U.v. irradiation-induced crosslinking of solid poly(ethylene oxide) modified with tetraalkyl ammonium salt

Crosslinked poly(ethylene oxide) (PEO) modified with a quaternary tetraalkyl ammonium salt, ethyl methacrylate dimethyldodecylammonium bromide, was prepared by exposure of the solid blend to ultraviolet radiation from a high-pressure 150 W mercury lamp. The photochemical crosslinking of the blends proceeded in the presence of benzophenone as a hydrogen-abstracting agent. Gel fraction yield exceeded 85%, equilibrium swelling in water varied from 3.0 to 5.0, and the equilibrium swelling in chloroform from 6.5 to 12.5. The networks obtained have been characterized by elemental analysis, i.r.,¹H n.m.r., and d.s.c. measurements and their microstructure, water absorption and equilibrium swelling have been discussed.     

The C-terminal domains of gammaS-crystallin pair about a distorted twofold axis

The 2-domain gammaS-crystallin, a highly conserved early evolutionaryoff-shoot of the gamma-crystallin family, is located in the water-richregion of eye lenses. The expressed C-terminal domain, gammaS-C, has beencrystallized and the 2.56 A X-ray structure determined. There are twodomains in the asymmetric unit which pair about a distorted twofold axis.One of the domains has an altered conformation in a highly conserved regionof the protein, the tyrosine corner. The distorted gammaS-C dimer ofdomains is compared with the highly symmetrical, equivalent recombinantdimer of C-terminal domains from gammaB- crystallin. Sequence changes closeto the interface, that distinguish gammaS from the other gamma-crystallins,are examined in order to evaluate their role in symmetrical domain pairing.     

Multiple steady states in combined buoyancy and wind driven natural ventilation: The conditions for multiple solutions and the critical point for initial conditions

Natural ventilation systems may have multiple steady states in the combined buoyancy and wind driven mode in a single space. In this paper, dynamical system analysis is applied both graphically and quantitatively to investigate the multiple steady state behavior of such a natural ventilation system.     

UV Radiation-Induced Degradation of Poly(n-Propylmethylsilane-Co-Isopropylmethylsilane) in Solution

The photodegradation of poly(n-propylmethylsilane-co-isopropylmethylsilane) (NPIPSC) in solution was investigated. The results obtained indicate that a low-pressure Hg lamp photoinduces degradation. Therefore, this light source can be used as an acceptable radiation source for the photobleaching of NPIPSC. Gel permeation chromatography/light scattering (GPC/LS) measurements indicate that two photodegradation stages exist in this process. The first occurs at less than 6 s of exposure, where scission is very rapid. The second occurs between 6 and 12 s of exposure. The latter does not result in a significant loss of molecular weight. A change of slope in the plot of molecular weight as a function of elution volume is observed in the degradation process. This result indicates the presence of at least two species with different conformations. The ratio of scissions to cross-linking related to photodegradation was calculated and revealed that the scission process predominates over cross-linking. The presence of isopropylmethylsilane (IPMS) units in the copolymer appears to induce a decrease in the NPIPSC degradation efficiency. The linear plot of degradation degree as a function of exposure time suggests that there are no weak links in the copolymer. This result can be correlated with the chemical composition of the copolymer, which was nearly the same between 0 and 10 s of UV exposure. After 12 s of exposure, the IPMS was removed from the NPIPSC.     

Bleaching and photodegradation of textile dyes by H2O2 and solar or ultraviolet radiation

The photooxidation of textile dyes Yellow Procion H-4R, Bright Blue Remazol (blue reagent-19), Red Procion H-E7B, and the mixture of the two last dyes were investigated. The efficiency of photooxidation were compared using hydrogen peroxide (30%) as a bleaching reagent, solar and ultraviolet radiation, common glass borosilicate, quartz assay tubes, and no solid catalysts. The colour of blue dye and a mixture of blue and red dyes were almost completely removed after 3 h, either by solar or ultraviolet radiation. The best results of colour removal (93%) for the red and yellow dyestuffs were obtained only after 6 h, using quartz tubes, hydrogen peroxide and ultraviolet radiation. Using non-parametrical statistical tests (χ²), the treatment showed significant differences among the processes investigated (P<0.01).