• Bulletin of the Korean Chemical Society
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• v.34 no.8
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• pp.2473-2479
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• 2013

The kinetics of the radical-polar molecule reaction $CH_3+HBr{\rightarrow}CH_4+Br$ has been studied at temperatures between 150 and 1000 K using classical dynamics procedures. Potential energy surfaces constructed using analytical forms of inter- and intramolecular interaction energies show a shallow well and barrier in the entrance channel, which affect the collision dynamics at low temperatures. Different collision models are used to distinguish the reaction occurring at low- and high-temperature regions. The reaction proceeds rapidly via a complex-mode mechanism below room temperature showing strong negative temperature dependence, where the effects of molecular attraction, H-atom tunneling and recrossing of collision complexes are found to be important. The temperature dependence of the rate constant between 400 and 1000 K is positive, the values increasing in accordance with the increase of the mean speed of collision. The rate constant varies from $7.6{\times}10^{-12}$ at 150 K to $3.7{\times}10^{-12}$ at 1000 K via a minimum value of $2.5{\times}10^{-12}\;cm^3\;molecule^{-1}\;s^{-1}$ at 400 K.

• Bulletin of the Korean Chemical Society
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• v.23 no.6
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• pp.851-856
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• 2002

The Reaction of S-methyl-S-cysteine(L-Smc) with racemic $s-cis-[Co(demba)Cl_2]-1$ (Hydmedba = $NN'-dimethylethylenediamine-NN'-di-\alpha-butyric$, acid) yields ${\Delta}$-s-cis-[Co(dmedba)(L-Smc)] 2 with N, O-chelation. Oxidation of sulfur of 2 with $H_2O_2$ in a 1 : 1 mole ratio gives ${\Delta}$-s-cis[Co(dmedba)(L-S(O)mc)] 3 having an uncoordinated sulfenate group. Oxidation of sulfur of L-Sm with $H_2O_2in$ a 1: 1 mole ratio produces S-methyl-L-cysteinesulfenate (L-S(O)me) 5. Direct reaction of 1 with 5 in basic medium gives an N.O-chelated ${\Delta}$s-cis[Co(dmedba)(L-S(O)mc)-N.O], which turmed out be same as obtained by oxidation of 2, while an N, S-chelated ${\Delta}$-s-cis-[Co(dmedba)(S-S(O)mc)-N,O] complex 4 is obtained in acidic medium from the reaction of 1 with 5. This is one of the rare $[$Co^{III}$(N_2O_2-type$ ligand)(amino acid)] type complex preparations, where the reaction conditions determine which mode of N, O and N, S caelation modes is favored.

• Bulletin of the Korean Chemical Society
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• v.34 no.6
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• pp.1689-1692
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• 2013

Food is a common source of chromium (Cr) exposure. However, it is difficult to analyze Cr in complex food matrices by using inductively coupled plasma mass spectrometry (ICP-MS) because the major isotope, $^{52}Cr$, is masked by interference generated by the sample matrix and the plasma gas. Among the systems available to minimize interference, the recently developed collision-reaction interface (CRI) has a different structure relative to that of other systems (e.g., collision cell technology, octopole reaction system, and dynamic reaction cell) that were designed as a chamber between the skimmer cone and quadrupole. The CRI system introduces collision or reaction gas directly into the plasma region through a modified hole of skimmer cone. We evaluated the use of an CRI ICP-MS system to minimize polyatomic interference of $^{52}Cr$ and $^{53}Cr$ in various foodstuffs. The $^{52}Cr$ concentrations measured in the standard mode were 2-3 times higher than the certified values. This analytical method based on an ICP-MS system equipped with a CRI of helium gas was effective for Cr analysis in complex food matrices.

• Journal of Korean Society for Atmospheric Environment
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• v.21 no.E1
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• pp.23-35
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• 2005

Size distribution of particulate water-soluble ion components was measured at Gosan, Korea using a micro-orifice uniform deposit impactor (MOUDI). Sulfate, ammonium, and nitrate showed peaks in three size ranges; Sulfate and ammonium were of dominant species measured in the fine mode ($D_{p} < 1.8 {\mu}m$). One peak was observed in the condensation mode ($0.218\sim0.532{\mu}m$), and the other peak was obtained in the droplet mode ($0.532\sim1.8{\mu}m$). Considering the fact that the equivalent ratios of ammonium to sulfate ranged from 0.5 to 1.0 in these size ranges, it is inferred that they formed sufficiently neutralized compounds such as ($NH_{4})_{2}SO_{4} and (NH_{4})_{3}H(SO_{4})_{2}$ during the long-range transport of anthropogenic pollutants. On the other hand, nitrate was distributed mainly in the coarse mode ($3.1\sim6.2{\mu}m$) combined with soil and sea salt. Two sets of MOUDI samples were collected in each season. One sample was collected when the concentrations of criteria air pollutants were relatively high, but the other represented relatively clean air quality. The concentrations of sulfate and ammonium particles in droplet mode were the highest in winter and the lowest in summer. When the air quality was bad, the increase of nitrate was observed in the condensation mode ($0.218\sim0.282{\mu}m$). It thus suggests that the nitrate particles were produced through gas phase reaction of nitric acid with ammonia. Chloride depletion was remarkably high in summer due to the high temperature and relative humidity.

