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41.
The newly synthesized 2‐(alk‐3‐en‐1‐ynyl)cyclohex‐2‐enones 4 undergo photodimerization (chemo‐ and regio‐)selectively at the exocyclic C?C bond to give diastereoisomeric mixtures of 1,2‐dialkynyl‐1,2‐dimethylcyclobutanes. On irradiation of 4 in the presence of 2‐chloroacrylonitrile, cyclobutane formation occurs again (chemo‐ and regio‐)selectively at the exocyclic C?C bond to afford diastereoisomeric mixtures of 2‐alkynyl‐1‐chloro‐2‐methylcyclobutanecarbonitriles. Similarly, compounds 4 undergo photoaddition to 2,3‐dimethylbuta‐1,3‐diene exclusively at the exocyclic C?C bond to afford mixtures of [2+2] and [4+2] cycloadducts. 相似文献
42.
Pesonen J 《The Journal of chemical physics》2008,128(4):044319
It is customary to describe molecular vibrations using as exact kinetic energy operators and as accurate potentials as possible. It has become a standard approach to express Hamiltonians in curvilinear internal displacement coordinates, because they offer a simple and physical picture of vibrational motions, including large amplitude changes in the shape. In the older normal mode model of molecular vibrations, the nuclei are thought to vibrate infinitesimally about the reference configuration, and the shape of the molecule is described using linearized approximations of the true geometrically defined internal displacement coordinates. It is natural to ask how the two approaches are related. In this work, I present a general yet practical way to obtain curvilinear displacement coordinates as closed function of their linearized counterparts, and vice versa. In contrast to the conventional power series approach, the body-frame dependency is explicitly taken into account, and the relations are valid for any value of the coordinates. The present approach also allows one to obtain easily exact kinetic energy operators in linearized shape coordinates. 相似文献
43.
Self‐Assembly of the Cyclic Lipopeptide Daptomycin: Spherical Micelle Formation Does Not Depend on the Presence of Calcium Chloride 下载免费PDF全文
Steven Kirkham Dr. Valeria Castelletto Prof. Ian William Hamley Dr. Katsuaki Inoue Dr. Robert Rambo Mehedi Reza Prof. Janne Ruokolainen 《Chemphyschem》2016,17(14):2118-2122
The cyclic lipopeptide Daptomycin, used as a treatment for infections where antimicrobial resistance is observed, is shown to self‐assemble into spherical micelles above a critical aggregation concentration. Micelles are observed either in the absence or presence of CaCl2, in contrast to claims in the literature that CaCl2 is required for micellization. 相似文献
44.
Copper mediated allylic substitutions and conjugate additions to geranyl, cinnamyl and allylic indole compounds have been investigated with the aim of finding a method for the creation of the all-carbon quaternary centre present in the natural product lyngbyatoxin A. Reaction conditions have been found giving a 68% SN2' selectivity in the copper mediated addition of PhMgBr to geranyl chloride, as well as 99% and 95% SN2' selectivity in the copper catalysed addition of EtMgBr to cinnamyl chloride and acetate, respectively. When the optimised reaction conditions were applied to the corresponding allylic compounds containing a 7-substituted indole moiety, the regioselectivity was reversed giving only the SN2 product. The allylic indole-containing substrates were also found to be unproductive in Pd- or Mo-catalysed SN2'-type substitution reactions. In related studies, copper catalysed conjugate addition of EtMgBr to the tricyclic lactam 6-methyl-pyrrolo[3,2,1-ij]quinolin-4-one gave a maximum of 20% of the 1,4-addition product. 相似文献
45.
Janne Heittokangas Risto Korhonen Jouni Rä ttyä 《Transactions of the American Mathematical Society》2008,360(2):1035-1055
Complex linear differential equations of the form with coefficients in weighted Bergman or Hardy spaces are studied. It is shown, for example, that if the coefficient of belongs to the weighted Bergman space , where , for all , then all solutions are of order of growth at most , measured according to the Nevanlinna characteristic. In the case when all solutions are shown to be not only of order of growth zero, but of bounded characteristic. Conversely, if all solutions are of order of growth at most , then the coefficient is shown to belong to for all and .
Analogous results, when the coefficients belong to certain weighted Hardy spaces, are obtained. The non-homogeneous equation associated to is also briefly discussed.
46.
