• Journal of the Korean Chemical Society
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• v.24 no.2
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• pp.115-120
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• 1980

A kinetic study of the methanolysis of t-butylbromide and benzoylchloride in methanol-acetonitrile mixtures is reported. First order rate constants for the methanolysis of t-butyl bromide show maximum at $X_{MeOH}$=0.75∼0.9 and 25∼$50^{\circ}C$. Apparent second order rate constants for the methanolysis of benzoylchloride also show maximum at $X_{MeOH}$= 0.6∼0.95 and 12∼$26^{\circ}C$. The maximum rate is ascribed to the solvent structure change; the addition of acetonitrile to methanol perturbs the methanol structure increasing the free methanol molecules available to stabilize the transition state for the methanolysis of t-butylbromide and benzoylchloride. It has been shown that methanol acts as nucleophilic and electrophilic catalyst upon methanolysis of t-butylbromide and as electrophilic catalyst upon methanolysis of benzoylchloride.

• Bulletin of the Korean Chemical Society
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• v.32 no.7
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• pp.2423-2427
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• 2011

Pseudo-first-order rate constants ($k_{obsd}$) have been measured spectrophotometrically for nucleophilic substitution reactions of 3,4-dinitrophenyl diphenylphosphinothioate 9 with alkali metal ethoxides (EtOM, M = Li, Na, K) in anhydrous ethanol at $25.0{\pm}0.1^{\circ}C$. The plot of $k_{obsd}$ vs. [EtOM] is linear for the reaction of 9 with EtOK. However, the plot curves downwardly for those with EtOLi and EtONa while it curves upwardly for the one with EtOK in the presence of 18-crown-6-ether (18C6). Dissection of $k_{obsd}$ into $k_{EtO^-}$ and $k_{EtOM}$ (i.e., the second-order rate constant for the reaction with dissociated $EtO^-$ and ion-paired EtOM, respectively) has revealed that the reactivity increases in the order $k_{EtOLi}$ < $k_{EtONa}$ < $k_{EtO^-}$ ${\approx}$ $k_{EtOK}$ < $k_{EtOK/18C6}$, indicating that the reaction is inhibited by $Li^+$ and $Na^+$ ions but is catalyzed by 18C6-crowned $K^+$ ion. The reactivity order found for the reactions of 9 contrasts to that reported previously for the corresponding reactions of 1, i.e., $k_{EtOLi}$ > $k_{EtONa}$ > $E_{EtOK}$ > $k_{EtO^-}$ ${\approx}$ $k_{EtOK/18C6}$, indicating that the effect of changing the electrophilic center from P=O to P=S on the role of $M^+$ ions is significant. A four-membered cyclic transition-state has been proposed to account for the $M^+$ ion effects found in this study, e.g., the polarizable sulfur atom of the P=S bond in 9 interacts strongly with the soft 18C6-crowned $K^+$ ion while it interacts weakly with the hard $Li^+$ and $Na^+$ ions.

• Journal of the Korean Chemical Society
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• v.29 no.2
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• pp.88-97
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• 1985

1-Anthracenesulfonyl chloride used as a substrate has been prepared from anthra-quinone, and its melting point ($124^{circ}C$) was confirmed to be considerably different from the literature value ($90^{circ}C$). Rates of nucleophilic substitution reactions of this substrate with some p-substituted anilines in dry acetone were determined by electroconductometric method, and their mechanism has been discussed. As a result, it has been found that these reactions proceed in parallel catalyzed by anilines together with noncatalyzed process, and that their catalytic activities are electrophilic. Judging from $Br{\phi}nsted\;{\beta}$ (0.77), Hammett ${\rho}$(-3.2), and activation parameters which were determined from the temperature dependence of noncatalyzed second order rate constants, it appears most appropriate that their mechanism should be discussed in terms of an associative $S_N2$ involving sulfonylammonium intermediate.

• Journal of the Korean Chemical Society
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• v.48 no.4
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• pp.379-384
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• 2004

4-pyrimidylideneacetonitrile derivatives containing $BF_2$-chelate have been synthesized from H-chelates of 4-pyrimidylideneacetonitrile derivatives and boron trifluoride diethyl etherate. These H-chelates were prepared by the electrophilic substitution of 2-cyanomethylpyridine derivatives with electrophiles such as 4,6-dichloropyrimidine, 4,6-dichloro-2-methylpyrimidine, 4,6-dichloro-2-heptadecylpyrimidine, 4,6-dichloro-2-phenylpyrimidine, 4,6-dichloro-5-phenylpyrimidine and 4,6-dichloro-2,5-diphenylpyrimidine. Structures of the target molecules were identified by spectra methods.

