• Bulletin of the Korean Chemical Society
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• 제16권12호
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• pp.1153-1162
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• 1995

The conformational details of β-lactose are investigated through molecular dynamics simulations in conjunction with the adiabatic potential energy map. The adiabatic energy map generated in vacuo contains five local minima. The lowest energy structure on the map does not correspond to the structure determined experimentally by NMR and the X-ray crystallography. When aqueous solvent effect is incorporated into the energy map calculation by increasing the dielectric constant, one of the local minima in the vacuum energy map becomes the global minimum in the resultant energy map. The lowest energy structure of the energy map generated in aquo is consistent with the one experimentally determined. Molecular dynamics simulations starting from those fivelocal minima on the vacuum energy map reveal that conformational transitions can take place among various conformations. Molecular dynamics simulations of the lactose and ricin B chain complex system in a stochastic boundary indicate that the most stable conformation in solution phase is bound to the binding site and that there are conformational changes in the exocyclic region of the lactose molecule upon binding.

• Bulletin of the Korean Chemical Society
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• 제17권2호
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• pp.201-205
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• 1996

The crystal and molecular structure of thiourea dioxide, (NH2)2CSO2, was determined by x-ray single crystal diffraction techniques. Lattice constants are a=10.669(2), b=10.119(2), and c=3.9151(5) Å with the space group Pnma and Z=4. The thiourea portion of the molecule has a planar conformation. When the two oxygen atoms are included, the sulfur atom is at the apex of a trigonal pyramid formed with the two oxygen atoms and the carbon atom as the base. The crystal structure is stabilized by strong intermolecular hydrogen bonds. Ab initio calculations were performed to investigate the bonding features and reactivity of thiourea dioxide. The calculated bond order of S-C is only 0.481. The hydrogen bond energy was computed to be 22.3 kcal/mol for dimer. MEP analysis reveals that the sites on nucleophilic reactions are S and C atoms.

• Advances in nano research
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• 제1권2호
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• pp.71-82
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• 2013

A simple chemical precipitation technique is reported for the synthesis of a hybrid nanostructure of single-wall carbon nanotubes (SWCNT) and titania ($TiO_2$) nanocrystals of average size 5 nm, which may be useful as a prominent photocatalytic material with improved functionality. The synthesized hybrid structure has been characterized by transmission electron microscopy (HRTEM), energy-dispersive X-ray analysis (EDAX), powder X-ray diffractometry (XRD), Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy. It is clearly revealed that nearly monodispersed titania nanocrystals (anatase phase) of average size 5 nm decorate the surfaces of SWCNT bundles. The UV-vis absorption study shows a blue shift of 16 nm in the absorbance peak position of the composite material compared to the unmodified SWCNTs. The photoluminescence study shows a violet-blue emission in the range of 325-500 nm with a peak emission at 400 nm. The low temperature electrical transport property of the synthesized nanomaterial has been studied between 77-300 K. The DC conductivity shows semiconductor-like characteristics with conductivity increasing sharply with temperature in the range of 175-300 K. Such nanocomposites may find wide applications as improved photocatalyst due to transfer of photo-ejected electrons from $TiO_2$ to SWCNT, thus reducing recombination, with the SWCNT scaffold providing a firm and better positioning of the catalytic material.

• 대한화학회지
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• 제58권3호
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• pp.258-266
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• 2014

Single crystals of cobalt(II) and nickel(II) complexes of 4-nitrobenzoic acid have been successfully grown by gel diffusion technique. The grown crystals were characterized by elemental analysis, FT-IR and UV-Visible spectroscopy. The structure of the grown crystals was elucidated using single crystal X-ray diffraction studies. The title compounds $[Co(Pnba)_2(H_2O)_4]{\cdot}2H_2O$ 1 and $[Ni(Pnba)_2(H_2O)_4]{\cdot}2H_2O$ 2 where PnbaH=4-nitrobenzoic acid, crystallize in centrosymmetric triclinic space group P-1. Magnetic susceptibility measurements reveal that the compounds are paramagnetic in nature. The mechanical strength of the grown crystals was determined by Vicker's microhardness studies. The ligand (4-nitrobenzoic acid) and the complexes have been screened for their biological activity against various bacteria and fungi. The activity data show that the biological activity of the complexes is higher than that of the ligand.

• Bulletin of the Korean Chemical Society
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• 제27권10호
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• pp.1572-1576
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• 2006

A dimeric precursor, $[Cu(dmae)(OCOCH_3)(H_2O)]_2$ for the CVD of copper metal films, (dmaeH = N,N-dimethylaminoethanol) was synthesized by the reaction of copper(II) acetate monohydrate ($Cu(OCOCH_3)_2{\cdot}H_2O$) and dmaeH in toluene. The product was characterized by m.p. determination, elemental analysis and X-ray crystallography. Molecular structure of $[Cu(dmae)(OCOCH_3)(H_2O)]_2$ shows that a dimeric unit $[Cu(dmae)(OCOCH_3)(H_2O)]_2$ is linked to another through hydrogen bond and it undergoes facile decomposition at 300 C to deposit granular copper metal film under nitrogen atmosphere. The decomposition temperature, thermal behaviour, kinetic parameters, evolved gas pattern of the complex, morphology, and the composition of the film were also investigated.

