMs. The good linearity was demonstrated at desired concentrations of the range 0–3.3 mg L−1. The detection limits were quite low, varying from 0.0061 to 0.0285 mg L−1. The recovery of Cr(VI) was between 97 and 106%, and the relative standard deviation (R.S.D.) was below 6%. 相似文献
34.
A graph is total domination edge-critical if the addition of any edge decreases the total domination number, while a graph
with minimum degree at least two is total domination vertex-critical if the removal of any vertex decreases the total domination
number. A 3
t
EC graph is a total domination edge-critical graph with total domination number 3 and a 3
t
VC graph is a total domination vertex-critical graph with total domination number 3. A graph G is factor-critical if G − v has a perfect matching for every vertex v in G. In this paper, we show that every 3
t
EC graph of even order has a perfect matching, while every 3
t
EC graph of odd order with no cut-vertex is factor-critical. We also show that every 3
t
VC graph of even order that is K
1,7-free has a perfect matching, while every 3
t
VC graph of odd order that is K
1,6-free is factor-critical. We show that these results are tight in the sense that there exist 3
t
VC graphs of even order with no perfect matching that are K
1,8-free and 3
t
VC graphs of odd order that are K
1,7-free but not factor-critical. 相似文献
35.
Sawyer BC Stuhl BK Yeo M Tscherbul TV Hummon MT Xia Y Kłos J Patterson D Doyle JM Ye J 《Physical chemistry chemical physics : PCCP》2011,13(42):19059-19066
Cold molecules promise to reveal a rich set of novel collision dynamics in the low-energy regime. By combining for the first time the techniques of Stark deceleration, magnetic trapping, and cryogenic buffer gas cooling, we present the first experimental observation of cold collisions between two different species of state-selected neutral polar molecules. This has enabled an absolute measurement of the total trap loss cross sections between OH and ND(3) at a mean collision energy of 3.6 cm(-1) (5 K). Due to the dipolar interaction, the total cross section increases upon application of an external polarizing electric field. Cross sections computed from ab initio potential energy surfaces are in agreement with the measured value at zero external electric field. The theory presented here represents the first such analysis of collisions between a (2)Π radical and a closed-shell polyatomic molecule. 相似文献
36.
37.
In the present paper, natural convective heat transfer in horizontal eccentric annulus is numerically studied by applying
the differential quadrature (DQ) method to solve the vorticity–stream function formulation. An explicit formulation for computing
the stream function value on the inner cylinder wall is derived from the pressure single-value condition. It is demonstrated
in this paper that the DQ method is an efficient approach in computing the weak global circulation in the domain. The present
method was validated by comparing its numerical results with available experimental data. Very good agreement has been achieved.
Then, a systematic study is conducted for the effect of eccentricity and angular position on the flow and thermal fields.
Received on 20 September 2000 / Published online: 29 November 2001 相似文献
38.
Predictions, by the Galerkin method, are presented of the stability of three-dimensional disturbances in laminar boundary-layer flow at zero pressure gradient along a concave surface. The analysis confirms Meksyn's finding of more than one critical state; predictions for the first agree with those of Kahawita and Meroney at low Goertler number G and with the vortex amplification predictions of Smith at high G. Both the first and second critical states have G values below those of Meksyn; the amplification field of the second, however, encompasses the range of available measurements, and therein, has dimensionless vortex energy levels only half those of the first. The plausibility of least vortex energy as a determining factor in favour of the second critical field is further strengthened by its limited G range, the upper limit of about 7 corresponding closely to Liepmann's observations4,5 of the onset of transition to turbulence. These findings are almost insensitive to mainstream Mach numbers up to 0.9, stagnation conditions up to 15 bar and 1200 K, and Reynolds numbers from 2000 to 6000 based on boundary layer thickness 相似文献
39.
It is well known that the phenomenon of Ag-photodoping into amorphous (a-) chalcogenide film depends on film thickness (d). Herein, we report that the effects of Ag-photodoping into a-GeSe thin films exhibit a systematical change dependent on d using a holographic exposure (HeCd laser) and the measurement of diffraction efficiency (η) in real time. The η-kinetics of Ag-photodoping in the sample structure of an a-GeSe/Ag/p-type Si substrate is divided into two steps. A photodarkening-dominant process related to the generation of valence-alternation pairs (VAPs) in the chalcogenide explains the first step while a doping-dominant process accounts for the second step. In particular, we confirmed that the d-dependencies of the η-kinetics are classified into 3 groups: (A) d < 2dP; (B) 2dP ? d < 4dP; (C) d > 4dP, where dP indicates the penetration depth of the HeCd laser. In group A, the Ag-doping process occurs simultaneously with the darkening process. In group C, the η-kinetics results from the darkening process only. Contrarily, in group B, the η-kinetics exhibits a sharp distinction between the photodarkening process and the Ag-doping process, and in particular, ηM increases almost linearly with an increase in d. 相似文献
40.
Cleaning the surfaces of the as-deposited Ge2Sb2Te5 was studied by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and X-ray diffraction (XRD). The mixed native oxides on the as-deposited Ge2Sb2Te5 surface can be easily removed by dipping Ge2Sb2Te5 in de-ionized water for 1 min, while the surface morphology remains unchanged after cleaning. Native oxides only re-grow after exposure to air for more than 4 min. Although dipping in water leads to a surface layer deficient in Ge and Sb, the surface composition of Ge2Sb2Te5 can recover to its stoichiometric value after annealing at 200 °C in vacuum. The phase remains amorphous at room temperature after dipping in water, and changes to fcc and hcp after annealing at 100 and 220 °C, respectively. 相似文献