• Applied Biological Chemistry
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• v.37 no.2
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• pp.124-129
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• 1994

The rate of hydrolysis of insecticidal $O,O-diethyl-{\alpha}-cyanobenzylideneamino-oxyphosphorothioate\;(Volaton^{\circledR})$ has been studied in 25% (v/v) aqueous dioxane. On the basis of solvent effect (pH 6.0; m=0.21, n=1.55, pH 12.0; m=0.42, n=3.14 & $|m|{\ll}|l|$), general base catalysis, hydrolysis product analysis, calculation of molecular orbital (MO) and rate equation, it may be concluded that the hydrolysis of Volaton proceeds through the $A_{AC}2$ mechanism via trigonal bipyramidal $(sp^3d^2)$ intermediate below pH 7.0, while above pH 9.0 the hydrolysis proceeds through the $B_{AC}2$ mechanism. Hydrolysis reactivity of Volaton depends on positive charge strength $(p{\gg}{\alpha}C_2)$ rather than steric hindrance. In the range between pH 7.0 and pH 9.0, these two reactions occur competitively.

• Bulletin of the Korean Chemical Society
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• v.27 no.2
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• pp.224-230
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• 2006

Escherichia coli transcription termination factor Rho catalyzes the unwinding of RNA/DNA duplex in reactions that are coupled to ATP binding and hydrolysis. We report here the kinetic mechanism of presteady state ATP binding and hydrolysis by the Rho-RNA complex. Presteady state chemical quenched-flow technique under multiple turnover condition was used to probe the kinetics of ATP binding and hydrolysis by the Rho-RNA complex. The quenched-flow presteady state kinetics of ATP hydrolysis studies show that three ATPs are bound to the Rho-RNA complex with a rate of $4.4\;{\times}\;10^5M^{-1}s^{-1}$, which are subsequently hydrolyzed at a rate of $88s^{-1}$ and released during the initiation process. Global fit of the presteady state ATP hydrolysis kinetic data suggests that a rapid-equilibrium binding of ATP to Rho-RNA complex occurs prior to the first turnover and the chemistry step is not reversible. The initial burst of three ATPs hydrolysis was proposed to be involved in the initialization step that accompanies proper complex formation of Rho-RNA. Based on these results a kinetic model for initiation process for Rho-RNA complex was proposed relating the mechanism of ATP binding and hydrolysis by Rho to the structural transitions of Rho-RNA complex to reach the steady state phase, which is implicated during translocation along the RNA.

• Journal of the Korean Applied Science and Technology
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• v.9 no.2
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• pp.119-126
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• 1992

The kinetics of the hydrolysis of indolylacrylophenone derivatives(IA) was investigated by ultraviolet spectrophotometry in 30% dioxane-$H_2O$ at 25$^{\circ}C$ Rate equations were obtained over a wide pH range. On the basis of rate equation, general base catalysis and Hammett's plot, the mechanism of hydrolysis to the (IA) were proposed: Below pH 3.0, the hydrolysis of (IA) was proportional to hydronium ion concentration, between pH 4.0${\sim}$9.0 neutral water molecule and hydroxide ion were added to carbon-carbon double bond and over pH 10.0 hydrolysis of (IA) was proportional to hydroxide ion concentration.

• Journal of the Korean Chemical Society
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• v.39 no.8
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• pp.650-656
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• 1995

Rate Constants of hydrolysis of N-(benzenesulfonyl)-C-(N-methylanilino)imidoyl chlorides were determined by UV spectrophotometry in 50% (v/v) aqueous methanol at 25$^{\circ}C.$ On the basis of rate equation, substituent effect, solvent effect, salt effect, thermodynamic parameters and hydrolysis product analysis, it may be concluded that the hydrolysis of N-(benzenesulfonyl)-C-(N-methylanilino)imidoyl chlorides proceed through $S_N1$ mechanism via azocarbonium ion intermediate below pH 9.0, while aebove pH 10.0 the hydrolysis proceeds through nucleophilic addition-elimination ($Ad_{N-E}$) mechanism.

• Journal of the Korean Chemical Society
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• v.37 no.6
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• pp.618-625
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• 1993

Rate constants of hydrolysis of N-(benzoyl)-C-(N-methylanilino)imidoylchlorides were determined by UV spectrophotometry in 50% (v/v) aqueous methanol at 25$^{\circ}C$. On the basis of rate equation, substituent effect, solvent effect, salt effect, thermodynamic parameters and hydrolysis product analysis, it may be concluded that the hydrolysis of N-(benzoyl)-C-(N-methylanilino)imidoylchlorides proceed through $S_N$1 mechanism via azocarbonium ion intermediate in the range of from pH 3.0 to pH 10.0, while above pH 10.0 and below pH 3.0 the hydrolysis proceeds through nucleophilic addition-elimination (A$d_{N-E}$) mechanism.

