• YAKHAK HOEJI
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• 제32권2호
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• pp.112-116
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• 1988

The resolution of N-trifluoroacetyl (N-TFA) ter-isopropylesters of Ala, Ile, Leu, Val and Phe by gas chromatography on the (S)-5-isobutyl-$N^3$-phenyl-2-thiohydantoin as stationary phase was investigated. The phase was employed at several column temperatures $(140^{\circ}C{\sim}200^{\circ}C)$ and the separation factors were $1.18{\sim}1.45$ range for five amino acid enantiomers. The possible mechanism of chiral recognition was investigated by NMR technique and the association constant$(K_c)$ was calculated as 201.3(r=0.98) for alanyl derivative.

• Textile Coloration and Finishing
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• 제13권5호
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• pp.312-319
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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-ethos y -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 $S_N2$ 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 auto 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.

• Journal of the Korean Chemical Society
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• 제9권1호
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• pp.8-15
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• 1965

Justifications for the use of ${\sigma}$ and Y as independent potential energy variables in the general equation have been reviewed and some mechanistic significances of the relationship discussed. Analysis of the activation parameters for the solvolysis of benzyl chlorides in ethanol-water mixture showed that there are two distinct series of substrate constants ${\alpha}'$, which can be correlated linearly within a series with the substituent constants ${\sigma}$ conforming to the generally accepted concept of change in mechanism from $S_N1$ to $S_N2$.

• Journal of the Korean Chemical Society
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• 제34권5호
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• pp.483-489
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• 1990

The rate of hydrolysis of insecticidal 2-chloro-l-(2,4,5-trichlorophenyl)-vinyldimethylphosphate(Gardona) have been investigated in 25${\%}$ aqueous methanol. Studies at varying pH suggest that the hydrolysis of Gardona proceeds through the bimolecular (Ad$_{N-E}$) mechanism involving the transition state and carbanion intermediate as evidenced by solvent effect (m < 0.4, n < 0.7, [m] ${\ll}$ [l](associative SN$_2$ type)), thermodynamic parameters (${\{Delta}S^{\neq}$ = -27∼-32 e.u. & ${\{Delta}H^{\neq}$ = 13∼18 Kcal/mole), hydrolysis rate equation (k = k$_A+_B$ [OH-]), general base catalysis and hydrolysis product analysis, respectively.

• Journal of the Korean Chemical Society
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• 제37권3호
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• pp.287-293
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• 1993

Ultraviolet spectrophotometric investigation has been carried out on the system of charge-transfer(CT) complex with iodine and tetramethyltin in n-hexane and acetone. From these results, the transient CT absorption spectrum can be observed and the subsequent disappearance of CT absorption spectrum is accompained by the cleavage of tetramethyltin with iodine (iododestannylation). Therefore, the rate constants for the iododestannylation were determined at 10, 25 and 35$^{\circ}C$ up to 1600 bar and the rates of reaction were increased with increasing temperature and pressure. From these rate constants, the values of the activation parameters (${\Delta}V^{\neq}$, ${\Delta}{\beta}^{\neq}$, ${\Delta}H^{\neq}$ and ${\Delta}S^{\neq}$) were obtained and discussed in terms of solvent structure variation of transition state and mechanism from these values. It could postulated that the reaction is followed with S$_F$2 mechanism and weakened S$_F$2 mechanism nature by increasing pressure.

• Journal of Microbiology and Biotechnology
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• 제19권1호
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• pp.37-41
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• 2009

Previous studies have demonstrated that Shewanella decolorationis S12 can grow on the azo compound amaranth as the sole electron acceptor. Thus, to explore the mechanism of energy generation in this metabolism, membranous vesicles (MVs) were prepared and the mechanism of energy generation was investigated. The membrane, which was fragmentized during preparation, automatically formed vesicles ranging from 37.5-112.5 nm in diameter under electron micrograph observation. Energy was conserved when coupling the azoreduction by the MVs of an azo compound or Fe(III) as the sole electron acceptor with $H_2$, formate, or lactate as the electron donor. The amaranth reduction by the vesicles was found to be inhibited by specific respiratory inhibitors, including $Cu^{2+}$ ions, dicumarol, stigmatellin, and metyrapone, indicating that the azoreduction was indeed a respiration reaction. This finding was further confirmed by the fact that the ATP synthesis was repressed by the ATPase inhibitor N,N'-dicyclohexylcarbodiimide (DCCD). Therefore, this study offers solid evidence of a mechanism of microbial dissimilatory azoreduction on a subcell level.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 한국윤활학회 2000년도 제32회 추계학술대회 정기총회
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• pp.406-413
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• 2000

