This article described the preparation and the protection of 3′-DMP and dihydrouridine (Dr) as well as the synthesis of four oligoribonucleotides composed of them. DMP and Dr were obtained by hydrogenation of 3′-UMP and Ur under acidic conditions in the presence of platinum dioxide. They were monomethoxytritylated and benzoylated to (MeOTr)-Dbzp and (MeOTr) Dbzs, respectively. The latter was converted to Dbzs, by demonomethoxytritylation. The oligoribonucleotides containing DMP or Dr—ApGpD, DpApG, ApGpDpC and ApGpDpCpGpG were synthesized via phosphodiester approach and DCC was used as condensing reagent. DpApG was also synthesized via phosphotriester approach and TPST, MSTe, MSNI and MSNT were used as condensing reagents for a preliminary comparison of the coupling yields. These synthetic oligoribonucleotides were checked for purity and nucleotide sequences as usual. ApGpDpCpGpG and DpApG had been used for enzymatic synthesis of ApGpDpCpGpGpDpApG, which had been in turn successfully used for the total syntheses of the 5′-half molecule and the whole molecule of yeast alanine t-RNA 相似文献
The Nagumo equationut ut=△u+bu(u-a)(1-u),t>0 is investigated with initial data and zero Neumann boundary conditions on post-critically finite (p.c.f.) self-similar fractals that have regular harmonic structures and satisfy the separation condition. Such a nonlinear diffusion equation has no travelling wave solutions because of the“pathological” property of the fractal. However, it is shown that a global Hoelder continuous solution in spatial variables exists on the fractal considered. The Sobolev-type inequality plays a crucial role, which holds on such a class of p.c.f self-similar fractals. The heat kernel has an eigenfunction expansion and is well-defined due to a Weyl‘s formula. The large time asymptotic behavior of the solution is discussed, and the solution tends exponentially to the equilibrium state of the Nagumo equation as time tends to infinity if b is small. 相似文献
The deformation measurement of electrosynthesized polythiophene (Pth) thin films is difficult because of the small thickness
and high flexibility of the specimen. An electronic speckle pattern interferometry (ESPI) method is used to measure the deformation
of Pth films of thicknesses in the range of 4–65 μm. Their stres-strain curve are obtained. It is found that the mechanical
properties of Pth films are sensitive to the specimen thickness. The tensile strength increases with decreasing thickness
of thin film from 10 μm. The influence of the electrochemical synthesis conditions on the mechanical properties of Pth films
is also discussed.
Project supported by the Basic-Research Foundation of Tsinghua University (JC2000057), and the Visiting Scholar Foundation
of Solid Mechanical Key Lab in Tongji University of the Ministry of Education of China. Received 10 September 2001; revision
received 9 November 2001. 相似文献
A sensitive, specific and rapid colorimetric aptasensor for the determination of the plasticizer bisphenol A (BPA) was developed. It is based on the use of gold nanoparticles (AuNPs) that are positively charged due to the modification with cysteamine which is cationic at near-neutral pH values. If aptamers are added to such AuNPs, aggregation occurs due to electrostatic interactions between the negatively-charged aptamers and the positively-charged AuNPs. This results in a color change of the AuNPs from red to blue. If a sample containing BPA is added to the anti-BPA aptamers, the anti-BPA aptamers undergo folding via an induced-fit binding mechanism. This is accompanied by a conformational change, which prevents the aptamer-induced aggregation and color change of AuNPs. The effect was exploited to design a colorimetric assay for BPA. Under optimum conditions, the absorbance ratio of A527/A680 is linearly proportional to the BPA concentration in the range from 35 to 140 ng∙mL−1, with a detection limit of 0.11 ng∙mL−1. The method has been successfully applied to the determination of BPA in spiked tap water and gave recoveries between 91 and 106 %. Data were in full accordance with results obtained from HPLC. This assay is selective, easily performed, and in our perception represents a promising alternative to existing methods for rapid quantification of BPA.
The negatively-charged anti-BPA aptamers can absorb onto the positively-charged cysteamine-capped AuNPs (cysteamine-AuNPs) via electrostatic interactions, which can cause the aggregation of AuNPs accompanied by a red-to-blue color change. In the presence of BPA, the specific binding of BPA to the aptamers induces the conformation changes of anti-BPA aptamers, which can release the aptamers from cysteamine-AuNPs and thus prevent the aggregation and color change of cysteamine-AuNPs.
In this paper, we study an inexact version of the alternating direction method of multipliers (ADMM) for solving two-block separable linearly constrained convex optimization problems. Specifically, the two subproblems in the classic ADMM are allowed to be solved inexactly by certain relative error criteria, in the sense that only two parameters are needed to control the inexactness. Related convergence analysis are established under the assumption that the solution set to the KKT system of the problem is not empty. Numerical results on solving a class of sparse signal recovery problems are also provided to demonstrate the efficiency of the proposed algorithm. 相似文献