• Bulletin of the Korean Chemical Society
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• 제25권5호
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• pp.699-703
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• 2004

Solvolyses of isopropylsulfonyl chloride (IPSC) in water, D_2O,\;CH_3OD$, and in aqueous binary mixtures of acetone, ethanol and methanol are investigated at 25, 35 and 45$^{\circ}C$. The Grunwald-Winstein plot of first-order rate constants for the solvolytic reaction of IPSC with $Y_{Cl}$ (based on 2-adamantyl chloride) shows marked dispersions into three separate lines for three aqueous mixtures with a small slope (m < 0.30). The extended Grunwald-Winstein plots for the solvolysis of IPSC show better correlation. The kinetic solvent isotope effects determined in water and methanol are in consistent with the proposed mechanism of the general base catalyzed and/or $S_AN/S_N2$ reaction mechanism for IPSC solvolyses based on mass law and stoichiometric solvation effect studies.

• Bulletin of the Korean Chemical Society
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• 제35권8호
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• pp.2263-2270
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• 2014

Solvolysis rate constants of 2-phenylethyl-(2-$PhCH_2CH_2OCOCl$, 1) and 2,2-diphenylethyl chloroformate (2,2-$Ph_2CHCH_2OCOCl$, 2), together with the previously studied solvolyses of ${\alpha}$- and ${\beta}$-substituted chloroformate ester derivatives, are reported in pure and binary solvents at $40.0^{\circ}C$. The linear free energy relationship (LFER) and sensitivities (l and m) to changes in solvent nucleophilicity ($N_T$) and solvent ionizing power ($Y_{Cl}$) of the solvolytic reactions are analyzed using the Grunwald-Winstein equation. The kinetic solvent isotope effects (KSIEs) in methanol and activation parameter values in various solvents are investigated for 1 and 2. These results support well the bimolecular pathway with same aspects. Furthermore, the small negative values of the entropies of activation of solvolysis of 1 and 2 in the highly ionizing aqueous fluoroalcohols are consistent with the ionization character of the rate-determining step, and the KSIE values of 1.78 and 2.10 in methanol-d indicate that one molecule of solvent acts as a nucleophile and the other acts as a general-base catalyst. It is found that the ${\beta}$-substituents in alkyl chloroformate are not the important factor to decide the solvolysis reaction pathway.

• BMB Reports
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• 제31권2호
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• pp.177-182
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• 1998

A pool of cis-acting hammerhead ribozymes randomized in their substrate recognition sequences was constructed. A variety of active cis-acting ribozymes which had various structures of stems I and III was selected from the pool by in vitro selection. The selected ribozymes were cloned and sequenced. The relationship between the cleavage efficiency and base-pairing in stems I and III of the selected ribozymes was investigated. The ribozymes with the smaller difference in folding energies between the active conformation and the stable but inactive conformation showed a tendency to have the better cleavage efficiency. The optimum length of stem I was 5 or 6 bases while the longer stem III, in general, appeared to be required for efficient cleavage. The specificity of the ribozyme reaction is discussed in terms of the length of stems I and III.

• Bulletin of the Korean Chemical Society
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• 제28권6호
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• pp.953-958
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• 2007

Anchoring quantum dots (QDs) onto thermodynamically stable, large band gap oxide semiconductors is a very important strategy to enhance their quantum yields for solar energy conversion in both visible and near-IR regions. We describe a general procedure for anchoring a few chalcogenide QDs onto the titanium oxide layer. To anchor the colloidal QDs onto a mesoporous TiO2 layer, linker molecules containing both carboxylate and thiol functional groups were initially attached to TiO2 layers and subsequently used to capture dispersed QDs with the thiol group. Employing the procedure, we exploited cadmium selenide (CdSe) and cadmium telluride (CdTe) quantum dots (QDs) as inorganic sensitizers for a large band gap TiO2 layer of dye-sensitized solar cells (DSSCs). Their attachment was confirmed by naked eyes, absorption spectra, and photovoltaic effects. A few QD-TiO2 systems thus obtained have been characterized for photoelectrochemical solar energy conversion.

