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
The structure and phase behaviour of a colloidal dispersion of plate-like particles are described. The plates are nickel (II)
hydroxide and have short-range, repulsive interactions and a low polydispersity. As the concentration of the plates is increased,
an equilibrium phase separation between a columnar phase and a less ordered phase is observed. Complementary measurements
using small-angle neutron and small-angle X-ray scattering have been used to distinguish the columnar phase from other possible
ordered structures. Previously isotropic-nematic phase transitions have been observed [#!ref1!#], however this dispersion
forms the more highly ordered columnar phase, due to the aspect ratio and the low polydispersity of the plate-like particles.
The concentration at which phase separation occurs, increases as the range of the particle interactions is reduced. This system
provides an interesting model for comparison with theory and calculations of structures in liquid crystal and mesophase in
which the particle interactions can be altered.
Received 24 February 1999 相似文献
Let it shine! The impact of the anchoring group on photovoltaic performance by a series of phthalocyanine sensitisers (see figure) has been demonstrated.
The crystal structure of β-BaZr(PO4)2, archetype of the high-temperature forms of BaM(PO4)2 phosphates (with M=Ti, Zr, Hf and Sn), has been solved ab initio by Rietveld analysis from synchrotron X-ray powder diffraction data. The phase transition appears as a topotactic modification of the monoclinic (S.G. C2/m) lamellar α-structure into a trigonal one (S.G. ) through a simple mechanism involving the unfolding of the layers. The thermal expansion is very anisotropic (e.g., −4.1<αi<34.0×10−6 K−1 in the case of α-BaZr(PO4)2) and quite different in the two forms, as a consequence of symmetry. It stems from a complex combination of several mechanisms, involving bridging oxygen rocking in M-O-P linkages, and “bond thermal expansion”. 相似文献
We study second and fourth order semilinear elliptic equations with a power-type nonlinearity depending on a power p and a parameter λ>0. For both equations we consider Dirichlet boundary conditions in the unit ball B⊂Rn. Regularity of solutions strictly depends on the power p and the parameter λ. We are particularly interested in the radial solutions of these two problems and many of our proofs are based on an ordinary differential equation approach. 相似文献
We study two different versions of a supercritical biharmonic equation with a power-type nonlinearity. First, we focus on
the equation Δ2u = |u|p-1u over the whole space , where n > 4 and p > (n + 4)/(n − 4). Assuming that p < pc, where pc is a further critical exponent, we show that all regular radial solutions oscillate around an explicit singular radial solution. As it was already known, on the other hand, no such oscillations occur in the remaining case p ≥ pc. We also study the Dirichlet problem for the equation Δ2u = λ (1 + u)p over the unit ball in , where λ > 0 is an eigenvalue parameter, while n > 4 and p > (n + 4)/(n − 4) as before. When it comes to the extremal solution associated to this eigenvalue problem, we show that it is regular as long as p < pc. Finally, we show that a singular solution exists for some appropriate λ > 0.
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The low-energy collisions of I(2)(B,v' = 21) with He involving collision-induced vibrational relaxation of I(2) are investigated both experimentally and by means of wave packet simulations. The theoretical cross sections exhibit a structure of peaks originated by orbiting resonances of the I(2)(B,v' = 21) - He van der Waals complex formed in the I(2) + He collisions. Such a structure has similar characteristics as the structure of peaks found in the experimental cross sections. In fact, four of the five peaks of the measured cross sections appear at positions nearly coincident with those of four of the peaks found in the theoretical cross sections. Thus this result confirms the experimental finding that enhancement of I(2) vibrational relaxation is caused by the population of I(2)(B,v' = 21) - He orbiting resonances populated upon the low-energy collisions. The possibility of using this mechanism in the vibrational cooling of diatomic molecules is discussed. 相似文献
A mathematical model is developed to simulate the thin layer boilover phenomenon. This model takes into account convective
currents as well as conduction and radiation absorption through the fuel layer and is resolved numerically employing a scheme
of Runge–Kutta, combined with the numerical method of lines. Solutions of the model showed a good agreement with the experimental
data, both from this work and by other authors, demonstrating the importance of the convective currents. The model provided
velocities of these currents, of the same order of magnitude as the values reported in the technical literature. Thickness
of the remaining fuel and the interface temperature are correctly calculated by the model, allowing the prediction of the
time required for the boilover to start. 相似文献
A portable fibre optic instrument for oxygen sensing based on luminescence lifetime is presented. The instrument is based
on measurement of the quenching by oxygen of the room temperature phosphorescence (RTP) emitted by aluminium tris(8-hydroxy-7-iodo-5-quinolinesulfonic
acid) chelate incorporated in an inorganic matrix by sol–gel technology. The comparatively long RTP lifetime of this sensing
material (450 μs) and the large singlet–triplet splitting (λexc 390 nm, λem 590 nm) allow the use of simple opto-electronic circuits and low-cost processing electronics. Standard electronic components
have been applied in development of the low-cost lifetime-measurement instrumentation presented here. Two optical sensor configurations,
“flow-through cell” and “probe”, have been designed and evaluated for the determination of very low levels of oxygen, in gaseous
argon streams and in waters. The basic technology, design parameters and performance characteristics of the optical sensors
are discussed. Applications to determination of dissolved oxygen in river, tap and sewage waters are described. The advantages
of luminescence lifetime measurements over conventional RTP intensity measurements for oxygen sensing are discussed.
Received April 1, 1999. Revision November 4, 1999. 相似文献
Transport in Porous Media - We investigate local aspects and heterogeneities of porous medium morphology and relate them to the relevant mechanisms of momentum transfer. In the inertial flow range,... 相似文献