Engineering of a metal coordinating site into human glutathione transferase M1-1 based on immobilized metal ion affinity chromatography of homologous rat enzymes

Rat glutathione transferase (GST) 3-3 binds to Ni(II)-iminodiaceticacid (IDA)-agarose, whereas other GSTs that are abundant inrat liver do not bind to this immobilized metal ion affinitychromatography (IMAC) adsorbent Rat GST 3-3 contains two superficiallylocated amino acid residues, His84 and His85, that are suitablypositioned for coordination to Ni(II)-IDA-agarose. This particularstructural motif is lacking in GSTs that do not bind to theIMAC matrix. Creation of an equivalent His-His structure inthe homologous human GST M1-1 by protein engineering affordeda mutant enzyme that displays affinity for Ni(II)-IDA-agarose,in contrast to the wild-type GST M1-1. The results identifya distinct site that is operational in IMAC and suggest an approachto the rational design of novel integral metal coordinationsites in proteins.     

Gas permeation of polymer blends. I. PVC/ethylene–vinyl acetate copolymer (EVA)

The transport behavior of O₂ and N₂ were studied for series of physical blends of PVC with EVA having different vinyl acetate (VAc) contents in the EVA (45 and 65 wt-%) and using different milling temperatures (160° and 185°C). The polymer blends were further characterized by dynamic mechanical measurements, density measurements, and x-ray diffraction. At higher VAc content in EVA and with higher milling temperature, the rate of permeation (P) and the rate of diffusion (D) decrease, and the activation energy of D (from Arrhenius plots) increases. Furthermore, the experimental density values of PVC/EVA-45 blends agree well with calculated values, assuming volume additivity of the two components, while those of PVC/EVA-65 blends are higher than the calculated densities. These results are interpreted as due to denser packing of polymer molecules and increased PVC-EVA interaction at higher VAc content and with higher milling temperature, indicating better compatibility between the blend components. The x-ray diffraction data give no evidence of crystallinity. Sharp increases in P and D values at about 7.5% EVA (by weight) are found for PVC/EVA-45 blends (in agreement with our previous work) but not for PVC/EVA-65 blends. This is interpreted as due to a phase inversion at increasing EVA content in the former blends but not in the latter blends. The dynamic mechanical measurements show that the PVC/EVA-65 blends milled at 160°C behave largely as semicompatible systems with maximum interaction between the two polymers at compositions of about 50/50 by weight.     

Photoinitiated surface grafting of synthetic fibers,III. Photoinitiated surface grafting of poly(ethylene terephthalate) fibers

Photoinitiated surface grafting of acrylic acid (AA), acrylamide (AM) and 4-vinyl pyridine (VP) onto poly(ethylene terephthalate) (PET) fibers (a commercial textile yarn) has been studied using benzophenone (BP) as photoinitiator. A continuous process as previously described has been applied, which involves presoaking of the PET yarn in a solution of initiator and monomer in acetone and UV irradiation in nitrogen atmosphere. The resulting grafted polymer on the fiber surface has been analyzed by ESCA, titration of carboxy groups (grafted AA), and dye absorption. The relative ESCA intensities (RI) of O1s/C1s and N1s/C1s are used as measure for grafted AA, AM and VP, respectively, after recording the RI-values for ungrafted fibers. For grafting with AA, the RI-values increased from 32.8% (background) to 48.6% after 20 s irradiation time. The amount of carboxy groups measured by titration increased from 0.045 to 0.106 mmol/m². Assuming an even coverage of grafted AA polymer, this means a grafted layer of 4.8 nm thickness. After grafting, the adsorption of the dye Crystal Violet (CV) from aqueous solution increased by about 3 times. With AM as monomer, the RI-values increased from 2.6 (background) to 14.8% and the adsorption of a direct dye Sirius Lichtbordo B-LL increased by about 6 times. With VP as grafted monomer, the RI-values increased from about 2.6 (background) to 5.1% and the adsorption of the direct dye increased by about 4 times.     

