• Bulletin of the Korean Chemical Society
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• v.32 no.2
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• pp.583-589
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• 2011

Fluorescence correlation spectroscopy (FCS) is a sophisticated and an accurate analytical technique used to study the diffusion of molecules in a solution at the single-molecule level. FCS is strongly affected by many factors such as the stability of the excitation power, photochemical processes, mismatch between the refractive indices, and variations in the cover glass thickness. We have studied FCS near the surface of a cover glass by using rhodamine 123 as a fluorescent probe and have observed that the surface has a strong influence on the measurements. The temporal autocorrelation of FCS decays with two characteristic times when the confocal detection volume is positioned near the surface of the cover glass. As the position of the detection volume is moved away from the surface, the FCS autocorrelation becomes one-component decaying; the characteristic time of the decay is the same as the faster-decaying component in the FCS autocorrelation near the surface. This observation suggests that the faster component can be attributed to the free diffusion of the probe molecules in the solution, while the slow component has its origin from the interaction between the probe molecules and the surface. We have characterized the surface contribution to the FCS measurements near the surface by changing the position of the detection volume relative to the surface. The influence of the surface on the diffusion of the probe molecules was monitored by changing the chemical properties of the surface. The surface contribution to the temporal autocorrelation of the FCS strongly depends on the chemical nature of the surface. The hydrophobicity of the surface is a major factor determining the surface influence on the free diffusion of the probe molecules near the surface.

• IMMUNE NETWORK
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• v.1 no.1
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• pp.14-25
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• 2001

Background: Bone marrow stromal cells (BMSCs) express many cell surface molecules, which regulate the proliferation and differentiation of immune cells within the bone marrow. Methods: To identify cell surface molecules, which can regulate cell proliferation through cell interaction, monoclonal antibodies (MoAbs) against BMSCs were produced. Among them, 1H8 MoAb, which recognized distinctly an 80 kDa protein, abolished myeloma cell proliferation that was induced by co-culturing with BMSCs. Results: IL-6 gene expression was increased when myeloma or stromal cells were treated with 1H8 MoAb. In addition, the expression of IL-6 receptor and CD40 was up-regulated by 1H8 treatment, suggesting that the molecule recognized by 1H8 MoAb is involved in cell proliferation by modulating the expression of cell growth-related genes. Myeloma cells contain high levels of reactive oxygen species (ROS), which are related to gene expression and tumorigenesis. Treatment with 1H8 decreased the intracellular ROS level and increased PAG antioxidant gene concomitantly. Finally, 1H8 induced the tyrosine phosphorylation of several proteins in U266. Conclusion: Taken together, 1H8 MoAb recognized the cell surface molecule and triggered the intracellular signals, which led to modulate gene expression and cell proliferation.

• Journal of the Korean Ceramic Society
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• v.32 no.8
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• pp.901-908
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• 1995

In aqueous slurry processing of silicon nitride, the interaction of dispersant and binder used as polymeric processing additives on the silicon nitride particle surface was studied to identify the effect of these processing polymeric additives on the ceramic powder processing. The adsoprtion isotherm study of anionic organic molecule as dispersant and nonionic organic molecules as binder of silicon nitricde was studied to investigate the effect of these processing organic additives on the physicochemical properties of silicon nitride particles. As anionic molecule adsorbed onto silicon nitrice surface, the IEP of silicon nitride shifted toward acidic pH and changed the stability of silicon nitride particle. However, the adsorption of binder as nonionic organic molecule onto silicon nitride surface did not changed the IEP but caused the decrease of electrostatic potentials of silicon nitride. These distinctive adsorption behaviors of organic additives on silicon nitride particles can be closely correlated to the stability of silicon nitride particles suspended in aqueous media.

