Oxidative degradation of polyamide reverse osmosis membranes: Studies of molecular model compounds and selected membranes

Selected aromatic amides were used to model the chemical reactivity of aromatic polyamides found in thin‐film composite reverse osmosis (RO) membranes. Chlorination and possible amide bond cleavage of aromatic amides upon exposure to aqueous chlorine, which can lead to membrane failure, were investigated. Correlations are made of the available chlorine concentration, pH, and exposure time with chemical changes in the model compounds. From the observed reactivity trends, insights are obtained into the mechanism of RO membrane performance loss upon chlorine exposure. Two chemical pathways for degradation are shown, one at constant pH and another that is pH‐history dependent. An alternative strategy is presented for the design of chlorine‐resistant RO membranes, and an initial performance study of RO membranes incorporating this strategy is reported. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1173–1184, 2003     

Effect of the OH Radical Scavenger Hydrogen Peroxide on Secondary Organic Aerosol Formation from α-Pinene Ozonolysis

Hydrogen peroxide (HOOH) is a potentially valuable hydroxyl radical (OH) scavenger in secondary organic aerosol experiments focused on ozonolysis yields. Here, we present results for α-pinene ozonolysis. The OH scavenging produces solely HO₂ radicals and the resulting high [HO₂]/[RO₂] ratio causes an increase in aerosol formation from α-pinene ozonolysis, compared to experiments performed with butanol OH scavengers. The majority of the increase comes in the 100 μg m^?3 volatility range, suggesting that instead of more volatile products formed under higher RO₂ conditions, less volatile, multifunctional hydroperoxides form under the high-HO₂ conditions here. This dependence on the [HO₂]/[RO₂] ratio can be parameterized in a similar fashion to the way high- and low-NO _x yields are currently treated in models.     

SMALL-SCALE RECOVERY AND SEPARATION OF ACTINIDES USING TRI-n-BUTYL PHOSPHATE EXTRACTION CHROMATOGRAPHY

The small-scale recovery and separation of the actinides U, Np, Pu and Am using the commercial product, Lewatit OC 1023. has been studied. Conditions under which these actinides may be extracted or eluted and methods for separation of any combination of these elements are presented. A separation scheme for all four actinides achieved complete separation of Np from U and Am from Pu and U. Good separation of U, Np and Pu was achieved. Quantitative separation is possible by repeating the procedure.

Since Np and Am follow one another in the above scheme, a further procedure for their quantitative separation is presented.

Reductants investigated for separation of Pu from U were ferrous sulfamate and hydroxylamraonium nitrate. The latter is only effective if small amounts of U are present.

The behaviour of Ru and Zr under the conditions for the separation of U, Np, Pu and Am was also investigated The behaviour of these two troublesome elements was shown to be similar to that in the purex process.     

High internal phase emulsion templating as a route to well-defined porous polymers

The use of high internal phase emulsions (HIPEs) as templates to create highly porous materials (PolyHIPEs) is described. Polymerisation occurs around emulsion droplets, which create voids in the final material. The void fraction is very high and can reach levels of 0.99. Varying the emulsion composition can control features of the morphology of the resulting porous materials, such as the void diameter and degree of interconnection. Other parameters can also be varied, for example surface area can be increased from 3 to around 700 m² g⁻¹. Rubbery materials can be produced from hydrophobic elsatomers and PolyHIPEs with high thermo-oxidative stability are prepared from high performance materials such as poly(ether sulfone). The highly porous materials so produced are finding applications in areas such as solid supported organic chemistry, sensors, cell culturing and tissue engineering.     

Stereological estimation of the total volume of MR visible brain lesions in patients with multiple sclerosis

Point counting represents a convenient and efficient technique for estimating the area of transects through multiple sclerosis (MS) lesions on magnetic resonance (MR) images obtained for sections through the brain. When sectioning has been performed according to the Cavalieri method, unbiased estimates of the total volume of MR-visible MS plaques can be obtained with a precision of 3–5% in 5–10 min.     

Effect of Temperatures up to 90°C on the Early Hydration of Portland–Blastfurnace Slag Cements

Isothermal conduction calorimetry has been used to monitor the early hydration of Portland–blastfurnace slag (BFS)-blended cements. Portland:BFS composite cements with ordinary Portland cement replacements from 0 to 90 wt% were studied at curing temperatures from 12° to 90°C. Peak II, principally associated with alite (Ca₃SiO₅) hydration, was accelerated with increasing temperature for all blends. Peak S, associated with BFS hydration, was particularly noticeable at 40° and 60°C. At higher curing temperatures, peak S merged with peak II, indicating thermal activation of BFS. Novel plots of total heat output against percentage replacement show that BFS contributes to the heat of hydration, even at temperatures below its thermal activation.     

