• 공업화학
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• 제1권1호
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• pp.52-62
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• 1990

폴리카보네이트 폴리올, MDI 및 N-methyldiethanolamine(MDEA)로부터 폴리카보네이트형 우레탄 수지를 합성하고, MDEA의 4차 암모늄염화 반응에 의해서 양이온성 폴리카보네이트 우레탄 수지를 제조하였다. 우레탄 연쇄내 이온기의 함량이 증가함에 따라 인장강도 탄성율은 현저하게 증가되었으나 내가수분해성등은 저하되는 경향을 표시하였다. 에탄올/물 혼합용액 분리실험에서 양이온성 폴리카보네이트형 우레탄 막의 선택도는 20정도였으며, 이때의 분리기구는 carrier mediated transport mechanism을 따른 것으로 생각된다.

• Applied Biological Chemistry
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• 제26권2호
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• pp.125-131
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• 1983

Dimethyl-2,2-dichlorovinylphosphate (DDVP) 분자를 정량적으로 이해하기 위한 시도의 일환으로 분자궤도함수를 계산하여 구성 원자의 알짜 전하, 결합차수, 원자 궤도계수, 에너지 성분 분석 및 형태 둥의 결과로 부터 분자의 안정성과 반응성을 검토하였다. 또한 DDVP분자의 가수분해 반응 메카니즘을 제안하기 위하여 가수분해 반응 생성물을 분석한 결과 주 생성물은 2,2-dichlorovinylphosphate와 dimethylphosphate임을 재확인하여 염기성 용액중에서의 가수분해 반응속도와 pH에 대한 변화로 부터 유도된 반응 속도식은 다음과 같다. ${\therefore}\;k_{obs}=k_{OH}[OH-]{\cdot}kw/[H_3O^+]$ $=2.10{\times}10^{-11}/[H_3O^*]$ 이상과 같은 사실로 부터 DDVP분자의 가수분해 반응 메카니즘은 다음과 같이 설명된다. 즉, 단일 결합성인 $C_2({\alpha})-O_3$를 회전축으로 나타낸 가장 안정한 형태는 staggered conformation $({\mu}=4.90debye)$이였으며, 전하의 분리가 크게 이루워진 $C_1({\beta})=C_2({\alpha})$결합의 양하전이 큰 평면상의 $C_2({\alpha})$원자에 강한 친핵체인 OH-이온이 수직으로 첨가하여 파이-반결합궤도$({\pi}^*)$를 가지는 $C_2({\alpha})-O_3$의 단일결합이 불균형 분해하여 2,2-dichloroacetaldehyde와 dimethylphosphate를 생성하는 일련의 복잡한 전형적인 Michael형의 친핵성 첨가반응 매카니즘을 제안하였다.

• 한국산림과학회지
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• 제79권4호
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• pp.376-387
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• 1990

대기오염(大氣汚染)과 산성우(酸性雨)가 삼림토양(森林土壤)의 완충능(緩衝能)에 미치는 영향(影響)을 규명하기 위하여 이동오염원지역(移動汚染源地域)으로 서울지역(地域), 고정오염원지역(固定汚染源地域)으로 울산(蔚山) 및 여천지역(麗川地域) 그리고 대조지역(對照地域)으로 강원도(江原道) 평창지격(平昌地域)에서 토양시료(土壤試料)를 채취하여 인공산성우(人工酸性雨)를 처리(處理)하고 조사분석(調査分析)한 결과(結果)를 고찰(考察)해 볼 때 다음과 같았다. pH 3.0-5.7 수준(水準)의 인공산성우(人工酸性雨)에 대하여 토양용탈용액(土壤溶脫溶液)波이 나타낸 용액(溶液) pH의 수준(水準)은 강원도지역(江原道地域)에서 pH 6.2-7.1이었고, 다음이 울산(蔚山)으로 pH 3.8-6.0, 여천(麗川)은 pH 4.0-5.4, 서울이 pH 4.0-5.5로 나타나므로써 산성우(酸性雨)에 대한 토양완충능(土壤緩衝能)은 강원도(江原道)가 가장 컸으며 서울이 가장 낮았다. 그러나 pH 2.0의 산성우처리(酸性雨處理)에서는 각 지역(地域)에서 모두 토양완충능(土壤緩衝能)이 급격히 낮아졌다. 인공산성우(人工酸性雨)의 처리(處理)에 대한 토양완충능(土壤緩衝能)은 강원도지역(江原道地域)의 경우 화강암(花崗岩) 지역(地域)과 석탄암지역간(石炭岩地域間)의 유의적(有意的)인 차이(差異)를 나타냈고 서울과 울산지역(蔚山地域)의 경우 pH 3.0-5.7의 산성우(酸性雨)에 대해서는 오염원(汚染源)으로부터 거리(距離)가 멀어 질수록 토양완충능(土壤緩衝能) 유의적(有意的)으로 증가(增加)하였다. 인공산성우처리(人工酸性雨處理)에 대한 토양완충능(土壤緩衝能)의 기작(機作)은 강원도지역(江原道地域)의 경우 양(陽)이온치환(置換)이었으며, 서울지역(地域)에서는 pH 3.0 이상(以上)의 산성우(酸性雨)에 대해서는 양(陽)이온치환(置換)이 완충작용(緩衝作用)을 주도(主導)하였으나 pH 2.0에서는 Aluminum 및 Silicate hydrolysis가 주도(主導) 하였다. 울산지역(蔚山地域)의 경우 pH 3.0 이상(以上)에서는 양(陽)이온치환(置換)이, pH 4.5 이하(以下)에서는 Aluminum hydrolysis가, 그리고 pH 3.0 이하(以下)에서는 Aluminum hydrolysis 및 Silicate hydrolysis가 주도(主導)하였다. 여천지역(麗川地域)에서는 pH 4.5에서 Silicate hydrolysis가, pH 4.5 이하(以下)에서는 Aluminum hydrolysis가 주도(主導)하였다.

