PRESSURIZED ELECTROOSMOTIC DEWATERING IN A FILTER CYCLE

This paper describes the role of pressurized electroosmotic dewatering (EOD) in a filter cycle. A laboratory-scale filter-press was used to filter a highly conductive silica suspension under constant pressure, followed by washing and mechanical precompression of the filter cake and finally by pressurized EOD at constant electric current. The influence of filter cycle parameters (filtration and washing pressure and duration, mechanical pressure, and electric field intensity) on the final cake dryness and energy consumption was studied. Electrodes of different materials, forms, and surfaces were used.

The optimal conditions of each filter cycle operation were found to minimize the energy consumption during EOD and maximize the cake dryness. With mechanical pressure and electric field intensity increasing, the total energy consumption increased, but the specific energy consumption (per kg of expressed water) decreased, and the final filter cake was dryer. The pressurized EOD also used less energy than thermal drying.     

Microporous membranes prepared from blends of polysulfone and sulfonated poly(2,6‐dimethyl‐1,4‐phenylene oxide)

Membranes were prepared from solutions containing Udel‐type polysulfone (PSf) and sulfonated poly(2,6‐dimethyl‐1,4‐phenylene oxide) (SPPO). Polymer solutions in 1‐methyl‐2‐pyrrolidone were cast on a nonwoven textile and precipitated in a water bath. The permeabilities and selectivities of the prepared membranes depended on the concentrations of both polymers in the casting solution. The higher the concentration of PSf, the lower were the permeabilities to water and average pore sizes of the membranes. On the other hand, a very small amount of SPPO in the casting solution (about 1–4 wt % relative to the casting solution weight) brought about a considerable increase in water permeabilities and had a small influence on the average pore sizes. The effects were most pronounced if SPPO with a degree of sulfonation of 20–40% was used. The considerable increase in water permeabilities was explained by separation of the PSf and SPPO phases during precipitation in water and by the concentration of hydrophilic SPPO on the surface of the membrane and its pores. The determinations of the oriented concentration potentials proved the presence of a negative surface charge in the membranes. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 134–142, 2001     

Detailed Structure–Function Correlations of Bacillus subtilis Acetolactate Synthase

Isobutanol is deemed to be a next‐generation biofuel and a renewable platform chemical. 1 Non‐natural biosynthetic pathways for isobutanol production have been implemented in cell‐based and in vitro systems with Bacillus subtilis acetolactate synthase (AlsS) as key biocatalyst. 2 – 6 AlsS catalyzes the condensation of two pyruvate molecules to acetolactate with thiamine diphosphate and Mg²⁺ as cofactors. AlsS also catalyzes the conversion of 2‐ketoisovalerate into isobutyraldehyde, the immediate precursor of isobutanol. Our phylogenetic analysis suggests that the ALS enzyme family forms a distinct subgroup of ThDP‐dependent enzymes. To unravel catalytically relevant structure‐function relationships, we solved the AlsS crystal structure at 2.3 Å in the presence of ThDP, Mg²⁺ and in a transition state with a 2‐lactyl moiety bound to ThDP. We supplemented our structural data by point mutations in the active site to identify catalytically important residues.     

Synthesis and Analysis of Specific Covalent Inhibitors of endo‐Xyloglucanases

A series of N‐bromoacetylglycosylamines and bromoketone C‐glycosides were synthesised from complex xyloglucan oligosaccharide (XyGO) scaffolds as specific active‐site affinity labels for endo‐xyloglucanases. Compounds based on XXXG (Xyl₃Glc₄) and XLLG (Xyl₃Glc₄Gal₂) oligosaccharides exhibited strikingly higher affinities and higher rates of irreversible inhibition than known cellobiosyl and new lactosyl disaccharide congeners when tested with endo‐xyloglucanases from two distinct glycoside hydrolase (GH) families. Intact‐protein mass spectrometry indicated that inactivation with XyGO derivatives generally resulted in a 1:1 labelling stoichiometry. Together, these results indicate that XyGO‐based affinity reagents have significant potential as inhibitors and proteomic reagents for the identification and analysis of diverse xyloglucan‐active enzymes in nature, to facilitate industrial enzyme applications.     

Aggregation‐Prone Amyloid‐β⋅CuII Species Formed on the Millisecond Timescale under Mildly Acidic Conditions

Metal ions and their interaction with the amyloid beta (Aβ) peptide might be key elements in the development of Alzheimer's disease. In this work the effect of Cu^II on the aggregation of Aβ is explored on a timescale from milliseconds to days, both at physiological pH and under mildly acidic conditions, by using stopped‐flow kinetic measurements (fluorescence and light‐scattering), ¹H NMR relaxation and ThT fluorescence. A minimal reaction model that relates the initial Cu^II binding and Aβ folding with downstream aggregation is presented. We demonstrate that a highly aggregation prone Aβ ? Cu^II species is formed on the sub‐second timescale at mildly acidic pH. This observation might be central to the molecular origin of the known detrimental effect of acidosis in Alzheimer's disease.     