• Bulletin of the Korean Chemical Society
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• v.33 no.12
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• pp.4169-4172
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• 2012

To elucidate the roles of cysteine residues in rice Phi-class GST F3, in this study, all three cysteine residues were replaced with alanine by site-directed mutagenesis in order to obtain mutants C22A, C73A and C77A. Three mutant enzymes were expressed in Escherichia coli and purified to electrophoretic homogeneity by affinity chromatography on immobilized GSH. The substitutions of Cys73 and Cys77 residues in OsGSTF3 with alanine did not affect the glutathione conjugation activities, showing non-essentiality of these residues. On the other hand, the substitution of Cys22 residue with alanine resulted in approximately a 60% loss of specific activity toward ethacrynic acid. Moreover, the ${K_m}^{CDNB}$ value of the mutant C22A was approximately 2.2 fold larger than that of the wild type. From these results, the evolutionally conserved cysteine 22 residue seems to participate rather in the structural stability of the active site in OsGSTF3 by stabilizing the electrophilic substrates-binding site's conformation than in the substrate binding directly.

• Bulletin of the Korean Chemical Society
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• v.20 no.8
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• pp.948-952
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• 1999

Electrophilic substitutions on β-position of 2,5-dimethyl pyrrole have been investigated theoretically. The electron donating methyl groups enrich electron densities on C-3, C-4 positions and π* interactions with methyl groups substituted on C-2 and C-5 positions pushed up the HOMO level of the pyrroles consequently induce rapid substitutions on C-3, C-4 sites. Substitution of phenylsulfonyl group on nitrogen stabilized LUMO levels through weak π bonding interactions. Unexpected deoxidation reaction underwent on the sulfonyl group substituted at C-3 position. The structures were solved by X-ray crystallography. Meanwhile, gas phase HF/6-31G* and density functional method (B3LYP/6-31G*) calculations gave favorable energies for 1-phenylsulfinyl pyrrole (6) over 3-phenylsulfinyl pyrrole (5) by 3.6-4.7 kcal/mol which is contrary to the experimental result. However the methods involve the effects of molecular polarizability and solvent, molecular dynamics (MD) and ab-initio self consistent reaction field (SCRF) calculations showed same trend as experiments. According to MD calculations, compound 5 is more stable than compound 6 by 4.15 kcal/mol and the SCRF, HF/6-31G* calculations gave more stable energy value for structure 5 than 6 by 0.03 kcal/mol.

• Bulletin of the Korean Chemical Society
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• v.16 no.6
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• pp.524-528
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• 1995

The reaction of [IrCl(cod)]2 with ppol ligand, Ph2PCH2CH2CH2P(Ph)CH2CH2CH=CH2, in ethanol gives an iridium complex, whose structure is converted from an ionic form, [Ir(cod)(ppol)]Cl·2C2H5OH (1),in polar solvents (ethanol, methanol and acetonitrile), to a molecular form, [IrCl(cod)(ppol)], in non-polar solvents (benzene and toluene). The cationic complexes, [Ir(cod)(ppol)]AsF6·1/2C2H5OH and [Ir(cod)(ppol)]PF6·1/2CH3CN, were prepared to compare with the ionic form by 31P NMR spectroscopy. When carbon monoxide is introduced to 1, cod is replaced by CO to give the 5-coordinated complex, [IrCl(CO)(ppol)]. Hydrogenation of 1-octene was not successful in the presence of 1. In order to verify the reason for 1 not behaving as a good catalyst for hydrogenation, electrophilic reactions with HCl, I2 and HBF4·etherate were performed, which yielded the oxidative addition product, [IrHCl2(ppol)], the substitution product, [IrI(cod)(ppol)], and another cationic product, [Ir(cod)(ppol)]BF4, respectively. Thus, the iridium complex is not sufficiently basic to activate hydrogen atoms or the olefin of the ppol ligand.

