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991.
Shen J Nguyen TT Goh YP Ye W Fu X Xu J Tan CH 《Journal of the American Chemical Society》2006,128(42):13692-13693
Chiral bicyclic guanidine 1 was found to be an excellent catalyst for reactions between anthrones and various dienophiles. The catalyst can tolerate a range of substituents and substitution patterns, making several anthrone derivatives suitable for this reaction. Both Diels-Alder and Michael adducts were obtained in excellent yields, high regioselectivities, and high enantioselectivities. This is the first case of a highly enantioselective base-catalyzed anthrone Diels-Alder reaction. 相似文献
992.
The synthesis and structural characterization of a new pro-chelating agent, isonicotinic acid [2-(4,4,5,5-tetramethyl-[1,3,2]dioxaborolan-2-yl)-benzylidene]-hydrazide (BSIH), are presented. BSIH only weakly interacts with iron unless hydrogen peroxide (H2O2) is present to remove the boronic ester protecting group to reveal a phenol that is a key metal-binding group of tridentate salicylaldehyde isonicotinoyl hydrazone (SIH). BSIH prevents deoxyribose degradation caused by hydroxyl radicals that are generated from H2O2 and redox-active iron by sequestering Fe3+ and preventing iron-promoted hydroxyl radical formation. The rate-determining step for iron sequestration is conversion of BSIH to SIH, followed by rapid Fe3+ complexation. The pro-chelate approach of BSIH represents a promising strategy for chelating a specific pool of detrimental metal ions without disturbing healthy metal ion distribution. 相似文献
993.
Truong TN Nayak M Huynh HH Cook T Mahajan P Tran LT Bharath J Jain S Pham HB Boonyasiriwat C Nguyen N Andersen E Kim Y Choe S Choi J Cheatham TE Facelli JC 《Journal of chemical information and modeling》2006,46(3):971-984
With the expansion of the Internet and World Wide Web (or the Web), research environments have changed dramatically. As a result, the need to be able to efficiently and securely access information and resources from remote computer systems is becoming even more critical. This paper describes the development of an extendable integrated Web-accessible simulation environment for computational science and engineering called Computational Science and Engineering Online (CSE-Online; http://cse-online.net). CSE-Online is based on a unique client-server software architecture that can distribute the workload between the client and server computers in such a way as to minimize the communication between the client and server, thus making the environment less-sensitive to network instability. Furthermore, the new software architecture allows the user to access data and resources on one or more remote servers as well as on the computing grid while having the full capability of the Web-services collaborative environment. It can be accessed anytime and anywhere from a Web browser connected to the network by either a wired or wireless connection. It has different modes of operations to support different working environments and styles. CSE-Online is evolving into middleware that can provide a framework for accessing and managing remote data and resources including the computing grid for any domain, not necessarily just within computational science and engineering. 相似文献
994.
An electrochemical impedance immunosensor was developed for detecting the immunological interaction between human immunoglobulin
(IgG) and protein A from Staphylococcus aureus based on the immobilization of human IgG on the surface of modified gold-coated magnetic nanoparticles. The nanoparticles
with an Au shell and Fe oxide cores were functionalized by a self-assembled monolayer of 11-mercaptoundecanoic acid. The electrochemical
analysis was conducted on the modified magnetic carbon paste electrodes with the nanoparticles. The magnetic nanoparticles
were attached to the surface of the magnetic carbon paste electrodes via magnetic force. The cyclic voltammetry technique
and electrochemical impedance spectroscopy measurements of the magnetic carbon paste electrodes coated with magnetic nanoparticles–human
IgG complex showed changes in its alternating current (AC) response both after the modification of the surface of the electrode
and the addition of protein A. The immunological interaction between human IgG on the surface of the modified magnetic carbon
paste electrodes and protein A in the solution could be successfully monitored. 相似文献
995.
One of the most promising approaches for clustering is based on methods of mathematical programming. In this paper we propose new optimization methods based on DC (Difference of Convex functions) programming for hierarchical clustering. A bilevel hierarchical clustering model is considered with different optimization formulations. They are all nonconvex, nonsmooth optimization problems for which we investigate attractive DC optimization Algorithms called DCA. Numerical results on some artificial and real-world databases are reported. The results demonstrate that the proposed algorithms are more efficient than related existing methods. 相似文献
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Positivity results are derived for explicit two-step methods in linear multistep form and in one-leg form. It turns out that, using the forward Euler starting procedure, the latter form allows a slightly larger step size with respect to positivity. AMS subject classification (2000) 65L06 相似文献
1000.
Amorphous soft magnetic ribbons Fe73.5−xCrxSi13.5B9Nb3Cu1 (x=1–5) have been fabricated by rapid quenching on a single copper wheel. The differential scanning calorimetry (DSC) patterns showed that the crystallization temperature of α-Fe(Si) phase is ranging from 542 to 569 °C, a little higher than that of pure Finemet (x=0). With the same annealing regime, the crystallization volume fraction as well as the particle size of α-Fe(Si) crystallites decreased with increasing Cr amount substituted for Fe in studied samples. Especially, the interesting fact is that the laminar structure of heat-treated ribbons on the surface contacted to copper wheel in the fabricating process has been firstly discovered and explained to be related to the existence of Cr in studied samples. The hysteresis loop measurement indicated that there is the pinning of displacement of domain walls. The giant magnetocaloric effect (GMCE) has been found in amorphous state of the samples. After annealing, the soft magnetic properties of investigated nanocomposite materials are desirably improved. 相似文献