Deoxycholate‐Based Glycosides (DCGs) for Membrane Protein Stabilisation

Detergents are an absolute requirement for studying the structure of membrane proteins. However, many conventional detergents fail to stabilise denaturation‐sensitive membrane proteins, such as eukaryotic proteins and membrane protein complexes. New amphipathic agents with enhanced efficacy in stabilising membrane proteins will be helpful in overcoming the barriers to studying membrane protein structures. We have prepared a number of deoxycholate‐based amphiphiles with carbohydrate head groups, designated deoxycholate‐based glycosides (DCGs). These DCGs are the hydrophilic variants of previously reported deoxycholate‐based N‐oxides (DCAOs). Membrane proteins in these agents, particularly the branched diglucoside‐bearing amphiphiles DCG‐1 and DCG‐2, displayed favourable behaviour compared to previously reported parent compounds (DCAOs) and conventional detergents (LDAO and DDM). Given their excellent properties, these agents should have significant potential for membrane protein studies.     

The Phosphoinositide 3‐Kinase Signaling Pathway is Involved in the Control of Modified Low‐Density Lipoprotein Uptake by Human Macrophages

The transformation of macrophages into lipid‐loaded foam cells is a critical early event in the pathogenesis of atherosclerosis. Both receptor‐mediated uptake of modified LDL, mediated primarily by scavenger receptors‐A (SR‐A) and CD36 along with other proteins such as lipoprotein lipase (LPL), and macropinocytosis contribute to macrophage foam cell formation. The signaling pathways that are involved in the control of foam cell formation are not fully understood. In this study, we have investigated the role of phosphoinositide 3‐kinase (PI3K) in relation to foam cell formation in human macrophages. The pan PI3K inhibitor LY294002 attenuated the uptake of modified LDL and macropinocytosis, as measured by Lucifer Yellow uptake, by human macrophages. In addition, the expression of SR‐A, CD36 and LPL was attenuated by LY294002. The use of isoform‐selective PI3K inhibitors showed that PI3K‐β, ‐γ and ‐δ were all required for the expression of SR‐A and CD36 whereas only PI3K‐γ was necessary in the case of LPL. These studies reveal a pivotal role of PI3K in the control of macrophage foam cell formation and provide further evidence for their potential as therapeutic target against atherosclerosis.     

Phase Stability and Optoelectronic Properties of the Bixbyite Phase in the Gallium–Indium–Tin–Oxide System

X‐ray diffraction techniques were used to determine the phase boundaries of the In₂O₃ solid solution phase in the Ga₂O₃–In₂O₃–SnO₂ ternary system. The effects of Ga and Sn content on the unit cell dimensions of the bixbyite phase were calculated by a linear regression fit, the results of which indicate the two substitutive cations have opposite and independent effects on the lattice parameter. These results suggest that the cations do not strongly interact with each other in the crystal. Measurements of optoelectronic properties were also taken on single‐phase bulk specimens within the solid solution to establish their dependence on composition. As anticipated, Sn doping yields corresponding increases in conductivity, reduction in the absolute value of Seebeck coefficient, and increase in optical band gap. In contrast, these properties are not significantly affected by varying Ga content, confirming that Ga behaves as an isovalent dopant at the low doping levels involved.     

Confirmation of the Dominant Defect Mechanism in Amorphous In–Zn–O Through the Application of In Situ Brouwer Analysis

The dominant point defect mechanism of amorphous (a‐) indium zinc oxide (IZO) was probed through in situ electrical characterization of sputtered a‐IZO thin films in response to changes in oxygen partial pressure (pO) at 300C. The results yielded a power law dependence of conductivity (σ) versus pO of ～?1/6. This experimental method, known as Brouwer analysis, confirms doubly‐charged oxygen vacancies as the dominant defect species in a‐IZO. The success of this study suggests that Brouwer analysis is a viable method for studying the defect mechanisms of amorphous oxides.     

Planar,Polysilazane‐Derived Porous Ceramic Supports for Membrane and Catalysis Applications

Porous, silicon carbonitride‐based ceramic support structures for potential membrane and catalysis applications were generated from a preceramic polysilazane precursor in combination with spherical, ultrahigh‐molecular weight polyethylene microparticles through a sacrificial filler approach. A screening evaluation was used for the determination of the impact of both porogen content and porogen size on pore structure, strength, and permeability characteristics of planar specimens. By optimizing both the composition as well as cross‐linking parameters, maximum characteristic biaxial flexural strengths of 65 MPa and porosities of 42% were achieved. The evolution of an interconnected, open‐pore network during thermal porogen removal and conversion of the preceramic polymer led to air permeabilities in the order of 10^?14 m². The materials were further exposed to long‐term heat treatments to demonstrate the stability of properties after 100 h at 800°C in oxidizing, inert, and reducing environments. The determined performance, in combination with the versatile preparation method, illustrates the feasibility of this processing approach for the generation of porous ceramic support structures for applications at elevated temperatures in a variety of fields, including membrane and catalysis science.