• Bulletin of the Korean Chemical Society
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• v.24 no.8
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• pp.1181-1187
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• 2003

Condensation of 4-cyano-5,6-dimethyl-3-pyridazinone 1 with aromatic aldehydes gave the novel styryl derivatives 2a-c. Refluxing of compound 2a with phosphorus oxychloride furnished 3-chloropyridazine derivative 3. Compound 3 was reacted with thiourea and produced pyridazine-3(2H)thione 4. Thieno[2,3-c]- pyridazines 5a-e were achieved by cycloalkylation of compound 4 with halocompounds in methanol under reflux and in the presence of sodium methoxide. Also, refluxing of compound 4 with N-substituted chloroacetamide in the presence of potassium carbonate afforded thienopyridazines 6a-e. Cyclization of compound 6 with some electrophilic reagents as carbon disulfide and triethyl orthoformate furnished the novel pyrimido[4',5':4,5]thieno[2,3-c]pyridazines 12 and 13a-c, respectively. Diazotisation of compound 6 with sodium nitrite in acetic acid produced the pyridazino[4',3':4,5]thieno[3,2-d][1,2,3]triazines 14a-c. Ternary condensation of compound 1, aromatic aldehydes and malononitrile in ethanol containing piperidine under reflux afforded the novel phthalazines 16a-c. Compound 3 was subjected to some nucleophilic substitution reactions with amines and sodium azide and formed the aminopyridazines 17a, b and tetrazolo[1,5-b]-pyridazine 19, respectively. The structures of the synthesized compounds were established by elemental and spectral analyses.

• Journal of Microbiology and Biotechnology
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• v.17 no.11
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• pp.1789-1796
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• 2007

A ${\beta}$-glucosidase with the molecular mass of 160,000 Da was purified to homogeneity from cell extract of a cellulolytic bacterium, Cellulomonas uda CS1-1. The kinetic parameters ($K_m$ and $V_{max}$) of the enzyme were determined with pNP-cellooligosccharides (DP 1-5) and cellobiose. The molecular orbital theoretical studies on the cellulolytic reactivity between the pNP-cellooligosaccharides as substrate (S) molecules and the purified ${\beta}$-glucosidase (E) were conducted by applying the frontier molecular orbital (FMO) interaction theory. The results of the FMO interaction between E and S molecules verified that the first stage of the reaction was induced by exocyclic cleavage, which occurred in an electrophilic reaction based on a strong charge-controlled reaction between the highest occupied molecular orbital (HOMO) energy of the S molecule and the lowest occupied molecular orbital (LUMO) energy of the hydronium ion ($H_3O^+$), more than endocyclic cleavage, whereas a nucleophilic substitution reaction was induced by an orbital-controlled reaction between the LUMO energy of the oxonium ion ($SH^+$) protonated to the S molecule and the HOMO energy of the $H_2O_2$ molecule. A hypothetic reaction route was proposed with the experimental results in which the enzymatic acid-catalyst hydrolysis reaction of E and S molecules would be progressed via $SN_1$ and $SN_2$ reactions. In addition, the quantitative structure-activity relationships (QSARs) between these kinetic parameters showed that $K_m$ has a significant correlation with hydrophobicity (logP), and specific activity has with dipole moment, respectively.

• Bulletin of the Korean Chemical Society
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• v.30 no.7
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• pp.1579-1582
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• 2009

The reaction rates of 4-X-2,6-dinitrochlorobenzenes (X = $NO_2,\;CN,\;CF_3$) with Y-substituted pyridines (Y = 3-$OCH_3,\;H,\;3-CH_3,\;4-CH_3$) in methanol-acetonitrile mixtures were measured by conductometry at 25 ${^{\circ}C}$. It was observed that the rate constant increased in the order of X = 4-$NO_2\;>\;4-CN\;>\;4-CF_3$ and the rate constant also increased in the order of Y = 4-$CH_3\;>\;3-CH_3\;>\;H\;>\;3-OCH_3$. When the solvent composition was varied, the rate constant increased in order of MeCN > 50% MeOH > MeOH. The electrophilic catalysis by methanol may be ascribed to the formation of hydrogen bonds between alcoholic hydrogen and nitrogen of pyridines in ground state. Based on the transition parameters, ${\rho}_S,\;{\rho}_N,\;{\beta}_Y,\;{\rho}_{XY}$ and solvent effects, the reaction seems to proceed via $S_N$Ar-Ad.E mechanism. We also estimated the isokinetic solvent mixtures (${\rho}_{XY}$ = 0) based on cross-interaction constants, where the substituent effects of the substrate and nucleophile are compensated.