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991.
Sterling F. Alfred Zoha M. Al‐Badri Ahmad E. Madkour Karen Lienkamp Gregory N. Tew 《Journal of polymer science. Part A, Polymer chemistry》2008,46(8):2640-2648
The synthesis of three different poly(ethylene oxide) macromonomers with a norbornene and oxanorbornene end group is presented. The macromonomers were polymerized to comb‐polymers by ring‐opening metathesis polymerization (ROMP) using Grubbs' Catalyst G3 to produce water soluble polymers with polydispersities between 1.04 and 1.30 and molecular weights between 14,000 and 50,000 g/mol. Characterization by static and dynamic light scattering reveals that the comb‐polymers with norbornene backbone are molecularly disperse in aqueous solution, while the oxanorbornene‐backbone polymers form small water‐soluble aggregates. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2640–2648, 2008 相似文献
992.
Solène I. Cauët Karen L. Wooley 《Journal of polymer science. Part A, Polymer chemistry》2010,48(12):2517-2524
The kinetics of the RAFT polymerization of p‐acetoxystyrene using a trithiocarbonate chain transfer agent, S‐1‐dodecyl‐S′‐(α,α′‐dimethyl‐α″‐acetic acid)trithiocarbonate, DDMAT, was investigated. Parameters including temperature, percentage initiator, concentration, monomer‐to‐chain transfer agent ratio, and solvent were varied and their impact on the rate of polymerization and quality of the final polymer examined. Linear kinetic plots, linear increase of Mn with monomer conversion, and low final molecular weight dispersities were used as criteria for the selection of optimized polymerization conditions, which included a temperature of 70 or 80 °C with 10 mol % AIBN initiator in bulk for low conversions or in 1,4‐dioxane at a monomer‐to‐solvent volume ratio of 1:1 for higher conversions This study opens the way for the use of DDMAT as a chain transfer agent for RAFT polymerization to incorporate p‐acetoxystyrene together with other functional monomers into well‐defined copolymers, block copolymers, and nanostructures. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2517–2524, 2010 相似文献
993.
S. J. Dilworth Denka Kutzarova Karen L. Shuman V. N. Temlyakov P. Wojtaszczyk 《Journal of Fourier Analysis and Applications》2008,14(5-6):609-628
We study the convergence of certain greedy algorithms in Banach spaces. We introduce the WN property for Banach spaces and prove that the algorithms converge in the weak topology for general dictionaries in uniformly smooth Banach spaces with the WN property. We show that reflexive spaces with the uniform Opial property have the WN property. We show that our results do not extend to algorithms which employ a ‘dictionary dual’ greedy step. 相似文献
994.
This paper describes the preparation, characterization, and application of a chemically bonded and endcapped C18 stationary phase having a doubly zirconized silica support. The stationary phase was characterized using infrared and nuclear magnetic resonance (13C and 29Si) spectroscopies, elemental analysis, and surface and thermogravimetric determinations, and evaluated chromatographically using several test mixtures, indicating acceptable efficiency, and asymmetry. The new phase was used for several different applications including the determination of the possible presence of six pesticides in orange juice, using a modified QuEChERS procedure for extraction.
相似文献995.
Mohd Abdul Fatah Abdul Manan Karen A. Crouse M. Ibrahim M. Tahir Rozita Rosli Fiona N.-F. How David J. Watkin Alexandra M. Z. Slawin 《Journal of chemical crystallography》2011,41(11):1630-1641
Abstract
Schiff bases were prepared from S-benzyldithiocarbazate with 5-fluro-, 5-chloro- and 5-bromoisatin. All are potential tridentate nitrogen, oxygen, sulfur donors. They were found to be selectively active against MCF-7 cell line (Human non-metastatic mammary gland adenocarcinoma cell line). The bromide and fluoride compounds were the most active with IC50 values of 6.40 μM (2.6 μg/mL) and 9.26 μM (3.2 μg/mL) respectively while the chloride derivative was weakly active with an IC50 value of 38.69 μM (14.0 μg/mL). The cytotoxic activity of the halo substituted isatins against the breast cancer cell lines tested is in the order of Br > F > Cl. Planarity of the isatin ring in the Schiff bases can be arranged in the following order SB5FISA > SB5ClISA > SB5BrISA while the perpendicularity of the benzyl ring towards the dithiocarbazate plane can be ordered as follows, SB5FISA > SB5BrISA > SB5ClISA. 相似文献996.