• 한국초등과학교육학회지:초등과학교육
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• 제29권3호
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• pp.341-349
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• 2010

In this study, the effects of concept mapping with feedbacks providing explanatory comments on students' achievement, science learning anxiety, and science learning motivation were investigated in the undergraduate general chemistry course. The aptitude-treatment interactions between students' level of mastery goal orientation and the concept mapping with explanation feedback treatment were also examined. Sixty-seven freshmen from an university of education were assigned to a control group and a treatment group. The tests of mastery goal orientation, science anxiety, and science learning motivation were administered as pretests. For the treatment group, feedback providing students with explanatory comments through whole class discussion was presented after each concept mapping. Whereas the control group students were presented with opportunities solving excercise problems followed by explanation feedback. The intervention was lasted for 10 weeks (30 class periods). After the instructions, a researcher-made achievement test, the science learning anxiety test, and the science learning motivation test were administered. The results indicated that no statistically significant difference was found in students' achievement. In the science learning anxiety, however, the scores of the treatment group was significantly lower than those of the control group. The scores of the treatment group also tended to be higher, though not significant, than those of the control group in the science learning motivation. However, no significant aptitude-treatment interactions were found in all dependent variables.

• 한국과학교육학회지
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• 제22권2호
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• pp.378-386
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• 2002

1999학년도부터 지난 3년 동안 시행된 대학수학능력시험에서 공통과학 중 화학 영역 문항에 대한 학생들의 응답을 조사하였다. 내용 영역과 탐구 과정에 따른 문항수, 내용 영역과 탐구 과정에 따른 평균 정답률, 정답률 수준에 따른 문항 분포, 정답률이 높거나 낮은 문항 등을 분석하였다. '환경' 영역에서의 문항수가 매우 적었는데, 특히 '오존층'에 대해서는 한문항도 출제되지 않았다. 가장 어려운 내용 영역은 '환경' 영역의 '산성비'였다. 탐구 과정별로는 '자료 분석 및 해석'에서 가장 많은 문항이 출제되었고, '문제 인식 및 가설 설정'이 가장 어려운 것으로 나타났다. '아주 어려운 수준'의 문항은 하나도 없고. '쉬운 수준'이나 '아주 쉬운 수준'에 해당하는 문항이 많았다. 학생들은 여러 가지 개념이나 지식을 요구하는 문항을 해결하는 데에 많은 어려움을 느꼈고, 저학년에서 다루어진 개념만을 요구하는 문항을 쉽게 해결하였다. 교육학적 함의에 대해 논의하였다.

• Bulletin of the Korean Chemical Society
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• 제4권3호
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• pp.103-114
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• 1983

The NMR shift arising from the electron angular momentum and the electron spin dipolar-nuclear spin angular momentum interaction has been examined for a $3d_1$ system in a strong octahedral crystal field when the threefold axis is chosen as the quantization axis. To investigate the NMR shift in this situation, first, we have extended the evaluation of the hyperfine integrals to any pairs of 3d orbitals adopting a general method which is applicable to a general vector R, pointing in arbitrary direction in space. Secondly, a general expression using a nonmultipole technique is derived for the NMR shift resulting from the electron angular momentum and the electron spin dipolar-nuclear spin angular momentum interactions. From this expression all the multipolar terms are determined. ${\Delta}B/B$ for the $3d_1$ system in this case is compared with that for the 3d1 system when the z axis is chosen as the quantization axis. When we choose the threefold axis as the quantization axis, it is found that along the , and axes, ${\Delta}B/B$ values are significantly different from each other and along the , <-1-1-1>, <-11-1>, , <-1-11>, , and <-111> axes, ${\Delta}B/B$ values are however the same. We also find that the 1/R7 term contributes dominantly to the NMR shift for all values of R. When 1/$R^5$ term is included, there is good agreement between the exact solution and the multipolar terms when $R\; {\leqslant}\;0.35\;nm.$.

• 대한화학회지
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• 제62권2호
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• pp.124-136
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• 2018

