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71.
Xuan Jiang Brad M. Rosen Virgil Percec 《Journal of polymer science. Part A, Polymer chemistry》2010,48(2):403-409
Cu(0) was prepared via disproportionation of Cu(I)Br in the presence of Me6‐TREN in various solvents in a glove box. The resulting nanopowders were used as mimics of “nascent” Cu(0) catalyst in the single‐electron transfer living radical polymerization (SET‐LRP) of methyl acrylate (MA), providing faster polymerization than any commercial Cu(0) powder, Cu(0) wire, or Cu(I)Br and achieving 80% conversion in only 5 min reaction time. Despite the high rate, a living polymerization was observed with linear evolution of molecular weight, narrow polydispersity, no induction period, and high retention of chain‐end functionality. In addition to providing an unprecedentedly fast, yet controlled LRP of MA, these studies suggest that the very small “nascent” Cu(0) species formed via disproportionation in SET‐LRP are the most active catalysts. Thus, when bulk Cu(0) powder or wire may be the most abundant catalyst and dictates the overall kinetics, any Cu(0) produced via disproportionation will be rapidly consumed and contributes to the overall catalytic cycle. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 403–409, 2010 相似文献
72.
Nga H. Nguyen Brad M. Rosen Xuan Jiang Sven Fleischmann Virgil Percec 《Journal of polymer science. Part A, Polymer chemistry》2009,47(21):5577-5590
SET‐LRP is mediated by a combination of solvent and ligand that promotes disproportionation of Cu(I)X into Cu(0) and Cu(II)X2. Therefore, the diversity of solvents suitable for SET‐LRP is limited. SET‐LRP of MA in a library of solvents with different equilibrium constants for disproportionation of Cu(I)X such as DMSO, DMF, DMAC, EC, PC, EtOH, MeOH, methoxyethanol, NMP, acetone and in their binary mixtures with H2O was examined. H2O exhibits the highest equilibrium constant for disproportionation of Cu(I)X. The apparent rate constant of the polymerization exhibits a linear increase with the addition of H2O. This is consistent with higher equilibrium constants for disproportionation generated by addition of H2O to organic solvents. Furthermore, with the exception of alcohols and carbonates, the rate constant of polymerization in binary mixtures could be correlated with the Dimroth‐Reichardt solvent polarity parameter. This is consistent with the single‐electron transfer mechanism proposed for SET‐LRP that involves a polar transition state. These experiments demonstrate that the use of binary mixtures of solvents with H2O provides a new, simple and efficient method for the elaboration of a large diversity of reaction media that are suitable for SET‐LRP even when one of the two solvents does not mediate disproportionation of Cu(I)X. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5577–5590, 2009 相似文献
73.
In several applications, underestimation of functions has proven to be a helpful tool for global optimization. In protein–ligand
docking problems as well as in protein structure prediction, single convex quadratic underestimators have been used to approximate
the location of the global minimum point. While this approach has been successful for basin-shaped functions, it is not suitable
for energy functions with more than one distinct local minimum with a large magnitude. Such functions may contain several
basin-shaped components and, thus, cannot be underfitted by a single convex underestimator. In this paper, we propose using
an underestimator composed of several negative Gaussian functions. Such an underestimator can be computed by solving a nonlinear
programming problem, which minimizes the error between the data points and the underestimator in the L
1 norm. Numerical results for simulated and actual docking energy functions are presented. 相似文献
74.
