• Proceedings of the Mineralogical Society of Korea Conference
• /
• 2001.06a
• /
• pp.45-47
• /
• 2001

Jeju island is composed mainly of volcanic rocks such as basalts, trachytic andesites, tracytes, and sedimentary rocks. About 80% of Jeju soils are classified as Andisols. The amount of annual precipitation in Jeju island is about 1872mm, which is 1.5 times the annual precipitation of south Korea. There is a significant difference In amount of precipitation with regions even within Jeju island. In study area, the annual amount of rainfall is about 1280mm, the lowest in Jeju island while south part of the island has the annual precipitation of 2056mm, though they are only tens of kilometers apart. The parent materials of soils in study area are pyroclastic rocks and tuffs. The soils of non-andic properties have developed in this area since pedogenic process of pyroclastic materials is strongly influenced by climatic factor, especially precipitation. In order to investigate the mineralogical characteristics of soils, X-ray analysis for <0.2 and 2-0.2$\mu\textrm{m}$ size fractions was performed with ethylene glycol solvation, K-, Mg-saturation, heat treatment(110, 330, 550$^{\circ}C$). Acid-oxalate and DCB(sodium hydrosulfite, sodium citrate, sodium bicarbonate) dissolution method was used to assess tile total amounts or Al, si, and hydroxy interlayer or 2:1 layer silicates. XRD was also applied for samples treated with DCB only and DCB-oxalate sequentially. XRD patterns showed that 2:1 and 1:1 layer silicates were found, which are different from soils of Andisols. Vermiculite, chlorite, hydroxy interlayered minreals, and interstratified minerals(vermiculite/chlorite) were observed in 2-0.2$\mu\textrm{m}$ size fractions. After DCB treatments, ethylene glycolated samples with Mg-saturation showed expanded d-spacing, suggesting the possibility of hydroxy interlayered minerals. The amounts of hydroxy interlayered minerals increased in surface soil. Unlike Andisols, short range ordered minerals such as allophane, imogolite and gibbsite were hardly found. Mica and kaolinte existed in small amounts. Results are summarized in Fig 1 and Fig. 2.

• Bulletin of the Korean Chemical Society
• /
• v.24 no.4
• /
• pp.431-436
• /
• 2003

Solvolytic rate constants at 25℃ are reported for solvolyses of cinnamyl bromide (1) in binary mixtures of water with acetone, ethanol, methanol, methanol-d, and 2,2,2-trifluoroethanol. Product selectivities are reported for solvolyses of 1 in aqueous ethanol and methanol. Rate ratios in solvents of the same $Y_{Br}$ value and different nucleophilicity provide measures of the minimum extent of nucleophilic solvent assistance (e.g. $[k_{40EW}/k_{97TFE}]$Y = 2.88, EW = ethanol-water). With use of the extended Grunwald-Winstein equation, the l and m values are similar to the values of 0.43 and 0.88 obtained for the solvolyses of 1 using the equation (see below) which includes a parameter (I) for solvation of aromatic rings. The magnitude of l and m values associated with a change of solvent composition predicts the $S_{N1}$ reaction mechanism rather than an $S_{N2}$ channel. Product selectivities (S), defined by S = [ether product]/[alcohol product]×[water]/[alcohol solvent] are related to four rate constants for reactions involving one molecule of solvent as nucleophile and another molecule of solvent as general base catalyst. A linear relationship between 1/S and molar ratio of solvent is derived theoretically and validated experimentally for solvolyses of the above substrates from water up 75% 1/S = $(k_{wa}/k_{aw})$([alcohol solvent]/[water]) + $k_{ww}/k_{aw}$ alcohol-water. The results are best explained by product formation from a “free” carbocation intermediate rather than from a solvent-separated ion pair.

• Journal of the Korean Chemical Society
• /
• v.24 no.6
• /
• pp.444-451
• /
• 1980

In order to further elucidate the process of electron solvation in liquids, the medium effect, as the difference between the free energy of $H^+$ in aqueous and non-aqueous states (${\Delta}{\Delta}G_0$), of THF-water mixtures has been investigated. (${\Delta}{\Delta}G_0$) were determined by electromotive force masurements of the cell Pt$H_2Q$, Q, HCI, THF, $H_2O$|KC1 | $Hg_2Cl_2$|Hg(Pt), where $H_2Q$ and Q are hydroquinone and quinone respectively. The effect of dielectric constant on the difference of free energy and the absorption energy of solvated electrons have been studied. For the consideration of these effect the polymerization of water in THF has been studied. Near infrared spectrum of O-H stetching energy has been used to measure the extent of water aggregates. The expermental results indicate that at least in some composition of binary mixtures the electrons or other ions are solvated preferentially with one component of solvents.

