• Proceedings of the Polymer Society of Korea Conference
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• 2006.10a
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• pp.29-30
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• 2006

The synthesis of dendritic dipeptides $(4-3,4-3,5)12G2-CH_{2}-Boc-_{L}-Tyr-X-OMe\;where\;X\;=\;Gly,\;_{L}-Val,\;_{L}-Leu,\;_{L}-Ile,\;_{L}-Phe$, and L-Pro will be discussed. Their self-assembly in bulk and in solution and the structural and retrostructural analysis of their periodic assemblies will be compared to that of the previously reported and currently reinvestigated dendritic dipeptide with $X=_{L}-Ala$. All dendritic dipeptides containing as X nonpolar ${\alpha}-amino$ acids self-assemble into helical porous columns. The principles via which the aliphatic and aromatic substituents of X program the structure of the helical pores indicate synthetic pathways to helical pores with bioinspired functions based on artificial nonpolar ${\alpha}-amino$ acids will be discussed.

• Journal of the Korean Chemical Society
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• v.38 no.10
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• pp.710-718
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• 1994

We suggest a statistical thermodynamic theory for the conformational transition of a synthetic alanine (Ala), ${\alpha}$-aminoisobutyric acid (Aib) alternative oligopeptide, Buo-(Ala-Aib)$_n$-oMe, where the terminal groups Buo and oMe stand for t-butoxy and methoxy, respectively. Pure Aib homo-oligomers have always been found to adopt $3_{10}$ helical conformations, while polyalanine has always $\alpha$ helical conformation. In an organic solvent (e.g. $CD_3$CN) it shows that the length for the $3_{10}$/${\alpha}$ helix transitions of Buo-(Ala-Aib)$_n$-oMe, is 8 at room temperature. In an aqueous solution oligopeptide has always coil conformation at room temperature. In an organic solution, helical structures of the oligopeptide are more stable than coil structure, so we studied the $$3_{10}/\alpha$ helix transitions, considering coiled-conformations, coiled and $3_{10}$ helical conformations, and coiled and $\alpha$ helical conformations by using the zipper model. We determined the values of parameters ($\sigma_A$, $\sigma_T$, $\xi_A$, $\xi_T$) from the relating published data; $\sigma_A$ = 0.00011, $\sigma_T$ = 0.0060, $\xi_A$ = 10.1, $\xi_T$ = 3.90. The distributions of $\alpha$ helical length can be N-2, N-3, N-4, ${\cdots}$, 3, 2, 1 (N = 2n) while those of $3_{10}$ helical length, N-1, N-2, N-3, N-4, ${\cdots}$, 3, 2, 1.

• BMB Reports
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• v.44 no.11
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• pp.747-752
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• 2011

To investigate the effects of disulphide bond position on the salt resistance and lipopolysaccharide (LPS)-neutralizing activity of ${\alpha}$-helical homo-dimeric antimicrobial peptides (AMPs), we synthesized an ${\alpha}$-helical model peptide ($K_6L_4W_1$) and its homo-dimeric peptides (di-$K_6L_4W_1$-N, di-$K_6L_4W_1$-M, and di-$K_6L_4W_1$-C) with a disulphide bond at the N-terminus, the central position, and the C-terminus of the molecules, respectively. Unlike $K_6L_4W_1$ and di-$K_6L_4W_1$-M, the antimicrobial activity of di-$K_6L_4W_1$-N and di-$K_6L_4W_1$-C was unaffected by 150 mM NaCl. Both di-$K_6L_4W_1$-N and di-$K_6L_4W_1$-C caused much greater inhibitory effects on nitric oxide (NO) release in LPS-induced mouse macrophage RAW 264.7 cells, compared to di-$K_6L_4W_1$-M. Taken together, our results indicate that the presence of a disulphide bond at the N- or C-terminus of the molecule, rather than at the central position, is more effective when designing salt-resistant ${\alpha}$-helical homo-dimeric AMPs with potent antimicrobial and LPS-neutralizing activities.

• BMB Reports
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• v.39 no.3
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• pp.270-277
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• 2006

Helices 4 and 5 of the Bacillus thuringiensis Cry4Ba $\delta$-endotoxin have been shown to be important determinants for mosquito-larvicidal activity, likely being involved in membrane-pore formation. In this study, the Cry4Ba mutant protein containing an additional engineered tryptic cleavage site was used to produce the $\alpha4$-$\alpha5$ hairpin peptide by an efficient alternative strategy. Upon solubilization of toxin inclusions expressed in Escherichia coli and subsequent digestion with trypsin, the 130-kDa mutant protoxin was processed to protease-resistant fragments of ca. 47, 10 and 7 kDa. The 7-kDa fragment was identified as the $\alpha4$-loop-$\alpha5$ hairpin via N-terminal sequencing and mass spectrometry, and was successfully purified by size-exclusion FPLC and reversed-phase HPLC. Using circular dichroism spectroscopy, the 7-kDa peptide was found to exist predominantly as an $\alpha$-helical structure. Membrane perturbation studies by using fluorimetric calcein-release assays revealed that the 7-kDa helical hairpin is highly active against unilamellar liposomes compared with the 65-kDa activated full-length toxin. These results directly support the role of the $\alpha4$-loop-$\alpha5$ hairpin in membrane perturbation and pore formation of the full-length Cry4Ba toxin.

