• Journal of the Mineralogical Society of Korea
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• v.21 no.3
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• pp.321-329
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• 2008

Amorphous silica nanoparticles are among the most fundamental $SiO_2$ compounds, having implications in diverse geological processes and technological applications. Here, we explore structural details of amorphous silica nanoparticles with varying particle sizes (7 and 14 nm) using $^{29}Si$ and $^{1}H$ MAS NMR spectroscopy together with quantum chemical calculations to have better prospect for their size-dependent atomic structures. $^{29}Si$ MAS NMR spectra at 9.4 T resolve $Q^2,\;Q^3$ and $Q^4$ species at -93 ppm, -101 ppm, -110 ppm, respectively. The fractions of $Q^2,\;Q^3,\;O^4$ species are $7{\pm}1%,\;27{\pm}2%$, and $66{\pm}2%$ for 7 nm amorphous silica nanoparticles and $6{\pm}1%,\;21{\pm}2%$, and $73{\pm}2%$ for 14 nm amorphous silica nanoparticles. Whereas it has been suggested that $Q^2$ and $Q^3$ species exist on particles surfaces, the difference in $Q^{2}\;+\;Q^{3}$ fraction in both 7 and 14 nm particles is not significant, suggesting that $Q^2$ and $Q^3$ species could exist inside particles. $^{1}H$ MAS NMR spectra at 11.7 T shows diverse hydrogen environments, including physisorbed water, hydrogen bonded silanol, and non-hydrogen bonded silanol with varying hydrogen bond strength. The hydrogen contents in the 7nm silica nanoparticles (including water and hydroxyl groups) are about 3 times of that of 14 nm particles. The larger chemical shills for proton environments in the former suggest stronger hydrogen bond strength. The fractions of non-hydrogen bonded silanols in the 14 nm amorphous silica nanoparticles are larger than those in 7 nm amorphous silica nanoparticles. This observation suggests closer proximity among hydrogen atoms in the nanoparticles with smaller diameter. The current results with high-resolution solid-state NMR reveal previously unknown structural details in amorphous silica nanoparticles with particle size.

• Journal of the Korean Ceramic Society
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• v.40 no.5
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• pp.434-440
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• 2003

The powders of L $a_{0.8}$C $a_{0.2}$Mn $O_3$ Colossal Magnetoresistance (CMR) materials were synthesized by sol-gel process. Lanthanum(H), Calcium(II) and Manganese(III) 2,4-Pentanedionate were dissolved in a mixed binary solution consisted of propionic acid and methanol with PEG (15 wt%) aqueous solution. The progress of reactions was monitored by FT-IR spectroscopy. The Lao scao.2Mn03 gel powders were annealed at various temperatures. The structural changes were investigated by FT-IR, CP/MAS $^{ 13}$C solid state NMR spectroscopy and XRD. The thermochemical property, particle characterization, microstructure of sintered sample, and cation composition of gel powder were studied by TG/DTA, FE-SEM and ICP-AES. The magnetic characterizations were identified through measurement of magnetic moment by VSM.

• Journal of the Korean Magnetic Resonance Society
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• v.20 no.4
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• pp.129-137
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• 2016

Transmembrane(TM) proteins are closely related to transport, channel formation, signaling, cell to cell interaction, so they are the crucial target of modern medicinal drugs. In order to study the structure and function of these TM proteins, it is important to prepare reasonable amounts of proteins. However, their preparation is seriously difficult and time-consuming due to insufficient yields and low solubility of TM proteins. We tried to produce large amounts of Syndecan-4 containing TM domain(SDC4-TM) that is related to the wound healing and tumor. Also, mutated SDC4-TM was studied to investigate structural change by modification of dimerization motif. We performed the structure determination by the Polarity Index at Slanted Angle (PISA) wheel pattern analysis based on $^{15}N-^1H$ 2D SAMPI-4 solid-state NMR of SDC4-TM and computational modeling using Discovery Studio 2016.

• BMB Reports
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• v.34 no.5
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• pp.446-451
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• 2001

The interaction of cytochrome c with binary phospholipid mixtures was investigated by solid-state $^2H$- and $^{31}P$-NMR. To examine the effect of the interaction on the glycerol backbones, the glycerol moieties of phosphatidylcholine (PC), and cardioliph (CL) were specifically deuterated. On the binding of cytochrome c to the binary mixed bilayers, no changes in the quadrupole splittings of each of the components were observed for the PC/PG, PE/CL and PE/PG liposomes. In contrast, the splittings of CL decreased on binging of protein to the PC/CL liposomes, although those of PC did not change at all. This showed that cytochrome c specifically interacts with CL in PC/CL bilayers, and penetrates into the lipid bilayer to some extent so as to perturb the dynamic structure of the glycerol backbone. This is distinctly different from the mode of interaction of cytochrome c with other binary mixed bilayers. In the $^{31}P$-NMR spectra, line broadening and a decrease of the chemical shift anisotropy were observed on the binding of cytochrome c for all binary mixed bilayers that were examined. These changes were more significant for the PC/CL bilayers. Furthermore, the line broadening is more significant for PC than for CL in PC/CL bilayers. Therefore, it can be concluded that with the polar head groups, not only CL but also PC are involved in the interaction with cytochrome c.

