• 공업화학
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• 제26권1호
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• pp.86-91
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• 2015

BHT (2,6-di-tert-butyl-4-methylphenol), TBC (4-tert-butylcatechol), 스테아린산구리 등 여러 가지 중합방지제를 사용하여 MPPO (3-methyl-1-phenyl-2-phospholene-1-oxide)를 제조하였다. 제조한 시료에 대해 FTIR, $^1H$-NMR, GC/MS 등을 이용하여 분석한 결과 중합방지제의 종류에 관계없이 MPPO 합성이 확인되었다. 반응 시간이 증가하면 MPPO의 수율은 증가하지만, 순도는 약간 저하하는 경향을 보였다. 합성 온도가 높아지면 MPPO의 수율과 순도가 증가하였지만, 스테아린산구리를 사용한 경우 MPPO의 순도 변화는 나타나지 않았다. 중합방지제 양이 증가하면 MPPO의 수율은 변화가 나타나지 않았다. 순도는 중합방지제 양이 증가하면 증가하였지만, BHT를 사용한 경우에는 중합방지제 양에 따른 MPPO의 순도 변화가 없었다. Diphenylcarbodiimide 합성에 대한 MPPO의 촉매 활성은 스테아린산구리를 사용하여 제조한 MPPO가 가장 높았다.

• Journal of Microbiology and Biotechnology
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• 제10권6호
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• pp.764-769
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• 2000

The lipase gene(lip) from Bacillus stearothermophilus was recombined in vitro by utilizing the DNA shuffling technique. After four rounds of shuffling, transformation, and screening based on the initial rate of clear zone formation on a tricaprylin plate, a clone (M10) was isolated, the cell extract of which showed about 2.8-fold increased lipase activity. The DNA sequence of the mutant lipase gene (m10) showed 3 base changes, resulting in two cryptic mutations and one amino acid substitution: S113($AGC{\rightarrow}AGT$), L252 ($TTG{\rightarrow}TTA$), and G275E ($GGA{\rightarrow}GAA$). SDS-PAGE analysis revealed that the increased enzyme activity observed in M10 was partly caused by high expression of the m10 lipase gene. The amount of the expressed G275E lipase was estimated to comprise as much as 41% of the total soluble proteins of the cell. The maximum velocity ($V_{max}$) of the purified mutant enzyme for the hydrolysis of olive oil was measured to be 3,200 U/mg, which was 10% higher than that of the parental (WT) lipase (2,900 U/mg). Its optimum temperature for the hydrolysis of olive oil was $68^{\circ}C$ and it showed a typical $Ca^{2+}$-dependent thermostability, properties fo which were the same as those of the WT lipase. However, the mutant enzyme exhibited a high enantiospecificity towards (S)-naproxen compared with the WT lipase. In addition, it showed increased hydrolytic activity towards triolein, tricaprin, tricaprylin, and tricaproin.

• Macromolecular Research
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• 제12권2호
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• pp.156-171
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• 2004

We describe the precision synthesis schemes of siloxane-containing polymers, i.e., the control of their molecular weight, stereoregularity, and higher-order structures. First, we found a new catalytic dehydrocoupling reaction of water with bis(dimethylsilyl)benzene to give poly(phenylene-disiloxane). Together with this reaction, we applied hetero-condensations to the synthesis of thermally stable poly(arylene-siloxane)s. The dehydrocoupling reaction was applied to the synthesis of syndiotactic poly(methylphenylsiloxane) and poly(silsesquioxane)s, which we also prepared by hydrolysis and deaminative condensation reactions. We discuss the tendency for loop formation to occur in the synthesis of poly(silsesquioxane) by hydrolysis, and provide comments on the design of functionality of the polymers produced. By taking advantage of the low energy barrier to rotation in the silicon-oxygen bond, we designed selective oxygen-permeable membrane materials and liquid crystalline materials. The low surface free energy of siloxane-containing systems allows surface modification of a blend film and the design of holographic grating materials.

