• Bulletin of the Korean Chemical Society
• /
• 제30권7호
• /
• pp.1521-1525
• /
• 2009

Thermosensitive block copolymers of ethylene oxide and N-isopropylacrylamide (NIPAM) were synthesized. A five armed star shape oligo(ethylene oxide) initiator with a cyclotriphosphazene core was prepared and used for the atom transfer radical polymerization (ATRP) of NIPAM. The lower critical solution temperatures (LCSTs) of the copolymers were 36 to 46 ${^{\circ}C}$, higher than that of PNIPAM (32 ${^{\circ}C}$), depending on their molecular weights. The copolymers were soluble in water below the LCSTs but formed micelles above the LCSTs. The thermosensitive micellization behaviors of the polymers were investigated by fluorescence spectroscopy. With increasing the temperature of an aqueous solution of P2 and pyrene above the LCST, the peak of 333 nm red-shifted to appear around 339 nm and its intensity increased significantly, indicating the micelle formation. The transfer of pyrene into the micelles was also confirmed by a confocal laser scanning microscope. The fluorescence image obtained from P2 in an aqueous pyrene solution exhibited a green emission resulting from the pyrene transferred into the micelles. Salt effects on the solubility of the copolymers in an aqueous solution were investigated. The LCST of P2 decreased sharply as the concentration of sodium chloride increased, while decreased slowly with potassium chloride.

• Bulletin of the Korean Chemical Society
• /
• 제18권7호
• /
• pp.743-749
• /
• 1997

Local structure refinement of the BaFe1-xSnxO3-y system (x=0.00-0.50) has been carried out with Fe K-edge x-ray absorpion spectroscopic studies. It is found out that the Fe ions are placed in two different symmetric sites such as tetrahedral and octahedral sites in the compounds by comparison with Fe K-edge x-ray absorption near edge structure (XANES) spectrum of the γ-Fe2O3 compound as a reference. Small absorption peaks of dipole-forbiden transitions appear at a pre-edge region of 7111 eV due to the existence of Fe ions in the tetrahedral and octahedral sites. The peak intensity decreases with the substitution amount of Sn ion. Three different absorption peaks of 1s→4p dipole-allowed transition appear on the energy region between 7123 and 7131 eV. The peaks correspond to 1s→4p main transition of Fe ions in tetrahedral and octahedral sites and 1s→4p transition followed by the shakedown process of ligand to metal charge transfer. The bond distances between Fe ions in the tetrahedral site and nearest neighboring oxygen atom (Fe-4O), and those in octahedral site (Fe-6O) are determined with the extended x-ray absorption fine structure (EXAFS) analysis. Two different interatomic distances increase with the substitution amount of Sn ion and also the bond lengths of Fe-4O are shorter than those of Fe-6O in all compounds.

• Bulletin of the Korean Chemical Society
• /
• 제21권9호
• /
• pp.891-895
• /
• 2000

Transmission of substituent effects through 5-membered heteroaromaticrings isinvestigated theoretically at the RHF/6-31+G* and B3LYP/6-31+G* levelsusing the deprotonation equilibria of phenol analogues with heteroatoms Y = NH, O, PHand S. The incr ease in the resonance delocalization of the $\pilone-pair$ on the phe-nolic oxygen atom, $n\pi(O)$, accompanied with the deprotonation depends on the heteroatom Y,in the order NH < O < PH < S. This represents the $\pielectron$ accepting ability, or conversely reverse order of the $\pielectron$ donating ability of the $\pilone-pair$ on Y, $n\pi(Y).$ The transmission efficiency of substituenteffects is, however,in the reverse order NH > O > S, which represents the order of delocalizability of $n\pi(Y).$ A better correlation is obtained with ${\sigma}p$ - than with ${\sigma}p$ for the Hammett type plots with the positive slope, $\rho-$ > 0, of the magnitude in the same order as that for the delocalizability of $n\pi(Y).$ Thedeprotonation energy, ΔG = [G(PA) + G(H+)] -G(P), decreases with the increasein the extence delocalization in the order NH > O > PH > S.

• Nuclear Engineering and Technology
• /
• 제55권2호
• /
• pp.555-565
• /
• 2023

Despite many advantages as structural materials, austenitic stainless steels (SSs) have been avoided in many next generation nuclear systems due to poor void swelling resistance. In this paper, we report the results of heavy ion irradiation to the recently developed advanced radiation resistant austenitic SS (ARES-6P) with nanosized NbC precipitates. Heavy ion irradiation was performed at high temperatures (500 ℃ and 575 ℃) to the damage level of ~200 displacement per atom (dpa). The measured void swelling of ARES-6P was 2-3%, which was considerably less compared to commercial 316 SS and comparable to ferritic martensitic steels. In addition, increment of hardness measured by nano-indentation was much smaller for ARES-6P compared to 316 SS. Though some nanosized NbC precipitates were dissociated under relatively high dose rate (~5.0 × 10^-4 dpa/s), sufficient number of NbC precipitates remained to act as sink sites for the point defects, resulting in such superior radiation resistance.

