• Applied Biological Chemistry
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• v.37 no.5
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• pp.414-420
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• 1994

Birnessite, pyrolusite and hausmannite were synthesized and tested for the ability to oxidize Cr(III) to Cr(VI). These oxides differed in zero point of charge, surface area, and crystallinity. The kinetic study showed that Cr(III) oxidation on the Mn-oxide surface is a first-order reaction. The reaction rate was various for different oxide at different conditions. Generally the reaction by hausmannite, containing Mn(III), was faster than the others, and oxidation by pyrolusite was much slower. Solution pH and initial Cr(III) concentration had a significant effect on the reaction. Inhibited oxidation at higher pH and initial Cr(III) concentration could be due to the chance of Cr(III) precipitation or complexing on the oxide surface. Oxidations by birnessite and hausmannite were faster at lower pH, but pyrolusite exhibited increased oxidation capacity at higher pH in the range between 3.0 and 5.0. Reactions were also temperature sensitive. Although calculated activation energies for the oxidation reactions at pH 3.0 were higher than the general activation energy for diffusion, there is no experimental evidence to suggest which reaction is the rate limiting step.

• Macromolecular Research
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• v.13 no.6
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• pp.467-476
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• 2005

The main objective of this study was to develop and characterize pH-sensitive biodegradable polymeric materials. For pH-sensitivity, we employed three kinds of moieties: 2-amino-3-(lH-imidazol-4-yl)-propionic acid (H), N-[4-( 4,6-dimethyl-pyrimidin-2ylsulfamoyl)-phenyl]succinamic acid (SM), and 2- {3-[ 4-( 4,6-dimethyl-pyrim­idin- 2-ylsulfamoyl)-phenylcarbamoyl]-propionylamino} -3-(3 H - imidazol-4-yl)-propionic acid (SH). The pH -sensitive diblock copolymers were synthesized by ring opening polymerization and coupling reaction from poly(ethylene glycol) (MPEG), $\varepsilon$-caprolactone (CL), D,L-lactide (LA) and pH-sensitive moieties. The pH-sensitive SH molecule was synthesized in a two-step reaction. The first step involved the synthesis of SHM, a methyl ester derivative of SH, by coupling reaction of SM and L-histidine methyl ester dihydrochloride, whereas the second step involved the hydrolysis of the same. The synthesized SM, SHM and SH molecules were characterized by FTIR, $^{1}H$-NMR and $^{13}C$-NMR spectroscopy, whereas diblock copolymers and pH-sensitive diblock copolymer were characterized by $^{1}H$-NMR and GPC analysis. The critical micelle concentrations were determined at various pH conditions by fluorescence technique using pyrene as a probe. The micellization and demicellization studies of pH-sensitive diblock copolymers were also done at different pH conditions. The pH-sensitivity was further established by acid-based titration and DLS analysis.

• Journal of environmental and Sanitary engineering
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• v.19 no.1
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• pp.1-7
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• 2004

This study was conducted to supply basic informations on development of water treatment process for the ozonation of ammonia depend on pH variation with or without bromide catalysis. The results were as follows: The oxidation rate of ammonia increased depend on pH increase at ozone/bromide process. It was found that overall kinetics was zero order with respect to reaction time and reaction velocity constant of zero order increased depend on pH increase from 4.9 to 9.5 and the equation of linearization was $k_{o}$ = 0.00565 ${\times}$ [pH] + 0.0069 at ozone/bromide process. The denitrification reaction of ammonia was superior as the pH increase in the presence of bromide.

• Journal of Microbiology and Biotechnology
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• v.28 no.8
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• pp.1346-1351
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• 2018

Oxidoreductases are effective biocatalysts, but their practical use is limited by the need for large quantities of NAD(P)H. In this study, a whole-cell biocatalyst for NAD(P)H cofactor regeneration was developed using the economical substrate glycerol. This cofactor regeneration system employs permeabilized Escherichia coli cells in which the glpD and gldA genes were deleted and the gpsA gene, which encodes $NAD(P)^+-dependent$ glycerol-3-phosphate dehydrogenase, was overexpressed. These manipulations were applied to block a side reaction (i.e., the conversion of glycerol to dihydroxyacetone) and to switch the glpD-encoding enzyme reaction to a gpsA-encoding enzyme reaction that generates both NADH and NADPH. We demonstrated the performance of the cofactor regeneration system using a lactate dehydrogenase reaction as a coupling reaction model. The developed biocatalyst involves an economical substrate, bifunctional regeneration of NAD(P)H, and simple reaction conditions as well as a stable environment for enzymes, and is thus applicable to a variety of oxidoreductase reactions requiring NAD(P)H regeneration.

• Korean Journal of Crystallography
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• v.11 no.4
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• pp.224-230
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• 2000

We have been investigated the flaking mechanism of the soda-line glass. The pH of aqueous solution approached to 10 and increased with reaction time by ion exchange reaction between Na/sup +/ ion of glass and H/sup +/ ion of aqueous solution under the conditions of below pH 9 of start solution. The relationship between the pH of solution and reaction time shows logarithm. Total dissolution reaction of glass components by OH/sup -/ ion in aqueous seems to be dominant after the pH solution reached to 10 and the dissolution rate linearly increased with reaction time. The above tow reactions are simultaneously occurred. The dissolved Ca/sup 2+/ ions are reprecipitated on the glass surface to Ca-compound. The flakes are formed by the separation of leached layer of glass due to the different thermal expansion coefficient.