• Journal of the Korean Chemical Society
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• v.41 no.4
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• pp.198-204
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• 1997

The rate constants for the hydrolysis of N-(2,4-dinitrophenyl)benzhydrazonyl bromide and its derivatives were determined by ultraviolet visible spectrophotometry at 20$^{\circ}C$ and a rate equation which could be applied over a wide pH range was obtained. On the basis of rate equations derived and judging from the solvent effect, substituent effect, salt effect, thermodynamic parameter, plausible mechanisms of hydrolysis have been proposed. It may be concluded that the hydrolysis through SN1 mechanism via carbonium ion intermdiate to pH 3.0, and pH 10.0, the hydrolysis proceeds through 1,3-dipolar or SN2 mechanism.

• Journal of the Korean Chemical Society
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• v.41 no.7
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• pp.351-356
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• 1997

Extended Huckel Molecular Orbital (EHMO) calculations of haloallene (1-halo-3-phenyl-1,2-propadiene) derivatives have been performed. From the MO calculation data and kinetic experimental results, the mechanism for the hydrolysis of haloallenes is proposed.; Below pH 8.0, the hydrolysis proceeds through a solvent assisted $S_N1$ mechanism involving the formation of carbonium ion Ⅱ as intermediate. However above pH 9.5, the hydrolysis proceeds through an $S_N2'$ mechanism via transition state Ⅲ.

• Journal of the Korean Applied Science and Technology
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• v.11 no.1
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• pp.27-31
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• 1994

The rate constants of hydrolysis of ${\alpha}$-phenly-N-iso-propylnitrone and its derivatives have been determined by UV spectrophotometry at $25^{\circ}C$ and a rate equation which can be applied over a wide pH range was obtained. On the basis of rate equations derived and judging from the hydrolysis products obtained and general base and substituent effects, plausible mechanism of hydrolysis in various pH range have been proposed. Below pH 4.5, the hydrolysis was initiated by the protonation and followed by the addition of water to ${\alpha}$-carbon. Above pH 10.0, the hydrolysis was proceeded by the addition of hydroxide ion to ${\alpha}$-carbon. In the range of $4.5{\sim}10.0$, the addition of water to nitrone was rate controlling step.

• Journal of Korean Society of Water and Wastewater
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• v.25 no.3
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• pp.367-373
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• 2011

Mechanism of rapid mixing effect on chemical phosphorus removal is evaluated in this study. Assuming that chemical phosphorus removal is unaffected by mixing time, only rapid mixing intensity is evaluated. In order to find out the mechanism, it is hypothesized that rapid mixing affects the Al hydrolysis speciation, and that formation of more monomeric species ($Al^a$) results in better removal of phosphorus. According to a ferron assay, more $Al^a$ formed at higher mixing intensity than at lower intensity. Subsequent experiments revealed that better phosphorus removal was obtained at higher intensity than at lower intensity, in terms of the molar ratio of $Al_{added}/P_{removed}$. The proposed hypothesis was proved in this study. Chemical phosphorus removal is affected by rapid mixing intensity due to its effect on the Al hydrolysis speciation.

• Textile Coloration and Finishing
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• v.13 no.5
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• pp.24-24
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• 2001

Kinetics and mechanism for alkaline hydrolysis of C. I. Disperse Blue 79(B-79) which is 4-N, N-diacetoxyethyl-2-acylamino-5-ethoxy -2′-bromo-4′,6′-dinitroazobenzene were investigated. The color strength of B-79 in acetone/water solutions of various NaOH concentrations decreased continuously. The hydrolysis rate of B-79 increased with increasing alkali concentration and appeared following first order reaction. The observed rate constants for various concentrations of B-79 showed similar values, and B-79 was hydrolyzed by first order reaction for dye concentration. Therefore, it was confirmed that the overall reaction follow second order kinetics and proceed via S/sub n/2 reaction. From the study on kinetics and spectrometric analysis, it was proposed that the rate determining step of the hydrolysis reaction of B-79 is the nucleophilic substitution reaction - that is the reaction of the rapid attack of $OH^{-}$ on the carbon atom, which is in acceptor ring, adjacent to azo group to break the C-N bond. And it was also found that the final hydrolysis products of B-79 include both the acceptor ring in the form of sodium salt and the donor ring possessing 4-N,N-dihydroxyethyl group converted from 4-N,N-diacetoxyethyl group.