Lone AM Bachovchin DA Westwood DB Speers AE Spicer TP Fernandez-Vega V Chase P Hodder PS Rosen H Cravatt BF Saghatelian A 《Journal of the American Chemical Society》2011,133(30):11665-11674
Peptidases play vital roles in physiology through the biosynthesis, degradation, and regulation of peptides. Prolyl endopeptidase-like (PREPL) is a newly described member of the prolyl peptidase family, with significant homology to mammalian prolyl endopeptidase and the bacterial peptidase oligopeptidase B. The biochemistry and biology of PREPL are of fundamental interest due to this enzyme's homology to the biomedically important prolyl peptidases and its localization in the central nervous system. Furthermore, genetic studies of patients suffering from hypotonia-cystinuria syndrome (HCS) have revealed a deletion of a portion of the genome that includes the PREPL gene. HCS symptoms thought to be caused by lack of PREPL include neuromuscular and mild cognitive deficits. A number of complementary approaches, ranging from biochemistry to genetics, will be required to understand the biochemical, cellular, physiological, and pathological mechanisms regulated by PREPL. We are particularly interested in investigating physiological substrates and pathways controlled by PREPL. Here, we use a fluorescence polarization activity-based protein profiling (fluopol-ABPP) assay to discover selective small-molecule inhibitors of PREPL. Fluopol-ABPP is a substrate-free approach that is ideally suited for studying serine hydrolases for which no substrates are known, such as PREPL. After screening over 300,000 compounds using fluopol-ABPP, we employed a number of secondary assays to confirm assay hits and characterize a group of 3-oxo-1-phenyl-2,3,5,6,7,8-hexahydroisoquinoline-4-carbonitrile and 1-alkyl-3-oxo-3,5,6,7-tetrahydro-2H-cyclopenta[c]pyridine-4-carbonitrile PREPL inhibitors that are able to block PREPL activity in cells. Moreover, when administered to mice, 1-isobutyl-3-oxo-3,5,6,7-tetrahydro-2H-cyclopenta[c]pyridine-4-carbonitrile distributes to the brain, indicating that it may be useful for in vivo studies. The application of fluopol-ABPP has led to the first reported PREPL inhibitors, and these inhibitors will be of great value in studying the biochemistry of PREPL and in eventually understanding the link between PREPL and HCS. 相似文献
75.
Peterca M Imam MR Ahn CH Balagurusamy VS Wilson DA Rosen BM Percec V 《Journal of the American Chemical Society》2011,133(7):2311-2328
The synthesis, structural, and retrostructural analysis of two libraries containing 16 first and second generation C(3)-symmetric self-assembling dendrimers based on dendrons connected at their apex via trisesters and trisamides of 1,3,5-benzenetricarboxylic acid is reported. A combination of X-ray diffraction and CD/UV analysis methods demonstrated that their C(3)-symmetry modulates different degrees of packing on the periphery of supramolecular structures that are responsible for the formation of chiral helical supramolecular columns and spheres self-organizable in a diversity of three-dimensional (3D) columnar, tetragonal, and cubic lattices. Two of these periodic arrays, a 3D columnar hexagonal superlattice and a 3D columnar simple orthorhombic chiral lattice with P222(1) symmetry, are unprecedented for supramolecular dendrimers. A thermal-reversible inversion of chirality was discovered in helical supramolecular columns. This inversion is induced, on heating, by the change in symmetry from a 3D columnar simple orthorhombic chiral lattice to a 3D columnar hexagonal array and, on cooling, by the change in symmetry from a 2D hexagonal to a 2D centered rectangular lattice, both exhibiting intracolumnar order. A first-order transition from coupled columns with long helical pitch, to weakly or uncorrelated columns with short helical pitch that generates a molecular rotator, was also discovered. The torsion angles of the molecular rotator are proportional to the change in temperature, and this effect is amplified in the case of the C(3)-symmetric trisamide supramolecular dendrimers forming H-bonds along their column. The structural changes reported here can be used to design complex functions based on helical supramolecular dendrimers with different degree of packing on their periphery. 相似文献
76.
A convenient, general, and high yielding Pd-catalyzed cross-coupling of methanesulfonamide with aryl bromides and chlorides is reported. The use of this method eliminates concern over genotoxic impurities that can arise when an aniline is reacted with methanesulfonyl chloride. The application of this method to the synthesis of dofetilide is also reported. 相似文献
77.
M. Shepherd E. R. Weaver P. G. Ledig Aktiebolaget Carba K. Melanby H. L. Harden P. Borinski H. Murschhauser R. Staufer R. Krais H. Markert H. Mogilnickij H. Heinicke K. Heimberger L. C. Mc Nair H. C. Gull St. Hediger E. Lieber R. Rosen K. M. Watson und N. H. Ceaglske 《Fresenius' Journal of Analytical Chemistry》1933,92(1-2):31-40
Ohne Zusammenfassung 相似文献
78.
M. B. Sapadinsky L. Tschugajeff L. Rosen F. Penzoldt und Emil Fischer 《Fresenius' Journal of Analytical Chemistry》1928,74(8):273-275
Ohne Zusammenfassung 相似文献
79.
80.
B. Rosen 《Zeitschrift für Physik A Hadrons and Nuclei》1929,52(1-2):16-20