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排序方式: 共有109条查询结果,搜索用时 15 毫秒
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Pengpeng Liu Dr. Patrik Neuhaus Dr. Dmitry V. Kondratuk Prof. T. Silviu Balaban Prof. Harry L. Anderson 《Angewandte Chemie (International ed. in English)》2014,53(30):7770-7773
α‐ and β‐Cyclodextrins have been used as scaffolds for the synthesis of six‐ and seven‐legged templates by functionalizing every primary CH2OH with a 4‐pyridyl moiety. Although these templates are flexible, they are very effective for directing the synthesis of macrocyclic porphyrin oligomers consisting of six or seven porphyrin units. The transfer of chirality from the cyclodextrin templates to their nanoring hosts is evident from NMR and circular dichroism spectroscopy. Surprisingly, the mean effective molarity for binding the flexible α‐cyclodextrin‐based template within the six‐porphyrin nanoring (74 M ) is almost as high as for the previously studied rigid hexadentate template (180 M ). The discovery that flexible templates are effective in this system, and the availability of a template with a prime number of binding sites, open up many possibilities for the template‐directed synthesis of larger macrocycles. 相似文献
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Reda Moubah Silviu Colis Mathieu Gallart Guy Schmerber Pierre Gilliot Aziz Dinia 《Journal of luminescence》2012,132(2):457-460
Recent studies on the physical properties of Ca3Co2O6 nanometric samples have shown that their properties are significantly different from those of the bulk samples. The origin of this change is not trivial. We have carried out optical measurements on Ca3Co2O6 thin films with different thicknesses in order to characterize their electronic structure using optical spectroscopy measurements. The absorption spectra show a dependence on the film thickness that is correlated to the grain size in the polycrystalline layers. We found that the optical band gap increases from 1.3 to 1.55 eV when the thickness changes from 35 to 100 nm. The change in the band gap evolution with the film thickness is discussed in terms of both the amorphous effect and the grain size in the Ca3Co2O6 thin films. Finally, we show that these results are consistent with recent measurements concerning magnetic and electrical properties of Ca3Co2O6 nanometric samples. 相似文献
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Comorosan S Polosan S Jipa S Popescu I Marton G Ionescu E Cristache L Badila D Mitrica R 《Journal of photochemistry and photobiology. B, Biology》2011,102(1):39-44
Free radicals generation is inhibited through green light (GL) irradiation in cellular systems and in chemical reactions. Standard melanocyte cultures were UV-irradiated and the induced cellular reactive oxygen species (ROS) were quantified by the fluorescence technique. The same cell cultures, previously protected by a 24h GL exposure, displayed a significantly lower ROS production. A simple chemical reaction is subsequently chosen, in which the production of free radicals is well defined. Paraffin wax and mineral oil were GL irradiated during thermal degradation and the oxidation products checked by chemiluminescence [CL] and Fourier transform infrared spectra [FT-IR]. The same clear inhibition of the radical oxidation of alkanes is recorded. A quantum chemistry modeling of these results is performed and a mechanism involving a new type of Rydberg macromolecular systems with implications for biology and medicine is suggested. 相似文献
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Silviu Guiaşu 《Reports on Mathematical Physics》1975,7(1):59-65
In the present paper the so-called weighting process is defined. Conditions on the weights implying the converse H-theorem are given. These conditions are satisfied by the iterated weighting process which contains, as a particular case, the Bayesian model for prediction and retrodiction given by S. Watanabe. 相似文献
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Balaban TS Linke-Schaetzel M Bhise AD Vanthuyne N Roussel C Anson CE Buth G Eichhöfer A Foster K Garab G Gliemann H Goddard R Javorfi T Powell AK Rösner H Schimmel T 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(8):2267-2275
We report two crystal structures of a synthetic porphyrin molecule which was programmed for self-assembly. The same groups which ensure that bacteriochlorophylls c, d, and e can self-assemble into the chlorosomal nanorods, the photosynthetic antenna system of some green bacteria, have been engineered into desired positions of the tetrapyrrolic macrocycle. In the case of the 5,15-meso-substituted anchoring groups, depending upon the concentration, by using the same crystallization solvents, either a tetragonal or a layered structure of porphyrin stacks were encountered. Surprisingly, pi-pi interactions combined with extensive dispersive interactions, which also encompass cyclohexane, one of the crystallization solvents, win over putative hydrogen bonding. We are aware that our compounds differ considerably from the natural bacteriochlorophylls, but based upon our findings, we now question the hydrogen-bonding network, previously proposed to organize stacks of bacteriochlorophylls. Transmission electron microscopy (TEM), atomic force microscopy (AFM), and small-angle X-ray scattering (SAXS) on various isomeric compounds support our challenge of current models for the chlorosomal antenna as these show structures, astonishingly similar to those of chlorosomes. 相似文献
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We evaluate the Poynting vector generated by a heavy quark moving through a thermal state of N=4 gauge theory using the gauge-string duality. A significant diffusion wake is observed as well as a Mach cone. We discuss the ratio of the energy going into sound modes to the energy coming in from the wake. 相似文献