• Proceedings of the KSME Conference
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• 2004.04a
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• pp.810-815
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• 2004

In this paper, we propose new parallel mechanism of a 3 dimensional biped robot whose each leg is composed of two 3-dof parallel platforms linked serially. This proposed parallel mechanism is able to move freely in the man-made environment and is applied to various fields, such as medical, welfare, and so on. And a total weight of each leg is expected to be lighter than serial linked leg. One side leg consists of a 3-dof orientation platform and 3-dof asymmetric parallel platform. The former consists of three active linear actuators and seven passive joints, and the latter of two active linear actuators, one active rotational actuator and eight passive joints. Thus, there are two kinds of parallel platforms each chain's elements and active joint's positions are different for the biped robot to move freely like a serial link without the kinematics constraints. The effectiveness and the performance of the proposed parallel mechanism and locomotion trajectory are shown in computer simulations with a 12-DOF parallel biped robot.

• Journal of the Korean Society of Safety
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• v.18 no.3
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• pp.81-87
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• 2003

Latex polymers are widely used for adhesive, binder, paint etc. Especially the PVAc(Polyvinyl acetate) latex which manufactured by vinyl acetate and vinyl alcohol as protective colloid is a useful environmentally friendly adhesive. To increase useful property of PVAc latex, this study was carried out for checking thermal characteristics and physical condition of PVAc latex by DSC, FT-IR, Pyrolyzer GC-MS. The activation energies of thermal decomposition for 40, 48, 56, 64% solid content of PVAc latex were found as 28.1-36.0kcal/mol by Kissinger's method and 17.2-22.0kcal/mol by DSC method. Actually, reasonable solid content could be consiered as 56% because of activation energy and adhesive characteristics. According to the effect of protective colloid for 4, 10, 15, 20wt%, the activation energy shows same tendency to both method and in case of l5wt% has been found as the highest activation energy. The mechanism of thermal decomposition was mainly estimated by main chain scission, not by side group on FT-IR analysis. Main component of Pyrolzer GC-MS result were consisted of $CH_3COOH$, $CH_3$, $H_2O$ and light gases(CO, $CO_2$, $CH_4$ etc).

• Bulletin of the Korean Chemical Society
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• v.22 no.9
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• pp.984-988
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• 2001

Since anti-angiogenesis could lead to the suppression of tumor growth, angiogenesis inhibitors have received particular attention for their therapeutic potential. In this study, two angiogenic inhibitors using the bioactive sequence from the kring le 5, AK1(KLYDY), AK2(KLWDF) were designed and synthesized. We have investigated their solution structures using NMR spectroscopy and their activities as angiogenesis inhibitors. AK2 has an intramolecular hydrogen bon d between the side chain amino proton of Lys1 and the carboxyl oxygen of Asp4 with a N ${\cdot}{\cdot}{\cdot}$O distance of $3.27\AA$, while AK1 shows more flexible structures than AK2. Indole ring in Trp is much bigger than the phenyl ring in Tyr and may have good face-to-edge interaction enforcing more rigid and constrained conformational features of AK2. Because of this relatively stable structure, Trp3 in AK2 may have better hydrophobic interaction with Phe5 than Tyr3 in AK1 if two adjacent aromatic groups are located in hydrophobic pocket of receptor. Since AK2 shows the similar anti-angiogenic activities to AK1, we are also able to confirm that the activity of AK1 is irrelevant to the Tyr phosphorylation. More rigid drug with higher activities can be provided by the mimetic approaches. For the further development of the angiogenesis inhibitors, these conformational studies on our lead peptides will be helpful in design of peptidomimetics.

• Bulletin of the Korean Chemical Society
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• v.14 no.4
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• pp.491-496
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• 1993

A class A ${\beta}$-lactamase from Staphylococcus aureus PC1 complexed with 3R,5R-clavulanate is studied. The starting geometry for the computation is the crystal structure of the ${\beta}$-lactamase. Docking of the clavulanate to the enzyme is done exploiting the requirements of electrostatic and shape complementarity between the enzyme and clavulanate. This structure is then hydrated by water molecules and refined by energy minimization and short molecular dynamics simulation. In the energy refined structure of this complex, the carboxyl group of the clavulanate is hydrogen bonded to Lys-234, and the the carbonyl carbon atom of the clavulanate is adjacent to the $O_{\gamma}$ of Ser-70. It is found that a crystallographic water molecule initially located at the oxyanion hole, which is formed by the two -NH group of Ser-70 and Gln-237, is replaced by the carbonyl oxygen atom of the 3R,5R-clavulanate after docking and energy reginement. The crystallographic water molecules are proved to be important in ligand binding. Glu-166 residue is found to be repulsive to the binding of clavulanate, which is in agreement with experimental observation. Arg-244 residue is found to be important to the binding of clavulanate as well as to interaction with C2 side chain of the clavulanate. The electron density redistribution of the clavulanate on binding to the ${\beta}$-lactamase in studied by an ab initio quantum-mechanical calculation. A significant redistribution of electron density of the clavulanate is induced by the enzyme, toward the enzyme, toward the transition state of the enzymatic reaction.

