• Journal of Microbiology and Biotechnology
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• v.6 no.6
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• pp.432-438
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• 1996

Native crystalline chitin was hydrolyzed in an agitated bead reaction system using crude chitinase excreted from Aspergillus fumigatus JC-19. The reaction was enhanced significantly, and the concentration and yield of reducing sugar after 48 hours were measured to be 35.42 g/I (w/v) and 0.64, respectively, around 1.86 times higher than those of the conventional system that was carried out without glass beads. The effect of reaction conditions, such as the amounts of chitin, chitinase and glass beads, and the size of glass bead, were examined. Ball milled chitin was also hydrolyzed in the agitated bead reaction system, the conversion yield and reaction rate of ball milled chitin for 24 hours increased up to 0.87 and 48.02 g/I, respectively. Chitinase showed relatively high stability in the agitated bead reaction system, particularly in the presence of enzyme stabilizer, $Ca^{++}$, which played a critical role in preventing the deactivation of chitinase by the physical impact of glass beads. The variations of the structural features of chitin during the reaction were followed by SEM and X-ray diffraction, and the enhanced hydrolysis reaction was caused by both the fragmentation of chitin particles and the destruction of the crystalline structure owing to the synergic effects of the attrition of glass beads and the hydrolytic action of chitinase.

• YAKHAK HOEJI
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• v.40 no.3
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• pp.279-292
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• 1996

To assess their stability as a prodrug of 5-fluorouracil (5-FU), four N-acyloxycarbonyl derivatives (1-(N-tert-butyloxycarbonyl)glycyloxymethyl-5-FU :BGFU, 1-(N-tert-butyloxycar bonyl)-leucyloxymethyl-5-FU:BLFU, 1-(N-tert-carbobenzyloxymethyl) glycyloxymethyl-5-FU:CGFU and 1-(N-tert-carbobenzlyoxymethyl)leucyloxymethyl-5-FU:CLFU) possessing differently protected amino acids, and two acetic acid derivatives (5FU-1-acetylpentane:FUAP and 5-FU-1-acetylhexane:FUAH) were synthesized and their physicochemical properties, hydrolysis kinetics, acute toxicity and antitumor activity were evaluated. The lipid-water partition coefficients of six 5-FU prodrugs were higher than that of 5-FU and their aqueous solubilities were in the following rank order; BGFU>FUAP>CGFU>BLFU>CLFU${\simeq}$FUAH. The hydrolysis of N-acyloxycarboyl derivatives, greater at higher pH, was enhanced in presence of liver homogenate or human plasma. Meanwhile, acetic acid ester derivatives, very stable, were hydrolyzed by liver homogenate. Absorption rate constants were 0.181, 0.121, 0.111, 0.168, 0.168, 0.116 and 0.125 $hr^{-1}$ for 5-FU, BGFU, BLFU, CGFU, CLFU, FUAP and FUAH, respectively. The cytotoxicity of N-acyloxycarbonyl derivatives was 4 to 5 times lower than that of 5-FU, but that of acetic acid ester derivatives was negligeble. The $LD_{50}$ values were 204, 325.97 (133.59, amount as 5-FU), 708.16 (262.13), 663.50 (211.77), 382.33 (192.54) and 272.33 (130.09) mg/kg for 5-FU, BGFU, CGFU, CLFU, FUAP and FUAH, respectively. While N-acyloxycarbonyl derivatives showed enhanced antitumor activity and therapeutic ratio (3.30, 3.06, 4.19, 3.11 and 1.81 for BGFU, BLFU, CGFU, CLFU and 5-FU, respectively), FUAH and FUAP showed a smaller therapeutic ratio (0.79 and 0.83).

• Bulletin of the Korean Chemical Society
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• v.32 no.1
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• pp.179-182
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• 2011

Second-order rate constants ($k_{OH^-}$) have been measured spectrophotometrically for reactions of Y-substituted phenyl phenyl thionocarbonates (4a-i) with $OH^-$ in 80 mol % $H_2O$/20 mol % DMSO at $25.0{\pm}0.1^{\circ}C$. The $k_{OH^-}$ values for the reactions of 4a-i have been compared with those reported previously for the corresponding reactions of Y-substituted phenyl phenyl carbonates (3a-i) to investigate the effect of changing the electrophilic center from C=O to C=S on reactivity and mechanism. Thionocarbonates 4a-i are less reactive than the corresponding carbonates 3a-i although 4a-i are expected to be more reactive than 3a-i. The Bronsted-type plot for reactions of 4a-i is linear with $\beta_{lg}$ = -0.33, a typical $\beta_{lg}$ value for reactions reported to proceed through a stepwise mechanism with formation of an intermediate being the rate-determining step (RDS). Furthermore, the Hammett plot correlated with $\sigma^o$ constants results in much better linearity than that correlated with $\sigma^-$ constants, indicating that expulsion of the leaving group is not advanced in the RDS. Thus, alkaline hydrolysis of 4a-i has been concluded to proceed through a stepwise mechanism with formation of an intermediate being RDS, which is in contrast to the forced concerted mechanism reported for the corresponding reactions of 3a-i. Enhanced stability of the intermediate upon modification of the electrophilic center from C=O to C=S has been concluded to be responsible for the contrasting mechanisms.

