• Bulletin of the Korean Chemical Society
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• 제30권12호
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• pp.3025-3030
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• 2009

Novel poly(aspartic acid) derivatives conjugated with $\gamma$-amino butyric acid, GABA, moieties, and their amphiphilic analogs were synthesized and characterized. The chemical structures of these polymers were confirmed by FT-IR and $^1H$ NMR spectroscopy. Their physicochemical properties in aqueous media were characterized by electrophonetic light scattering spectrophotometry (ELS), acid-base titration, and UV-spectroscopy. In addition, the in vitro cell activity of the GABA-conjugated polymer was examined. These results indicated that GABA-conjugated poly(aspartic acid) derivatives showed cell-growth activity and nanoparticle formation of a suitable size within aqueous media. These polymers have potential application in the cosmetic and pharmaceutical fields.

• Bulletin of the Korean Chemical Society
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• 제31권12호
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• pp.3735-3739
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• 2010

Branched oligopeptides prepared by coupling a very hydrophobic aspartic diamino acid ethyl ester such as Asp $(LeuEt)_2$, $Asp(IleEt)_2$ and $Asp(PheEt)_2$ to glycine or glycylphenylalanine were grafted to the cyclotriphosphazene backbone bearing an equimolar hydrophilic poly(ethylene glycol) (PEG). The properties of the resultant amphiphiles were examined in comparison with those of the linear oligopeptide analogues previously reported. All cyclic phosphazene trimers grafted with the branched tetra- and pentapeptides displayed a normal trend of thermosensitivity depending on their hydrophilic to hydrophobic balance, but the stability and particle size of their micelles were found to be greatly dependent on the fine structure of the branched oligopeptides grafted. The trimers bearing branched tetrapeptides with a low hydrophobicity were found to form unstable micelles initially, which reassemble into thermodynamically more stable polymersomes.

• Corrosion Science and Technology
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• 제9권6호
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• pp.265-269
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• 2010

This paper describes the exfoliation and surface modification of muscovite mica for UV coating formulation. For the exfoliation of the mica, hydrothermal process was used in the presence of lithium nitrate ($LiNO_3$). After the cation exchange with $Li^+$ ions, the surface of the mica was modified with several amphiphilic substances to increase compatibility and storage stability in UV coating formulation. Such a hydrophobic surface modification affected colloidal stability as well as dispersibility of the exfoliated mica in UV coating solution. Anticorrosive property of mica/UV coated steel plates was tested by salt spray test (SST) and compared with sodium montmorillonite ($Na^+$-MMT)/UV coated steel plates.

• 한국세라믹학회지
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• 제48권5호
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• pp.463-466
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• 2011

Wet foams formed through direct foaming were stabilized using various concentrations of amiphiphilic particles that could control pore size and porosity. These porous materials showed moderate strength upon compression with high porosity. Bubble size and wet foam stability were tailored by amphiphile concentration, particle concentration, contact angle, and pH of the suspension to obtain crack-free porous solid after sintering. Closed and open pores were obtained with sizes of 30~300 ${\mu}m$ and porosities of over 80%.

• Bulletin of the Korean Chemical Society
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• 제18권9호
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• pp.933-938
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• 1997

The interaction of mastoparan B, a tetradecapeptide toxin found in the hornet Vespa basalis, with phospholipid bilayers was investigated. Synthetic mastoparan B and its analogs, obtained by substituting one hydrophilic amino acid (2-Lys, 4-Lys, 5-Ser, 8-Ser, 11-Lys, or 12-Lys) in mastoparan B with Ala, were studied. Mastoparan B and its analogs were synthesized by the solid-phase method. As shown by circular dichroism spectra, mastoparan B and its analogs adopted an unordered structure in buffer solution. All peptides took an α-helical structure, and the α-helical content of its analogs increased in the presence of neutral and acidic liposomes as compared to that of mastoparan B. In the calcein leakage experiment, we observed that mastoparan B interacted more weakly with lipid bilayers in neutral and acidic media than its analogs. Mastoparan B also showed slightly lower antimicrobial activity and hemolytic activity towards human erythrocytes than its analogs. These results indicate that the greater hydrophobicity of the amphiphilic α-helix of mastoparan B by replacement with alamine residues results in the increased biological activity and helical content.

