• Bulletin of the Korean Chemical Society
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• v.35 no.12
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• pp.3559-3566
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• 2014

Study on the unimolecular reaction for $CH_2FO$ and $CD_2FO$ is carried out. The structures, energy barriers and zero point energy of the three channels in the title unimolecular reactions are computed with the MP2/6-311++G(3df, 3pd) method. RRKM theory is used to calculate the rate constants of canonical case at temperature range of 500-5000 K and microcanonical system at total energy of 19.05-71.68 kcal/mol. The results indicate that the anharmonic effect and isotope effect are very small for the three channels, and the anharmonic rate constants, around $10^9-10^{11}s^{-1}$, are close to the experimental prediction reasonably.

• Journal of Life Science
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• v.8 no.4
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• pp.410-415
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• 1998

Procine pepsin hydrolysis of hexapeptide L-S-pNF-Nle-A-OMe in the presence of dipeptide L-L generates a new peak on HPLC analysis of reaction mixtures that is not seen when enzyme is incubated with either peptide alone. The peaks can be detected spectroscopically at either 214 or 254 nm, the latter consistent with a new peptide containing the p-nitro-F residue. The data suggest acyl transpeptidation between E(L-S-pNF) and L-L to form L-S-pNF-L-L. Consistent with this inference are (1) the ability of L-L-NH$_{2}$ and inability of Boc-L-L to undergo a similar transpeptidation reaction, and (2) the data from electrospray mass spectrum. This synthesis requires that Nle-A-L-OMe be released before L-S-pNF, an order opposite to that proposed on the basis of product inhibition kinetics. Consistent with this inference are reciprocal solvent isotope effects ; normal isotope effects of 1.736$\pm$0.121 on the formation of Nle-A-L-OMe and 2.281$\pm$0.184 in the formation of L-S-pNF, coupled to an inverse isotope effects of 0.576$\pm$0.045 on the formation of L-S-pNF-L-L. Because transpeptidation precedes faster in D$_{2}$O, the isotopically-sensitive step must occur after release of Nle-A-L-OMe. Isotopically-enhanced transpeptidation is consistent with the Uni-Bi iso memchanism postulated on the basis of an isotope effects on Vmax but not on Vmax/Km$^{1)}$ and confirmed by isotope effects on the onset of inhibition by pepstatin$^{2)}$.

• Economic and Environmental Geology
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• v.33 no.6
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• pp.491-504
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• 2000

Environmental isotope $^{18}O$, $^{2}H$, $^{3}H$,$^{13}C$, $^{34}S$and $^{87}Sr/^{86}Sr$) studies on ${CO_2}$-rich waters in the Kangwon Province were carried out to elucidate the origin, residence time, water-rock interaction and mixing process of their. ${\delta}^{18}O$ and ${\delta}D$ data indicate that ${CO_2}$-rich waters were derived from the local meteoric water. It also shows that each type of ${CO_2}$-rich water has distinct isotopic composition and Na-${HCO_3}$ type water (-10.8 to -12.1${\textperthousand}$, ${\delta}^{18}O$ ) is lighter than other type waters. These depleted isotopic values supposedly indicate that, considering the altitude effect of isotope in Korea, the recharge area of Na-${HCO_3}$ type water can be estimated to be relatively higher in elevation than those of Ca-${HCO_3}$ and Ca-Na-${HCO_3}$ type waters. Tritium contents close to zero are observed in the Na-${HCO_3}$ type water, confirming a long residence time and the possibility of a ${CO_2}$ inflow into the aquifer at great depth. These isotope data also show that the Ca-${HCO_3}$ type water has undergone mixing process with surface water during ascending at depth, whereas Na-${HCO_3}$ type water was less mixed with surface waters. The carbon isotope data (-8.8 to ＋0.8 ${\textperthousand}$ ${\delta}^{13}C$) indicate that dissolved carbon in the ${CO_2}$-rich waters was possibly derived from deep seated ${CO_2}$ gas. The high ${\delta}^{34}S$ values (up to 38.1${\textperthousand}$) of dissolved sulfates suggest that sulfate reduction by microbial activity had occurred at depth. Strontium isotopic data ($^{87}Sr/^{86}Sr$) of ${CO_2}$-rich waters indicate that the chemistry of the ${CO_2}$-rich waters is determined by water-rock (granite) interaction.