• Bulletin of the Korean Chemical Society
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• v.32 no.3
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• pp.988-992
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• 2011

$CO_2$ adsorption on mineral sorbents has a potential to sequester $CO_2$. This study used a density functional theory (DFT) study of $CO_2$ adsorption on barium oxide (BaO) in the presence of $H_2O$ to determine the role of $H_2O$ on the $CO_2$ adsorption properties on the ($2{\times}2$; $11.05\;{\AA}{\times}11.05\;{\AA}$) BaO (100) surface because BaO shows a high reactivity for $CO_2$ adsorption and the gas mixture of power plants generally contains $CO_2$ and $H_2O$. We investigated the adsorption properties (e.g., adsorption energies and geometries) of a single $CO_2$ molecule, a single $H_2O$ molecule on the surface to achieve molecular structures and molecular reaction mechanisms. In order to evaluate the coordinative effect of $H_2O$ molecules, this study also carried out the adsorption of a pair of $H_2O$ molecules, which was strongly bounded to neighboring (-1.91 eV) oxygen sites and distant sites (-1.86 eV), and two molecules ($CO_2$ and $H_2O$), which were also firmly bounded to neighboring sites (-2.32 eV) and distant sites (-2.23 eV). The quantum mechanical calculations show that $H_2O$ molecule does not influence on the chemisorption of $CO_2$ on the BaO surface, producing a stable carbonate due to the strong interaction between the $CO_2$ molecule and the BaO surface, resulting from the high charge transfer (-0.76 e).

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.109-110
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• 2008

We have performed a density functional theory study to investigate the reaction of the $HfCl_4$ molecule on $H_2O$ terminated Si (001)-$(2\times1)$ surface. The reaction of the $HfCl_4$ molecule is more favorable on OH-terminated site than H-terminated site. The first $HfCl_4$ molecule is adsorbed on a OH-terminated site with 0.21 eV energy benefit. The second $HfCl_4$ molecule is adsorbed on the most adjacent OH-terminated site of the first molecule and the energy benefit is 0.28 eV. The third and forth molecules have same tendency with the first and second ones. The adsorption energies of the fifth and sixth $HfCl_4$ molecules are 0.01 eV, -0.06 eV respectively. Therefore, we find that the saturation Hf coverage is approximately 5/8 of the available hydroxyl site, which is $2.08\times10^{14}/cm^2$. Our model is well matched with an experimental study by reference.

• Bulletin of the Korean Chemical Society
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• v.24 no.3
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• pp.377-383
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• 2003

Physicochemical properties of a series of PC monolayers with different alkyl chains (C24, C20, C16, and C8), at the air/water interface were investigated. The surface pressure is influenced mainly by the hydrophobicity of the PCs, which is confirmed by the curve shape and the on-set value of π-A isotherms at the air/water interface by increasing the number of alkyl chain. The on-set values of surface pressure were 125 Ų/molecule for DOPC(C8), 87 Ų/molecule for DPPC(C16), 75 Ų/molecule for DAPC(C20), and 55 Ų/molecule for DLPC(C24), respectively. The orientations of alkyl chains at the air/water interface are closely connected with the rigidity of the monolayers, and it was confirmed by the tendency of monolayer thickness in ellipsometry data. The temperature dependence of a series of PCs shows that the surface pressure decreases by increasing temperature, because the longer the alkyl chain length, the larger the hydrophobic interaction in surface pressure. The temperature effects and the conformational changes of unsaturated and saturated PCs were confirmed by the computer simulation study of the cis-trans transition with POPC and DPPC(C16). The cistrans conformational energy difference of POPC is 62.06 kcal/mol and that of DPPC(C16) is 6.75 kcal/mol. Due to the high conformational energy barrier of POPC, phase transition of POPC is limited in comparison with DPPC(C16).