The friction and wear behaviors of Magnetron Sputtered MoS$_2$films were investigated by using a pin on disk type tester which was designed and manufactured for this experiment. The experiment was conducted by using silicon nitride (Si$_3$N$_4$) as a pin material and Magnetron Sputtered MoS$_2$on bearing steel (STB2) as a disk material, under operating conditions that include different surface roughness (Polishing specimen, Grinding specimen)(2types), linear sliding velocities in the range of 22, 44, 66mm/sec (3types), normal loads vary from 9.8N, 19.6N, 29.4N(3types), corresponding to contact pressures of 1.9∼2.7GPa and atmospheric conditions of high vacuum( 1.3${\times}$10$\^$-4/Pa), medium vacuum( 1.3${\times}$10$\^$-l/Pa), ambient air(10$\^$5/Pa)(3types). We investigated fracture mechanism in magnetron sputtered MoS$_2$films with Magnetron Sputtering method in each experiment.

• Journal of the Korean Chemical Society
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• 제28권3호
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• pp.155-162
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• 1984

Kinetic studies for the nucleophilic substitution reactions of para-substituted benzyl bromides and benzyl iodide with anilines were carried out in MeOH-MeCN mixtures at 35.0$^{\circ}$C. Hammett $ {\rho}_N,\;{\rho}_C$, Bronsted $ {\beta}$ and solvatochromic correlation coefficient a, s values were determined in order to clarify the transition state variations caused by changing nucleophiles, substituents, leaving group and solvents. The results of solvatochromic equation showed that ${\pi}^{ast}$effect was a dominant factor for the reaction systems studied. It was shown that the reaction proceeds via the dissociative $S_N$2 mechanism using the potential energy surface model approach. The potential energy surface model approach however failed to account for the transition state variation due to leaving group changes. The quatum mechanical approach showed that kinetic results were consistent with proposed dissociative $S_N$2 mechanism.

• Bulletin of the Korean Chemical Society
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• 제32권5호
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• pp.1539-1542
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• 2011

The aminolysis of O-methyl S-aryl thiocarbonates with benzylamines are studied in acetonitrile at -45.0$^{\circ}C$. The ${\beta}_X$(${\beta}_{nuc}$) values are in the range 0.62-0.80 with a negative cross-interaction constant, ${\rho}_{XZ}$ = -0.42, which are interpreted to indicate a concerted mechanism. The kinetic isotope effects involving deuterated benzylamine nucleophiles ($XC_6H_4CH_2ND_2$) are large, $k_H/k_D$ = 1.29-1.75, suggesting that the N-H(D) bond is partially broken in the transition state by forming a hydrogen-bonded four-center cyclic structure. The concerted mechanism is enforced by the strong push provided by the MeO group which enhances the nucleofugalities of both benzylamine and arenethiolate from the putative zwitterionic tetrahedral intermediate.

• Journal of the Korean institute of surface engineering
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• 제32권3호
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• pp.416-422
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• 1999

The characteristics of inductively coupled Cl$_2$/BCl$_3$ plasmas during the GaN etching were studied using plasma mass spectrometry by measuring the relative amounts of reactive ions, neutrals, and etch products. GaN etch rates increased with the increase of pressure and showed a maximum near 25mTorr for the pure $Cl_2$ and near 30mTorr for $Cl_2$$BCl_3$. The addition of$ BCl_3$ to $Cl_2$ also was increased GaN etch rates until 50%BCl$_3$ was mixed to $Cl_2$. The GaN etching with pure $Cl Cl_2$ appears to be related to the combination of Cl$_2^{+}$ ion bombardment and the chemical reaction of Cl radicals. In the case of the GaN etching with Cl$_2$/BCl$_3$, in addition to the combined effect of$_2^{ +}$ ions and Cl radicals, $_BCl2^{+ }$ ions appear to be responsible for some of GaN etching even though they do not have significant effect on the GaN etching compared to $Cl_2^{+}$ and Cl. $Ga^{+ }$ , $GaCl^{+}$ , $GaCl_2^{+}$ , and $N_2^{+}$ were observed as the positive ions of etch products, and the intensities of these etch products showed the same trends as those of GaN etch rate. Among the etch products, Ga and $N_2$ appear to be the main etch products.