• Microbiology and Biotechnology Letters
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• v.22 no.2
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• pp.190-196
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• 1994

Alkali soluble(AS) fraction, revealed the highest antitumor activity of the alkali extracted fractions of G. lucidum IY 009, was loaded on DEAE cellulose(OH$^{-}$ form) column. AS-1, AS-2, AS-3, AS-4 and AS-5 were obtained by stepwise elution with H$_{2}$O, 0.1 M NaHCO$_{3}$, 0.3 M NaHCO$_{3}$, 0.5 M NaHCO$_{3}$ and 0.5 N NaOH respectively, and their antitumor activities(I.R. %) against the sarcoma 180 were 97.5%, 68.0%, 73.0%, 81.0% and 66.0% respectively. AS-1 observed highest antitumor activity was appeared as single peak on the Sepharose CL-4B column chromatography, and their molecular weight was about 580,000 dalton. The carbohydrate content of AS-1 was 98.9%, their monosaccharide consisted of 67.5% of mannose, 22.5% of xylose, 5.8% of glucose, 1.8% of galactose and 2.0% of ribose. AS-1 was assumed $\alpha $linkaged xylomannan having infrared absorption at 864.3 cm$^{-1}$. The main alditol acetates of AS-1 were identified as 1,5-Di-O-acetyl1-2,3,4-Tri-O-methylxylitol, 1,4,5-Tro-O-acety1-2,3,6-Tri-O-methylmannitol and 1,3,4,5-Tetra-O-acety1-2,6-Di-O-methylmannitol by methylation analysis, and their molar ratio was 1 : 2 : 1. The core portion of AS-1 might be $\alpha $-(1$\longrightarrow $ 4)mannopyranosyl unit branched with side chain, C1 of xylopyranosyl residue linked to C3 of every 3 mannopyranosyl units, and the degree of polymerization of structural unit in AS-1 was about 835.

• Korean Chemical Engineering Research
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• v.44 no.5
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• pp.540-546
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• 2006

Effects of organic and inorganic additives on the SNCR reaction of NOx were investigated in a pilot scale flow reactor with a variation of operating parameters. NOx reduction efficiency increased with the increase of a residence time and an initial NOx concentration. NOx reduction reaction by urea solution started to appear about 850 and then reached to maximum value around $970^{\circ}C$. NOx reduction efficiency also increased with the increase of NSR (Normalized Stoichiometric Ratio) up to 2.0. Addition of ethanol and phenol as an organic additives shifted the optimum temperature window to lower region with decreasing the maximum NOx reduction efficiency. This might be due to the side reaction of hydrocarbon in ethanol structure. NaOH addition widened the temperature window and enhanced the NOx reduction efficiency about 10％ due to the chain reaction of NaOH and the reduction of $N_2O$.

• Polymer(Korea)
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• v.36 no.3
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• pp.380-392
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• 2012

Four kinds of N,O-hydroxypropyl chitosans (HPCTOs) with degree of substitution(DS) and molar substitution (MS) ranging from 2.47 to 2.52 and 4.9 to 7.8, respectively were synthesized, and their molecular chracteristics and thermotropic and lyotropic liquid crystalline properties were investigated. MS was exceedingly larger than DS, showing that in the later stages of reaction, propylene oxide was preferentially added to the side chains rather than the main chain. All the derivatives formed thermotropic cholesteric phases. The glass and clearing temperatures were decreased with increasing MS. The optical pitches (${\lambda}_m$'s) of the thermotropic cholesteric phases increased with temperature. However, the ${\lambda}_m$'s of the derivatives at the same temperature increased with increasing MS. Solutions of HPCTOs in water, methanol, ethanol, acetic acid, and formic acid containing more than 30 wt% polymer also formed cholesteic phases whose ${\lambda}_m$'s decreased exponentially with increasing polymer concentration. The concentration dependence of ${\lambda}_m$ of HPCTO solutions, however, highly depended on the nature of the solvent and MS. The thermotropic and lyotropic mesophase properties of HPCTOs were significantly different from those reported for hydroxypropyl celluloses. The results indicate that the secondary amino group in the C-2 position plays an important role on the formation, stabilization, and temperature and concentration dependencies of ${\lambda}_m$ of the cholesteric mesophase.