Lin LY Tiemann KM Li Y Pinkner JS Walker JN Hultgren SJ Hunstad DA Wooley KL 《Journal of the American Chemical Society》2012,134(9):3938-3941
Amphiphilic block copolymer nanoparticles are conjugated with uropathogenic Escherichia coli type 1 pilus adhesin FimH(A) through amidation chemistry to enable bladder epithelial cell binding and internalization of the nanoparticles in vitro. 相似文献
997.
Developments in specific DNA detection assays have been shown to be increasingly beneficial for molecular diagnostics and biological research. Many approaches use optical spectroscopy as an assay detection method and, owing to the sensitivity and molecular specificity offered, surface enhanced Raman scattering (SERS) spectroscopy has become a competitively exploited technique. This study utilises SERS to demonstrate differences in affinity of dye labelled DNA through differences in electrostatic interactions with silver nanoparticles. Results show clear differences in the SERS intensity obtained from single stranded DNA, double stranded DNA and a free dye label and demonstrate surface attraction is driven through electrostatic charges on the nucleotides and not the SERS dye. It has been further demonstrated that, through optimisation of experimental conditions and careful consideration of sequence composition, a DNA detection method with increased sample discrimination at lower DNA concentrations can be achieved. 相似文献
998.
The penetration of compressed CO(2) in hydrocarbon and fluorocarbon regions of concentrated surfactant mesophases are interpreted from differences in the CO(2)-processed pore expansion of mesoporous silica thin films templated by three surfactants containing varying degrees of hydrocarbon and fluorocarbon functionality. Ordered silica thin films are synthesized for the first time using the 16-carbon (C(16)) partly fluorinated surfactant, 11,11,12,12,13,13,14,14,15,15,16,16,16-tridecafluorocetyl pyridinium bromide (HFCPB), as a templating agent. Silica films templated with surfactants containing a 8-carbon (C(8)) fluorocarbon tail (3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluorooctyl pyridinium chloride (HFOPC)) and a 16-carbon (C(16)) hydrocarbon tail (cetyl pyridinium bromide (CPB)) and HFCPB (C(16)) are processed in compressed CO(2) (69-172 bar, 25 °C and 45 °C) during synthesis. CO(2) processing results in significant pore expansion for films templated with both fluorinated surfactants, while pore expansion is negligible for the hydrocarbon templated material suggesting that preferential CO(2) penetration occurs in the 'CO(2)-philic' fluorocarbon segments of the surfactant template. The effect of substrate surface energy on the final uniformity of the dip-coated films is studied by varying the substrate from unmodified glass to a fluorocarbon-capped substrate. The ability to create dip-coated thin films on low surface energy substrates through favorable interaction of surfactant template tail with the substrate surface functional groups is demonstrated. 相似文献
999.
GM Rankin BJ Compton KA Johnston CM Hayman GF Painter DS Larsen 《The Journal of organic chemistry》2012,77(16):6743-6759
A family of naturally occurring mycobacterial phosphatidylinositol (PI) and its dimannosides (PIM(2), AcPIM(2), and Ac(2)PIM(2)) that all possess the predominant natural 19:0/16:0 phosphatidyl acylation pattern were prepared to study their mass spectral fragmentations. Among these, the first synthesis of a fully lipidated PIM (i.e., (16:0,18:0)(19:0/16:0)-PIM(2)) was achieved from (±)-1,2:4,5-diisopropylidene-d-myo-inositol in 16 steps in 3% overall yield. A key feature of the strategy was extending the utility of the p-(3,4-dimethoxyphenyl)benzyl protecting group for its use at the O-3 position of inositol to allow installation of the stearoyl residue at a late stage in the synthesis. Mass spectral studies were performed on the synthetic PIMs and compared to those reported for natural PIMs identified from a lipid extract of M. bovis BCG. These analyses confirm that fragmentation patterns can be used to identify the structures of specific PIMs from the cell wall lipid extract. 相似文献
1000.
Hélène Lebel Michaël Parmentier Olivier Leogane Karen Ross Cédric Spitz 《Tetrahedron》2012,68(17):3396-3409
A Cu(I)-catalyzed asymmetric aziridination of styrenes with a chiral N-tosyloxycarbamate has been developed. Double stereodifferentiation was observed and both the N-tosyloxycarbamate substituent and the bis(oxazoline) ligand have a significant effect on the yields and diastereoselectivities. The best results for the aziridination were obtained with electron-deficient styrenes. Subsequent ring-opening reactions of styrene-derived aziridines at the benzylic position were observed with various oxygen and nitrogen nucleophiles under Lewis acid catalysis affording the corresponding products with complete inversion of stereochemistry. The strategy was used to synthesize the β-blocker, (R)-nifenalol. 相似文献