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101.
Santosh B. Rahane J. Alaina Floyd Andrew T. Metters S. Michael Kilbey II 《Advanced functional materials》2008,18(8):1232-1240
Surface‐initiated photoiniferter‐mediated photopolymerization (SI‐PMP) in presence of tetraethylthiuram disulfide is used to directly synthesize surface‐grafted poly(methacrylic acid)‐block‐poly(N‐isopropylacrylamide) (PMAA‐b‐PNIPAM) layers. The response of these PMAA‐b‐PNIPAM bi‐level brushes to changes in pH, temperature and ionic strength is investigated by using in‐situ multi‐angle ellipsometry to measure changes in solvated layer thickness. As expected for a block copolymer architecture, PMAA blocks swell as pH is increased, with the maximum change in the thickness occurring near pH = 5, and PNIPAM blocks exhibit lower critical solution temperature (LCST) behavior, marked by a broad transition between swollen and collapsed states. The response of the bi‐level brushes to changes in added salt at constant pH is complex, as the swelling behaviors of both the weak polyelectrolyte, PMAA, and thermoresponsive PNIPAM are affected by changes in ionic strength. This work demonstrates not only the robustness of SI‐PMP for making novel, bi‐level stimuli‐responsive brushes, but also the complex links between synthesis, structure, and response of these materials. 相似文献
102.
Planar MESFET grid oscillators using gate feedback 总被引:2,自引:0,他引:2
Weikle R.W. II Kim M. Hacker J.B. De Lisio M.P. Rutledge D.B. 《Microwave Theory and Techniques》1992,40(11):1997-2003
A method for quasi-optically combining the output power of MESFETs in which drain and source leads couple directly to the radiated field is introduced. The design consists of a planar grid of devices placed in a Fabry-Perot cavity. Capacitive feedback is provided to the gate, allowing oscillation at much higher frequencies than previous grids. The oscillation frequency is dependent on the device characteristics, the resonator cavity, and the symmetries of the grid. A transmission-line model for the grid is discussed and used to design two oscillator arrays. A 16-element grid has produced 335 mW of power at 11.6 GHz with a DC-to-RF conversion efficiency of 20%. This design was scaled to produce a 36-element grid oscillator with output power of 235 mW at 17 GHz. These results represent a significant improvement in the performance of planar grid oscillators. The planar configuration of the grid is very convenient for monolithic integration and is easily scalable to millimeter-wave frequencies 相似文献
103.
David C. Johnson II 《Tetrahedron letters》2004,45(46):8483-8487
The benzyl groups of β-hydroxy-N-benzyl sulfonamides are labile toward hydrogenolysis-unlike N-benzyl sulfonamides lacking the β-hydroxy moiety. We find that N-acyl-N-benzyl sulfonamides undergo hydrogenolysis under very mild conditions. Based upon these observations, we developed a reversible safety-catch method using tert-butoxycarbonyl moieties to activate N-benzyl sulfonamides toward hydrogenolysis. We also explored the utility of the safety-catch activation method for other nitrogen-based functionality such as N-benzyl carboxamides, imides, and related functionality. 相似文献
104.
A. J. A. Aquino L. A. Soares II A. B. F. Da Silva M. Trsic 《Journal of Molecular Structure》1986,139(3-4):327-332
Semiempirical MNDO calculations are performed on various models for the polythiazyl polymer with increasing chain sizes. Population analysis, geometry optimization and the evolution of the frontier orbital energies are discussed. A low-lying broken symmetry structure with (SN)2 repeating units is detected. 相似文献
105.
Daryle H. Busch Rebecca A. Roesner Thomas L. Allison II Elena V. Rybak-Akimova Liszu Chung 《Journal of inclusion phenomena and macrocyclic chemistry》1998,30(3):185-196
The compressibilities of seven liquidphase, macrocyclic host-guest systems were determinedat approximately 25 °C and 3.4 × 107 Pa.Each two-component system consisted of a cyclodextrin,a calixarene, or a crown ether as host and anappropriate solvent as guest. In each case studied,the host-guest system was found to be lesscompressible than the pure solvent, with thedifferences ranging from 2 to 18% of the magnitudesof the pure solvent compressibilities. These findingshave enabled us to better understand how strong,ambient pressure, intermolecular host–guestinteractions influence the compressibility ofsolutions. Both inclusion and solvationcontribute. 相似文献
106.
107.
The ν3 band of UF6 isolated in solid xenon is shown to consist of a single sharp spectral feature. 相似文献
108.
We have described a convenient regioselective one-pot approach to pyrazolo[1,5-a]- and imidazo[1,2-a]pyrimidine derivatives from α,β-unsaturated imines generated in situ and amino heterocycles. Reaction is general with respect to all three components, namely (i) nitrile, (ii) aldehyde, and (iii) amino heterocycle reagents. Good yields (52-77%), convenient isolation of the targeted molecules are the distinct characteristics of the developed protocol. 相似文献
109.
液相色谱-电喷雾离子阱质谱法测定贝类中软骨藻酸 总被引:1,自引:0,他引:1
记忆缺失性贝类毒素(amnesicshellfishtoxin,简称.ASP)主要成分软骨藻酸(domoicacid,简称DA)是一种氨基酸类的生理活性物质(图1),因最早从红藻属的树枝软骨藻(chondriaarmata)分离出来而被命名为软骨藻酸。自1987年加拿大首次发生集体贝类食品中毒事件后,人们从赤潮藻类中的硅藻属(diatom)的多列尖刺菱形藻(nitzschpungensf.multiseries)中检测到了DA,随后,美国、加拿大、北欧一些国家,澳大利亚、日本等国先后从紫贻贝(myltilusedulis)、扇贝(pectenmaximus)、文蛤(callistachione)等贝类体内以及鲭鱼和石蟹的内脏中检测到了DA。鱼、贝通过滤食毒藻,将DA富积在体内,人类因食用被DA污染的鱼、贝而中毒,中毒症状包括恶心、呕吐、腹痛、腹泻等,同时有晕眩、 相似文献
110.
Dr. Monika Srebro Dr. Emmanuel Anger Barry Moore II Dr. Nicolas Vanthuyne Prof. Christian Roussel Prof. Régis Réau Prof. Jochen Autschbach Dr. Jeanne Crassous 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(47):17100-17115
The properties of mono‐ and bis‐Ru–vinyl[6]helicene complexes ( 2 a and 2 b , respectively), recently synthesized by using molecular engineering of helicenes based on the grafting of lateral organometallic substituents on the π‐helical backbone through a vinyl bridge, are presented. These helicene derivatives are thoroughly characterized, with special attention given to their chiroptical properties and redox switching activity. The UV/Vis and electronic circular dichroism (ECD) spectra of P and M enantiopure species, both in the neutral and oxidized states ([ 2 a ] . +, [ 2 b ] . +, and [ 2 b ]2+), are analyzed with the aid of quantum‐chemical calculations. The extended π‐conjugation facilitated by the vinyl moiety, clearly visible in the electronic structures of 2 a , b , introduces new active bands in the ECD spectra that consequently lead to a significant increase in optical rotation of Ru–vinylhelicenes compared with the organic precursors. The vibrational circular dichroism (VCD) spectra were measured and calculated for both the organic and organometallic species and constitute the first examples of VCD for metal‐based helicene derivatives. Finally, the redox‐triggered chiroptical switching activity of 2 a , b is examined in detail by using ECD spectroscopy. The modifications of the ECD spectra in the UV/Vis and NIR region are well reproduced and rationalized by calculations. 相似文献