Alanine : glyoxylate aminotransferase of Saccharomyces cerevisiae-encoding gene AGX1 and metabolic significance

Alanine : glyoxylate aminotransferase is one of three different enzymes used for glycine synthesis in Saccharomyces cerevisiae. The open reading frame YFL030w (named AGX1 in the following), encoding this enzyme, was identified by comparing enzyme specific activities in knockout strains. While 100% activity was detectable in the parental strain, 2% was found in a YFL030w::kanMX4 strain. The ORF found at that locus was suspected to encode alanine : glyoxylate aminotransferase because its predicted amino acid sequence showed 23% identity to the human homologue. Since the YFL030w::kanMX4 strain showed no glycine auxtrophic phenotype, AGX1 was replaced by KanMX4 in a Delta GLY1 Delta SHM1 Delta SHM2 background. These background mutations, which cause inactivation of threonine aldolase, mitochondrial and cytosolic serine hydroxymethyltransferase, respectively, lead to a conditional glycine auxotrophy. This means that growth is not possible on glucose but on ethanol as the sole carbon source. Additional disruption of AGX1 revealed a complete glycine auxotrophy. Complementation was observed by transformation with a plasmid-encoded AGX1.     

Improving surface meshing from discrete data by feature recognition

In this paper, we propose a method to identify, on a mesh, geometric primitives commonly used in mechanical parts (plane, sphere, cylinder, torus, cone) in order to improve the quality of the surface remeshing. We have already presented techniques to adapt an existing surface mesh based on a mesh-free technique denoted as diffuse interpolation. In this approach, a secondary local geometrical model is built from the mesh. From this model, principal curvatures are calculated and the type of surface can be determined from the computation of the curvatures. Some of the concepts presented here are original while others have been adapted from techniques used in reverse engineering. Our approach is not limited to feature recognition on meshes but has been extended to a set of points.     

Improvement of the catalytic isomerization performance for sulfated zirconias by use of templating techniques

New sulfated zirconias covering a wide range of pore diameters from micropores to macropores have been prepared by a combined use of two different structure-directing templates. The catalytic performance of these sulfated zirconias for the n-butane isomerization could be improved significantly compared to a standard displaying a maximum rate of isomerization of 1490 μmol/g h at 423 K. The materials remained their high activity even at 348 K. Moreover, deactivated materials could be reactivated to the original activity in an air-flow at 673 K several times. The newly designed materials were fully characterized by XRD, XPS, TPD of ammonia, IR spectroscopy and N₂ adsorption to describe the formation of active surface centres and their morphology. The formation of active pyrosulfates with sulfate bands above 1400 cm^?1 was followed by DRIFTS. An increased ratio of Brønsted-to-Lewis centres could be detected which can be accounted for the unexpected high activity.     

Polymerization in magnetic field: XVIII. Influence of surfactant nature on the synthesis and thermal properties of poly(methyl methacrylate) and poly[(methyl methacrylate)‐co‐(epoxypropyl methacrylate)]

BACKGROUND: The possibility to use β‐cyclodextrin as biodegradable tensioactive and an electromagnetic field in order to improve the kinetic parameters of radical emulsion polymerization is of interest. Thus, the influence of different surfactants—sodium lauryl sulfate (SLS) and β‐cyclodextrin (CD)—on the pathway of emulsion polymerization of methyl methacrylate (MMA) and emulsion copolymerization of MMA with 2,3‐epoxypropyl methacrylate (GMA) performed with or without the presence of a continuous electromagnetic field (MF) was studied. RESULTS: The presence of the MF leads to a considerable increase of the conversion during the first part of the reaction if the classic surfactant (SLS) is used. The reactions performed without MF and with CD exhibit a decrease of the conversion and of the polymerization rate as compared with the variants using SLS. The swelling rate and the maximum degree of swelling vary with the surfactant nature and with the reaction conditions and MF presence. Data from thermogravimetry and differential scanning calorimetry evidence the dependences between the polymer characteristics and the preparation conditions. CONCLUSION: This research underlines the coupling possibilities of the influence of a MF—growth of the reaction rate and conversion explained through radical pairs mechanism—with a combination of the ‘cage’ effect and ‘conformational control’ afforded by CD. The presence of MF and CD during the syntheses leads to an increase of T_g and an increase of PMMA and P(MMA‐co‐GMA) thermal stability. Copyright © 2007 Society of Chemical Industry     

Preparation and Reinforcement of Dual‐Porous Biocompatible Cellulose Scaffolds for Tissue Engineering

