• Macromolecular Research
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• 제8권1호
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• pp.44-52
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• 2000

Styrenic macromonomers with/without a silyloxy-functional group were synthesizedvia chain-end functionalization using 4-vinylbenzyl chloride as a terminating agent insec-butyllithium-initiated polymerization of styrene. The yields were 92 mol% for the silyloxy group and 88 mol% for the styrenic unit. Crystalline polystyrene-g-amorphous polystyrenes were synthesized by (η$^{5}$ -indenyl)-trichlorotitanium ((Ind)TiCl$_3$)-catalyzed copolymerizations of the macromonomers with styrene in the presence of methyl-aluminoxane (MAO) in toluene at 4$0^{\circ}C$. The macromonomer having $\alpha$, $\alpha$'-bis (4-[tert-butyldimethylsilyl-oxy]phenyl) group was also utilized for the preparation of a precursor of hydroxyl-functionalized syndio-tactic polystyrene. The obtained polymers were characterized by a combination of$^1$H, $^{13}$ C NMR spectroscopic, size exclusion chromatographic, and differential scanning calorimetric analysis. The (Ind)TiCl$_3$-catalyzed copolymerization of styrene with the macromonomer carrying the silyloxy functional group was found to be an efficient method to modify syndiotactic polystyrene without a great loss of physica] property by controlling the feud ratio of the macromonomer.

• 대한화학회지
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• 제42권2호
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• pp.190-196
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• 1998

셀룰로스시료를 치환체로 만들지 않고 분자량 및 분자량분포를 결정하기 위한 새로운 시료처리 및 크기배제크로마토그래피방법을 확립하였다. 먼저 셀룰로스시료를 N-methylmorpholine N-oxide (NMMO)에 녹인 후 dimethyl sulfoxide (DMSO)에 희석함으로써 50/50(w) NMMO/DMSO에 녹은 약 0.1%의 시료용액을 만들었다. 컬럼으로는 글루코오스를 입힌 polydivinylbenzene 겔을 채운 크기배제크로마토그래피용 컬럼을 이용하였으며 용리액으로는 0.05M의 LiBr와 2.5%의 바탕용액을 포함하는 DMSO를 이용하였다.유속은 1 mL/min로 일정하게 유지하였고, DMSO의 점도를 낮추기 위해 컬럼을 포함하는 전체 시스템을 80$^{\circ}C$ 로 유지하였다. 0.05M의 LiBr를 가함으로써 SEC바탕선의 표류를 방지할 수 있었고 2.5%의 바탕용액을 가함으로써 시료와 컬럼충진물질 사이의 상호작용을 감소시키는 효과를 얻었다. 좁은 분포를 가지는 pullulan표준물질로부터 얻은 컬럼보정곡선을 이용하여 두 개의 I 펄프시료와 두 개의 셀룰로스 스펀지 시료의 평균분자량을 결정함으로써 펄프로부터 스펀지를 만드는 서로 다른 두 가지 공정에서의 셀룰로스 분자들의 분해정도를 결정, 비교할 수 있었다.

• BMB Reports
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• 제39권3호
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• pp.270-277
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• 2006

Helices 4 and 5 of the Bacillus thuringiensis Cry4Ba $\delta$-endotoxin have been shown to be important determinants for mosquito-larvicidal activity, likely being involved in membrane-pore formation. In this study, the Cry4Ba mutant protein containing an additional engineered tryptic cleavage site was used to produce the $\alpha4$-$\alpha5$ hairpin peptide by an efficient alternative strategy. Upon solubilization of toxin inclusions expressed in Escherichia coli and subsequent digestion with trypsin, the 130-kDa mutant protoxin was processed to protease-resistant fragments of ca. 47, 10 and 7 kDa. The 7-kDa fragment was identified as the $\alpha4$-loop-$\alpha5$ hairpin via N-terminal sequencing and mass spectrometry, and was successfully purified by size-exclusion FPLC and reversed-phase HPLC. Using circular dichroism spectroscopy, the 7-kDa peptide was found to exist predominantly as an $\alpha$-helical structure. Membrane perturbation studies by using fluorimetric calcein-release assays revealed that the 7-kDa helical hairpin is highly active against unilamellar liposomes compared with the 65-kDa activated full-length toxin. These results directly support the role of the $\alpha4$-loop-$\alpha5$ hairpin in membrane perturbation and pore formation of the full-length Cry4Ba toxin.