• Advances in Energy Research
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• 제1권1호
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• pp.1-12
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• 2013

In this work, we present the catalytic dehydrogenation of hydrazine borane $N_2H_4BH_3$ (HB) using supported nickel catalysts at $50^{\circ}C$. In the presence of monometallic nickel catalysts, the dehydrogenation of HB is a one-step reaction consisting of the hydrolysis of the $BH_3$ group only. The challenge is to activate nickel to make it reactive towards the $N_2H_4$ moiety of HB. A set of 52 catalysts were prepared by using 2 supports ($Al_2O_3$ and $TiO_2$), 5 nickel precursors and 3 preparation methods. For the first time, we show that the supported nickel catalysts are able to dehydrogenate the $NH_3$ moiety of HB. In our experimental conditions, the best results were obtained with 20 wt% Ni-$Al_2O_3$ and 20 wt% Ni-$TiO_2$, with ca. 190 mL $H_2+N_2$ generated over a total theoretical volume of 283 mL, suggesting $H_2$ selectivity of 37 and 32%, respectively. Both catalysts were then characterized by EDX, XPS, and XRD. Our achievement is the first step forward and opens new perspectives for developing catalysts for the total dehydrogenation of HB.

• 공업화학
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• 제7권4호
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• pp.794-801
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• 1996

Isopropanol 용매 내에서 titanium isopropoxide($Ti(O-^iPr)_4$)의 가수분해반응에 의하여 $TiO_2$ 미분말을 합성하였고 가수분해 반응 속도를 자외선분광법에 의하여 측정하였다. 반응은 $Ti(O-^iPr)_4$의 농도에 비하여 물 농도를 크게 하여 유사일차반응으로 진행시켰고, 물 농도 및 온도의 변화에 따른 반응속도상수를 Guggenheim method로 계산하였다. 또한 물의 동위원소 효과를 측정하여 반응에 참여하는 물분자의 촉매성을 확인하였다. 입도분석과 미세구조 관찰 결과, 얻어진 $TiO_2$ 미분말은 $0.3{\mu}m$정도의 입자크기를 갖는 구형의 입자로 확인되었다. 또한 반응속도로부터 전이상태에 참여하는 n value와 열역학적 파라메타를 계산한 결과, $Ti(O-^iPr)_4$의 가수분해반응은 이분자 반응인 $S_N2$ mechanism으로 진행하는 것으로 추정되었다.

• 한국세라믹학회지
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• 제41권11호
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• pp.864-871
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• 2004

폐 염화알루미늄(AlCl$_3$) 수용액과 수산화나트륨(NaOH) 용액의 가수분해 반응에 의해 무정형의 수산화알루미늄 겔을 석출시키고, 이를 숙성하여 다공성 유사베마이트(pseudo-boehmite) 겔을 제조하였다 pH를 7.6～11.6 범위로 조절하고 반응온도를 60～10$0^{\circ}C$로 변화시켜 2～24시간 숙성시켰을 때, 겔 침전물의 결정변화, 적외선흡수스펙트럼의 변화, 비표면적 및 기공구조의 변화를 조사하여 최대 기공부피를 갖는 유사베마이트 겔의 제조조건을 확립하였다. pH 7.6～9.6 범위에서 석출된 겔 침전물로부터 250～357 $m^2$/g 정도의 비표면적과 0.4～0.74 cc/g의 기공부피 그리고 58～l14$\AA$의 평균기공크기를 갖는 다공성 유사베마이트가 제조되었으며, pH 10.6～11.6 범위에서 석출된 겔 침전물로부터는 기공이 거의 없는 베이어라이트(bayerite)가 제조되었다.

• Journal of Microbiology and Biotechnology
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• 제18권5호
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• pp.901-907
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• 2008

Thermotoga neapolitana $\beta$-glucosidase (BglA) was subjected to site-directed mutagenesis in an effort to increase its ability to synthesize arbutin derivatives by transglycosylation. The transglycosylation reaction of the wild-type enzyme displays major ${\beta}(1,6)$ and minor ${\beta}(1,3)$ or ${\beta}(1,4)$ regioselectivity. The three mutants, N291T, F412S, and N291T/F412S, increased the ratio of transglycosylation/hydrolysis compared with the wild-type enzyme when pNPG and arbutin were used as a substrate and an acceptor, respectively. N291T and N219T/F412S had transglycosylation/hydrolysis ratios about 3- and 8-fold higher, respectively, than that of the wild-type enzyme. This is due to the decreased hydrolytic activity of the mutant rather than increased transglycosylation activity. Interestingly, N291T showed altered regioselectivity, as well as increased transglycosylation products. TLC analysis of the transglycosylation products indicated that N291T retained its ${\beta}(1,3)$ regioselectivity, but lost its ${\beta}(1,4)$ and ${\beta}(1,6)$ regioselectivity. The altered regioselectivity of N291T using two other acceptors, esculin and salicin, was also confirmed by TLC. The major transglycosylation products of the wild type and N291T mutant were clearly different. This result suggests that Asn-291 is highly involved in the catalytic mechanism by controlling the transglycosylation reaction.