Biocompatible cellulose‐based aerogels composed of nanoporous struts, which embed interconnected voids of controlled micron‐size, have been prepared employing temporary templates of fused porogens, reinforcement by interpenetrating PMMA networks and supercritical carbon dioxide drying. Different combinations of cellulose solvent (Ca(SCN)₂/H₂O/LiCl or [EMIm][OAc]/DMSO) and anti‐solvent (EtOH), porogen type (paraffin wax or PMMA spheres) and porogen size (various fractions in the range of 100–500 μm) as well as intensity of PMMA reinforcement have been investigated to tailor the materials for cell scaffolding applications. All aerogels exhibited an open and dual porosity (micronporosity >100 μm and nanoporosity extending to the low micrometer range). Mechanical properties of the dual‐porous aerogels under compressive stress were considerably improved by introduction of interpenetrating PMMA networks. The effect of the reinforcing polymer on attachment, spreading, and proliferation of NIH 3T3 fibroblast cells, cultivated on selected dual‐porous aerogels to pre‐evaluate their biocompatibility was similarly positive.     

Co-pyrolysis of pine cone with synthetic polymers

Biomass from pine cone (Pinus pinea L.) was co-pyrolyzed with synthetic polymers (PE, PP and PS) in order to investigate the effect of biomass and plastic nature on the product yields and quality of pyrolysis oils and chars. The pyrolysis temperature was of 500 °C and it was selected based on results from thermogravimetric analysis of the studied samples. Co-pyrolysis products namely gases, aqueous and tar fraction coming from biomass, oils from synthetic polymers and residual char were collected and analyzed. Due to the synergistic effect in the pyrolysis of the biomass/polymer mixtures, higher amounts of liquid products were obtained compared to theoretical ones. To investigate the effect of biomass content on the co-pyrolysis, the co-pyrolysis of pure cellulose as model natural polymer for biomass with polymer mixture was also carried out. In the presence of cellulose, degradation reaction leading to more gas formation and less char yield was more advanced than in the case of co-pyrolysis with pine cone. Co-pyrolysis gave polar oxygenated compounds distributed between tar and aqueous phase and hydrocarbon oils with composition depending on the type of synthetic polyolefin. Co-pyrolysis chars had higher calorific values compared to pyrolysis of biomass alone.     

Supramolecular and nanochemistry

The following contributions describe various research activities of the Department of Chemistry, University of Basel in the area of nanochemistry and supramolecular chemistry.     

Chemical oxidation of residual carbon from ZnAl2O4 powders prepared by combustion synthesis

The removal of carbon residue from ZnAl₂O₄ nanopowders by annealing at 500–800 °C leads to a decrease of specific surface area from 228.1 m²/g to 47.6 m²/g. At the same time, the average crystallite size increased from 5.1 nm to 14.9 nm. In order to overcome these drawbacks, a new solution for removing the carbon residue has been suggested: chemical oxidation using hydrogen peroxide. In terms of carbon removal, a H₂O₂ treatment for 8 h at 107 °C proved to be equivalent to a heat treatment of 1 h at 600 °C. The benefits of chemical oxidation over thermal oxidation were obvious. The specific surface area was much larger (188.1 m²/g) in the case of the powder treated with H₂O₂. The average crystallite size (5.8 nm) of ZnAl₂O₄ powder treated with H₂O₂ was smaller than the crystallite size (8.2 nm) of the ZnAl₂O₄ powder annealed at 600 °C.     

Enhancement of β phase crystals formation with the use of nanofillers in PVDF films and fibres

Nanoclay and carbon nanotubes (CNT) have been in focus recently as means of enhancing β phase crystals formation in poly(vinylidene fluoride)(PVDF). Dominantly, the so-far work has been carried out on films/thin sheets filled with nanoclay. It has been found, mainly from combined XRD and DSC data, that nanoclay influences the PVDF structure, and particularly the β phase crystals formation is enhanced. Results published by various groups are in fairly good agreement. There are no results for nanoclay filled melt-spun PVDF fibres.The influence of CNT on PVDF structure has been less studied. XRD data indicating an enhancing role of multi-wall carbon nanotubes (MWNT) on β phase crystals formation in solution compounded PVDF films are available. Published results for MWNT/PVDF films are not in good agreement. The only study into single-wall carbon nanotube (SWNT)/PVDF has been made on electrospun nanofibres.We explore above findings towards melt-spun nanofilled PVDF fibres. We present new results obtained by us for melt-spun PVDF fibres containing non-functionalized and amino-functionalized double-wall carbon nanotubes (DWNT). The key finding is that amino-DWNT can influence the β to α polymorphic balance.