Silica xerogels with different structures and morphology, synthesized using a sol-gel procedure, were used as a carrier of vanadium catalysts (VOCl3/AlEt2Cl) for ethylene polymerization. Two techniques of catalyst synthesis were applied: slurry impregnation and gas-phase adsorption and the relevant polymerization methods were then employed. The effect of the carrier structure and morphology on the vanadium loading in the catalysts, the catalyst’s activity and kinetic stability were investigated. 相似文献
L5178Y-R and L5178Y-S cells differ in sensitivity to UVC radiation (D0 values: 2.8 and 9.0 J m-2 respectively, exposure in Fischer's medium). The UVC sensitivity is related to the excision repair ability. Benzamide (Bz), an inhibitor of adenosine diphosphoribosyl transferase (ADPRT), does not modify the lethal effect of UVC radiation in L5178Y-R cells, whereas it sensitizes L5178Y-S cells. The content of NAD+ after irradiation decreases only in the latter cells and this decrease can be prevented by 2 mM Bz treatment. In agreement with the survival data, in L5178Y-R cells neither the proportion of abnormal cells nor the frequency of chromatid aberration are affected by 2 mM Bz treatment, in contrast with L5178Y-S cells. Bz slightly reverses inhibition of 3H-thymidine incorporation only in L5178Y-S cells, but it does not affect the proportions of cells in the different phases of the cell cycle in either cell strain after UVC exposure. These data could be taken as an indirect indication of the involvement of ADPRT in DNA repair in UVC-irradiated L5178Y-S cells. However, the increase in the number of DNA strand breaks in UVC-exposed, Bz-treated cells compared with UVC-exposed untreated cells is the same in both L5178Y strains. 相似文献
Due to narrowband emission and high quantum efficiencies, polycyclic aromatic heterocycles with multi-resonance thermally activated delayed fluorescence (MR-TADF) properties have recently gained considerable attention in the organic optoelectronic field. Albeit their great promise in the full visible region covering from blue to red, MR-TADF emitters with ultraviolet emission have been rarely reported. Through locking the two ortho-positions of a triphenylamine core by sulfone groups, a simple polycyclic aromatic heterocycle, BTPT, was facilely constructed, exhibiting 368 nm ultraviolet emission with a narrow full width at half maximum (FWHM) of 33 nm. Its neat film exhibited distinct TADF property with a main emission peak at 388 nm. Noteworthily, the enantiomeric crystals of BTPT not only demonstrated significant circularly polarized luminescence (CPL) with large luminescence dissymmetry factor in the 10?3 order but also displayed obvious room temperature phosphorescence (RTP). The relationship between this innovative helical unit and unique photophysical properties, including ultraviolet MRTADF, CPL, and RTP, was reasonably revealed.
Differential mutual diffusion coefficients of n-alkyltrimethylammonium bromides [CH3(CH2)n–1N(CH3)3Br, CnTAB] (n=10, 12, 14, 16) have been measured in aqueous solutions at 298.15 K using a conductimetric cell and an automatic apparatus to follow diffusion. The cell is based on an open-ended capillary, and the technique follows the diffusion process by measuring the resistance of a solution inside the capillaries at various times. The electrical conductances of those solutions have also been measured to calculate the critical micellar concentration (cmc). Thermodynamic analysis of the data suggests that the free ion concentration decreases at concentrations above the cmc, in agreement with theoretical predictions. The obtained values of the micellization parameters were used to model the mutual diffusion coefficients of CnTAB aqueous solutions. 相似文献
A theory is developed for the potential distribution around a charged spherical colloidal particle carrying ionized groups on the particle surface in a medium containing its counterions (i.e., counterions produced from dissociation of the particle surface groups) and a small amount of added salts on the basis of the theory of Imai and Oosawa. Numerical solutions to the Poisson–Boltzmann equation for the potential distribution are obtained for the case of dilute (but not infinitely dilute) particle suspensions of volume fraction1 for
a1 (where is the Debye–Hückel parameter and a is the particle radius). Here we have taken into account the effects of (i) counterions from the particle surface groups, and (ii) the finite particle volume fraction. These effects, which are usually neglected in the conventional Poisson–Boltzmann equation, are found to be important. It is found that, as in the case of completely salt-free media, there is a certain critical value of the particle charge (which is the same as that for the completely salt-free case). When the particle charge is lower than the critical value, the potential is given by a Coulomb potential. If the particle charge is higher than the critical value, then counterions are accumulated in the vicinity of the particle surface (counterion condensation) and the potential becomes less dependent on the particle charge. The above behaviors can be observed even for the case where the electrolyte concentration is higher than the concentration of counterions from the particle surface groups, if the conditions1 and a1are both satisfied. 相似文献
Thermolysis of benzannulated enyne-isocyanates 13 and enyne-isocyanates 36 and 37 promoted the cycloaromatization reactions to generate in situ O,4-didehydro-2-hydroxyquinolines and O,4-didehydro-2-hydroxypyridines, respectively, as reactive intermediates. These cycloaromatized intermediates could be captured either as biradicals and/or as zwitterions depending on the nature of the substituent at the alkynyl terminus. The intermediate derived from cycloaromatization of 13a bearing a phenyl substituent could be regarded as biradical 14, which then abstracts hydrogen atoms from gamma-terpinene leading to 2(1H)-quinolinone 15. Alternatively, the same intermediate could also be regarded as zwitterion 14', which then undergoes an initial hydride abstraction from gamma-terpinene followed by protonation to produce 15. The presence of a 2-phenylethyl substituent in 13b and 37a or a 2-methylphenyl substituent in 37b also allowed the resulting intermediates to be captured intramolecularly either as biradicals or as zwitterions, producing 2(1H)-quinolinone 19, 2(1H)-pyridone 39, and benzopyranopyridine 43, respectively. On the other hand, with a 2-methoxyphenyl, a 2-(dimethylamino)phenyl, or a 3-methoxypropyl substituent, the chemical behavior of the cycloaromatized adduct could be best accounted for in terms of a zwitterionic intermediate leading to benzofuro[3,2-c]quinolin-6(5H)-one (20), 5,11-dihydro-11-methyl-6H-indolo[3,2-c]quinolin-6-one (25), benzofuro[3,2-c]pyridin-1(2H)-one 44, 2,5-dihydro-2,5-dimethyl-1H-pyrido[4,3-b]indol-1-one 46, and related compounds. Interestingly, thermolysis of 37f bearing a 2-(methoxymethyl)phenyl substituent at the alkynyl terminus produced the unexpected benzopyranopyridine 56 as the major product in a process involving the cleavage of the bond between the methoxyl oxygen and the adjacent methylene carbon. The efficiency and selectivity of the cycloaromatization reaction could also be enhanced by the introduction of 1.1 to 10 equiv of dimethylphenylsilyl chloride to the reaction mixture to capture the resulting zwitterion. 相似文献