• Title, Summary, Keyword: 2D-NMR

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Complete Assignment of $^{1}H$ and $^{13}C$-NMR Signals for (20S) and (20R)-Protopanaxadiol by 2D-NMR Techniques (2D-NMR 기법을 이용한 (20S)와 (20R)-Protopanaxadiol의 $^{1}H$- 및 $^{13}C$-NMR 완전 동정)

  • 백남인;김동선
    • Journal of Ginseng Research
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    • v.19 no.1
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    • pp.45-50
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    • 1995
  • (20S)- and (20R)-protopanaxadiol were prepared from crude ginseng saponin by chemical treatment. The $^{1}H$- and $^{13}C$-NMR signals of these compounds were fully assigned by various NMR techniques such as DEPT, 1H-1H COSY, HMQC, HMBC and NOESY.

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새로운 분석법으로서의 2D NMR 분광법에 관한 이론적 배경 및 고찰

  • Kim, Taek-Je;Jeong, Min-Hwan;Lee, Gang-Bong
    • Analytical Science and Technology
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    • v.5 no.2
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    • pp.1096-1113
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    • 1992
  • 분자구조, 동력학, 그리고 분자들의 화학분응에 관한 정확한 지식은 분자들의 기능과 성질을 이해하는 데 중요한 정보를 제공한다. 2D NMR 분광법의 개발은 용액상의 분자들에 관한 이러한 의문을 해결하는 데 결정적인 역할을 하게 되었다. 그동안 아주 다양한 NMR기술들이 개발되어 왔으며 현재 그들에 대한 이용이 활발하게 진행되고 있다. 그러나 성공적인 2D NMR 분광법의 적용을 위해서는 적당한 기계뿐만 아니라 실험실의 정확한 선택 및 최적 조건의 변수들을 선택해야 하며 스펙트럼의 세밀하고도 정확한 해석을 필요로 한다. 곱연산자 방식(product operator formalism)의 도입은 펄스 FT NMR 분광학을 정성, 정량적으로 이해하도록 하는 것을 가능케 했으며, 이번 해설은 연속적으로 주어지는 펄스의 이해를 위해서 필요로 하는 상의 순환(phase cycle) 및 곱연산자 방식을 이용하여 다양한 2D NMR 기술의 이해를 돕고, 분석기기로서 2D NMR 분광법이 널리 사용 및 활용되어지고자 하는 데 목적이 있다.

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NMR Chemical Shift for 4d$^n$System (Ⅳ). Calculation of NMR Chemical Shift for 4d$^2$ System in a Strong Crystal Field Environment of Octahedral Symmetry

  • Ahn, Sang-Woon;Oh, Se-Woong;Yang, Jae-Hyun
    • Bulletin of the Korean Chemical Society
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    • v.6 no.5
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    • pp.255-259
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    • 1985
  • The NMR chemical shift arising from 4d electron orbital angular momentum and 4d electron spin dipolar-nuclear Spin angular momentum interactions for a $4d^2$ system in a strong crystal field environment of octahedral symmetry has been investigated when the four fold axis is taken as the quantization axis. The NMR results are comparted with the multipolar shift at various R-values and we find that the exact results are in agreement with the multipolar shift when $R{\geqslant}0.20 nm.$ We also separate the NMR shift into the contribution of the $1/R^5$ and $1/R^7$ terms. It is found that the contribution of the $1/R^5$term to the NMR shift is dominant than the contribution of the $1/R^7$ term. Temperature dependence analysis shows that the $1/T^2$ term is the dominant contribution to the NMR shift for a $4d^2$ system but the contribution of the 1/T term may not negligible. The similar results are obtained for a $4d^1$ system from the temperature dependence analysis.

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An Investigation of the Sample Rotation Effects on Suppression of Convective Flows in PGSE Diffusion NMR Experiments

  • Kim, Minkyoung;Chung, Kee-Choo
    • Journal of the Korean Magnetic Resonance Society
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    • v.20 no.2
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    • pp.61-65
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    • 2016
  • Undesirable convective flow in an NMR tube inhibits the accurate measurement of diffusion coefficients by NMR spectroscopy. To minimize the convection effects, various methods have been suggested, and it has been known that the use of sample rotation can be useful. However, it has not been clearly examined that the convection suppressing effect of the sample rotation under the different spinning speeds. In this study, the relation between convective flow and the sample rotation was investigated using PGSE NMR diffusion experiments to reveal the feasibility for controlling the convective flow in an NMR tube by sample rotation itself. The viscosity effect was also examined using solvents with four different viscosities, acetone-$d_6$ chloroform-d, pyridine-$d_5$, and $D_2O$. The sample rotation showed apparent convection suppressing effects at all temperature range for the low viscosity solvents, acetone-$d_6$ and chloroform-d, even at the faster than 5 Hz spinning rate. The similar patterns were also observed for pyridine-$d_5$ and $D_2O$, which have higher viscosity. This effect was observed even at high temperatures where convective flow arises conspicuously.

Calculation of the NMR Chemical Shift for a 3d$^2$ System in a Strong Crystal Field of Octahedral Symmetry

  • Ahn, Sang-Woon;Kim, Dong-Hee;Park, Eui-Suh
    • Bulletin of the Korean Chemical Society
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    • v.6 no.2
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    • pp.63-67
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    • 1985
  • The NMR chemical shift arising from 3d electron spin dipolar nuclear spin angular momentum interactions for a 3d$^2$ system in a strong crystal field environment of octahedral symmetry has been investigated when the fourfold axis is chosen to be our axis of quantization. The NMR shift is separated into the contribution of 1/R$^5$ and 1/R$^7$ terms. A comparision of the multipolar terms with nonmultipolar results shows that the 1/R$^5$ term contributes dominantly to the NMR shift and there is in good agreement between the exact solution and the multipolar results when R ${\ge}$ 0.25. A temperature dependence analysis may lead to the results that the 1/T$^2$ term has the dominant contribution to the NMR shift for a paramagnetic 3d$^2$ system but the contribution of the 1/T term may not be negligible.