이 연구에서는 거꾸로 교실을 교사 주도성이 강한 국내 대학의 일반화학실험 강좌에 적용하고, 이를 통해 거꾸로 교실을 적용한 대학 실험 강좌에 대한 효과와 가능성을 탐색하였다. 이를 위하여 수도권 소재의 사범대학 과학교육과에 재학 중인 30명의 학생들을 15명씩 거꾸로 교실 수업 집단과 전통적 수업 집단의 두 그룹으로 각각 무선배치 하였다. 그런 다음, 동영상 자료와 함께 대학에서 적용 가능한 일반화학실험 수업 안을 개발 및 적용하였고, 모든 수업을 마친 후에는 일반화학실험 강좌에 대한 학생들의 인식을 살펴보기 위한 설문 조사를 실시하였다. 일반화학실험 수업에 대한 전반적인 인식 분석 결과, 수업 활동의 유용성, 성공적 학습을 위한 각 활동 요소 별 중요도, 학습 수준, 추후 수강 의향 등의 측면에서 거꾸로 교실 수업 집단의 학생들이 전통적 수업 집단의 학생들 보다 긍정적인 인식을 나타냈음을 알 수 있었다. 실험 수행이나 보고서 작성 등과 같은 일반화학 실험 활동과 실험 내용의 이해 측면에서 학생들의 인식을 분석해 본 결과, 거꾸로 교실 수업 집단의 평균 점수가 전통적인 수업집단의 평균 점수 보다 높았고, 이와 같은 결과의 주된 원인은 담당 강사가 사전 학습 활동으로 제공한 동영상 자료 때문인 것으로 나타났다. 또한 수업 중 상호작용과 자기 주도적 학습 측면에서 학생들의 인식을 분석한 결과, 거꾸로 교실 수업 집단의 평균 점수가 전통적 수업 집단의 평균 점수 보다 전반적으로 높았으며, 특히 학생들 간의 상호작용과 자기 주도적 학습의 수월성은 두 집단 간에 통계적으로 유의미한 차이가 있는 것으로 나타났다. 그리고 동영상 자료에 대한 학생들의 인식이 매우 긍정적이었고, 이 때 학생들이 가장 선호한 동영상은 담당 강사가 직접 실험 이론과 방법을 설명해 주는 동영상이었던 것으로 분석되었다. 이에 대한 교육적 시사점을 논의하였다.

• 한국환경농학회지
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• 제32권2호
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• pp.142-147
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• 2013

국내 유통 농산물의 잔류농약 안전성을 평가하고자 2012년 전국 6개 도시에서 유통되고 있는 과실류인 사과와 복숭아에 대하여 123점의 시료를 수거하여 잔류농약을 분석하였다. 122종의 농약에 대해 GC-ECD, GC-NPD 및 HPLCUVD을 이용한 다성분분석법으로 잔류농약을 분석하였고, 분석 결과 총 농약이 검출된 시료는 관행농산물에서 38점, 저농약농산물에서 6점, GAP농산물에서 1점으로 시료에서 16종의 농약이 검출되어 33.6% 검출률을 나타내었다. 농약 성분별 검출 빈도는 cypermethrin, lufenuron, fenvalerate, bifenthrin, chlorfenapyr, iprodione 순이었다. 농약이 검출된 시료 중 잔류허용기준을 초과하는 시료는 18점으로 14.6% 검출되었으며, 해당 작물에 대한 잔류허용기준이 설정되어 있지 않거나 품목고시 되어있지 않은 농약은 2점의 시료에서 2종의 농약이 검출되어 1.6% 검출률을 보였다. 본 연구에서 검출된 농약이 해당 농산물의 섭취로 인체에 유입될 잔류농약의 일일섭취허용량 대비 일일섭취추정량은 최저 0.033%에서 최고 2.748%로 농산물 섭취에 의한 위해성은 낮은 것으로 나타났다.

• Macromolecular Research
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• 제17권7호
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• pp.499-505
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• 2009

General, fast, and efficient stitching methods are presented for the synthesis of Fr$\acute{e}$chet-type dendrimers with linear units at a core, as a preliminary investigation for the synthesis of dendritic-linear-dendritic materials. The synthetic strategy involved an inexpensive, 1,3-dipolar, cycloaddition reaction between an alkyne and an azide in the presence of the Cu(I) species, which is known as the best example of click chemistry. The linear core building blocks, 1,7-octadiyne and 1,6-diazidohexane, were chosen to serve as the alkyne and azide functionalities for dendrimer growth via click reactions with the azide and alkyne-dendrons, respectively. These two building blocks were employed together with the azide- and alkyne-functionalized Fr$\acute{e}$chet-type dendrons in a convergent strategy to synthesize two kinds of Fr$\acute{e}$chet-type dendrimers with different linear core units. This comparative efficiency of the click methodology supports the fast and efficient synthesis of dendritic-linear-dendritic materials with the tailor made core unit.