• Korean Journal of Food Science and Technology
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• v.18 no.1
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• pp.55-60
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• 1986

The effects of temperature (70-$100^{\circ}C$), pH (3-8) and various sugars were investigated on the reaction rate, activation energy and z-value of Maillard reaction of 0.8m sugar and 0.8m glycine mixture. The sugars compared were glucose, fructose, lactose and sucrose, and the reaction was evaluated by absorbances at 278nm for pyrazine compounds and at 400nm for brown pigments. Fructose-glycine mixture showed a faster initial reaction rate than that of glucose-glycine, which was reversed by the order of glucose > fructose > lactose > sucrose after 10 hrs of reaction at pH 5.8 and $100^{\circ}C$. Generally, higher activation energy was required for forming pyrazines than that of brown pigment development. The highest z-value was obtained for lactose-glycine mixture, followed by glucose or fructose-glycine which had almost same z-value. The reaction rate was little affected by the pH change in the range of 4-6, while pH < 3 and pH 6-8 caused a significant increase in the rates.

• Preventive Nutrition and Food Science
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• v.13 no.1
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• pp.54-59
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• 2008

This study was conducted to investigate the effect of pH on the formation of furfural compounds from glucose and fructose reacting with amino acid enantiomers in the Maillard reaction. Hydroxymethylfurfural (HMF) content was highest at pH 4.0, and decreased with increasing pH. HMF was significantly higher in glucose-based systems than fructose-based systems. Furfuryl alcohol (FFA) and 5-methyl-2-furaldehyde (MF) were not increased with increasing pH, and only small amounts were formed. In addition, 2-furaldehyde (F) was found to increase in the systems, as pH increased. However, the content was small and variable. 2,5-Dimethyl-4-hydroxy-3(2H)-furanone (DMHF) was only found in Glc/D-Asn, Glc/L-Lys and Fru/D-Lys system, but the content was not increased with increasing pH. 2-acetylfuran (AF) was higher in Glc (or Fru)/L-Lys and Glc (or Fru)/D-Lys systems at pH 7.0. However, at pH 4.0, the content of AF was higher in the Glc (or Fru)/Gly and Glc (or Fru)/L-Asn systems. Therefore, this study aimed to observe the effect of pH, sugars and amino acid enantiomers on the production of furfural and related compounds by the Maillard reaction. A clear tendency was observed for some classes of compounds to be more easily formed at higher or lower pH. HMF was more readily formed at lower pH, while FFA, F, DMHF and MF were inhibited by acidic conditions. Particularly, compounds like FFA, F and MF were not affected by pH changes. In addition, DMHF and MF were only formed in L-Lys and D-Lys system.

• KSBB Journal
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• v.13 no.3
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• pp.284-288
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• 1998

Production of inulo-oligosaccharides from inulin was carried out with the maximum yield of 94% using a purified endoinulinase from Aspergillus ficcum. The optimum reaction temperature and pH were 55-60$^{\circ}C$ and pH 5.5-6.0, respectively. The Michaelis constant and maximum reaction velocity of the endoinuinase for inulin were 13.27 g/L and 0.13 g/L$.$min at 55$^{\circ}C$, pH 5.5, respectively. Inulin source had no significant effect on oligosaccharide yield and product composition, although initial production rate differed according to inulin origins. The reaction pH was a critical factor in inulo-oligosaccharide production because considerable free monosaccharides were released, decreasing oligosaccharide yield at low pH conditions. An empirical relationship describing the reaction performance was developed from kinetic data: the time to reach maximum oligosaccharide yield (tw) as a function of initial concentration of inulin (lo) and enzyme (Eo); i.e., log tM = -1.025 log Eo - 0.011 l0 + 2.655.

• Journal of the Korean Wood Science and Technology
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• v.30 no.3
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• pp.1-11
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• 2002

This study was conducted to investigate the effects of reaction pH conditions and hardener types on the reactivity, chemical structure and adhesion performance of UF resins. Three different reaction pH conditions, such as traditional alkaline-acid (7.5 → 4.5), weak acid (4.5), and strong acid (1.0), were used to synthesize UF resins which were cured by adding three different hardeners (ammonium chloride, ammonium citrate, and zinc nitrate) to measure adhesion strength. Fourier transform infrared (FT-IR) and carbon-13 nuclear magnetic resonance (¹³C-NMR) spectroscopies were employed to study chemical structure of the resin prepared under three different reaction pH conditions. Adhesion strength of the resins cured with three different hardeners was determined with lap shear specimens in tension. The gel time of UF resins decreased with an increasing in the amount of both ammonium chloride and ammonium citrate added in the resins. However, the gel time increased for zinc nitrate. Both FT-IR and ¹³C-NMR spectroscopies showed that the strong reaction pH condition produce uronic structures in UF resin, while both alkaline-acid and weak acid conditions produce quite similar chemical species in the resins. The maximum adhesion strength was occurred with the resin prepared under strong acid pH condition. However, this study indicated that the weak acid reaction condition provide a balance between increasing resin reactivity and improving adhesion strength of UF resin. The measurement of formaldehyde emission from the panels bonded with the UF resins prepared is planned for future work.

• Journal of the Korean Chemical Society
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• v.18 no.6
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• pp.423-429
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• 1974

The rate constant of the addition of hydrogen cyanide to $ ${\alpha}$-cyano-\beta-piperonylacrylic$ acid (CPA) were determined by UV spectrophotometry at various pH and a rate equation which can be applied over wide pH range was obtained. From this equation, one may conclude that below pH 3 the reaction is started by the addition of hydrogen cyanide molecule to CPA, however, at pH 6~8, hydrogen cyanide is added to $ {\alpha}$-cyano-$ {\beta}$-piperonyl acrylate anion. From pH 3 to 6, these two reaction are competitive. Above pH 9, the reaction is proceeded by the addition of cyanide ion to $ {\alpha}$-cyano-$ {\beta}$-piperonyl acrylate ion. From pH 3 to 9, the complex reaction mechanism can also be fully explained by the rate equation obtained.