• Bulletin of the Korean Chemical Society
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• v.23 no.2
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• pp.205-214
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• 2002

The reaction of gas-phase atomic hydrogen with hydrogen atoms chemisorbed on a silicon surface is studied by use of the classical trajectory approach. Especially, we have focused on the mechanism changes with the hydrogen surface coverage difference. On the sparsely covered surface, the gas atom interacts with the preadsorbed hydrogen atom and adjacent bare surface sites. In this case, it is shown that the chemisorption of H(g) is of major importance. Nearly all of the chemisorption events accompany the desorption of H(ad), i.e., adisplacement reaction. Although much less important than the displacement reaction, the formation of $H_2(g)$ is the second most significant reaction pathway. At gas temperature of 1800 K and surface temperature of 300 K, the probabilities of these two reactions are 0.750 and 0.065, respectively. The adsorption of H(g) without dissociating H(ad) is found to be negligible. In the reaction pathway forming $H_2$, most of the reaction energy is carried by $H_2(g)$. Although the majority of $H_2(g)$ molecules are produced in sub-picosecond, direct-mode collisions, there is a small amount of $H_2(g)$ produced in multiple impact collisions, which is characteristic of complex-mode collisions. On the fully covered surface, it has been shown that the formation of $H_2(g)$ is of major importance. All reactive events occur on a subpicosecond scale, following the Eley-Rideal mechanism. At gas temperature of 1800 K and surface temperature of 300 K, the probability of the $H_2(g)$ formation reaction is 0.082. In this case, neither the gas atom trapping nor the displacement reaction has been found.

• Journal of the Korean Vacuum Society
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• v.7 no.2
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• pp.135-140
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• 1998

We investigated the initial growth mode of Cu deposited on polyimide at high temperature($350^{\circ}C$) using x-ray photoelectron spectroscopy. We could find that when Cu is sputter-deposited on the polyimide at high temperature, Cu-C-N complex is formed first, Cu-N-O complex and Cu-oxide are mainly formed successively, and then funally metallic Cu grows. In the chemical reaction point of view, the interface of Cu/polyimide at high temperature is than that at room temperature.

• Bulletin of the Korean Chemical Society
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• v.27 no.7
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• pp.1005-1008
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• 2006

The reaction of $AgClO_{4}$ with acyclic potential tridentate N,N,N',N',N''-pentamethyldiethylenetriamine (pmdeta) has given colorless crystals suitable for X-ray crystallography. The crystal structure ($P2_{1}$/n, a = 14.413(1) $\AA$, b = 25.270(2) $\AA$, c = 16.130(1) $\AA$, b = $103.012(1){^{\circ}}$, V = 5723.7(8) A$\AA^{3}$, Z = 4, R = 0.0349) has been solved and refined. Three silver(I) ions connect four pmdeta ligands to produce discrete complex of $[Ag_3(pmdeta)_4](ClO_4)_3$. A pmdeta ligand is bridged to three silver(I) ions, and three other pmdeta ligands are chelated to each silver(I) center in a tridentate mode. Thus, the product is a rare tri-nuclear silver(I) complex with two different chemical environments. $^{13}C$ NMR and $MAS\;^{13}$C NMR indicate that the tri-nuclear silver(I) complex is not rigid in solution. The contact angles and thermal analyses of the complex are measured and discussed.

• Bulletin of the Korean Chemical Society
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• v.1 no.1
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• pp.30-35
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• 1980

The thermal decomposition reaction of ethyl bromide was studied in the temperature range of 724.5-$755.1^{\circ}K$. Pressure dependence of the reaction was observed in its fall-off region. A theoretical evaluation of the rate constants was carried out adopting RRKM formulation in the region and was compared with the experimental observation.The validity of theory was also reevaluated by using the observed results. The observed activation energy in this study and Arrhenius A-factor were 51.7 kcal/mole and $10^{12.5}$, respectively. The small A-factror in the study was discussed in terms of the formation of a tight activated complex and the molecular elimination as a prevalent reaction mode.

• Journal of the Korean Magnetic Resonance Society
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• v.10 no.1
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• pp.115-125
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• 2006

Hippuryl-L-histidyl-L-leucine(HHL) is widely used as a substrate of angiotensin converting enzyme(ACE) cleaving the neurotransmitter angiotensin(I) to the octapeptide angiotensin(II). The structure of the substrate molecules should provide information regarding the geometric requirements of the ACE active site. For the purpose of determination of in vivo reaction, metallo(Cu, Zn)-HHL complexes were synthesized and the degree of complex formation were identified by MALDITOF, ESI mass spectrometric analysis. Tn addition, the pH-dependent species distribution curves were obtained by potentiometric titration. Nitrogen atoms of imidazole ring and oxygen atom of caboxylate groups in the peptide chain were observed to be participated in the metal complex formation. After purification of complexes further structural characterization were made by utilizing UV-Vis, electrochemical methods and NMR. Complete NMR signal assignments were carried out by using 2D-spectrum techniques COSY, TOCSY, NOESY, HETCOR. A complex that two imidazole and carboxylate groups are asymmetrically participating to coordination mode was predicted to the solution-state structure of $Cu(II)-HHL_2$ based on $^{13}C-NMR$ signal assignment and NOE information.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.11a
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• pp.192-195
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• 2003

There has been increasing interest in the applications of synthesized molecules of nanometer scale in recent years due to their potential utilization in various fields such as biology, optoelectronics and molecular electronics. In this study, the terpyridine-platinum (II) complex on the periphery of the dendritic carbosilane has been prepared from the reaction of Pt(COD)Cl2 and the 4'-functionalized-(2,2':6',2"-terpyridine) on dendrimers. The self-assembly process was carried out to obtain indivially dispersed dendrimer on Au (111) substrate. It was found that STM was unsuitable to obtain a obvious image of dendrimers. Tapping-mode atomic force microscopy(AFM) has been used to investigate the shape and size of dendrimers individually dispersed on Au (111)substrate. As a result, the imaged single dendrimer show that dendrimer is dome shaped and its size can be measured by tapping-mode AFM.