• Journal of Microbiology and Biotechnology
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• 제31권1호
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• pp.43-50
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• 2021

A newly cloned 4-α-glucanotransferase (αGT) from Deinococcus geothermalis and two typical bacterial αGTs from Thermus scotoductus and Escherichia coli (MalQ) were investigated. Among 4 types of catalysis, the cyclization activity of αGTs that produces cycloamylose (CA), a valuable carbohydrate making inclusion complexes, was intensively studied. The new αGT, DgαGT, showed close protein sequence to the αGT from T. scotoductus (TsαGT). MalQ was clearly separated from the other two αGTs in the phylogenetic and the conserved regions analyses. The reaction velocities of disproportionation, cyclization, coupling, and hydrolysis of three αGTs were determined. Intriguingly, MalQ exhibited more than 100-fold lower cyclization activity than the others. To lesser extent, the disproportionation activity of MalQ was relatively low. DgαGT and TsαGT showed similar kinetics results, but TsαGT had nearly 10-fold lower hydrolysis activity than DgαGT. Due to the very low cyclizing activity of MalQ, DgαGT and TsαGT were selected for further analyses. When amylose was treated with DgαGT or TsαGT, CA with a broad DP range was generated immediately. The DP distribution of CA had a bimodal shape (DP 7 and 27 as peaks) for the both enzymes, but larger DPs of CA quickly decreased in the DgαGT. Cyclomaltopentaose, a rare cyclic sugar, was produced at early reaction stage and accumulated as the reactions went on in the both enzymes, but the increase was more profound in the TsαGT. Taken together, we clearly demonstrated the catalytic differences between αGT groups from thermophilic and pathogenic bacteria that and showed that αGTs play different roles depending on their lifestyle.

• Bulletin of the Korean Chemical Society
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• 제32권5호
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• pp.1669-1678
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• 2011

Six new binuclear copper(II) complexes have been prepared by template condensation of the dialdehydes 1,8-[bis(3-formyl-2-hydroxy-5-methyl)benzyl]-l,4,8,11-tetraazacyclotetradecane (PC-a) and 1,8-[bis(3-formyl-2-hydroxy-5-bromo)benzyl]-l,4,8,11-tetraazacyclotetradecane (PC-b) with appropriate aliphatic diamines, and copper(II) perchlorate. The structural features of the complexes have been confirmed by elemental analysis, IR, UV-vis and mass spectra etc. The electrochemical behavior of all the copper(II) complexes show two irreversible one electron reduction process. The room temperature magnetic moment studies depict the presence of an antiferromagnetic interaction in the binuclear complexes. The catechol oxidation and hydrolysis of 4-nitrophenylphosphate were carried out by using the complexes as catalyst. The antimicrobial screening data show good results. The binding of the complexes to calf thymus DNA (CT DNA) has been investigated with absorption and emission spectroscopy. The complex [$Cu_2L^{1a}$] displays significant cleavage property of circular plasmid pBR322 DNA in to linear form. Spectral, electrochemical, magnetic and catalytic studies support the distortion of the copper ion geometry that arises as the macrocyclic ring size increases.

• 공업화학
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• 제10권7호
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• pp.1020-1027
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• 1999

헤테로폴리산(HPW)을 표면적이 서로 다른 담체인 $SiO_2$ MCM-41, MCM-48에 담지농도와 소성온도를 달리하며 담지시켰다. X-선 회절분석, 질소 흡착법, 적외선 흡수 스펙트럼, $^{31}P$ 고체 핵자기 공명을 통해서 이 담지촉매의 특성을 조사하였다. IR과 NMR의 결과로부터 HPW가 담체안에서 케긴 구조를 유지하면서 존재함을 확인할 수 있었다. MCM-41의 경우에는 35 wt %, MCM-48의 경우에는 65 wt %로 담지시킨 경우에도 X-선 회절패턴에서 HPW 고유의 피크가 나타나지 않았으며, 이와 같은 특성을 통해서 HPW가 고분산 되어 있음을 알 수 있었다. Di, bis, tri-pentaerythritol의 가수분해 반응에서 이들 담지 촉매는 높은 촉매 활성을 보였으며 HPW, $HPW/SiO_2$보다 HPW/MCM-41, 48의 촉매 활성이 더 우수하였다.