Multiple steady states in ideal two-product distillation

Simple distillation columns with ideal vapor-liquid equilibrium may display multiple steady-state solutions. Two fundamentally different sources for the multiplicity are presented. Both bring about the unexpected result that increasing reflux makes separation worse in the top part of the column. It corresponds to an unstable operating point. The first type of multiplicity is found for columns with mass or volume inputs (e.g., mass reflux and molar boilup). Even for constant molar flows, the transformation from the actual input units to molar units may become singular (corresponding to a pitchfork bifurcation point), resulting in multiple steady-state solutions. The results are highly relevant in practice, as industrial columns usually have inputs on a mass or volume basis. The second type for specifications on a molar basis (e.g., molar reflux and molar boilup) depends on the presence of an energy balance in the model. The multiplicity is caused by interactions between flows and compositions in the column.     

Film extrusion and film weldability of poly(lactic acid) plasticized with triacetine and tributyl citrate

Film extrusion and welding of biodegradable polymer films are important processes that must be considered in the development of compostable packaging materials. Film extrusion of poly(lactic acid) (PLA) has proved to be rather difficult because of its brittleness, but the flexibility of PLA can be improved by incorporation of a plasticizer in the material. PLA was plasticized with triacetine (TAc) and tributyl citrate (TbC). The blended materials and neat PLA were film extruded and the films were welded with constant heat (CH) welding. The films were analyzed by means of gas chromatography (GC), dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), gel permeation chromatography (GPC), contact angle measurements, and tensile testing. Storage of the plasticized films resulted in an increased crystallinity and changes in the film properties, rendering CH welding difficult. The welding process had no influence on thermal properties, such as cold crystallization temperature, melting temperature, crystallization temperature, and degree of crystallinity, of neat PLA but caused significant changes in the crystallinity of the plasticized materials. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 3239–3247, 2003     

How reasonable are oil production scenarios from public agencies?

According to the long-term scenarios of the International Energy Agency (IEA) and the US Energy Information Administration (EIA), conventional oil production is expected to grow until at least 2030. EIA has published results from a resource-constrained production model which ostensibly supports such a scenario. The model is here described and analyzed in detail. However, it is shown that the model, although sound in principle, has been misapplied due to a confusion of resource categories. A correction of this methodological error reveals that EIA's scenario requires rather extreme and implausible assumptions regarding future global decline rates. This result puts into question the basis for the conclusion that global “peak oil” would not occur before 2030.     

Degradation of low‐density polyethylene during extrusion. VI. Effects of oxygen content in air gap

In our previous papers polyethylene degradation during extrusion coating has been studied and the type of degradation products that are formed and from which step they originate have been discussed. A trained sensory panel has rated the off‐flavor intensities in water samples that have been in contact with various extruded films. Encouraged by the results from these investigations and the documented synergism between aldehydes and ketones and aldehydes and carboxylic acids in off‐flavor intensity, the present study was aimed at confirming the belief that the off‐flavor depends on the presence of oxidative degradation products that have migrated from the film into the water. By decreasing the oxygen concentration in the atmosphere surrounding the extruded melt presence of the highly oxidized species (i.e., carbonyl compounds and carboxylic acids) would decrease and thus the off‐flavor in the water should decline. From this study it could be concluded that the extrusion temperature and the oxygen content in the atmosphere nearest the molten film before quenching are the most important parameters for oxidative degradation and residence time in the air gap influence the amount of oxidative degradation products formed. Furthermore we concluded that the off‐flavor intensity is strongly correlated to the surface oxidation index of the film. Carboxylic acids are present in the water extracts of extruded films and are related to the off‐flavor intensities. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1767–1775, 2005     

An efficient method for smart well production optimisation

A method for dynamic optimisation of water flooding with smart wells is presented. The method finds the optimal injection and production rates for every well segment of the smart wells. We formulate the problem as a constrained optimisation problem and state this problem as an augmented Lagrangian saddle point problem. Comparisons are made with a more traditional optimal control method based on solving the adjoint systems of equations. In the examples tested the method obtains same maximum profit while using less computational effort.