• Bulletin of the Korean Chemical Society
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• v.32 no.4
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• pp.1117-1124
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• 2011

We present a brief review for theoretical/computational studies of proton transfer processes of some simple biomolecules promoted by microsolvating water molecules. Focus is given on the relative stability of the canonical vs. zwitterionic forms of amino acids, tautomeric forms of the DNA base adenine, and the biologically active vs. inactive forms of nicotine. The biochemical implications of these findings are also discussed.

• Bulletin of the Korean Chemical Society
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• v.30 no.10
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• pp.2265-2268
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• 2009

Terahertz time domain spectroscopy (THz-TDS) is applied in transmission to identify the five forms of modifications of furosemide and one commercial product from 0.3 THz to 1.6 THz at room temperature. The different absorption spectra of the different forms are sensitive to crystal structures. Density function theory (DFT) calculation was used to understand the vibrational modes of furosemide in the THz region. X-ray powder diffractometry (XRPD) was applied to confirm the different forms of modifications. The results demonstrate that THz-TDS is a potential analytical technique in investigating polymorphic forms in the pharmaceutical fields.

• Korean Journal of Ecology and Environment
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• v.41 no.2
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• pp.166-173
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• 2008

Chemical forms and release potential of heavy metals were studied in the lime treated sediment of lake Chungcho. Chemical forms of heavy metals were analyzed using a sequential extraction method, and release potential of heavy metals was evaluated by the ratio of the content of labile forms to total metal one. Dominant form of Cd, Cu, Pb, and Zn in the untreated sediments was organic/sulfidic form that is stable in the reducing environment such as the bottom of Lake Chungcho. With liming of the sediment, the chemical forms of studied metals were greatly changed from organic/sulfidic form to adsorbed and reducible form, especially Cd and Cu to adsorbed and reducible form, but Pb and Zn to reducible form. It is believed that increase of unstable form of heavy metals in the sediments by liming was caused by the increase of pH of the pore water at the expense of organic/sulfidic form. Thus, we concluded that the liming approach currently used in the treatment of dredged sediments might cause the increase of labile form which is easily dissolved, and may increase the release of metals from the sediment into overlying water.

• Bulletin of the Korean Chemical Society
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• v.30 no.9
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• pp.2007-2010
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• 2009

Donepezil hydrochloride is a reversible acetylcholinesterase inhibitor that is used in the treatment of Alzheimer’s disease to improve the cognitive performance. It shows different crystalline forms including hydrates. Therefore, it is very important to confirm the polymorphic forms in the formulations of pharmaceutical materials because polymorphs of the same drug often exhibit significant differences in solubility, bioavailability, processability and physical/chemical stability. In this paper, four different forms of donepezil hydrochloride were prepared and characterized using X-ray powder diffraction, Fourier transform infrared, and solid-state nuclear magnetic resonance (NMR) spectroscopy. This study showed that solid-state NMR spectroscopy is a powerful technique for obtaining structural information and the polymorphology of pharmaceutical solids.

• Bulletin of the Korean Chemical Society
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• v.31 no.1
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• pp.59-63
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• 2010

Calculations are presented for the $\gamma$-aminobutyric acid-$(H_2O)_n$ (n = 0-5) clusters in both canonical and zwitterionic forms. We examine the effects of microsolvation on the structures and transformation between the canonical and zwitterionic forms. The canonical forms are predicted to be more stable for n = 0-4. With five microsolvating water molecules, the two forms of $\gamma$-aminobutyric acid become quasidegenerate, with the energies of zwitterionic forms slightly (by 1 - 3 kcal/mol) higher. The lowest energy zwitterionic conformer of $\gamma$-aminobutyric acid-$(H_2O)_5$ cluster is calculated to isomerize to canonical form through a barrier-less proton transfer process and is thus predicted to be kinetically unstable. Therefore, we predict that the canonical conformers of $\gamma$-aminobutyric acid should be observed predominantly in the gas phase at low temperature in presence of up to five water molecules.

• Bulletin of the Korean Chemical Society
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• v.11 no.3
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• pp.209-214
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• 1990

A series of compounds consisting of 4'-oxybenzylidene-4-n-butylaniline, a mesogen, and a p-substituted phenoxyterephthaloyl structure a non-mesogen, interconnected through a central hexamethylene spacer were synthesized and their thermal behavior and liquid crystallinity were studied. p-Substituents included in this study are H, Cl, CN, $NO_2,\;n-C_4H_9O$ and phenyl groups. The compounds having phenyl and $n-C_4H_9O$ substituents are enantiotropic and form smectic-A(SA) and nematic (N) phases. The compound with $NO_2$ substituent is monotropic and forms only a nematic phase on heating the solid, whereas it forms nematic as well as $S_A$ phases on cooling the isotropic liquid. The rest compounds were found to be non-liquid crystalline. This is in great contrast to the fact that the monomesogenic model compound 4'-n-hexyloxybenzylidine-4-n-butylaniline forms $S_B,\;S_C,\;S_A$ and N phases enantiotropically.