• Bulletin of the Korean Chemical Society
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• 제13권5호
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• pp.479-482
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• 1992

Several poly(alkyl methacrylate-b-t-butyl methacrylate) diblock copolymers were synthesized by group transfer polymerization. The molecular weight of poly(t-butyl methacrylate) segments and the composition of the resulting block copolymers were controlled by the monomer feed ratios and mole ratios of monomer to initiator. The poly(t-butyl methacrylate) block was quantitatively hydrolyzed to poly(methacrylic acid) block by refluxing with a catalytic amount of p-toluenesulfonic acid in dioxane at $100^{\circ}C$ for 12 hrs. The thermogravimetric analysis of poly(alkyl methacrylate-b-t-butyl methacrylate) exhibited the lose of isobutylene and subsequent anhydride formation in the range of $205-300^{\circ}C$.

• Journal of Plant Biology
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• 제33권1호
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• pp.81-84
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• 1990

The chloroplast has been the prime light-energy harvesting organelle on earth. It also carries out several key metabolic processes, such as lipid synthesis and nitrogen metabolism. Even though the chloroplast has its own genome, its coding capacity can afford only dozens of proteins, and most of the proteins functioning in the chloroplast are imported from the cytosol where nuclear encoded chloroplast genes are synthesized on free cytosokic ribosomes. Precursor proteins synthesized on cytosolic ribosomes have transit peptides at the amino termini of the proteins, and the transit peptide is sufficient to transfer chloroplast proteins from the cytosol into the chloroplast. When comparing amino acid sequences duduced from the nucleotide sequences of the clones of the chloroplast proteins, high homologies can be found among the transit peptides of proteins with the same function. Overall amino acid compositions of the transit peptides show amphiphilic characters of the transit peptides, and the amphiphilicity indicates that three dimensional structure of the transit peptide is responsible for the translocation of the chloroplast proteins.

• Bulletin of the Korean Chemical Society
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• 제18권2호
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• pp.190-193
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• 1997

In search of new amphiphiles that form coordinatively polymerized bilayer membranes (CPBMs) in water, N-dodecyl-3-[2-hydroxy-3-(4-carboxymethyl-2-thiazolylazo)-5-methylphenyl]propanamide (5) was prepared. The bilayer membranes of 5 prepared in the presence of 2 equivalents of NaOH were further sonicated in the presence of transition metal ions such as Ni(Ⅱ), Cu(Ⅱ), Co(Ⅱ), or Co(Ⅲ) at > 80 ℃ to obtain CPBMs. The CPBMs of 5 were characterized by transmission electron microscopy, gel filtration, resistivity against disruption in aqueous ethanol, visible spectra, and release of entrapped 5(6)-carboxyfluorescein. Remarkable stabilization of the bilayer membranes through coordinative polymerization was evidenced by the resistivity of the Ni(Ⅱ)-CPBM of 5 against disruption in 40%(v/v) ethanol upon incubation for 20 hr.

• Bulletin of the Korean Chemical Society
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• 제17권3호
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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.

• Bulletin of the Korean Chemical Society
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• 제8권3호
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• pp.158-161
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• 1987

A Series of hydrophilic-hydrophobic copolymeric surfaces of 2-hydroxyethyl methacrylate (HEMA) and various alkyl methacrylate (RMA) have been prepared by in-situ solution copolymerization using a redox radical initiator. Contact angles of various probing fluids on the polymeric surfaces were determined in air (hydrophobic environment) and under water (hydrophilic environment). From contact angle data, the dispersive interaction contribution (${\gamma}^d_s$) and the polar contribution (${\gamma}^p_s$) to the total surface free energy (${\gamma}^d_s$) and interfacial energetic quantities (e.g., water-polymer, liquid-polymer interface, etc.) were estimated by surface and interface physicochemical theory. From the comparison of surface energetic components between hydrophobic and hydrophilic media, it is found that surface and interface energetic components of polymeric surface as a representative low-energy surface are highly dependent on environmental fluids. Also, from the correlation between interfacial energetic results and surface energetic criterion of biocompatibility, we found that HEMA/BMA, HEMA/HMA copolymer systems are in the region of biocompatibility.