• Journal of the Korean Chemical Society
• /
• v.50 no.6
• /
• pp.440-446
• /
• 2006

ZnO nanoparticles were prepared by laser ablation of the ZnO powder dispersed in deionized water and surfactant solutions, and characterized using UV-VIS absorption spectroscopy, X-ray diffractometer and Transmission electron microscopy(TEM). ZnO nanoparticles produced show the pure ZnO crystal state without mixed state with Zn(OH)2 or Zn, and have the band gap energy of 3.35 eV, which is comparable to that of bulk ZnO. While ZnO nanoparticles prepared in SDS solution have the average diameter of 28nm with near spherical shape, those prepared in CTAB solution have the average size of 40 nm with mainly rod-like shape. ZnO colloidal solution of CTAB is more stable than that of SDS. These difference according to surfactants can be explained by difference of electrostatic interaction between surface charge of ZnO and surfactant molecules and by solvation effect in solution.

• Asian Pacific Journal of Cancer Prevention
• /
• v.14 no.12
• /
• pp.7473-7482
• /
• 2013

The G-protein coupled receptor 87 (GPR87) is a recently discovered orphan GPCR which means that the search of their endogenous ligands has been a novel challenge. GPR87 has been shown to be overexpressed in squamous cell carcinomas (SCCs) or adenocarcinomas in lungs and bladder. The 3D structure of GPR87 was here modeled using two templates (2VT4 and 2ZIY) by a threading method. Functional assignment of GPR87 by SVM revealed that along with transporter activity, various novel functions were predicted. The 3D structure was further validated by comparison with structural features of the templates through Verify-3D, ProSA and ERRAT for determining correct stereochemical parameters. The resulting model was evaluated by Ramachandran plot and good 3D structure compatibility was evidenced by DOPE score. Molecular dynamics simulation and solvation of protein were studied through explicit spherical boundaries with a harmonic restraint membrane water system. A DRY-motif (Asp-Arg-Tyr sequence) was found at the end of transmembrane helix3, where GPCR binds and thus activation of signals is transduced. In a search for better inhibitors of GPR87, in silico modification of some substrate ligands was carried out to form polar interactions with Arg115 and Lys296. Thus, this study provides early insights into the structure of a major drug target for SCCs.

• Journal of the Korean Chemical Society
• /
• v.34 no.2
• /
• pp.123-129
• /
• 1990

The rate constants for the solvolysis of $trans-[Cr(en)_2Br_2]^+$ ion were determined by the spectrophotometric method in methanol-, ethanol-, acetone-, and acetonitrile-water mixtures, at 20, 25, 30, and 35$^{\circ}C$, respectively. The rate constants increased with increasing co-solvent compositions. The rate constant did not show any relation with the reciprocal of dielectric constant of the solvent-mixtures. The m values of Grunwald-Winstein equation for methanol-, ethanol-, acetonitrile-, and acetone-water mixtures are 0.109, 0.103, 0.101, and 0.095, respectively. A free energy cycle for the process from the initial state to the transition state in water and water + co-solvent mixtures shows that the change in solvation at the transition state has a dominant effect on the rate. From the above results, it is believed that the mechanism for the aquation of this complex is the Id mechanism.

• Journal of Environmental Science International
• /
• v.14 no.2
• /
• pp.241-249
• /
• 2005

This study deals with micellar effects on dephosphorylation of diphenyl-4- nitrophenylphosphate (DPNPPH), diphenyl-4-nitrophenylphosphinate (DPNPlN) and isopropylphenyl-4-nitrophenyl phosphinate (IPNPlN) mediated by $OH^\Theta$ or o-iodosobenzoate ion $(IB^\Theta)$ in aqueous and CTAX solutions. Dephosphorylation of DPNPPH, DPNPIN and IPNPIN mediated by $OH^\Theta$ or o-iodosobenzoate ion $(IB^\Theta)$ is relatively slow in aqueous solution. The reactions in CTAX micellar solutions are, however, much accelerated because CTAX micelles can accommodate both reactants in their Stem layer in which they can easily react, while hydrophilic $OH^\Theta\;(or\;IB^\Theta)$ and hydrophobic substrates are not mixed in water. Even though the concentrations $(>10^{-3}\;M)\;of\;OH^\Theta\;(or\;IB^\Theta)$ in CTAX solutions are much larger amounts than those $(6\times10^{-6}\;M)$ of substrates, the rate constants of the dephosphorylations are largely influenced by the change of concentration of the ions, which means that the reactions are not followed by the pseudo first order kinetics. In comparison to effect of the counter ions of CTAX in the reactions, CTACI is more effective on the dephosphorylation of substrates than CTABr due to easier expelling of $Cl^\Theta$ ion by $OH^\Theta\;(or\;IB^\Theta)$ ion from the micelle, because of easier solvation of $Cl^\Theta$ ion by water molecules. The reactivity of IPNPlN with $OH^\Theta\;(or\;IB^\Theta)$ is lower than that of DPNPlN. The reason seems that the 'bulky' isopropyl group of IPNPIN hinders the attack of the nucleophiles.