• 한국재료학회지
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• 제26권4호
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• pp.222-227
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• 2016

Tin oxides have been studied for various applications such as gas detecting materials, transparent electrodes, transparent devices, and solar cells. p-type SnO is a promising transparent oxide semiconductor because of its high optical transparency and excellent electrical properties. In this study, we fabricated p-type SnO thin film using rf magnetron sputtering with an SnO/Sn composite target; we examined the effects of various oxygen flow rates on the SnO thin films. We fundamentally investigated the structural, optical, and electrical properties of the p-type SnO thin films utilizing X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV/Vis spectrometry, and Hall Effect measurement. A p-type SnO thin film of $P_{O2}=3%$ was obtained with > 80% transmittance, carrier concentration of $1.12{\times}10^{18}cm^{-3}$, and mobility of $1.18cm^2V^{-1}s^{-1}$. With increasing of the oxygen partial pressure, electrical conductivity transition from p-type to n-type was observed in the SnO crystal structure.

• Carbon letters
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• 제12권4호
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• pp.229-235
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• 2011

Isotactic polyacrylonitrile (PAN) with triad isotacticity of 0.53, which was determined by $^{13}C$ NMR, using dialkylmagnesium as an initiator, was successfully synthesized. Isothermal treatment of iso-PAN was conducted in air at 200, 220, 250 and $280^{\circ}C$. Structural evolutions and chemical changes were studied with Fourier transformation infrared and wide-angle X-ray diffraction during stabilization. A new parameter $CNF={I_{2240cm}}^{-1}/ ({I_{1595cm}}^{-1}+f^*{I_{1595cm}}^{-1})$ was defined to evaluate residual nitrile groups. Crystallinity and crystal size were calculated with X-ray diffraction dates. The results indicated that the nitrile groups had partly converted into a ladder structure as stabilization proceeded. The rate of reaction increased with treatment temperature; crystallinity and crystal size decreased proportionally to pyrolysis temperature. The iso-conversional method coupled with the Kissinger and Flynn-Wall-Ozawa methods were used to determine kinetic parameters via differential scanning calorimetry analysis with different heating rates. The active energy of the reaction was 171.1 and 169.1 kJ/mol, calculated with the two methods respectively and implied the sensitivity of the reaction with temperature.

• 한국세라믹학회지
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• 제47권2호
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• pp.136-141
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• 2010

ACF/ZnO photocatalyst was synthesized by a sol-gel method using activated carbon fiber (ACF) and Zn $(NO_3)_2$ as precursors. Samples were characterized by Brunauer-Emmett-Teller measurements (BET), scanning electron microscope (SEM), X-ray diffraction (XRD), and energy dispersive X-ray (EDX). The XRD results showed that ACF/ZnO composites only included a hexagonal phase by heat-treated temperature at $400^{\circ}C$, $500^{\circ}C$, $600^{\circ}C$, and $700^{\circ}C$. The SEM analysis revealed that the ACF/ZnO composites did not exhibit any morphological changes of the catalyst surface according to the different heat-treated temperatures. The photocatalytic activity of the samples was tested for degradation of methylene blue (MB) solutions under ultraviolet (UV) light and ultrasonication respectively. The results showed that the photocatalytic activity of ACF/ZnO composites heat-treated at $500^{\circ}C$ was higher than other samples, which is ascribed to the fine distribution of ZnO particles on the surface of the ACF. In addition, an ultrasound of low power (50 W) was used as an irradiation source to successfully induce ACF/ZnO composites to perform sonocatalytic degradation of MB. Results indicated that the sonocatalytic method in the presence of ACF/ZnO composites is an advisable choice for the treatments of organic dyes.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2002년도 하계학술대회 논문집
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• pp.375-378
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• 2002

We investigated the reduction of etching damage by additive O$_2$ in etching gas and recovery of etching damage by O$_2$ annealing. The PZT thin films were etched using additive Ar or O$_2$ into Cl$_2$/CF$_4$ gas mixing ratio of 8/2. In order to recover ferroelectric properties of PZT thin films after etching, the etched PZT thin films were annealed at 600 C in O$_2$ atmosphere for 10 min. The remanent polarization is decreased seriously and fatigue is accelerated in the PZT sample etched in Ar/(C1$_2$+CF$_4$) plasma, whereas these characteristics are improved in O$_2$/(Cl$_2$/CF$_4$). From x-ray photoelectron spectroscopy (XPS) analysis, the intensities of Pb-O, Zr-O and Ti-O peaks are changed and the etch byproducts such as metal chloride and metal fluoride are reduced by O$_2$ annealing. From electron probe micro analyzer (EPMA) and auger electron spectroscopy(AES), O$_2$ vacancy is observed after etching. In x-ray diffraction (XRD), the structure damage in the additive O$_2$ into C1$_2$/CF$_4$ is reduced and the improvement of ferroelectric behavioral annealed sample is consistent with the increase of the (100) and (200) PZT peaks.

• 한국기계가공학회지
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• 제13권1호
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• pp.100-106
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• 2014

It is well known that fatigue failures occur on welded structures in industrial application due to repetitive load force. In order to decrease the incidence of fatigue failure, we analyzed the mechanical properties based on structural aspects in rolled steel(SS 400) welded onto stainless steel (STS 304) by the MIG welding method as well as the structure of rolled steel welded onto itself. We compared the hardness, tensile and fatigue properties with two types of samples which had no defects on the welding parts as observed by X-ray topographic analysis. It was found that the tensile and fatigue strength levels of SS 400 welded onto STS 304 by the MIG welding method were higher than those of STS 304 welded onto itself.