• 대한화학회지
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• 제16권3호
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• pp.119-134
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• 1972

Various MO methods with differing degrees of sophistication are shown to yield qualitatively consistent results for methyl isoalloxazins. However, with crude methods such as the HMO and ${\omega}$-technique, the choice of Coulomb and resonance integralsis critical, in contrast with simpler molecular systems. The empirical value of ${\omega}$=0.5 appears to be more reasonable than 1.4. Methyl groups in these flaving are best treated by the group orbital approximation. The pseudo-heteroatom approximation overestimates methyl hyperconfiguration with the Pariser-Parrpole SCR MO method. siglet ${\pi}{\rightarrow}{\pi}^*$ transition energies are calculated by the P-P-P method and agree reasonably with the experimental values. 2- and 4-Thioisoalloxazine analogs are also treated. Reactivity indices of the flavin molecule are presented, includeing superdelocalizability. frontier orbital and radical densities. Various aspects of the applications of these indices of the methyl groups on dipolemoments, inozation potentialsm elctron affinities, and spectra are decribed in detail.

• Bulletin of the Korean Chemical Society
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• 제23권5호
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• pp.715-720
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• 2002

Kinetic studies of the reaction of Z-aryl cyclobutanecarboxylates with X-pyridines in acetonitrile at $55.0^{\circ}C$ have been carried out. The reaction proceeds by a stepwise mechanism in which the rate-determining step is the breakdown of the zwitterion ic tetrahedral intermediate, T $\pm$ . These mechanistic conclusions are drawn based on (i) the large magnitude of ${\rho}X$ and $\rhoZ$, (ⅱ) the positive sign of ${\rho}XZ$ and the larger magnitude of $\rhoXZ$ than normal SN2 processes, (ⅲ) a small positive enthalpy of activation, ${\Delta}H{\neq}$, and a large negative, ${\Delta}S{\neq}$, and lastly (iv) adherence to the reactivity-selectivity principle (RSP) in all cases.

• 대한화학회지
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• 제38권5호
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• pp.372-376
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• 1994

Penicillin으로부터 유도된 4-mercaptoazetidin-2-one(2a)은 염기조건에서 불안정하지만 Et3N이나 pyridine 염기하에서 acetyl chloride, methyl chloroformate, ethyl iodoacetate, diethyl azodicarboxylate 등의 친전자체와 반응하여 sulfur에 acetyl, methoxycarbonyl, ethoxycarbonylmethyl, diethoxycarbonylhydrazineo원자단이 부착된 화합물이 된다. 반면 thiol의 methylation은 methyl iodide와의 반응으로 얻을 수 없고 diazomethane을 사용해야 한다. 또한 화합물 2a의 이성질체인 화합물 3a의 반응성도 화합물 2a와 거의 비슷하다.

• 대한화학회지
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• 제27권6호
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• pp.429-433
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• 1983

Spermine은 DNase 1에 대한 native 및 denatured calf thymus DNA의 susceptibility에 상반된 효과를 갖는다. spermine은 그 native DNA의 susceptibility를 증가시키지만 그 denatured DNA의 것은 감소 시킨다. spermine이 존재하지 않을 경우에는 그 deoxyribonuclease의 반응성은 native 및 denatured DNA의 conformation차이에 외견상 무감각한 것으로 나타난다.

• Bulletin of the Korean Chemical Society
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• 제23권3호
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• pp.481-487
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• 2002

A selective enzyme-linked immunosorbent assay (ELISA) for the insecticide chlorpyrifos was developed. Four haptens for chlorpyrifos were synthesized and two of them were used as immunogens after coupling to keyhole limpet hemocyanin by two differe nt approaches. Rabbits were immunized with either of them and the sera were screened against 4 haptens coupled to ovalbumin (OVA). Using the sera of highest specificity, an antigencoated ELISA was developed, which shows an I50 of 160 ppb with a detection limit of 10 ppb. An antibody-coated ELISA was also developed, which shows an $I_{50}$ of 20 ppb with a detection limit of 0.1 ppb. The antibodies showed negligible cross-reactivity with other organophosphorus pesticides except for insecticides chlorpyrifos-methyl and bromophos-ethyl, which makes these assays suitable for the selective detection of chlorpyrifos.