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.280-280
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• 2013

Using both experimentaland theoretical methods, we have investigated the structural and electronic properties of self-assembled two-dimensional organic molecule (hexaaza-triphenylene-hexacarbonitrile, HATCN), which is used as an efficient OLED hole injection material, on Au(111) surfaces. Low-temperature scanning tunneling microscope (STM) measurements revealed that self-assembled linear and hexagonal porous structures are formed at atomic steps and terraces of Au(111), respectively. We also found that the hexagonal porous structure have chirality and forms only small (＜1,000 nm2) phase-separated chiral domains that can easily change their chiral phase in subsequence STM images at 80 K. To explain these observations, we calculated the molecular-molecular and molecule-surface interaction energies by using first-principles density functional theory method. We found that the change of their chiral phase resulted from the competition between the two energies. These results have not only verified our experimental observations, but also revealed the delicate balance between different interactions that caused the self-assembed structures at the surface.

• Bulletin of the Korean Chemical Society
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• v.35 no.3
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• pp.875-880
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• 2014

Adsorption of 4,4'-bis(mercaptomethyl)biphenyl (44BMBP) on silver nanoparticles has been investigated by surface-enhanced Raman scattering (SERS) spectroscopy. In addition, the Raman spectra of 44BMBP in solid state and in basic condition have been obtained for comparative study to elicit the characteristics of adsorption. The observed Raman and SERS spectra were analyzed comparing with the normal modes and vibrational frequencies from density functional theory (DFT) calculations performed for the feasible structures of 44BMBP molecule. On the basis of excellent agreement between the calculated and the experimental results, the molecule is found to have both the cis- and trans-forms for the mercaptomethyl groups in the solid state as well as in the basic condition. In contrast, the molecule is found to be chemisorbed on the silver surface by forming two Ag-S linkages only in the cis-form but not in the trans-form due to the steric interruption, which indicates the parallel orientation of molecules on the surface. Particularly, the spectral features in the SERS spectra such as the absence of the C-H stretching band and enhancement for the out-of-plane skeletal modes are confirmatory for the parallel geometry through ${\pi}$ interaction between the phenyl rings and the metal surface, based on the electromagnetic surface selection rule.

• Bulletin of the Korean Chemical Society
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• v.17 no.3
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• pp.239-244
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• 1996

Mastoparan B (MP-B) that is a novel MP isolated from the hornet Vespa basalis, was studied as compared with MP, in terms of interaction with phospholipid bilayer and antimicrobial activity. MP-B has more hydrophilic amino acid residues in hydrophilic face of amphiphilic α-helical structure than MP. The both peptides exhibited considerably different effect on interaction with lipid bilayers, e.g. their conformation in the presence of acidic and neutral liposomes, dye-release ability from encapsulated liposomes, but on the whole the interaction mode was similar. On antimicrobial activity, MP had a strong activity against Gram-positive bacteria but no against Gram negative ones. Contrary to this, MP-B had a strong activity against Gram-positive and potent against Gram-negative ones. Since both peptides have almost same residues on the hydrophobic side, such more hydrophilic surface on the molecule seems to lead to the subtle change in its interaction with membranes, resulting in the alternation in its biological activity.

• Advances in nano research
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• v.1 no.3
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• pp.133-151
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• 2013

The availability of advanced nanotechnological methodologies (experimental and theoretical) has widened the investigation of biological/organic matter in interaction with substrates. Minerals are good candidates as substrates because they may present a wide variety of physico-chemical properties and surface nanostructures that can be used to actively condense and manipulate the biomolecules. Scanning Probe Microscopy (SPM) is one of the best suited techniques used to investigate at a single molecule level the surface interactions. In addition, the recent availability of high performance computing has increased the possibility to study quantum mechanically the interaction phenomena extending the number of atoms involved in the simulation. In the present paper, firstly we will briefly introduce new SPM technological developments and applications to investigate mineral surfaces and mineral-biomolecule interaction, then we will present results on the specific RNA-mineral interaction and recent basics and applicative achievements in the field of the interactions between other fundamental biological molecules and mineral surfaces from both an experimental and theoretical point of view.