• Bulletin of the Korean Chemical Society
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• 제17권4호
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• pp.353-357
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• 1996

Second-order rate constants have been measured spectrophotometrically for the reaction of 2,4-dinitrophenyl X-substituted benzenesulfonates with Z-substituted phenoxides in absolute ethanol at 25.0±0.1 ℃. The nucleophilic substitution reaction gives both S-O bond and C-O bond cleavage products. The extent of S-O bond cleavage increases significantly with increasing electron withdrawing ability of the sulfonyl substitutent X, while that of the C-O bond cleavage is independent on the electronic effect of the substituent. On the contratry, the effect of the substituent Z in the nucleophilic phenoxide is more significant for the C-O bond cleavage than for the S-O bond cleavage. Aminolyses of 2,4-dinitrophenyl benzenesulfonate (1) with various 1°, 2° and 3°amines have revealed that steric effect is little important. The extent of S-O bond cleavage increases with increasing the basicity of the amines, but decreases with increasing the basicity of the nucleophilic aryloxides, indicating that the HSAB principle is not always operative. Besides, reactant and solvent polarizability effect has also been found to be an important factor in some cases but not always to influence the reaction site.

• Bulletin of the Korean Chemical Society
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• 제25권11호
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• pp.1623-1624
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• 2004

• Applied Biological Chemistry
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• 제37권6호
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• pp.447-450
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• 1994

RNA의 가수분해시에 생성되는 cyclic phosphate 중간체의 모델 화합물인 ethylene phosphate의 P-O결합 분해속도 상수는 $100^{\circ}C$ 에서 $k=3{\times}10^{-7}s^{-1}({\Delta}H{\neq}=24\;kcal,\;{\Delta}S{\neq}=25.5\;eu)$이었으며 DNA모델 화합물인 dimethylphosphate는 $150^{\circ}C$에서 $1{\times}10^{-11}s^{-1}({\Delta}H{\neq}=36\;kcal,\;{\Delta}S{\neq}=25.5\;eu)$이었다. RNA모델 화합물인 hydroxyethylmethylphosphate의 가수분해는 dimethylphosphate의 C-O결합이 가수분해되는 반응속도와 비교될 만한 정도의 반응속도가 관측되었다.

• Bulletin of the Korean Chemical Society
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• 제29권10호
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• pp.1920-1926
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• 2008

We investigated the C-H bond activation mechanism of aldimine by the [RhCl$(PPH_3)_3$] model catalyst using DFT B3LYP//SBKJC/6-31G*/6-31G on GAMESS. Due to their potential utility in organic synthesis, C-H bond activation is one of the most active research fields in organic and organometallic chemistry. C-H bond activation by a transition metal catalyst can be classified into two types of mechanisms: direct C-H bond cleavage by the metal catalyst or a multi-step mechanism via a tetrahedral transition state. There are three structural isomers of [RhCl$(PH_3)_2$] coordinated aldimine that differ in the position of chloride with respect to the molecular plane. By comparing activation energies of the overall reaction pathways that the three isomeric structures follow in each mechanism, we found that the C-H bond activation of aldimine by the [RhCl$(PH_3)_3$] catalyst occurs through the tetrahedral intermediate.

• Journal of Photoscience
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• 제12권2호
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• pp.83-85
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• 2005

Photochemical reactivities of ${\beta}-ethoxypropiophenones$ are changed dramatically by putting a halogen at a position to the carbonyl functionality. ${\alpha}-Bromo-{\beta}-ethoxypropiophenone$ gives C-Br bond cleavage products solely, but ${\alpha}-chloro-{\beta}-ethoxypropiophenone$ forms mainly the Yang photocyclization products upon irradiation. The different reactivities of two compounds can be explained by relative rates of C-X bond cleavage and a-hydrogen abstraction.

• Bulletin of the Korean Chemical Society
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• 제18권8호
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• pp.824-827
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• 1997

Bis(ethylene)rhodium(Ⅰ) chloride dimer reacted with vinylcyclopropane to give σ,η3-allylrhodium(Ⅲ) complex 3. Complex 3 underwent C-C bond cleavage of 8-quinolinyl ethyl ketone 11, to form η3-1,3-dimethylallylrhodium(Ⅲ) complex 8, which was reductively eliminated by trimethyl phosphite to give 8-quinolinyl-1-methylbut-2-enyl ketone (10). More sterically hindered 8-quinolinyl alkyl ketones were allowed to react with complex 3 to afford corresponding alkenes as well as a mixture of complex 8 and η3-1-ethylallyl rhodium(Ⅲ) complex 19, identified as 10 and 8-quinolinyl-pent-2-enyl ketone (20) after reductive elimination. 8-Quinolinyl alkyl ketone bearing a sterically hindered alkyl group showed less reactivity for C-C bond cleavage and higher 20/10 ratio compared with those having a less sterically hindered alkyl group, such as 8-quinolinyl ethyl ketone (11).

• Journal of Microbiology and Biotechnology
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• 제33권12호
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• pp.1606-1614
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• 2023

Biochemical gut metabolism of dietary bioactive compounds is of great significance in elucidating health-related issues at the molecular level. In this study, a human gut bacterium cleaving C-C glycosidic bond was screened from puerarin conversion to daidzein, and a new, gram-positive C-glycoside-deglycosylating strain, Dorea sp. MRG-IFC3, was isolated from human fecal sample under anaerobic conditions. Though MRG-IFC3 biotransformed isoflavone C-glycoside, it could not metabolize other C-glycosides, such as vitexin, bergenin, and aloin. As evident from the production of the corresponding aglycons from various 7-O-glucosides, MRG-IFC3 strain also showed 7-O-glycoside cleavage activity; however, flavone 3-O-glucoside icariside II was not metabolized. In addition, for mechanism study, C-glycosyl bond cleavage of puerarin by MRG-IFC3 strain was performed in D₂O GAM medium. The complete deuterium enrichment on C-8 position of daidzein was confirmed by ¹H NMR spectroscopy, and the result clearly proved for the first time that daidzein is produced from puerarin. Two possible reaction intermediates, the quinoids and 8-dehydrodaidzein anion, were proposed for the production of daidzein-8d. These results will provide the basis for the mechanism study of stable C-glycosidic bond cleavage at the molecular level.

• Bulletin of the Korean Chemical Society
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• 제17권10호
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• pp.969-971
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• 1996

• Bulletin of the Korean Chemical Society
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• 제9권6호
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• pp.388-393
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• 1988

The chemisorption of CO molecules on polycrystalline nickel surface has been studied by investigating the resulting chemisorbed species with the X-ray photoelectron spectroscopy at temperatures between 300K through 433K. It is found that the adsorbed CO molecules are dissociated by the simple C-O bond cleavage as well as by the disproportionation reaction at temperatures above 373K. The former type dissociation is more favored at low coverages and at elevated temperatures. The isotherms of CO chemisorption are obtained from the xps intensities of C 1s peaks, and then the activation energy of the dissociative adsorption is estimated as a function of the CO exposure. These activation energies are extrapolated to zero coverage to obtain the activation energy of chemisorption in which thermal C-O bond cleavage takes place. The value obtained is 38.1 kJ/mol.

• Bulletin of the Korean Chemical Society
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• 제10권5호
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• pp.468-470
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• 1989