• 한국세라믹학회지
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• 제37권5호
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• pp.473-478
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• 2000

The TiO2 powder with the values of the large specific surface area more than 150$m^2$/g has been prepared with the homogeneous precipitation process below 5$0^{\circ}C$ and its formation mechanism was investigated using the SEM, TEM and Raman Spectroscopy. With the spontaneous hydrolysis of aqueous TiOCl2 solutions, all the precipitates were fully and homogeneously crystallized with the rutile TiO2 phase simply by heating, which as transformed to the anatase TiO2 phase as increasing the addition of SO42- ions to the aqueous TiOCl2 solution. The precipitates were formed with spherical secondary particles which consisted of acicular, spherical and mixed primary particles corresponding to the rutile, anatase and mixed phases, respectively. It can be thought that the formation and phase determination of crystalline TiO2 powders even at ambient temperature would be related with the existence of the capillary force. This force might be varied depending on the shape change of the primary particles.

• Genomics & Informatics
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• 제6권1호
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• pp.44-49
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• 2008

Protein kinase C (PKC) is a family of kinases involved in the transduction of cellular signals that promote lipid hydrolysis. PKC plays a pivotal role in mediating cellular responses to extracellular stimuli involved in proliferation, differentiation and apoptosis. Comparative analysis of the PKC-${\alpha},{\beta},{\varepsilon}$ isozymes of 200 recently sequenced microbial genomes was carried out using variety of bioinformatics tools. Diversity and evolution of PKC was determined by sequence alignment. The ser/thr protein kinases of Streptomyces coelicolor A3 (2), is the only bacteria to show sequence alignment score greater than 30% with all the three PKC isotypes in the sequence alignment. S.coelicolor is the subject of our interest because it is notable for the production of pharmaceutically useful compounds including anti-tumor agents, immunosupressants and over two-thirds of all natural antibiotics currently available. The comparative analysis of three human isotypes of PKC and Serine/threonine protein kinase of S.coelicolor was carried out and possible mechanism of action of PKC was derived. Our analysis indicates that Serine/ threonine protein kinase from S. coelicolor can be a good candidate for potent anti-tumor agent. The presence of three representative isotypes of the PKC super family in this organism helps us to understand the mechanism of PKC from evolutionary perspective.

• 상하수도학회지
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• 제18권2호
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• pp.128-136
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• 2004

The overall objective of this research was to find out the role of rapid mixing conditions in the species of hydrolyzed Al(III) formed by different Al(III) coagulants. When an Al(III) salt is added to water, monomers, polymers, or solid precipitates may form. Different Al(III) coagulants (alum and PACl) show to have different Al species distribution over a rapid mixing condition. During the rapid mixing period, for alum, formation of dissolved Al(III) (monomer and polymer) increases, but for PACl, precipitates of $Al(OH)_{3(s)}$. increases rapidly. Also, for alum, higher mixing speed favoured Al(III) polymers formation over precipitates of $Al(OH)_{3(s)}$ but for PACl, higher mixing speed formed more precipitates of $Al(OH)_{3(s)}$. At A/D and sweep condition, both $Al(OH)_{3(s)}$ and dissolved Al(III) (monomer and polymer) exist, concurrent reactions by both mechanism appear to cause simultaneous precipitation.