• Journal of the Korean Magnetic Resonance Society
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• v.5 no.1
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• pp.37-45
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• 2001

Synthetic pulmonary surfactants consisting of a mixture of phospholipids with synthetic peptides based on human surfactant-associated protein SP-B were prepared. These surfactants were analyzed f3r their secondary structures by circular dichroism (CD) spectroscopy and NMR spectroscopy. Two synthetic peptides (SP-B(3), SP-B(4)) combined with the phospholipid mixture displayed significant surfactant properties. The CD spectra showed that the u-helical propensities of the peptides in DPC micelles. In the NMR spectroscopy, the tertiary structures of SP-B(3) show that it has $\alpha$-helical structure from Gln5 to Arg13 in DPC micelle and SP-B(4) show that they have $\alpha$-helical structure from Gln5 to Leu12 in DPC micelle. Based on these structures, truncated peptides originated from SP-B protein, can be designed as effective synthetic surfactants for clinical use.

• Journal of the Korean Chemical Society
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• v.39 no.10
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• pp.776-782
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• 1995

A theory of the helix/coil transition for $\alpha$ helical dimer such as $\alpha$ tropomycin and paramycin is developed. The treatment differs from those formulated previously for oligopeptide dimer which is explained by the matrix method using Zimm-Bragg parameter: In the present treatement, it is explained by the zipper model which can account for the dangling H-bond. We calculate the fractional helicity in $\alpha$ helical dimer as a function of helix initiation $constant(\sigma)$, helix stability constant(${\xi}$) and hydrophobic interaction parameter(w). For $\alpha$ tropomycin, the helix stability profile is also calculated. The transitions of this oligomer due to the change of temperature and the concentration of oligopeptide involve simultaneous dissociation of the dimer. The transitions of dimers which have cross-linked S-S bonds or have long chains don't occur, because they keep always helical structures. The transitons due to the concentration of the oligopeptides are steeper than those due to the chain length or temperature.

• The KSFM Journal of Fluid Machinery
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• v.19 no.1
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• pp.11-17
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• 2016

In this paper, a numerical analysis was performed to investigate the effect of the pitch angle of a helical nozzle on the performance characteristics of a vortex tube. Three-dimensional numerical simulation has been performed with standard $k-{\varepsilon}$ turbulence model by using FLUENT 13.0. The effect of the pitch angle of helical nozzle was described in term of ${\beta}$. A CFD analysis was performed on ${\beta}=0^{\circ}$, $5^{\circ}$, $10^{\circ}$, $15^{\circ}$. In order to realize the influence of ${\beta}$ on performances of the vortex tube. Computation results were expressed by the ${\beta}-{\Delta}T_{h,c}$ graph and radial profiles of axial velocity and swirl velocity. The results showed that ${\beta}$ which improves energy separation capacity of vortex tube was $5^{\circ}$ at ${\alpha}=0.33$, 0.5 and $10^{\circ}$ at ${\alpha}=0.33$. Besides, It was confirmed that the results were closely related to axial velocity and swirl velocity.

• Journal of Microbiology and Biotechnology
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• v.28 no.8
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• pp.1299-1309
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• 2018

We previously reported on lactophoricin (LPcin), a cationic ${\alpha}-helical$ antimicrobial peptide derived from bovine milk, which has antimicrobial effects on Candida albicans as well as Gram-positive and Gram-negative bacteria. In this study, we designed the LPcin-YK3 peptide, a shorter analog of LPcin, and investigated its antimicrobial activity. This peptide, consisting of 15 amino acids with + 3 net charges, was an effective antimicrobial agent against the on the Gram-positive strain, Staphylococcus aureus (MIC: $0.62{\mu}g/ml$). In addition, the hemolytic activity assay revealed that the peptide was not toxic to mouse and human erythrocytes up to $40{\mu}g/ml$. We also used circular dichroism spectroscopy to confirm that peptide in the presence of lipid has ${\alpha}-helical$ structures and later provide an overview of the relationship between each structure and antimicrobial activity. This peptide is a member of a new class of antimicrobial agents that could potentially overcome the problem of bacterial resistance caused by overuse of conventional antibiotics. Therefore, it could be used as a therapeutic or natural additive, particularly in the cosmetics industry.

• Bulletin of the Korean Chemical Society
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• v.25 no.6
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• pp.838-842
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• 2004

Amyloid peptide (A${\beta}$) is the major component of senile plaques found in the brain of patient of Alzheimer's disease. ${\beta}$-amyloid peptide (25-35) (A${\beta}$25-35) is biologically active fragment of A${\beta}$. The three-dimensional structure of A${\beta}$25-35 in aqueous solution with 50% (vol/vol) TFE determined by NMR spectroscopy previously adopts an ${\alpha}$-helical conformation from $Ala^{30}$ to $Met^{35}$. It has been proposed that A${\beta}$(25-35) exhibits pH- and concentration-dependent ${\alpha}-helix{\leftrightarrow}{\beta}$sheet transition. This conformational transition with concomitant peptide aggregation is a possible mechanism of plaque formation. Here, in order to gain more insight into the mechanism of ${\alpha}$-helix formation of A${\beta}$25-35 peptide by TFE, which particularly stabilizes ${\alpha}$-helical conformation, we studied the secondary-structural elements of A${\beta}$25-35 peptide by molecular dynamics simulations. Secondary structural elements determined from NMR spectroscopy in aqueous TFE solution are preserved during the MD simulation. TFE/water mixed solvent has reduced capacity for forming hydrogen bond to the peptide compared to pure water solvent. TFE allows A${\beta}$25-35 to form bifurcated hydrogen bonds to TFE as well as to residues in peptide itself. MD simulation in this study supports the notion that TFE can act as an ${\alpha}$-helical structure forming solvent.

• Bulletin of the Korean Chemical Society
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• v.32 no.11
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• pp.4055-4058
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• 2011