Generation of protein lineages with new sequence spaces by functional salvage screen

A variety of different methods to generate diverse proteins,including random mutagenesis and recombination, are currentlyavailable and most of them accumulate the mutations on the targetgene of a protein, whose sequence space remains unchanged. Onthe other hand, a pool of diverse genes, which is generatedby random insertions, deletions and exchange of the homologousdomains with different lengths in the target gene, would presentthe protein lineages resulting in new fitness landscapes. Herewe report a method to generate a pool of protein variants withdifferent sequence spaces by employing green fluorescent protein(GFP) as a model protein. This process, designated functionalsalvage screen (FSS), comprises the following procedures: adefective GFP template expressing no fluorescence is first constructedby genetically disrupting a predetermined region(s) of the proteinand a library of GFP variants is generated from the defectivetemplate by incorporating the randomly fragmented genomic DNAfrom Escherichia coli into the defined region(s) of the targetgene, followed by screening of the functionally salvaged, fluorescence-emittingGFPs. Two approaches, sequence-directed and PCR-coupled methods,were attempted to generate the library of GFP variants withnew sequences derived from the genomic segments of E.coli. Thefunctionally salvaged GFPs were selected and analyzed in termsof the sequence space and functional properties. The resultsdemonstrate that the functional salvage process not only canbe a simple and effective method to create protein lineageswith new sequence spaces, but also can be useful in elucidatingthe involvement of a specific region(s) or domain(s) in thestructure and function of protein.     

Synthesis of the [Ga]-MFI under atmospheric pressure

The crystallization of the [Ga]-MFI was investigated as a function of synthesis time under atmospheric pressure. The molar composition of the reactants was 100SiO₂-Ga₂O₃-llNa₂O-llTPABr-3500H₂O. The crystallinity of the [Ga]-MFT was examined by using several analytical instruments, such as XRD, XPS, XRF, FT-IR, solid-statemas-NMR, DTG/DTA, and SEM. The [Ga]-MFI was successfully synthesized under atmospheric pressure at 97 ‡C in 72 h. It was found that the nucleation of the [Ga]-MFI took a quite long time, but the crystallization took place very fast. It is supposed that nucleation is the rate-controlling step in the [Ga]-MFI synthesis under atmospheric pressure. Consequently, if the induction period of the nucleation can be shortened, it would be possible to synthesize the [Ga]-MFI commercially under atmospheric pressure.     

Electrorheological responses of particulate suspensions and emulsions in a small-strain dynamic shear flow: Viscoelasticity and yielding phenomena

The dynamic rheological behavior of multiphase electrorheological (ER) fluids was considered, as continuation of a previous paper [Chin and Park, 2000]. Oil-in-oil emulsions, which differ in electrical conductivity and dielectric constant, were employed for an ER-active emulsion and also for a multiphase ER fluid with enhanced performance. The polyaniline particle suspension in an electric field showed viscoelastic behavior within a very limited range of strain amplitude, indicating the transition from viscoelasticity to viscoplasticity. Within the region of visco-elasticity, the linear region was restricted below the amplitude of 0.1%, whereas the ER-active emulsions showed a rather wide linear regime. Frequency dependence of the storage shear modulus in the linear viscoelastic region revealed the typical features of an elastic solid. When the fraction of emulsion drops (Ф) in multiphase ER fluids increased, the limiting strain for viscoelasticity showed a higher value.     

Superstructure of yOTs-the network-based chemical process operator training system for multiple trainees

OTS (Operator Training System) is becoming popular for the safe and effective operation of chemical processes and control systems. This paper outlines the total hardware system superstructure and software modules of yOTS (Yonsei Operator Training System) which we developed. yOTS is a network based multi-training system composed of a workstation-based server module and PC-based user modules. The user module has a DCS-like user interface and sends data to OM (yOTS Manager) over the network. Reliability and stability are essential for the successful development of distributed OTS.State-of-the-art technologies of efficiency and stability are mainly considered in this paper. yOTS is superior to other OTS in its ease of handling discrete events, managing process models, expanding module functionality and multi-training over the network. The structure of yOTS and core algorithm for a multiple trainer over the network is also presented. A batch process example is used to illustrate the proposed advantages of yOTS.     