• Journal of Pharmaceutical Investigation
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• 제36권5호
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• pp.315-320
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• 2006

Silymarin showed P-glycoprptein(P-gp) inhibitory activity as much as verapamil, a well-known P-gp inhibitor, by decreasing $IC_{50}$ value of daunomycin(DNM)($16.0{\pm}0.7{\mu}M$), increasing the DNM accumulation($224.9{\pm}3.2%$), and decreasing DNM efflux($58.5{\pm}6.7%$), concurrently. In this study, we clarified the mechanism of action of silymarin for P-gp inhibitory function. First, silymarin may bind to the ATP-binding site and thus, prevent ATP hydrolysis. Second, the P-gp inhibitory activity of silymarin is not related to changing the cellular P-gp level. Third, the cytotoxicity of silymarin was increased in the presence of verapamil, reflecting that silymarin is a competent P-gp substrate against verapamil in the P-gp-overexpressed adriamycin-resistant MCF-7 breast cancer(MCF-7/ADR) cells. Conclusively, silymarin had the P-gp inhibitory activity through the action of competent binding to the P-gp substrate-binding site. Therefore, silymarin can be a good candidate for safe and effective MDR reversing agent in clinical chemotherapy by administering concomitantly with anticancer drugs.

• BMB Reports
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• 제38권3호
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• pp.266-274
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• 2005

High temperature requirement A (HtrA) and its homologues constitute the HtrA familiy proteins, a group of heat shock-induced serine proteases. Bacterial HtrA proteins perform crucial functions with regard to protein quality control in the periplasmic space, functioning as both molecular chaperones and proteases. In contrast to other bacterial quality control proteins, including ClpXP, ClpAP, and HslUV, HtrA proteins contain no regulatory components or ATP binding domains. Thus, they are commonly referred to as ATP-independent chaperone proteases. Whereas the function of ATP-dependent chaperone-proteases is regulated by ATP hydrolysis, HtrA exhibits a PDZ domain and a temperature-dependent switch mechanism, which effects the change in its function from molecular chaperone to protease. This mechanism is also related to substrate recognition and the fine control of its function. Structural and biochemical analyses of the three HtrA proteins, DegP, DegQ, and DegS, have provided us with clues as to the functional regulation of HtrA proteins, as well as their roles in protein quality control at atomic scales. The objective of this brief review is to discuss some of the recent studies which have been conducted regarding the structure and function of these HtrA proteins, and to compare their roles in the context of protein quality control.

• Biomolecules & Therapeutics
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• 제31권2호
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• pp.141-147
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• 2023

Antibiotic resistance has emerged as a global threat to modern healthcare systems and has nullified many commonly used antibiotics. β-Lactam antibiotics are among the most successful and occupy approximately two-thirds of the prescription antibiotic market. They inhibit the synthesis of the peptidoglycan layer in the bacterial cell wall by mimicking the D-Ala-D-Ala in the pentapeptide crosslinking neighboring glycan chains. To date, various β-lactam antibiotics have been developed to increase the spectrum of activity and evade drug resistance. This review emphasizes the three-dimensional structural characteristics of β-lactam antibiotics regarding the overall scaffold, working mechanism, chemical diversity, and hydrolysis mechanism by β-lactamases. The structural insight into various β-lactams will provide an in-depth understanding of the antibacterial efficacy and susceptibility to drug resistance in multidrug-resistant bacteria and help to develop better β-lactam antibiotics and inhibitors.

• Journal of Animal Science and Technology
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• 제65권6호
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• pp.1151-1168
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• 2023

Tenderness and taste characteristics of meat are the key determinants of the meat choices of consumers. This review summarizes the contemporary research on the molecular mechanisms by which postmortem aging of meat improves the tenderness and taste characteristics. The fundamental mechanism by which postmortem aging improves the tenderness of meat involves the operation of the calpain system due to apoptosis, resulting in proteolytic enzyme-induced degradation of cytoskeletal myofibrillar proteins. The improvement of taste characteristics by postmortem aging is mainly explained by the increase in the content of taste-related peptides, free amino acids, and nucleotides produced by increased hydrolysis activity. This review improves our understanding of the published research on tenderness and taste characteristics of meat and provides insights to improve these attributes of meat through postmortem aging.