• The Korean Journal of Food And Nutrition
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• v.9 no.4
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• pp.452-458
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• 1996

A PPIase gene of Bacillus stearothermophilus was screened from a genomic library by plaque hybridization using the A-1 primer as a probe. A PPIase positive plaque contained a 3.0kb insert of the chromosomal DNA. A 3.0kb fragment was subcloned into pUC18, resulting pPI1-40. A DNA fragment encoding the N-terminal portion of the PPIase in pPi-40 was amplified by polymerase chain reaction(PCR) method using the A-1 and B-2 primers. The amplified fragment was cloned into the Sma I site of pUC18 and recombinant plasmid was designated as pSN-18. The nucleotide sequence of 167bp fragment was determined. The deduced amino acid sequence of PPIase was completely matched with the determined N-terminal amino acid sequence of PPIase B. stearothermophilus. The translated protein sequence of PPIase B. stearothermophilus was compared with sequence from periplasmic PPIase from Escherichina coil ; homogies of 16 and 58%, respectively, were found. The clond PPIase gene was over-expressed in E. coil cell using pUC19 as an expression vector. The enzyme was partially purified by heat treatment and colum chromatochraphy on DEAE-Sepharose CL-6B. The molecular weight of the enzyme was dermined to be about 18.0 kDal by SDS-PAGE.

• Applied Chemistry for Engineering
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• v.9 no.4
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• pp.579-584
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• 1998

Polymer dispersed liquid crystal(PDLC) composite films were made by polymerization induced phase separation method using UV-curing to investigate the effect of fabrication conditions, such as photoinitiator concentration, film thickness, polymerization temperature, and electric field during polymerization, etc., on the electro-optic properties. As the amount of photoinitiator increased, the driving voltage of PDLC device increased due to the increase of small-size liquid crystal phases. This was considered as the results from the increased interfacial area between liquid crystal (LC) and polymer matrix, since LC molecules at the interfacial regions were relatively difficult to response for the applied electric field. When the higher molecular weight oligomer (PTDA-1000) was used as matrix, the initial transmittance was observed to be relatively higher than that for the lower molecular weight oligomer (PTDA-250). Saturation transmittance for PTDA-1000 was observed at relatively lower voltage than that for PTDA-250, of which transmittance was not saturated even at 60 V. As polymerization temperature increased, the initial transmittance of resulting PDLC film increased due to the larger LC droplets formation and the more matched refractive index between LC and matrix than those cases for the lower polymerization temperature. Though driving voltage decreased for the thinner film, it was considered that optimum thickness of the film should be maintained to get some practical contrast, which is the ratio of off- and on-state transmittance. Furthermore, electro-optic properties such as initial transmittance, driving voltage, and response time were observed to be considerably affected by application of external field during polymerization.