• 대한화장품학회지
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• 제22권2호
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• pp.89-98
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• 1996

A novel polymeric sunscreen agent was developed. It was prepared by the coupling reaction of 2-ethylhexyl 4-hydroxycinnamate with poly vinylbenzyl chloride(PVBC, average MW 6,500). In this reaction the reactivity was mostly affected by catalyst. In the absence of catalyst the yield was approximately 55% and in the presence of tetrabutylammonium bromide the yield was about 65%, but in the presence of tetrabutylammonium iodide the yield was 100% to give a average molecular weight 20,000 polymeric sunscreen agent. There were no side reactions, and its structure and purity were confirmed by various analytical methods, such as NMR, IR, and so on. UV radiation absorption efficiency is more than 70% compared with that of octyl methoxycinnamate. The solubility in polar oil, for example C12-15 alkylbenzoate and caprylic/capric triglyceride, is more than 50%. It showed high stability in the time course of test including acceleration test. This polymer is safe to skin because of poor permeability to skin, no side products in the process of preparing, and easy elimination of excess starting materials.

• Bulletin of the Korean Chemical Society
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• 제31권11호
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• pp.3151-3155
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• 2010

This study was performed to develop analytical methods to better understand the properties and reactivity of petroleum, which is a highly complex organic mixture, using high-resolution mass spectrometry and statistical analysis. Ten crude oil samples were analyzed using negative-mode electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS). Clustering methods, including principle component analysis (PCA), hierarchical clustering analysis (HCA), and k-means clustering, were used to comparatively interpret the spectra. All the methods were consistent and showed that oxygen and sulfur-containing heteroatom species played important roles in clustering samples or peaks. The oxygen-containing samples had higher acidity than the other samples, and the clustering results were linked to properties of the crude oils. This study demonstrated that clustering methods provide a simple and effective way to interpret complex petroleomic data.

• 대한화학회지
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• 제13권4호
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• pp.281-287
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• 1969

Arymethychloride의 교환반응에 대한 반응속도 상수를 측정하고 또한 활성화 파라메터를 결정하였다.Substrate의 반응도를 섭동분자궤도(PMO)법으로 설명하였으며 HSAB원리를 이에 적용하였다. 또한 전이상태에서의 탄소-염소공명적분값이 탄소-탄소 공명자분값이 약 67%임을 밝혔다.

• 대한화학회지
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• 제16권2호
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• pp.64-69
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• 1972

1-염화 및 2-염화 훼네틸의 친핵성 반응에 대하여 분자 궤도론적 방법을 적용하여 상대적인 반응성을 연구하였다. EHT 계산에 의한 Population Analysis로 부터 할로겐 교환반응의 상대 속도를 설명할 수 있음을 밝혔으며 친핵성이 적은 Nucleophile의 경우 상대반응성이 바뀐다는 사실도 결합형성 과정이 중요하다는 것으로 이론적인 해석이 가능함을 밝혔다.

• 대한화학회지
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• 제25권6호
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• pp.361-366
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• 1981

이소시안산 에스테르와 알코올이 反應하는 우레탄 形成反應에서 알코올分子가 이소시안산 에스테르에 접근하는 配向成을 MO論的으로 고찰하였다. EHT 및 CNDO/2 계산결과에 의하면 알코올이 이소시안 산에스테르 平面과 同一한 平面으로 접근하는 4-중심 메카니즘으로 진행되는 것이 유리함을 알 수 있었다. 또한 알코올의 O-H基에 있는 산소가 수소보다 먼저 이소시안산 에스테르의 탄소에 접근함을 알 수 있었고 이 反應은 전하조절반응임을 밝혔다.