• Tribology and Lubricants
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• 제31권5호
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• pp.195-204
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• 2015

Several researches are focused on improving the value of fine chemicals based on biomass resources due to environmental and other concerns associated with the use of petroleum-based products. Therefore, the synthesis and application of estolides derived from plant-based waste oil materials and their application as lubricants and as processing oil for butyl rubber products have been studied. Four kinds of estolide were prepared with conversions of 71~92% over 24h using various vegetable oils, as determined by size exclusion chromatography (SEC) and nuclear magnetic resonance (NMR) spectroscopy. FT-IR spectroscopy determines the esterification of estolides using 2-ethylhexyl alcohol. The estolides have iodine values of 35~90, α-ester/α-acid ratios of 0.45~0.55, and total acid number of 114~134 mg KOH g^–1. Four ball wear tests show that the wear scar diameters (WSDs) of estolides as base oil significantly decreased to 0.328~0.494 mm, compared to WSDs of 0.735 and 0.810 mm of WSD for 150N and Yubase 6, respectively, as general base oil. Thus, the estolides have better wear resistance and satisfying design objectives for the engineering of a variety of lubricant base oils.

• 한국작물학회지
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• 제41권4호
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• pp.456-464
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• 1996

밀의 영양체 저장탄수화물인 fructan의 대사에 관련된 fructan exohydrolase(FEH) 효소의 특성을 구명하기 위해 FEH를 밀의 줄기와 엽초에서 정제, 실험한 결과를 요약하면 다음과 같다. 1. FEH의 분자량은 63.7kD이었으며, pH 5.5와 3$0^{\circ}C$에서 최고의 활성을 보였다. 2. FEH의 $K_{m}$ 과 $V_{max}$는 fructan의 크기에 따라 각각 10~37mM, 5g~179mM로 변이를 보였으며, tetrasaccharide가 본 실험에서 사용된 기질 중에서 가장 낮은 $K_{m}$ 과 $V_{max}$를 보였다. 3. 밀의 FEH는 $eta$(2 $\longrightarrow$1)로 연결된 fructan에 대하여 기질 특이성을 보였으며 $\beta$(2 $\longrightarrow$6) fructan과 sucrose는 분해할 수 없었다.

• Journal of Microbiology and Biotechnology
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• 제15권6호
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• pp.1250-1257
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• 2005

Two groups of exopolysaccharides (designated as Fr-I EPS and Fr-II EPS) were isolated from the culture filtrate of new fungal strain Trichoderma erinaceum DG-312 by Sepharose CL-6B chromatography. The structures of the exopolysaccharides were investigated using gas chromatography (GC), Fourier transform-infrared (FT-IR) spectroscopy, GCMS analysis, and NMR. GC analysis indicated that Fr-I EPS was composed of mainly mannose ($78.9\%$) and galactose ($21.1\%$), whereas Fr-II EPS contained mannose ($68.4\%$), galactose ($26.2\%$), and glucose ($5.4\%$). In the anomeric region ($950-700cm_{-1}$) of the FT-IR spectrum, both EPSs exhibited obvious characteristic absorption of $810\;cm_{-1}$, indicating the existence of mannose. The spectra of $\alpha-and\;\beta$-configurations were assigned at 880 and $914\;cm_{-1}$, respectively. The results of GC-MS analyses confirmed that both EPSs were complex heteropolysaccharides with a ($1{\rightarrow}3$)-linked mannan backbone. The C-1 region that appeared in the $^{13}C-NMR$ spectra of these EPSs indicated a typical anomeric carbon signal. The Fr-I EPS showed two anomeric carbon signals at 102.6 and 99.6 ppm, whereas the Fr-II EPS displayed four anomeric carbon signals at 102.5, 99.6, 98.5, and 94.3 ppm. The molecular characteristics of the EPSs were further investigated using a size exclusion chromatography/multi-angle laser light scattering (SEC/MALLS) system. The SEC/MALLS system revealed that the average molar masses of the EPSs were $6.592{\times}10^{4}$ (Fr-I EPS) and $1.920{\times}10^{4}$ (Fr-II EPS) g/mol, and the molecular conformation of both EPSs in aqueous solution was random coils.

• Journal of Microbiology and Biotechnology
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• 제19권10호
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• pp.1201-1205
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• 2009

Corn starches with different amylose contents were enzymatically modified using Thermus aquaticus 4-$\alpha$-glucanotransferase ($TA{\alpha}GTase$). Upon the enzyme treatment, the chain-length distributions of isoamylolytically debranched products became broader [degree of polymerization (DP): 3-40] than those of untreated corn starches. In addition, a variety of cycloamyloses (CAs) with different sizes were formed by the glucanotransfer activity of $TA{\alpha}GTase$. CAs with DP 5-40 were detectable in all of the $TA{\alpha}GTase$-treated corn starches. From the results of high-performance anion-exchange chromatography and high-performance size-exclusion chromatography analyses, it was suggested that the amount of CAs produced by the enzyme treatment increased as the amylose content of the starches increased. Thus, we concluded that the extent of modification of starch molecules was enhanced in proportion to amylose content by the transfer activity of $TA{\alpha}GTase$. This finding could be useful for developing an efficient process of CA production using this enzyme.