• Bulletin of the Korean Chemical Society
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• v.34 no.12
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• pp.3811-3816
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• 2013

Nucleophilic substitution reactions of ethyl methyl (2), ethyl propyl (4) and diisopropyl (7) chlorothiophosphates with substituted anilines and deuterated anilines are investigated kinetically in acetonitrile at $55.0^{\circ}C$. A concerted mechanism is proposed based on the selectivity parameters. The deuterium kinetic isotope effects (DKIEs; $k_H/k_D$) are secondary inverse ($k_H/k_D=0.66-0.99$) with 2, primary normal and secondary inverse ($k_H/k_D=0.78-1.19$) with 4, and primary normal ($k_H/k_D=1.06-1.21$) with 7. The primary normal and secondary inverse DKIEs are rationalized by frontside attack involving hydrogen bonded, four-center-type transition state, and backside attack involving in-line-type transition state, respectively. The anilinolyses of ten chlorothiophosphates are examined based on the reactivity, steric effect of the two ligands, thio effect, reaction mechanism, DKIE and activation parameter.

• Bulletin of the Korean Chemical Society
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• v.31 no.5
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• pp.1403-1406
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• 2010

• Bulletin of the Korean Chemical Society
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• v.29 no.10
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• pp.2065-2068
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• 2008

• Archives of Pharmacal Research
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• v.19 no.4
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• pp.302-306
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• 1996

The $^1H- and^{13}C-NMR$ spectra of alaternin, aurantio-obtusin, chryso-obtusin, obtusin and 2-glucosyl obtusifolin isolated from the seeds of Cassia tora have been assigned based on HMBC, long-range HETCOR, fully $^1H-coupled {13}^C-NMR$, deuterium isotope experiment, and by comparison with the model compounds.

• Economic and Environmental Geology
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• v.31 no.3
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• pp.265-271
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• 1998

In the hydrologic and hydrochemical studies of natural waters, oxygen and hydrogen isotope compositions of waters are very important to elucidate the origin and circulation pattern of water in the hydrologic system. The hydrogen isotope analysis of waters usually has been undertaken through the reduction of water to form hydrogen gas using pure metals (in general, zinc and uranium). In 1996, a new apparatus (H/Device) was developed to prepare the water samples (by the reduction with Cr metal) without some intrinsic problems that may yield incorrect and/or inaccurate data, and was installed at 1997 in the Center for Mineral Resources Research (CMR) in Korea University. However, the optimistic conditions of preparation and analysis of samples has not been established. In this paper, we introduce the efficiency of H/Device to obtain accurate hydrogen isotope values of water, and discuss both the optimum conditions including the effective reduction time and the probable mixing (memory) effect between successive samples. We obtained large amounts of a laboratory working standard (KUW; Korea University Water) with the average ${\delta}D_{SMOW}$ value of $-42.1{\pm}1.0$‰ $(1{\sigma})$.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.13 no.1
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• pp.83-88
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• 2008

Using micromill, discrete carbonate powders from the otolith of Argyrosomus argentatus were sampled along the growth band, and high-resolution stable isotope profiles were obtained. The ${\delta}^{18}O$ and ${\delta}^{13}C$ values are increasing gradually from the core to the margin. However, such increases do not seem to be attributed to the environmental property changes during the growth, but to the dominant effect of metabolic carbons during the early growth, and then, the isotopic composition seems to be equilibrium to the environmental condition. This paper allows the diverse applicability of high-resolution isotope research to the fish otoliths in the future.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2003.09a
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• pp.501-504
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• 2003

Sulfur isotope composition was used to identify the sources of groundwater contamination near abandonded coal mines. From the analysis of mine adit drainages, tailing seepages, and spring waters near the abandonded Hambaek and Hanchang coal mines in Kangwon Province, it was inferred that it the highly possible source of the contamination of spring water is acid mine drainage(AMD). Sulfur isotope composition showed that seepage from tailings seemed to have more effect on the groundwater contamination than mine adit drainage, which suggests the remediation and anti-contamination methods of tailing seepages not only mine adit drainage are required.