• Journal of Hydrogen and New Energy
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• v.24 no.1
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• pp.1-11
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• 2013

Additives such as glycerol, methanol, acetone, and ethanol were used to prevent $NaBO_2$ from precipitation, and their effects on hydrogen generation properties of $NaBH_4$ hydrolysis were investigated. When the concentration of additives was 5 wt%, the additives such as methanol, acetone, and ethanol could not prevent $NaBO_2$ precipitation. Although glycerol prevented $NaBO_2$ precipitation, conversion efficiency decreased to 78.0% due to its viscosity. Based on test results, hydrogen generation tests were also performed at various concentration of glycerol and methanol to investigate the concentration effects on hydrogen generation properties. As the concentration of glycerol increased from 1 wt% to 3 wt%, conversion efficiency increased owing to additive effect. When its concentration increased to 5 wt%, conversion efficiency decreased due to its viscosity. As the concentration of methanol increased from 5 wt% to 10 wt%, conversion efficiency increased owing to additive effect. When its concentration increased to 15 wt%, conversion efficiency decreased due to $NaB(OCH_3)_4$ precipitate. Although conversion efficiency decreased about 1% when 3 wt% glycerol was added, $NaBO_2$ precipitation was prevented. Consequently, addition of 3 wt% glycerol to $NaBH_4$ solution improves stability of hydrogen generation system.

• Journal of Microbiology and Biotechnology
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• v.3 no.1
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• pp.39-45
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• 1993

The effect of concentrations of phosphate buffer and acrylonitrile, pH, and various salts on the operational stability of the immobilized cells of Brevibacterium CH2 in a packed bed reactor were investigated. The effects of salts and carriers on the swelling of the immobilized beads during hydrolysis in a columnreactor were also investigated. Immobilization of the cells in Ba-alginate was more desirable than those in polyacrylamide and Ca-alinate for the swelling of the immobilized beads and the desired quality of the acrylamide produced. High quality acrylamide was produced using the Ba-alginate beads in a recycle fed-batch reactor without using an isotonic substrate. The conversion yield was nearly 100％, including a trace amount of acrylic acid produced as a by-product.

• YAKHAK HOEJI
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• v.37 no.6
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• pp.638-646
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• 1993

A cepfialosporin with an aminothiazoiylmethoxyimino-type side chain at the 7 position and bicyclic quinolone dithicarbamate at the 3' position was synthesized. It has broad and potent antivacterial activity in vitro. The antibacterial spectrum reflects contributions of both the cephalosporin moiety and the quinolone moiety. Thus, this compound was named DACD implying a dualaction cephalosporin derivative. In this paper, the physicochemical proper-ties (lipid-water partition, pKa), stability and pharmacokinetics of DACD were determined and compared with cefotaxime 3'-norfloxacin dithiocarbamate (CENO). Stability tests were studied in pH 1.20, 6.80 and 8.00 buffers and in the presence of AB type human plasma, rat liver homogenate and its .betha.-lactamase. The pharmacokinetic parameters of DACD were evaluated in mice after a single intravenous dose of 40 mg/kg. The results are as follows. The lipid-water partition coefficient of DACD was higher than that of CENO. The calculated pKa values of CENO and DACD, were 6.82$\pm$0.03, 7.53$\pm$0.21, respectively. In the hydrolysis test, half-lives (t$^{1/2}$) of CENO and DACD was 66.0 hr and 80.0 hr in pH 6.80 buffer, 190 hr and 91.4 hr in pH 8.00 buffer. CENO and DACD were rapidly hydrolyzed in human plasma and in rat liver hornogenate. Half-lives (t$_{1/2}$ of CENO and DACD were 1.29 hr and 1.15 hr in hyman plasma, 0.62 hr and 0.71 hr rat liver homogenate. In $\beta$-lactamase stability test, CENO and DACD were very stable to the .betha.-lactamases obtained from three different strains. Half-life (t$_{1/2}$) and areas under the curve (AUC) in mice were 2.33 hr and 15.97 (mg.h/1), respectively.