• Journal of the Korean Magnetic Resonance Society
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• v.14 no.2
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• pp.88-104
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• 2010

Human melanocortin-4 receptor (hMC4R) has a critical role in part of energy homeostasis, and their heterozygous mutations related in genetic cause of severe human obesity. In order to study the structure and function of these membrane proteins, it is important to prepare the samples. However, the preparation of transmembrane peptide is seriously difficult and time-consuming. Overexpression and purification of membrane proteins was reported to be difficult due to their innate insoluble and toxic properties. Among the many difficulties, the most important is the difficulty in obtaining sufficient quantities of purified protein. Recently, we succeed to produce large amounts of the second transmembrane domain from the wild-type hMC4R (wt-TM2) and D90N mutant hMC4R (m-TM2) and proposed the structural difference of them in membrane-like environments. In this paper, we demonstrate the optimization procedures to express and purify wt-TM2 or m-TM2 peptides, and solution NMR studies in different detergents to get high-resolution spectra were also described.

• Carbon letters
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• v.22
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• pp.60-69
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• 2017

Nitrogen-doped carbon nanosheets with a developed porous structure were prepared from polyurethane foams by hydrothermal carbonization following $ZnCl_2$ chemical activation. Scanning electron microscopy, thermogravimetric analysis, Fourier transform infrared spectroscopy, solid state $^{13}C$ nuclear magnetic resonance (NMR) spectra and X-ray photoelectron spectroscopy were used to characterize the nitrogen-doped carbon nanosheet structure and composition. The removal of Cr(VI) by the N-doped carbon nanosheets was investigated. The results showed that the maximum removal capacity for chromium of 188 mg/g was found at pH=2.0 with PHC-Z-3. pH had an important effect on Cr(VI) removal and the optimal pH was 2.0. Moreover, amino groups and carboxyl groups in the nitrogen-doped carbon nanosheet played important roles in Cr(VI) removal, and promoted the reduction of Cr(VI) to Cr(III).

• Journal of the Korean Chemical Society
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• v.54 no.2
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• pp.183-191
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• 2010

The phase changes of 1-palmitoyl-$d_{31}$-2-oleoyl-sn-glycero-3-phosphatidylcholine (POPC_$d_{31}$) bilayers distorted by an antimicrobial peptide, a magainin 2 or an aurein 3.3 were investigated by using $^2H$ solid-state NMR (SSNMR) spectroscopy. From the theoretical simulation of the experimental $^2H$ solid-state NMR spectra the geometric structure constants and the lateral diffusion coefficients were obtained in the peptide-lipid mixture phases. Within five days of the peptide action on the lipid bilayers only the distorted alignment of the bilayers were measured but after 100 days an elliptic toroidal pore structure and an inverted hexagonal phase were formed in the presence of magainin 2 and aurein 3.3, respectively. In order to investigate the effect of an anionic lipid molecule on the actions of two peptides on the lipid bilayer, the same experiments were performed on the POPC_$d_{31}$/1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylglycerol (POPG) bilayer and the significant differences in the actions of two peptides on two bilayers of POPC_$d_{31}$ and POPC_$d_{31}$/POPG were measured.

• Journal of the Korean Chemical Society
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• v.54 no.1
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• pp.23-26
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• 2010

A Schiff base ligand (Z)-N-((Z)-2-(sec-butylimino)-1,2-diphenylethylidene)butan-2-amine was synthesized by condensation of benzil with sec-butyl amine. Complexation of the ligand was carried out with first row transition elements, manganese(II) and nickel(II). Ligand and complexes were characterized by FTIR, elemental analysis and thermogravimetric analysis in solid state and by NMR ($^1H,\;^{13}C$) in solution form. Both the complexes demonstrate good catalytic activity for butadiene oligomerization under mild conditions with methylaluminoxane (MAO) as co-catalyst.

• Bulletin of the Korean Chemical Society
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• v.28 no.11
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• pp.2045-2050
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• 2007

The reactions of mercury(II) chloride with O3S2-donor macrocyclic ligands with (L1) and without (L2) dibenzosubunit afforded respective exo- (1) and endo-coordinated (2) complexes depending on the ring rigidity of the ligands. From the X-ray crystal structures and comparative NMR studies for the complexes 1 and 2, it is confirmed that the resulting species with different coordination modes exist not only in solid state but also in solution state.

• Korean Chemical Engineering Research
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• v.54 no.1
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• pp.36-43
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• 2016

Hydrosilylation reactions of 2.4.6.8-tetrahydro-2.4.6.8-tetramethylcyclotetrasiloxane with allyl butyrate catalyzed by Karstedt's, $H_2PtCl_6$ and Pt/C catalyst were studied and 2.4.6.8-tetra (propyl butyrate)-2.4.6.8-tetramethylcyclotetrasiloxane was obtained. The reaction order, activation energies and rate constants were determined. Ringopening polymerization of 2.4.6.8-tetra (propyl butyrate)-2.4.6.8-tetramethylcyclotetrasiloxane in the presence of $CaF_2$, LiF, KF and anhydrous potassium hydroxide in $60-70^{\circ}C$ temperature range was carried out and methylsiloxane oligomers with regular arrangement of propyl butyrate pendant groups were obtained. The synthesized products were studied by FTIR and NMR spectroscopy. The polysiloxanes were characterized by wide-angle X-ray, gel-permeation chromatography and DSC analyses. Via sol-gel processes of oligomers doped with lithium trifluoromethylsulfonate or lithium bis (trifluoromethylsulfonyl)imide, solid polymer electrolyte membranes were obtained. The dependences of ionic conductivity of obtained polyelectrolytes on temperature and salt concentration were investigated, and it was shown that electric conductivity of the polymer electrolyte membranes at room temperature changed in the range $3.5{\times}10^{-4}{\sim}6.4{\times}10^{-7}S/cm$.