• 폴리머
• /
• 제31권6호
• /
• pp.550-554
• /
• 2007

최근 ATRP를 이용하여 단백질에 조절된 구조의 고분자를 연결시키는 연구가 활발히 진행되고 있다. 이때, ATRF 개시제는 단백질에 있는 일차아민에 아미드화 반응을 통하여 도입할 수 있다. 그런데, 형성되는 $\alpha$-할로 아미드의 경우, 상대적으로 늦은 개시 속도를 나타내는 것으로 알려져 있어 원하는 구조의 고분자를 얻는 것이 쉽지 않다. 따라서 본 연구에서는 아미드기를 가지고 있는 개시제를 이용한 [poly(ethylene glycol)methyl ether] methacrylate(PEGMA)의 ATRP 반응에 대한 적절한 반응 조건을 찾고자 하였다. PEGMA는 FEG를 가지로 가지는 단량체로서 고분자로 만들어졌을 때, 물에 잘 녹고 단백질과의 비특이적 상호작용이 적어 단백질과의 결합을 통한 바이오 응용에 널리 사용되고 있다. 아미드기를 가지는 개시제를 이용하여 PEGMA를 성공적으로 중합하기 위한 최적의 중합 조건은 할로겐 교환 반응과 활성 감소제를 사용해서 얻을 수 있었다.

• 한국자기학회지
• /
• 제14권3호
• /
• pp.94-98
• /
• 2004

MgCCo$_3$에서 Mg와 Co로 이루어진 (001)표면(MgCo-Term) 또는 C와 Co로 이루어진 (001표면(CCo-term)의 전자구조와 자성을 FLAPW 에너지띠 방법을 이용하여 이론적으로 계산하였다. MgCo-Term의 경우 표면에서 Co원자의 자기모멘트는 1.00$\mu$$_{B}$로서 가운데층에 비하여 많이 증가하였고 표면 바로 밑층에서는 가운데층과 비슷한 값을 보였다. CCo-Term의 경우 Co원자의 자기모멘트는 표면에서 뿐만 아니라 표면 바로 밑층에서도 증가하여 각각 0.75와 0.80$\mu$$_{B}$의 값을 나타내고 있다. C와 Mg원자는 두 경우 모두 Co원자와 반대방향으로 스핀분극되었다. 계산된 상태밀도로부터 이러한 표면에서의 자기모멘트의 증가는 Co-3d 띠의 국소화에 의함을 알 수 있었고 여기서 Co-3d와 C-2p 사이의 띠 혼성이 중요한 역할을 하였다.

• 통합자연과학논문집
• /
• 제3권4호
• /
• pp.226-230
• /
• 2010

Calculation of partial charge is important in chemistry. However, because there are many methods developed, it is of considerable interest to know how to calculate and apply properly to address various chemical problems. For basis set, usually double zeta quality is acceptable, and double zeta polarization function would be enough for most cases. To describe electronic state more accurately, Many electron configurations would be necessary to describe highly strained or anionic species. The NPA population introduced new concept about amide bonds, i.e., the planar geometry of nitrogen atom may not come from resonance, but from the lowering of p-orbital energy by electronegative carbonyl carbon atom. The issues for hypervalent atomic charges was also addressed by various charge derivation scheme. When the charge schemes were applied to organolithium compounds, the ionic nature of boding was revealed. This comes from the fact that previous Mulliken partial atomic charges overemphasized the covalent character, wihout much justification. The other partial charge derivation schemes such as NPA(natural population analysis), IPP (Integrated Projected Population) showed that much more ionic picture. ESP potential derived charges are generally believed to be suitable to describe intermolecular interactions, therefore they are used for molecular dynamics simulations and CoMFA (comparative molecular field analysis). The charge derivation schemes using multipole polarization was mainly applied to reproduce experimental infrared spectroscopy. In some reports these schemes are also suitable for intermecular electrostatic interactions. Charges derived from electron density gradient have shown the some bonds are not straight, but actually bent. The proper choice of charge-calculation method along with suitable level of theory and basis set are briefly discussed.