Effect of Silica Surface Dopants on the Formation of Alumina/Aluminum Composites by the Directed Metal Oxidation of an Aluminum Alloy

This study focused on clarifying the effect of SiO₂ surface dopants on the formation of Al₂O₃/aluminum composites, especially on oxidation phenomena during the incubation period. The present results showed that a surface dopant decreased the incubation period of an Al-Mg-Si alloy, as well as that of an Al-Mg alloy, and that addition of an external surface dopant decreased the incubation period more effectively than did an internal alloying of silicon. A two-step oxidation process was also conducted. In the first step of the process, an aluminum alloy was oxidized without a surface dopant and cooled to room temperature during the incubation stage. In the second step, the same specimen was surface-doped with SiO₂ powder and reoxidized. The incubation time for the specimen subjected to the two-step oxidation process was the same as that for the single-step specimen oxidized with a surface dopant. The substantial decrease in the incubation period, especially for the Al-Mg alloy, is ascribed to interaction between the SiO₂ surface dopant and the MgO layer. This interaction made the MgO layer thinner and increased the number of magnesium vacancies in the MgO layer, thus providing an appropriate microstructure in the MgO layer for bulk-growth initiation.     

Enthalpies of Chromium Oxide Solution in Soda Lime Borosilicate Glass Systems

Chromium oxide (Cr₂O₃) solubility was measured in soda lime borosilicate glass from 1400 to 1500 K. The temperature dependence of the solubility increased with increased sodium oxide concentration. The enthalpies of solution for the equilibrium phases were calculated from the solubility data in the temperature range from 1400 to 1500 K. The enthalpy of fusion for Cr₂O₃ at 1450 K was calculated to be 108.0 kJ·mol⁻¹. This value was less than our measured values for enthalpy of solution, 111.0 ± 0.5 and 158.4 ± 0.3 kJ·mol⁻¹, indicating that all enthalpies of mixing were positive; that is, the mixing process was endothermic. This characterized the interaction between solute and solvent as repulsive.     

Effect of Coarse-Powder Portion on Abnormal Grain Growth during Hot Pressing of Commercial-Purity Alumina Powder

By classification, two powder portions, one consisting of coarse particles and the other consisting of fine particles, were separated from a MgO-doped (1000 ppm) commercial-purity Al₂O₃ powder. Examinations of microstructure evolution during hot pressing showed that extensive abnormal grain growth occurred for the coarse portion. For the fine portion, although there was an indication that grain-size distribution deviated from normal distribution on prolonged hot pressing, such extensive abnormal grain growth did not occur. Extensive abnormal grain growth also occurred when the coarse portion was mixed into a high-purity powder that exhibited no abnormal grain growth alone. Chemical analyses revealed that the coarse portion contained the higher concentration of impurities but lower concentration of magnesium than the fine portion. It was discussed that particle aggregates in the coarse portion might have been responsible for the higher concentration of impurities but lower concentration of magnesium and, thus, for the extensive abnormal grain growth.     

Author Index

Authors Index

Author Index     

Microstructure and rheological behavior of block copolymer/clay nanocomposites

Organic/Inorganic hybrid nanocomposites based on poly(styrene-butadiene-styrene) copolymer (SBS) and clay are fabricated by melt intercalation. The degree of intercalation is dependent on the surface properties of clay and SBS. The epoxized block in epoxized SBS acts as a strong attractive site with the clay surface, which yields the increased interlayer space in the layered silicates. It is also shown that the thermal stability of clay as well as the surface properties is very important in fabricating the polymer/clay nanocomposites. The rheological behavior of the SBS/clay nanocomposites is quite different from that of SBS itself. Both storage moduli and complex viscosity of the SBS/layered silicate nanocomposites increase and show non-terminal flow behavior.     

Benzene Alkylation with 1-Dodecene over H-Mordenite Zeolite

The alkylation of benzene with 1-dodecene was studied over solid-acid zeolites, such as H-mordenite, H-USY, HY, and H-ZSM-5, in a batch reactor at 140°C and 10 atm. H-mordenite showed the highest selectivity of 78.2% for 2-phenyldodecane with 100% conversion. Depending on the catalyst amount (from 0.5 to 1.0 g) and the molar ratio of benzene to 1-dodecene (from 7 to 10), the conversion of 1-dodecene varied in the range from 63.8 to 100%. Furthermore, modification of H-mordenite by dealumination using nitric acid and by solid ion exchange with Mg²⁺ and Fe³⁺ ions led to the improvement of the selectivity for 2-phenyldodecane, and simultaneously reduction of the conversion of 1-dodecene is observed. In addition, it was found by pyridine adsorption FT-IR study that both strong Brønsted and Lewis acid sites are closely related to the conversion.