• Bulletin of the Korean Chemical Society
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• v.9 no.5
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• pp.298-303
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• 1988

Kinetic studies on cupric ion ($Cu^{2+}$) oxidation of 1-benzyl- and 1-aryl-1,4-dihydronicotinamides (XNAH) in aqueous solution were performed. In the presence of dioxygen ($O_2$), the reaction followed first order kinetics with respect to both XNAH and $Cu^{2+}$. The oxidation reaction was found to be independent and parallel to the acid-catalyzed hydration reaction of XNAH. The catalytic role of $Cu^{2+}$ for the oxidation of XNAH in the presence of $O_2$ was attributed to $Cu^{2+}/Cu^+$ redox cycle by the reactions with XNAH and $O_2$. The second order rate constants of the Cu2+ oxidation reaction kCu, and acid-catalyzed hydration reaction $k_H$ were strongly dependent on the nature of the substituents in 1-aryl moiety. The slopes of log $k_{Cu}$ vs log $K_H$ and log $k_{Cu}$ vs ${\sigma}_p$ of the substituents plots were 1.64 and -2.2, respectively. This revealed the greater sensitivity of the oxidation reaction rate to the electron density on the ring nitrogen than the hydration reaction rate. A concerted two-electron transfer route involving XNAH-$Cu^{2+}$ complex was proposed for mechanism of the oxidation reaction.

• Applied Biological Chemistry
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• v.26 no.1
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• pp.1-7
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• 1983

The hydration of two japonica(Akibare and Milyang 15) and four indica(Milyang 30, Suweon 287, Suweon 294 and Iri 342) rice varieties was investigated in terms of mathematical rate equation. The hydration rate at temperatures of $4{\sim}32^{\circ}C$ was examined by a weighing method. The absorption of water was directly proportiponal to the square root of the hydration time(t) and was described by the diffusion equation: $1-\bar{M}=(2/\sqrt{\pi})(S/V)\;\sqrt{Dt},\;where\;\bar{M}$ is dimensionless moisture ratio, S/V is the surface-to-volume ratio and D is diffusion coefficient. The average D value was given by the Arrhenius relation: $D=D_0\;\exp(-E_a/TR)$. The activation energy was $4{\sim}5kcal/mole$. The rice samples could be classified into three groups based on hydration kinetics: Milyang 30-Suweon 287; Akibare-Milyang 15; and Suweon 294-Iri 342.

• Korean Journal of Food Science and Technology
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• v.16 no.3
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• pp.297-302
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• 1984

Kinetics of water diffusion during soaking of two brown rice varieties, Akibare (traditional rice) and Milyang 23 (high-yielding rice), were studied. Brown rice reached at the equilibrium moisture content after 18 hours. The absorption of liquid water by brown rice grain was directly proportional to the square root of hydration time and could be described by the simplified solution of Fick's diffusion equation. The diffusion coefficient was given by the Arrhenius relation: $D\;=\;2.738{\time}10^{-1}\;exp\;(-9,300/RT)$ for Akibare and $D\;=\;4.302{\time}10^{-1}\;exp\;(-9,500/RT)$ for Milyang 23. Hydration rate calculated from hardness change followed the equation of a first order reaction. Hydration mechanism of brown rice was changed at the gelatinization temperature of rice starch.

• Journal of Korean Society of Water and Wastewater
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• v.19 no.1
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• pp.53-60
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• 2005

Ferrous cement hydrates made from hydrating Portland cement doped with Fe (II) were reported to reductively dechlorinate chlorinated organics and to reduce Cr (VI) to Cr (III). In this study, kinetics of nitrate removal by ferrous cement hydrates were investigated. Nitrate removal kinetics were characterized by experimental variables such as cement hydration, amount of cement addition, Fe (II) dose, pH, and byproducts. As a result, hydrated cement showed better performances than non-hydrated cement due to the formation of LDH (layered double hydroxide). Doping of Fe (II) into the cement was found to improve removal efficiency at high pHs by association with Fe (II) sorbed on cement hydrates as a reactive reductant. Reduction of nitrate produced ammonium as a major product, which accounted for 63.5% of the final products, and nitrite (0.15%) as a minor product. These results indicate that the developed media are effective as sorbent/reducing agents in the nitrate removal and the reaction mechanisms of nitrate removal are sorption and reduction.

• Journal of the Korea Concrete Institute
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• v.17 no.6 s.90
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• pp.1019-1024
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• 2005

To research effects of various chemical superplasticizers(Lignosulfonic acid, Naphthalene sulfonated formaldehyde condensate, melamine sulfonated formaldehyde condensate, and Polycarboxylate) on the hydration of cement, experiments involving XRD, SEM, and DSC have been analysed with cement paste specimens. Regardless of types and dosages of superplasticizers, hydration reaction of specimen applied superplasticizer was delayed to 3 day, but then it showed similarity to plain which don't add superplasticizer. Moreover, the hydrating rate of cement paste was retarded as dosage of superplasticizer was increased. Also, kinetics related with hydrate of cement paste was slow in order of lignosulfonic acid, polycarboxylate, melamine and naphthalene sulfonated formaldehyde condensate. Nevertheless, when all kinds of chemical admixtures were used, morphologies of these hydrates were denser and more uniform than those of plain.