• Journal of Microbiology and Biotechnology
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• 제30권2호
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• pp.271-278
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• 2020

Glycerol dehydrogenase (GlyDH) catalyzes the oxidation of glycerol to dihydroxyacetone (DHA), which is the first step in the glycerol metabolism pathway. GlyDH has attracted great interest for its potential industrial applications, since DHA is a precursor for the synthesis of many commercially valuable chemicals and various drugs. In this study, GlyDH from Klebsiella pneumoniae (KpGlyDH) was overexpressed in E. coli and purified to homogeneity for biochemical and molecular characterization. KpGlyDH exhibits an exclusive preference for NAD⁺ over NADP⁺. The enzymatic activity of KpGlyDH is maximal at pH 8.6 and pH 10.0. Of the three common polyol substrates, KpGlyDH showed the highest k_cat/K_m value for glycerol, which is three times higher than for racemic 2,3-butanediol and 32 times higher than for ethylene glycol. The k_cat value for glycerol oxidation is notably high at 87.1 ± 11.3 sec^-1. KpGlyDH was shown to exist in an equilibrium between two different oligomeric states, octamer and hexadecamer, by size-exclusion chromatography analysis. KpGlyDH is structurally thermostable, with a T_m of 83.4℃, in thermal denaturation experiment using circular dichroism spectroscopy. The biochemical and biophysical characteristics of KpGlyDH revealed in this study should provide the basis for future research on its glycerol metabolism and possible use in industrial applications.

• 무역상무연구
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• 제19권
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• pp.7-31
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• 2003

The governments of almost countries have the rules and procedures that the purchasing entities have to follow, in order to ensure that the best value for money spent is obtained in procuring goods and services. However, there are often some of important problems in their rules relating to government procurement. Namely, almost countries have a variety of discriminatory regulations for foreign suppliers in the government procurement laws with the object of national security, economic welfare, and protection of domestic market from international competition. For this reason, several advanced countries had reached the Plurilateral Agreement on Government Procurement during Tokyo Round(1973-1979) and Uruguay Round(1986-1994). However, the provisions of two agreements do not apply to all products made by the government but only to those made by purchasing entities specified by each member country in its list in the Appendix. Accordingly, the size of goods and services purchased from foreign suppliers were comparatively not large. As we know well, the United States have spent a large amount of money from federal and state government budget. But the portion of procurement from foreign suppliers is still small, compared with the portion of procurement from domestic suppliers. The main reason are that U.S. has applied for long time the so-called Buy American Act to government procurement positively and maintained many kinds of other domestic regulations which have discriminatory provisions for foreign goods and foreign suppliers. On the recognition of these points, this thesis deals with the Buy American Act and other U.S. domestic laws, regional and bilateral, and plurilateral agreements including WTO Agreement on Government Procurement. As a result, the author found that there are several concerns and problems in the U.S. regulations relating to government procurement. It include the provisions on priority procurement of U.S.-produced products, local contents requirements, set-aside procurement from small business, and exclusion of preferential procurement from the developing countries.

• Journal of Microbiology and Biotechnology
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• 제24권8호
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• pp.1096-1104
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• 2014

$\small{L}$-Asparaginase from gram-positive bacteria has been poorly explored. We conducted recombinant overexpression and purification of $\small{L}$-asparaginase from Staphylococcus sp. OJ82 (SoAsn) isolated from Korean fermented seafood to evaluate its biotechnological potential as an antileukemic agent. SoAsn was expressed in Escherichia coli BL21 (DE3) with an estimated molecular mass of 37.5 kDa, determined using sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Consistent with asparaginases in gram-negative bacteria, size-exclusion chromatography determined SoAsn as a homodimer. Interestingly, the optimal temperature of SoAsn was $37^{\circ}C$ and over 90% of activity was retained between $37^{\circ}C$ and $50^{\circ}C$, and its thermal stability range was narrower than that of commercial E. coli $\small{L}$-asparaginase (EcAsn). Both SoAsn and EcAsn were active between pH 9 and 10, although their overall pH-dependent enzyme activities were slightly different. The $K_m$ value of SoAsn was 2.2 mM, which is higher than that of EcAsn. Among eight metals tested for enzyme activity, cobalt and magnesium greatly enhanced the SoAsn and EcAsn activity, respectively. Interestingly, SoAsn retained more than 60% of its activity under 2 M NaCl condition, but the activity of EcAsn was reduced to 48%. Overall, the biochemical characteristics of SoAsn were similar to those of EcAsn, but its kinetics, cofactor requirements, and NaCl tolerance differed from those of EcAsn.