• Bulletin of the Korean Chemical Society
• /
• v.23 no.9
• /
• pp.1263-1307
• /
• 2002

Pseudo-first-order rate constants (kobs) have been determined for the nucleophilic substitution reactions of p-nitrophenyl diphenyl phosphinate (PNPDPP) with substituted phenoxides (XC6H4O - ) and butane-2,3-dione monoximate (Ox- ) in 0.1 M borate buffer (pH = 10.0) at 25.0 ${\pm}0.1^{\circ}C$. The kobs value increases sharply upon addition of cethyltrimethylammonium bromide (CTAB) to the reaction medium up to near 7 ${\times}$ 10-4 M CTAB and then decreases smoothly upon further addition of CTAB. The rate enhancement upon the addition of CTAB is most significant for the reaction with -O2CC6H4O- and least significant for the one with C6H5O- , indicating that the reactivity of these aryloxides in the presence of CTAB cannot be determined by the basicity alone. The strength of the interaction of these anionic aryloxides with the positively charged micellar aggregates has been suggested to be an important factor to determine the reactivity in the presence of CTAB. The kobs value for the reaction with Ox- increases also upon the addition of CTAB. However, the increase in the kobs value is much more significant for the reaction with Ox- than for the one with ClC6H4O- , indicating that Ox- is less strongly solvated than ClC6H4O- in H2O. The ${\alpha}-effect$ shown by Ox- in H2O has been attributed to the ground-state solvation difference between Ox- and ClC6H4O- .

• Bulletin of the Korean Chemical Society
• /
• v.23 no.9
• /
• pp.1315-1327
• /
• 2002

The model compounds, 8-methoxypsoralen-CH2O(CH2)n-adenine (MOPCH2OCnAd, n=2, 3, 5, 6, 8, and 10) in which 5 position of 8-methoxypsoralen (8-MOP) is linked by various lengths of polymethylene bridge to N9 of adenine. UV absorption spectra are identical with the sum of MOPCH2OC3 and adenine absorption spectra. Solvent effects on the UV absorption and fluorescence emission spectra indicate that the lowest excited singlet state is the $(\pi${\rightarrow}$\pi*)$ state. The spectral characteristics of the fluorescence of MOPCH2OCnAd are strongly dependent upon the nature of the solvents. The fluorescence emission spectra in aprotic solvents are broad and structureless due to the excimer formation through the folded conformation accelerated by hydrophobic ${\pi}-{\pi}$ stacking interaction. Increasing polarity of the protic solvents leads to higher population of unfolded conformation stabilized through favorable solvation and H-bonding, and consequently to an increase in the fluorescence intensity, fluorescence lifetime, and a shift of fluorescence maximum to longer wavelengths. The decay characteristics of the fluorescence in polar protic solvents shows two exponential decays with the lifetimes of 0.6-0.8 and 1.6-1.9 ns in 5% ethanol/water, while MOPCH2OC3 shows 0.5 and 1.7 ns fluorescence lifetimes. The long-lived component of fluorescence can be attributed to the relaxed species (i.e., the species for which the solvent reorientation (or relaxation) has occurred), while the short-lived components can be associated with the unrelaxed, or only partially relaxed, species.

• Nuclear Engineering and Technology
• /
• v.52 no.2
• /
• pp.279-286
• /
• 2020

In this article, we develop a reactive distillation (RD) column configuration for the production of hydrogen. This RD column is in the HI decomposition section of the sulphur - iodine (SI) thermochemical cycle, in which HI decomposition and H₂ separation take place simultaneously. The section plays a major role in high hydrogen production efficiency (that depends on reaction conversion and separation efficiency) of the SI cycle. In the column simulation, the rigorous thermodynamic phase equilibrium and reaction kinetic model are used. The tuning parameters involved in phase equilibrium model are dependent on interactive components and system temperature. For kinetic model, parameter values are adopted from the Aspen flowsheet simulator. Interestingly, there is no side reaction (e.g., solvation reaction, electrolyte decomposition and polyiodide formation) considered aiming to make the proposed model simple that leads to a challenging prediction. The process parameters are determined on the basis of optimal hydrogen production as reflux ratio = 0.87, total number of stages = 19 and feeding point at 8th stage. With this, the column operates at a reasonably low pressure (i.e., 8 bar) and produces hydrogen in the distillate with a desired composition (H₂ = 9.18 mol%, H₂O = 88.27 mol% and HI = 2.54 mol%). Finally, the results are compared with other model simulations. It is observed that the proposed scheme leads to consume a reasonably low energy requirement of 327 MJ/kmol of H₂.