• Bulletin of the Korean Chemical Society
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• v.35 no.8
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• pp.2299-2303
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• 2014

Two diastereoisomers of cyclo(Pro-Tyr) have been synthesized simultaneously. The crystal structures and conformations of both cyclo($\small{L}$-Pro-$\small{L}$-Tyr) and a racemic mixture of cyclo($\small{D}$-Pro-$\small{L}$-Tyr) and cyclo($\small{L}$-Pro-$\small{D}$-Tyr), abbreviated as rac-cyclo($\small{D}$-Pro-$\small{L}$-Tyr/$\small{L}$-Pro-$\small{D}$-Tyr), have been determined by a single-crystal X-ray diffraction study at low temperature. The crystals of rac-cyclo($\small{D}$-Pro-$\small{L}$-Tyr/$\small{L}$-Pro-$\small{D}$-Tyr) belong to orthorhombic space group $Pna2_1$ with a = 10.755 (1), b = 12.699 (1), c = 9.600 (1) ${\AA}$ and Z = 4. The tyrosine side chain is folded towards the diketopiperazine (DKP) ring. The DKP ring adopts a twist boat conformation with pseudo symmetry $C_{2v}$. The pyrrolidine ring has an envelope conformation with the N5, C4, C7 and C8 atoms in a plane. The crystal of rac-cyclo($\small{D}$-Pro-$\small{L}$-Tyr/$\small{L}$-Pro-$\small{D}$-Tyr) is stabilized by hydrogen bonds between amide N2-H2 and carbonyl oxygen O2 in the neighbor. The hydroxyl group of tyrosine residue is also hydrogen bonded to the oxygen of the carbonyl group of the DKP ring in the next molecule. The spectroscopic properties of both isomers are also described.

• Elastomers and Composites
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• v.53 no.3
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• pp.124-130
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• 2018

Recently, microwaves have been used for desulfurization because they can selectively dissociate C-S and S-S bonds present in vulcanized rubber. In this study, we investigated the changes in structural and physical properties of EPDM (Ethylene propylene diene monomer) rubber by irradiating it with microwaves for different durations. The surface chemical composition of the irradiated EPDM rubber was analyzed by FT-IR, XPS, and EDS analyses. It was confirmed by XPS that C-S and S-S S2p peak heights greatly decreased when microwave irradiation was performed for more than 5 min. In the EPDM sample irradiated with microwaves for 10 min, the number of S-O bonds significantly increased owing to oxidation. As the microwave irradiation time was increased, SEM images showed cracks and voids on the EPDM surface. The 20% decomposition temperature of the EPDM rubber sample was investigated by TGA, and it was found to be about $435.23^{\circ}C$ for the EPDM rubber irradiated for 10 min. The crosslinking density of the EPDM rubber was determined by measuring the degree of swelling, and the highest value was observed for the E5 sample irradiated for 5 min. The degree of swelling of the E10 sample irradiated for 10 min was lower than that of the E5 sample. These results indicate that when irradiated with microwaves for more than a certain time, desulfurization occurs and the side chain of the EPDM rubber dissociates and forms additional crosslinking bonds.

• Bulletin of the Korean Chemical Society
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• v.33 no.6
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• pp.1861-1866
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• 2012

The new semiconducting copolymers with 4,4-dialkyl-$4H$-cyclopenta[2,1-$b$:3,4-$b^{\prime}$]dithiophene and 2,2-dimethyl-$2H$-benzimidazole units were synthesized. The fused aromatic rings, such as cyclopentadithiophene (CPDT) unit, can make the polymer backbone more rigid and coplanar, which induces long conjugation length, narrow band gap, and strong intermolecular ${\pi}-{\pi}$ interaction. The stacking ability was controlled through attaching of linear or branched alkyl side chains. The spectra of PEHCPDTMBI and PHCPDTMBI in the solid films show absorption bands with maximum peaks at 401, 759 and 407, 768 nm, and the absorption onsets at 925 and 954 nm, corresponding to band gaps of 1.34 and 1.30 eV, respectively. The devices comprising PHCPDTMBI with $TiO_X$ showed a $V_{OC}$ of 0.39 V, a $J_{SC}$ of 1.14 $mA/cm^2$, and a $FF$ of 0.34, giving a power conversion efficiency of 0.15%. The PHCPDTMBI with linear alkyl chain on CPDT shows good solubility in organic solvent with higher PCE value than that of PEHCPDTMBI.