• Korean Journal of Food Science and Technology
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• v.42 no.1
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• pp.39-44
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• 2010

The process of the preparation of branched-chain amino acid (BCAA)-enriched hydrolysates from corn gluten was optimized through the parameters of pre-treatment (heating and cellulosic hydrolysis), hydrolysis method (acid, protease, and microbe plus protease), concentration, and spray drying condition. The protein yield of corn gluten was increased by heating and cellulase treatments. Among three different hydrolysis methods, the combined use of microbes and protease was the most effective in terms of free amino acid (FAA) and BCAA content of the corn gluten hydrolysates. In addition, the FAA and BCAA content in the hydrolysates prepared by microbial and enzymatic combined treatment were improved by a concentration process. Spray drying conditions for the preparation of the powder from the hydrolyzed reactant were an inlet temperature of $185^{\circ}C$, outlet temperature of $80^{\circ}C$, and the use of maltodextrin as an anticaking agent. Thus, this study established an economical process for preparation of value-added hydrolysates of excellent productivity and quality, in terms of high BCAA content and product stability.

• Applied Chemistry for Engineering
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• v.5 no.4
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• pp.681-697
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• 1994

The enzymatic hydrolysate of gelatin extracted from fish skin was fractionated and recycled through the membrane reactor according to the molecular weight for the purpose of using as functional material. In addition, the enzymatic hydrolysis conditions of gelatin, enzyme stability by membrane and mechanical shear, and effect on the long-term operational stability of the recycle membrane reactor were investigated. Using the pH-drop technique, Alcalase, pronase E and collagenase were identified as the most suitable enzymes for the hydrolysis of fish skin gelatin. The optimum hydrolysis conditions in the 1st-step membrane reactor(1st-SMR) by Alcalase were enzyme concentration 0.2mg/ml, substrate-to-enzyme ratio(S/E) 50(w/w), $50^{\circ}C$, pH 8.0, reaction volume 600ml and flow rate 6.14ml/min. In the 2nd-SMR by pronase E were enzyme concentration 0.3mg/ml, S/E 33(w/w), $50^{\circ}C$, pH 8.0, reaction volume 600ml and flow rate 6.14ml/min. In the case of 3rd-SMR, enzyme concentration 0.1mg/ml, S/E 100(w/w), $37^{\circ}C$, pH 7.5, reaction volume 600ml and flow rate 10ml/min. Decreased enzyme activities by mechanical shear and membrane were 30% and 15% in the 1st-SMR, were 14% and 5% in the 2nd-SMR, and 18% and 8% in the 3rd-SMR, respectively. Under the optimum conditions, the degree of hydrolysis in the 1st, 2nd and 3rd-SMR were 3.5%(Kjeldahl method, 87%), 3.1%(77%) and 2.7%(70%), respectively. The productivity of hydrolysate in the continuous three-step membrane reactor was 430mg per enzyme(mg) for 10 times of volume replacements.

• 한국생물공학회:학술대회논문집
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• 2000.11a
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• pp.167-170
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• 2000

Proteolytic hydrolysis is one of the main enzymatic reaction of waste activated sludge (WAS) digestion. Pretense excreted from Bacillus stearothermophilus (ATCC 31197) showed optimum temperature of $75^{\circ}C$ for maxium heat stable proteolytic activity against azo casein. The dependency of $Ca^{2+}$, $Zn^{2+}$ on heat stability of proteolytic enzymes were measured with various concentrations. It was shown that $Ca^{2+}$ ion enhanced heat stability of these enzymes. Then thermophilic aerobic digestion (TAD) was performed using B. sterothermophilus with the addition of divalent ions. Performance of TAD process with ATCC 31197 activated by $Ca^{2+}$, $Zn^{2+}$ions in terms of dissolved organic carbon (DOC) concentration, extracellular protein concentration, and scanning electrion microscopy (SEM) analysis. The best result of protein reduction concentration in digestion test was obtained with the addition of 2 mM $Ca^{2+}$ ion.

• 한국정보디스플레이학회:학술대회논문집
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• 2005.07b
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• pp.1499-1502
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• 2005

Dense $BaMgAl_{10}O_{17}:Eu^{2+}$ phosphor particles with a spherical shape have been synthesized through spray pyrolysis method using basic aluminum nitrate precursor as a spray solution. This $BaMgAl_{10}O_{17}:Eu^{2+}$ particles prepared by the spray pyrolysis have shown the stronger emission intensity compared to the commercially-available $BaMgAl_{10}O_{17}:Eu^{2+}$. However, thermal stability of the BAM:Eu b lue phosphor is very poor due to changing from $Eu^{2+}$ to $Eu^{3+}$ at the thermal process, so brightness of the phosphor decreases. To improve the thermal stability of the dense BAM:Eu phosphor, the spherical BAM:Eu particles were coated with pure $BaMgAl_{10}O_{17}$ layer using the hydrolysis reaction in a solution system. The synthesized powders were characterized by XRD, SEM and PL. On the other hand, the emission properties of the BAM:Eu phosphors coated with $BaMgAl_{10}O_{17}$ layer before and after thermal treatment at $500^{\circ}C$ for 30 min were estimated under VUV excitation. The brightness of the coated phosphor was higher than that of the uncoated phosphor. Also, the coating thickness of BAM layer in the BAM:Eu particles was optimized.