• Korean Journal of Environmental Agriculture
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• v.23 no.2
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• pp.111-116
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• 2004

Salt occlusion in Zeolite is a unique phenomenon that takes place only when the salt size is similar to the window size of host zeolite. $KCIO_3$-occluded Zeolite, as an environment-friendly oxidant, has a high potential for effective removal of various organic pollutants. This study was carried to investigate the characteristics and the removal kinetics of fungicide chlorothalonil by zeolite-$KCIO_3$ complex. About 10% of $KCIO_3$ was occluded in zeolite pores synthesized by salt-thermal method from fly ash, although the occlusion amount was relatively less compared to that of nitrate salts. By occlusion with $KCIO_3$, no remarkable changes were found in X-ray diffraction patterns of cancrinite, whereas some decrease of overall peak intensities was found with those of sodalite. Different releasing kinetics of $CIO_3^-$ ion were observed in distilled water and soil solution from zeolite-$KCIO_3$ complex. Two reactions, hydration and diffusion, seem to be related with the release of $KCIO_3$. Therefore, the release isotherm of $CIO_3^-$ ion well fitted to the power function model which indicate the release was made by hydration and diffusion. The removal of chlorothalonil by zeolite and $KCIO_3$ reached at reaction equilibrium within 6 hours by 18% and 47% respectively. However, the chlorothalonil removal by the zeolite-$KCIO_3$ complex increased slowly and steadily up to 92% in 96 hours. These findings suggested that zeolite-$KCIO_3$ complex could be applied for effective removal of organic contaminants in the soil and aqueous environment.

• Journal of the Korean Chemical Society
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• v.35 no.6
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• pp.607-611
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• 1991

The stereochemical ratio cis and trans isomer of the hydration reaction of trans-$[Co(en)(tmd)Cl_2]^+$ complex ion were studied with varing temperature by the spectrophotometric method. It was observed that the ratio of cis-isomer was about 30%, and the intermediate was rearranged. And in order to investigate this mechanism more clearly, stability energy profile, interaction diagram and orbital correlation diagram were calculated by the EHT method. By the calculation, the mechanism of cis-isomer was in good agreement with the experimental results, and it was estimated that the hydration reaction was carried through some distorted square pyramid (sp).

• BMB Reports
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• v.35 no.4
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• pp.358-363
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• 2002

Chemical and photochemical processes during storage and preparation rapidly degrade retinol, the most active form of vitamin A. therefore, the efficacy of incorporation into liposomes in order to modulate the kinetics of retinol degradation was investigated. Retinol was readily incorporated into multilamellar liposomes that were prepared form soybean phosphatidylcholine; the extent of the incorporation was 98.14±0.93% at pH 9.0 at a ratio of 0.01 : 1 (wt:wt) retinol : phospholipid. It was only marginally lower at higher retinol concentrations. The pH of the hydration buffer had a small effect. The incorporation efficiency ranged from 99.25±0.47% at pH 3 to 97.45±1.13% at pH 11. The time course of the retinol degradation in the aqueous solution in liposomes was compared to that of free retinol and free retinol with α-tocopherol under a variety of conditions of pH(3, 7, and 11), temperature(4, 25, 37, and 50℃), and light exposure(dark, visible, and UV). The retinol that was incorporated into the liposomes degraded significantly slower than the free retinol or retinol with α-tocopherol at pH 7 and 11. At pH 3, where the free retinol degrades rapidly, the degradation kinetics were similar in liposomes and the presence of α-tocopherol. At pH 7.0 and 4℃ in the light, for example, free aqueous retinol was completely degraded within 2 days, while only 20% of the retinol in the liposomes were degraded after 8 days. In general, the protective effect of the liposome incorporation was greater at low temperatures, at neutral and high pH, and in the dark. The results suggest that protection is greater in the solid, gel phase than in the fluid liquid crystalline phase lipids. These results indicate that the incorporation into liposomes can extend the shelf-life of retinol under a variety of conditions of temperature, pH, and ambient light conditions.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.41 no.4
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• pp.357-364
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• 2021

The present study investigated the hydration properties and NO_x-removal performances of the cement pastes containing three different types of TiO₂. Two commercially available TiO₂ (P-25 and NP-400) and refined TiO₂ (GST) obtained from waste sludge were incorporated to cement paste at levels of 0, 5, 10, and 20 wt%. Isothermal calorimetry test results indicated that the TiO₂ incorporation induced a notable influence on the reaction kinetics of cement paste, showing the highest cumulative heat release in the samples containing P-25, followed by NP-400 and GST. Quantitative X-ray diffractometry as calculated by the Rietveld method identified that the incorporated TiO₂ promoted the formation of C-S-H, ultimately leading to the enhancement in the 28 day-compressive strength of cement pastes. As revealed by SEM/EDS analysis, the content of distributed Ti elements on the surface of the samples was in the order of P-25, GST, and NP-400. Regardless, the NO_x-removal performance was the highest in the sample containing P-25, followed by NP-400 and GST.

• Applied Biological Chemistry
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• v.27 no.3
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• pp.204-210
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• 1984

Hydration of twelve japonica (j) and nine j x indica rice varieties was analyzed in terms of mathematical rate equation and a tentative classification of milled rice was attempted primarily on the basis of water uptake race of rice grain at room temperature. No two rice varieties had the same water uptake rate or diffusion coefficient. The rice samples could be classified into three groups. Rices which are considered as having good eating quality had lower water uptake rate.