Phase transition in an occupationally disordered sulfate system

We have investigated the behavior of the Li_1.43Cs_0.57SO₄ single-crystal Raman spectra and dielectric permittivity as a function of temperature. It was observed that the crystal, which is an occupationally disordered system, with orthorhombic C_2v² structure at room temperature, undergoes a phase transition at 230 K. In the new phase the SO₄ tetrahedra remain in two non-equivalent sites and there is no evidence of the doubling of the unit cell.     

Scattering Parameters of FSS on Anisotropic Layers at Millimeter Wave Frequencies

The analysis of periodic structures on anisotropic substrates is presented for incident millimeter waves. Frequency selective surface structures composed by a periodic array of conducting crossed dipoles on anisotropic layers are analyzed. A full-wave analysis for the problem of scattering is performed. The formulation uses the moment method in combination with the immitance approach, in the Fourier domain, to determine the scattering parameters of the considered structures. A set of entire-domain type basis functions is used in the expansion for the unknown induced current. This analysis is computationally efficient, and its accuracy is verified by the agreement between results obtained in this work and those available in the literature, for particular cases.     

Comparative study of the electronic structure of conjugated polymers

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.     

PUVA-Induced Cell Mortality in NCTC 2544 Keratinocytes: Is It Related to the Microenvironmental Properties of the Excited States of Psoralens?

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.     

Peierls transition in helical structures

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.

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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.

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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.

     

Grease immobilized on polyethyleneimine cotton cloth

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.     

Determination of intrinsic properties of immobilized enzymes

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.