• Bulletin of the Korean Chemical Society
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• v.23 no.12
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• pp.1729-1732
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• 2002

The LB71350,(3S, 4R)-Epoxy-(5S)-[[N-(1-methylethoxy)carbonyl]-3-(methylsulfonyl)-L-valinyl]amino]-N-[2-methyl-(1R)-[(phenyl)carbonylpropyl-6-phenylhexanamide, is a novel HIV protease inhibitor. Its equilibrium solubility at room temperature was less than $40{\mu}g/mL.$ It was speculated that the low aqueous solubility might be due to the high crystalline lattice energy resulting from intermolecular hydrogen bonds. The present study was carried out to learn the solid-state characteristics of LB71350 using analytical methods such as NMR, FT-IR and XRD. $^{13}C$ Solid-state NMR, solution NMR, and FT-IR spectra of the various solid forms of LB71350 were used to identify the conformation and structure of the solid forms. The chemical shifts of $^{13}C$ solid-state NMR spectra suggest that the crystalline form might have 3 intermolecular hydrogen bondings between monomers.

• Korean Journal of Ecology and Environment
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• v.38 no.3 s.113
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• pp.334-340
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• 2005

The chemical forms of Cd, Cu, Pb, and Zn were analysed by sequential extraction technique to evaluate the effects of drying and heating of dredged sediments from Lake Chungcho. The most abundant fraction of Cd, Cu, and Zn in the wet and untreated sediment was organic/sulfidic fraction that is state in reducing environment such as the bottom condition of Lake Chungcho, while Pb dominated in residual fraction. This means that the source of Cd, Cu, and Zn in the Chungcho lake sediment is related to the organic degradation and Pb to the erosion from surrounding rocks. With drying and oxidation by dredging, heating treatment, and disposal of the lake sediment, the chemical forms of studied metals changed greatly from organic/sulfidic fraction to adsorbed and reducible fractions which are more labile in oxygenated environment. Organic/sulfidic fraction of Cd, Cu and Pb in the wet sediment was transformed with drying and heating treatments to the labile ones like adsorbed and reducible fraction, but Zn to carbonate and reducible fraction. Heating of the sediment at $320^{\circ}C$ greatly increased the labile fraction of Cd and Cu, while that at $105^{\circ}C$ for Pb and Zn. It is believed that the increase in labile forms of heavy metals in the sediments by drying and heating is caused by the contact with oxygen during drying and heating and by the increase of pH of the pore water at the expense of organic/sulfidic fraction. It is concluded that the drying and oxidation currently used in the treatment of dredged sediment can increase labile forms of heavy metals in the sediment, and the potential of the metal availability from the sediment.

• Bulletin of the Korean Chemical Society
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• v.30 no.4
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• pp.846-848
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• 2009

Two modifications of the ${\alpha}\;and\;{\beta}$ forms of propyl mercaptan nickel(II) cluster, [$Ni_6(SCH_2CH_2CH_3)_{12}$], have been synthesized and their crystal structures have been determined by single-crystal X-ray diffraction. The alkyl groups are away from $Ni_6$ ring in $\alpha$ form whereas they are near to the Ni atom in $\beta$ form. The distance of Ni-H in $\beta$ form [2.576(5) $\AA$] is much shorter than that in $\alpha$ form [3.101(2) $\AA$]. In the crystal lattice of $\beta$ form, the whole structure forms a flower shape.

• Bulletin of the Korean Chemical Society
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• v.6 no.5
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• pp.277-279
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• 1985

Orbital interactions of the types, ${\sigma}-{\pi},\;{\sigma}^*-{\pi},\;{\sigma}-{\pi}^*\;and\;{\sigma}^*-{\pi}^*$ are investigated for the rotamers of ${\alpha}$-X-acetones (X = F and Cl) using STO-3G method of calculation. It was found that the interactions are possible only in gauche forms, and the ${\sigma}^*-{\pi}^*$ interactions are in general greater than the $\sigma-\pi$ interactions due to the greater overlap, in spite of the greater energy gap involved; the greater ${\sigma}^*-{\pi}^*$ interaction causes greater lowering of ${\pi}^*$ level relative to the lowering of ${\sigma}$ in the ${\sigma}-{\pi}$ interaction so that both ${\sigma}-{\pi}^*$ and $n-{\pi}^*$ interactions are enhanced in the gauche forms. The extra stability of the gauche form and the red shift in the $n-{\pi}^*$ transition are thus found to be natural corollaries of the greater ${\sigma}^*-{\pi}^*$ interaction in the gauche forms.