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Calculation of NMR Shift in Paramagnetic System when the Threefold Axis is Chosen as the Quantization Axis (Ⅲ). The NMR Shift for 3d$^2$ System in a Strong Crystal Field of Octahedral Symmetry

  • Sang Woon Ahn;Se Woong Oh;Kee Hag Lee
    • Bulletin of the Korean Chemical Society
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    • v.5 no.3
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    • pp.93-97
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    • 1984
  • A general expression using the nonmultipole expansion method is derived for the NMR shift arising from 3d electron angular momentum and the 3d electron spin dipolar-nuclear spin angular momentum interactions for a 3$d^2$ system in a strong crystal field environment of octahedral symmetry when the threefold axis is chosen as the quantization axis. The NMR shift is separated to the contribution of constant, $1/R^5\;and\;1/R^7$ terms and compared with the multipolar terms. We find that $1/R^5$ term contributes dominantly to the NMR shift but the contribution of $1/R^7$ term may not be negligible. It is also found that the exact values of the NMR shift are in agreement with the multipolar results for distances larger than 0.35 nm.

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27Al Solid-state NMR Structural Studies of Hydrotalcite Compounds Calcined at Different Temperatures

  • Park, Tae-Joon;Choi, Sung-Sub;Kim, Yong-Ae
    • Bulletin of the Korean Chemical Society
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    • v.30 no.1
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    • pp.149-152
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    • 2009
  • Hydrotalcites are anionic clays that are quite prevalent in nature and their importance is growing more and more because of their very wide range of potential applications and uses. Understanding the structural and compositional changes that occur on the molecular scale during the thermal decomposition of hydrotalcite compounds is essential for the basic prediction and comprehensive understanding of the behavior and technical application of these materials. In this study, several hydrotalcite compounds calcined at different temperatures for applications in a chlorine resistant textile were prepared and 27-Aluminm solid-state nuclear magnetic resonance (NMR) spectroscopy was used as a tool to study their local structure and behavior. The changes in the Al coordination of the hydrotalcite compounds were investigated with one dimensional (1D) solid-state magic angle spinning (MAS) NMR spectroscopy. The two broad resonances arising from the structurally different Al coordinations of these compounds were clearly resolved by two dimensional (2D) triple quantum magic angle spinning (3QMAS) NMR spectroscopy.

Calculation of the NMR Cheimical Shift for a 4d$^1$ System in a Strong Crystal Field Environment of Trigonal Symmetry with a Threefold Axis of Quantization

  • Ahn, Sang-Woon;Oh, Se-Woung;Ro, Seung-Woo
    • Bulletin of the Korean Chemical Society
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    • v.7 no.3
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    • pp.170-178
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    • 1986
  • The NMR chemical shift arising from 4d electron angular momentum and 4d electron angular momentum and 4d electron spin dipolar-nuclear spin angular momentum interactions for a $4d^1$ system in a strong crystal field environment of trigonal symmetry, when the threefold axis is chosen to be the axis of quantization axis, has been examined. A general expression using the nonmultipole expansion method (exact method) is derived for the NMR chemical shift. From this expression all the multipolar terms are determined. We observe that along the (100), (010), (110), and (111) axes the NMR chemical shifts are positive while along the (001) axis, it is negative. We observe that the dipolar term (1/R3) is the dominant contribution to the NMR chemical shift except for along the (111) axis. A comparison of the multipolar terms with the exact values shows also that the multipolar results are exactly in agreement with the exact values around $R{\geqslant}0.2$ nm. The temperature dependence analysis on the NMR chemical shifts may imply that along the (111) axis the contribution to the NMR chemical shift is dominantly pseudo contact interaction. Separation of the contributions of the Fermi and the pseudo contact interactions would correctly imply that the dipolar interaction is the dominant contribution to the NMR chemical shifts along the (100), (010), (001), and (110) axes, but along the (111) axis the Fermi contact interaction is incorrectly the dominant contribution to the NMR chemical shift.

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NMR Study on Thermal Stability of the Double Helical Structures of d(CGAATTCG)2, d(CGTATACG)2 and their berenil complexes

  • Kim, Eun-Hee;Hong, Seok-Joo;Huh, Sung-Ho
    • Journal of the Korean Magnetic Resonance Society
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    • v.8 no.2
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    • pp.96-107
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    • 2004
  • We prepared two oligonucleotides containing same base pairing, but different base sequence in the middle region, d(CGAATTCG) and d(CGTATACG). NMR and UV absorbance data represented that such variation in base sequence could cause a significant difference in melting temperature and dynamics between d(CGAATTCG)$_2$ and d(CGTATACG)$_2$ duplexes, which are regarded to be associated with the stacked structure and the width of the minor groove of them. The latter showed poor stability compared to the former, because of poor stacking of bases. And berenil could bind to the minor groove of d(CGAATTCG)$_2$ which is relatively narrow, more strongly than d(CGTATACG)$_2$ and this gave rise to large improvement in thermal stability of the d(CGAATTCG)$_2$ duplex, compared to d(CGTATACG)$_2$.

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