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A series of β-ketoselenenic acids was generated at low temperature ( - 20° to - 50°) by selenoxide syn elimination of appropriate selenoxides (13-ox, 16-ox, 35-ox, 38-ox, and 39-ox). No evidence for the buildup of significant concentrations of selenenic acid was obtained. A selenolseleninate (15, 2,2' - diseleno - bis(1 - phenyl - 2 - methyl -1 - propanone) - Se - oxide) was detected as an intermediate in the decomposition of 13-ox and 16-ox. This compound, which is stable in solution below - 50° was charaeterized by NMR spectroscopy (1H, 13C,77Se) and by its thermal decomposition and reactions with phosphite (reduction to diselenide 6) and dialkylamines (formation of selenenamide 11). Decomposition of 15 in the presence of dibenzylamine resulted in trapping of a selenenic acid-like species (RSeSeOH) to give RSeSeN(CH2Ph)2 (R = PhC(O)C(CH3)2). Although 15 could not be prepared by oxidation of diselenide 6, it was possible to prepare a cyclic selenolseleninate (4,4-dimethyl-1,2-diselenolane monoxide, 20) by oxidation of the related diselenide (19). Attempts to prepare more stable aliphatic selenenic acids by blocking the principal decomposition pathway of 15 were not successful. Thus 1 - benzoyl -1 - cyclopropaneselenenic acid was generated from 35-ox and 38-ox and 1 - benzoyl - 2,2 - dimethylcyclopropaneselenenic from 39-ox. The former underwent normal disproportionation (to 36 and 37) even when prepared at -49°. The latter gave what appeared to be a selenolseleninate (40) which again disproportionated at -17°. 相似文献
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The spherical model ind=r+1 dimensions is treated using the hamiltonian formulation. The critical behaviour of the model is obtained and is found to be identical to the spherical model.Supported by the Studienstiftung des Deutschen Volkes 相似文献
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The synthesis of the first two arylenealkyne conjugated macrocycles containing a long alkylene bridge via Glaser coupling of template-directed tetraacetylenes was reported. Tetraacetylene intermediates with complex structures were
constructed rapidly via quadruple Hagihara coupling of monoprotected bisacetylenes to appropriate tetraiodides and subsequent desilylation. The characterization
of such compounds was carried out by NMR, GPC and UV-Vis spectra. Unfortunately, the two compounds were not liquid crystals
and had no biaxial nematic mesophase character as expected.
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Translated from Chemical Journal of Chinese Universities, 2007, 28(1): 65–70 [译自: 高等学校化学学报] 相似文献
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The hexagonal bilayer haemoglobin molecule from Nereis virens has been investigated in a comparative study using several different negative stain electron microscopical specimen preparations (i.e. by conventional adsorption to continuous carbon support films, by the negative staining-carbon film technique and by negative staining across the holes of holey carbon support films with air-drying and rapid freezing/cryo-negative staining). The benefits and limitations of these different approaches are indicated, with the overall conclusion that negative staining with ammonium molybdate across holes creates the best possibilities for molecular imaging, and also has the potential for the creation of two-dimensional (2D) crystals/arrays at the fluid-air interface. Of the different negative staining procedures presented, cryo-negative staining reveals the greatest details of N. virens haemoglobin. This is exemplified by the direct visualisation of the central linker-assembly within the haemoglobin molecule, a structural feature less clearly defined by the other negative staining techniques. A discoidal lipoprotein molecule (diameter 30-60nm; thickness ca 8nm) has been detected in N. virens, which represents the first documented account of an annelid haemolymph lipoprotein. The biological implications of this lipoprotein for lipid transport remain to be established. The presence of a low concentration of ferritin molecules in N. virens haemolymph is also shown, assisted by the formation of small 2D ferritin arrays in negatively stained specimens prepared across holes. 相似文献
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Csoka L Hoeger IC Peralta P Peszlen I Rojas OJ 《Journal of colloid and interface science》2011,363(1):206-212
Ultrathin films of cellulose nanocrystals (CNCs) are obtained by using a convective assembly setup coupled with a low-strength external AC electric field. The orientation and degree of alignment of the rod-like nanoparticles are controlled by the applied field strength and frequency used during film formation. Calculated dipole moments and Clausius-Mossotti factors allowed the determination of the critical frequencies, the peak dielectrophoresis as well as the principal orientation of the CNCs in the ultrathin films. As a result of the combination of shear forces and low electric field highly ultrathin films with controlled, unprecedented CNC alignment are achieved. 相似文献
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Ingrid C. Hoeger Sandeep S. Nair Arthur J. Ragauskas Yulin Deng Orlando J. Rojas J. Y. Zhu 《Cellulose (London, England)》2013,20(2):807-818
Laboratory mechanical softwood pulps (MSP) and commercial bleached softwood kraft pulps (BSKP) were mechanically fibrillated by stone grinding with a SuperMassColloider®. The extent of fibrillation was evaluated by SEM imaging, water retention value (WRV) and cellulase adsorption. Both lignin content and mechanical treatment significantly affected deconstruction and enzymatic saccharification of fibrillated MSP and BSKP. Fibrillation of MSP and BSKP cell walls occurs rapidly and then levels off; further fibrillation has only limited effect on cell wall breakdown as measured by water retention value and cellulase adsorption. Complete (100 %) saccharification can be achieved at cellulase loading of 5 FPU/g glucan for BSKP after only 15 min fibrillation with energy input of 0.69 MJ/kg. However, the presence of lignin in MSP affects the extent of fibrillation producing fibrils mainly above 1 μm. Lignin binds nonproductively to cellulases and blocks cellulose thereby reducing its accessibility. As a result, the cellulose saccharification efficiency of MSP fibrils (6 h of fibrillation, energy input of 13.33 MJ/kg) was only 55 % at same cellulase loading of 5 FPU/g glucan. 相似文献