• Bulletin of the Korean Chemical Society
• /
• 제32권3호
• /
• pp.857-862
• /
• 2011

Kinetic studies of the reactions of N-methyl-Y-${\alpha}$-bromoacetanilides with substituted X-benzylamines have been carried out in dimethyl sulfoxide at $25.0^{\circ}C$. The Hammett plots for substituent X variations in the nucleophiles (log $k_N$ vs ${\sigma}_X$) are slightly biphasic concave upwards/downwards, while the Bronsted plots (log $k_N$ vs $pK_a$) are biphasic concave downwards with breakpoints at X = H. The Hammett plots for substituent Y variations in the substrates (log $k_N$ vs ${\sigma}_Y$) are biphasic concave upwards/downwards with breakpoints at Y = H. The cross-interaction constant $\rho_{XY}$ values are all negative: $\rho_{XY}$ = -0.32 for X = Y = electron-donating; -0.22 for X = electron-withdrawing and Y = electron-donating; -1.80 for X = electron-donating and Y = electronwithdrawing; -1.43 for X = Y = electron-withdrawing substituents. Deuterated kinetic isotope effects are primary normal ($k_H/k_D$ > 1) for Y = electron-donating, while secondary inverse ($k_H/k_D$ < 1) for Y = electronwithdrawing substituent. The proposed mechanisms of the benzylaminolyses of N-methyl-Y-${\alpha}$-bromoacetanilides are a concerted mechanism with a five membered ring TS involving hydrogen bonding between hydrogen (deuterium) atom in N-H(D) and oxygen atom in C = O for Y = electron-donating, while a concerted mechanism with an enolate-like TS in which the nucleophile attacks the ${\alpha}$-carbon for Y = electronwithdrawing substituents.

• Bulletin of the Korean Chemical Society
• /
• 제31권6호
• /
• pp.1469-1473
• /
• 2010

Influences of alrylamino (R) substituents on the herbicidal activity ($pI_{50}$) of 1-(4-chloro-2-fluoro-5-propargyloxypheny)-3-(R)-thiourea analogues (1 ~ 35) against the barnyard grass (Echinochloa crusgalli) in the pre-emergence step were discussed quantitatively using comparative molecular field analysis (CoMFA) and comparative molecular similarity indices analysis (CoMSIA) as the three dimensional quantitative structure-activity relationship (3D-QSAR) method. The statistically most satisfactory CoMFA models for the herbicidal activity against the barnyard grass had the better predictability ($r^2{_{cv.}}$) and correlativity ($r^2{_{ncv.}}$) than those of CoMSIA models. The optimized CoMFA model 1($r^2{_{cv.}}$ = 0.531 & $r^2{_{ncv.}}$ = 0.931) with the sensitivity to the perturbation (${d_q}^{2'}{dr^2}_{yy'}$ = 1.081) and the prediction ($q^2$ = 0.475) produced by a progressive scrambling analyses were not dependent on chance correlation. And statistical qualities with the atom based fit alignment (AF) were slightly higher than those of the field fit alignment (FF). According to the optimized CoMFA model 1, the contribution ratio (%) of the steric field (76.9%) on the herbicidal activity of the Thioureas was three-fold higher than that of the electrostatic field (20.1%) and the hydrophobic field (3.0%) had the least influence. A steric favor group is on the vicinity of the nitrogen atom in alrylamino (R) substituent, and a steric disfavor group is on the outer side of alrylamino (R) substituent. Thus, as the size of alrylamino (R) substituent increases, so does the herbicidal activity of the substituent.

• Bulletin of the Korean Chemical Society
• /
• 제28권11호
• /
• pp.1958-1962
• /
• 2007

The title complex, Ir(H)(CO)(PEt3)2(η 2-C60) (2), has been prepared by the reaction of excess C60 (4 equiv) with a tetrairidium complex Ir4(CO)8(PEt3)4 (1) in refluxing chlorobenzene in 40% yield as green crystals. Compound 2 has been characterized by cyclic voltammetry (CV), spectroscopic methods (mass, IR, 1H and 31P NMR), and a single crystal X-ray diffraction study. The molecular structure reveals that the iridium atom of 2 is coordinated by two axial ligands of a hydrogen atom and a carbonyl group, and three equatorial ligands of two phosphorus atoms and an η 2-C60 moiety. The CV study exhibits three reversible one-electron redox waves for the successive reductions of 2, together with additional four redox waves due to free C60 reductions, which was formed by decomposition of 2 in the reduced states. The three reversible redox waves of 2 are shifted to more negative potentials by ca. 270 mV compared to free C60, reflecting both metal-to-C60 π-back-donation and the electron-donating nature of the two phosphorus ligands.