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91.
92.
We compare the electronic structures of trans-polyacetylene, poly - (p-phenylene), polypyrrole and polythiophene, computed by an Extended Hückel crystalline orbital scheme. Similarities in the valence and conduction densities of states are analyzed in terms of the connectivity of the different systems. 相似文献
93.
Cristina Sousa Teresa Sá e Melo Jean-Claude Mazière René Santus 《Photochemistry and photobiology》1998,67(5):561-564
The phototoxic effect of psoralen (PSO), 5-methoxypsoralen (5MOP), 8-methoxypsoralen (8MOP) and 4,5',8-trimethylpsoralen (TMP) has been compared on the NCTC 2544 keratinocyte cell line in terms of cell mortality and lipid peroxidation. The order of effectiveness for cell photokilling is TMP, 5MOP >> 8MOP, PSO, whereas a little lipid peroxidation is observed for the four psoralens under study. Oxygen-independent membrane damage seem to play a key role in the lethal photodamage because the biological effectiveness of the most hydrophobic lipid-soluble psoralens, TMP and 5MOP, is about an order of magnitude higher than that of the more water-soluble 8MOP and PSO. In relation to this hypothesis, and in contrast to 8MOP, TMP is readily extracted from cells by ethyl acetate, a good membrane solvent, as shown by GC/MS analysis on cell extracts. The results are discussed in terms of the highly microenvironment-dependent photophysical properties of psoralens. By the measure of the intracellular psoralen concentration, the neutral red uptake and the lipid peroxidation products, this work provides evidence that PUVA therapy-mediated cell mortality is a lipid peroxidation-independent phenomenon. 相似文献
94.
95.
Summary In long molecules with helical structure it is shown that the electron’s response functionF(q,T) is singular for various wave vectors. Then deformed phases associated with different periodicites can occur as a function
of external pressure. The calculation was done as a function of temperature and for small number of atoms per turn.
Riassunto Si mostra in lunghe molecole con struttura elicoidale che la funzione di risposta dell’elettroneF(q, T) è singolare per vari vettori d’onda. Allora possono verificarsi fasi deformate associate a diverse periodicità in funzione della pressione esterna. Si effettua il calcolo in funzione della temperatura e per un numero ridotto di atomi per spira.
Резюме В длинных молекулах с геликоидальной структурой показывается, что функция электронного откликаF(q, T) является сингулярной для различных волновых векторов. В связи с этим могут возникать деформированные фазы, связанные с различными периодичностями, в зависимости от внешнего давления. Проводятся вычисления в зависимости от температуры и для малого числа атомов на виток.相似文献
96.
Jack bean urease was immobilized on polyethylenimine-coated cotton cloth by adsorption following by crosslinking with dimethyl suberimidate. Of the various methods used, crosslinking with dimethyl suberimidate was found to stabilize the enzyme with minimal inactivation. Cloth-bound urease showed a shift in pH optimum towards the acidic side without appreciable change in temperature optimum and thermostability. Cloth-bound urease could be used repeatedly for urea hydrolysis without appreciable loss in activity. Alternatively, urease cloth could be stitched in the form of a bag containing ammonia adsorbent and used for urea hydrolysis with simultaneous removal of ammonia. 相似文献
97.
José M. Guisán Francisco V. Melo Antonio Ballesteros 《Applied biochemistry and biotechnology》1981,6(1):25-36
Staphylococcal nuclease has been insolubilized, directly through its amino groups, on CNBr-activated Sepharose 2B. For kinetic
studies, a small substrate (thymidine 5′-(p-nitrophenyl phosphate) 3′-phosphate) has been used to measure the hydrolytic activity. With this system the absence of diffusional
limitation has been proven. Eadie-Hofstee analysis of the data has been employed to determine the intrinsic kinetic constants
of the insolubilized enzyme. Thek
cat-pH andK
M−pH profiles and the activation energies are similar for the soluble and for the insolubilized nuclease. At the same time
conditions are established in which a stirred batch reactor containing particles of insolubilized nuclease behaves as an open
system. 相似文献
98.
Y.P. Yadava D.A. Landinez Tellez M.T. de Melo J.M. Ferreira J. Albino Aguiar 《Applied Physics A: Materials Science & Processing》1998,66(4):455-458
2 ZrO5.5 has been synthesized by solid-state reaction. Structural ordering in this material has been studied by X-ray diffraction
(XRD). The XRD spectra reveal that DyBa2ZrO5.5 has an ordered complex cubic perovskite structure. The presence of superstructure reflections in the XRD spectra is characteristic
of A2BB’O6-type crystalline structure. The chemical stability of DyBa2ZrO5.5 with YBa2CuO7-δ (YBCO) superconductors has been studied by XRD and electrical resistivity measurements. These studies show that DyBa2ZrO5.5 is chemically stable with YBCO and there is no degradation in the superconducting transition temperature Tc of YBCO even when mixed up to 1:1 vol%, with DyBa2ZrO5.5 in YBCO. Detailed study of the superconducting transition region shows that Tc(onset) and Tc(0) values of pure YBCO and YBCO–DyBa2ZrO5.5 composites are similar in both cases. The implications are discussed.
Accepted: 13 October 1997 相似文献
99.
D. Sen J. S. Melo J. Bahadur S. Mazumder S. Bhattacharya G. Ghosh D. Dutta S. F. D’Souza 《The European physical journal. E, Soft matter》2010,31(4):393-402
Morphological transformation during evaporation-induced self-assembly of a mixed colloidal suspension in micrometric droplets
has been investigated. It has been demonstrated that a buckling-driven shape transition of drying droplets of mixed colloidal
suspension takes place during evaporation-induced self-assembly. Further, it is also shown that the distortion modulations
get significantly amplified with enhancement in volume fraction of anisotropic soft colloidal component of the mixed colloids.
It has been argued that the reduction in elastic modulus of formed shell, at the boundary of a drying droplet, and the anisotropic
nature of one of the colloidal components facilitate the deformation process. Hierarchical structures of these assembled colloidal
grains have been probed using electron microscopy and scattering techniques. 相似文献
100.
Pina J Burrows HD Becker RS Dias FB Maçanita AL Seixas de Melo J 《The journal of physical chemistry. B》2006,110(13):6499-6505
The photophysics of six oligothiophenes end-capped with cyano groups (CNalphan) was investigated in solution at room and low temperature. The study comprises singlet-singlet and triplet-triplet absorption and emission spectra together with lifetimes and quantum yields for all the radiative and nonradiative processes. From the lifetimes and quantum yields, it was possible to extract the rate constants for all the processes. Singlet oxygen yields were also determined, revealing an efficient sensitization (SDelta approximately 1) of its formation by the triplet state of the CNalphan. The introduction of the cyano groups is found to decrease the energetic separation between the highest occupied molecular orbital and the lowest unoccupied molecular orbital, leading to a red shift of the absorption and the emission when compared with the unsubstituted counterparts, the alpha-oligothiophenes. Phosphorescence is only observed for the first member of the series, CNalpha1. 相似文献