Structure-function studies of an engineered scaffold protein derived from Stefin A. II: Development and applications of the SQT variant

Constrained binding peptides (peptide aptamers) may serve as tools to explore protein conformations and disrupt protein-protein interactions. The quality of the protein scaffold, by which the binding peptide is constrained and presented, is of crucial importance. SQT (Stefin A Quadruple Mutant-Tracy) is our most recent development in the Stefin A-derived scaffold series. Stefin A naturally uses three surfaces to interact with its targets. SQT tolerates peptide insertions at all three positions. Peptide aptamers in the SQT scaffold can be expressed in bacterial, yeast and human cells, and displayed as a fusion to truncated pIII on phage. Peptides that bind to CDK2 can show improved binding in protein microarrays when presented by the SQT scaffold. Yeast two-hybrid libraries have been screened for binders to the POZ domain of BCL-6 and to a peptide derived from PBP2', specific to methicillin-resistant Staphylococcus aureus. Presentation of the Noxa BH3 helix by SQT allows specific interaction with Mcl-1 in human cells. Together, our results show that Stefin A-derived scaffolds, including SQT, can be used for a variety of applications in cellular and molecular biology. We will henceforth refer to Stefin A-derived engineered proteins as Scannins.     

The use of transmission electron microscopy tomography to correlate copper catalyst particle morphology with carbon fiber morphology

In this study carbon fibers of various morphologies have been synthesized by the decomposition of acetylene over copper supported catalysts (Cu(NO₃)₂/TiO₂, at 250 °C). In order to investigate the relationship between the morphologies of the copper catalyst particle and that of the carbon fiber extruded, tilting procedures (±60 A axis and ±30 B axis) under TEM (120 kV) were performed. In this way a 3-D (rather than a 2-D) image of the Cu crystallites were obtained which permitted for the 3-D shape of the Cu catalyst particle to be linked to the morphology of the extruded carbon fiber. Whereby copper particles that give distorted decahedra are apt to form helical fibers, trigonal bi-pyramidal particles give linear fibers. Various plate-like particles were also investigated, and it was observed that as the number of sides varied (3, 4, 5 or 6) there was a corresponding change in the carbon fiber helicity. Herein we report on our findings that reveal the geometric structures involved in controlling the shape of morphologically diverse carbon coils, illustrating the influential role catalyst particle shape plays in carbon fiber synthesis.     

Hairpencil Volatiles Influence Interspecific Courtship and Mating Between Two Related Moth Species

Reproductive isolation between sympatric, closely related species can be accomplished through a variety of pre-zygotic isolating mechanisms, including courtship-signaling behavior that involves pheromones. In the moths Heliothis virescens and H. subflexa, males display abdominal hairpencils (HP), which release volatile chemicals during courtship. In this study, we demonstrated that HP volatiles released by male H. subflexa function to improve mating success with conspecific females. Interspecific mating experiments were conducted to determine any influence of HP volatiles on species isolation. Female H. virescens and H. subflexa were observed during courtship with males of the other species, following either sham-operation or ablation of HPs, both with and without concurrent presentation of HP volatiles. Mating success was improved by co-presentation of HP extract from males of the same species during courtship. Ablation of HPs improved mating between H. subflexa females and H. virescens males. During interspecific matings, male H. virescens attempted copulation less frequently in the presence of H. virescens HP extract, though H. subflexa males were not affected by the presence of H. subflexa HP extract. This suggests that HP volatiles produced by males of each species may inhibit mating between species through effects on males (H. virescens) and females (H. subflexa).     

A description of phase inversion behaviour in agitated liquid-liquid dispersions under the influence of the Marangoni effect

The influence of the Marangoni effect on phase inversion behaviour is examined by integrating a microscopic study of the drop coalescence process, in which thin film drainage in the presence of insoluble surfactant occurs, into a macroscopic phase inversion model which has been developed previously using a Monte Carlo technique. This is achieved via an immobility factor, obtained from a comparison of the film drainage times for surfactant-laden systems and surfactant-free systems as a function of the drop approach velocity, surface Péclet number, initial surfactant concentration and the Hamaker constant, which is then used to modify the coalescence probability in the phase inversion model. On the one hand, the results indicate that the Marangoni effect removes any influence that the viscosity ratio has on phase inversion due to immobilisation of the interface, thus shielding the flow in the film from the effects of the flow in the dispersed phase; the point at which phase inversion occurs therefore tends towards equivolume holdups with the addition of surfactant. On the other hand, when comparisons are made with pure systems in which surfactant is absent, the system is seen to be either stabilised or de-stabilised from inversion depending on the viscosity ratio of the system. This is attributed to the influence of surfactant on the dispersion morphologies on either side of the inversion (i.e. water-in-oil dispersions and oil-in-water dispersions) and depends on the dispersed phase holdup; the Marangoni effect is felt stronger when the dispersed phase holdup is low.