Tuomas Aitasalo Jorma Hls Hgne Jungner Jean-Claude Krupa Mika Lastusaari Janina Legendziewicz Janne Niittykoski 《Radiation measurements》2004,38(4-6):727-730
The UV excited and persistent luminescence properties as well as thermoluminescence (TL) of Eu2+ doped strontium aluminates, SrAl2O4:Eu2+ were studied at different temperatures. Two luminescence bands peaking at 445 and 520 nm were observed at 20 K but only the latter at 295 K. Both Sr-sites in the lattice are thus occupied by Eu2+ but at room temperature efficient energy transfer occurs between the two sites. The UV excited and persistent luminescence spectra were similar at 295 K but the excitation spectra were different. Thus the luminescent centre is the same in both phenomena but excitation processes are different. Two TL peaks were observed between 50 and 250 °C in the glow curve. Multiple traps were, however, observed by preheating and initial rise methods. With longer delay times only the high temperature TL peak was observed. The persistent luminescence is mainly due to slow fading of the low temperature TL peak but the step-wise feeding process from high temperature traps is also probable. 相似文献
47.
48.
The spatial performance variation of dye solar cell with standard liquid electrolyte was examined by dividing the cell into segments. Surprisingly large and permanent performance differences were found in different parts of the cell leading to significant losses in the overall cell efficiency. The decrease of open circuit voltage along the electrolyte filling direction suggests that 4-tert-butylpyridine is adsorbed non-uniformly as the electrolyte passes through the dyed TiO2 layer during the filling process. The result indicates that non-uniform electrolyte adsorption may limit the up-scaling of dye solar cells, which calls for the examination of electrolyte filling techniques and electrolyte compositions less prone to this effect. 相似文献
49.
High and low molecular weight (Mw) carboxymethyl celluloses (CMC) were adsorbed on a well-characterized fiber substrate (long fibers of a commercial bleached birch kraft pulp with the carboxylic acid groups in Na-form) to increase the charge of the fibers in a controlled fashion. The Mw played a role in the utilization of CMCs as a strength additive in paper sheets nearly doubling the tensile strength with the high Mw CMC. Swelling properties of the CMC treated fibers were measured with water retention value (WRV). The WRV increased more with the high Mw CMC. The swelling was further tuned by two highly cationic polyelectrolytes; high Mw poly(diallyldimethyl ammonium chloride) (PDADMAC) and low Mw polybrene (hexadimethrine bromide, [3,6]-ionene). They were chosen because of their known ability to neutralize the anionic charge either exclusively on the surface or in the whole fiber, respectively. Adsorption of PDADMAC could reduce WRV of the CMC pre-treated fibers to the level of the untreated reference, while polybrene adsorbed pulps with 3–10 times more cationic polyelectrolyte deswelled the fibers only slightly more than the surface neutralized fibers. These results indicated surface conformation differences with low and high Mw CMCs. While the conformation did play a role after physical alteration (drying and rewetting) of the fibers, the paper sheets produced from these fibers showed remarkable differences. In extreme cases, the strength of the paper could be retained after drying (low Mw CMC + PDADMAC) or paper, resistant to disintegration, could be achieved (CMC + polybrene). 相似文献
50.
Hua Jiang Janne Ruokolainen Neil Young Tetsuo Oikawa Albert G. Nasibulin Angus Kirkland Esko I. Kauppinen 《Micron (Oxford, England : 1993)》2012,43(4):545-550
Applications relevant to carbon based nano-materials have been explored using a newly installed JEOL-2200FS field emission gun (FEG) (scanning) transmission electron microscope (S)TEM which is integrated with two CEOS aberration correctors for both the TEM image-forming and the STEM probe-forming lenses. The performance and utility of this newly commission hardware has been reviewed with a particular focus on operation at an acceleration voltage of 80 kV, thus bringing the primary electron beam voltage below the knock-on threshold for carbon materials and opening up a range of possibilities for the study of carbon-based nanostructures in the aberration-corrected electron microscope. The ability of the microscope to obtain both atomic TEM images and high-quality electron diffraction patterns from carbon nanotubes was demonstrated. The chiral structure of a double-walled carbon nanotube was determined from its diffraction pattern. The aberration corrected TEM imaging technique facilitates a unique approach to accurate determination of single-walled carbon nanotube diameters. On the other hand, the probe-corrected high angle annular dark field (HAADF) STEM imaging performance allows for the detection of single gold atoms at 80 kV and was used to study the graphite interlayer spacing in a multi-walled carbon nanotube. 相似文献