• 한국자기공명학회논문지
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• 제18권1호
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• pp.36-40
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• 2014

Predicting secondary structure of protein through assigned backbone chemical shifts has been used widely because of its convenience and flexibility. In spite of its usefulness, chemical shift based analysis has some defects including isotopic shifts and solvent interaction. Here, it is shown that corrected chemical shift analysis for secondary structure of protein. It is included chemical shift correction through consideration of deuterium isotopic effect and calculate chemical shift index using probability-based methods. Enhanced method was applied successfully to one of the proteins from Mycobacterium tuberculosis. It is suggested that correction of chemical shift analysis could increase accuracy of secondary structure prediction of protein and small molecule in solution.

• Bulletin of the Korean Chemical Society
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• 제7권2호
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• pp.89-96
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• 1986

The NMR chemical shift arising from 4d electron angular momentum and 4d electron spin dipolar-nuclear spin angular momentum interaction for a $4d^1$ system in a strong crystal field of octahedral symmetry, when the threefold axis is chosen as the quantization axis, has been investigated. A general expression using a nonmultipole expansion method is derived for the NMR chemical shift. From this expression all the multipolar terms are determined. We find that the nonmultipolar results for the NMR chemical shift ${\Delta}B$, is exactly in agreement with the multipolar results when $R {\ge} 0.20$ nm. It is also found that the 1/$R^7$ term contributes to the NMR chemical shift almost the same as the 1/$R^5$ in magnitude. The temperature dependence analysis of ${\Delta}B$/B(ppm) at various values of R shows that the 1/$T^2$ term has the dominant contribution to the NMR chemical shift but the contributions of other two terms are certainly significant for a $4d^1$ system in a strong crystal field of octahedral symmetry when the threefold axis is chosen to be the axis of quantization.

• Bulletin of the Korean Chemical Society
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• 제6권5호
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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.

• 한국자기공명학회논문지
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• 제1권2호
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• pp.71-78
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• 1997

The magnetic anisotropy effects of peptide group in structured protein on proton chemical shift have been investigated using trialanine modeling. The structure dependent part of chemical shift of C${\alpha}$H of the second amino acid residue was assumed to come purely from the magnetic anisotropy effects of C=O and C-N bonds of peptide in the direct neighborhood and thus to be dependent on and $\psi$ angle of this dipeptide. A set of dipeptide models with different and $\psi$angles were generated and from these models the chemical shift values were calculated using known algorithm to emphasize the role of parameters used in the equation. Comparison of sets of different parameters resulted in an optimized parameters which could reproduce the statistical chemical shift values observed in proteins with respect ot the secondary conformation.

• 한국자기공명학회논문지
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• 제1권2호
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• pp.79-94
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• 1997

The solution structure of bovine pancreatic trypsin inhibitor(BPTI) has been refined by NMR chemical shift data of C${\alpha}$H using classical molecular dynamics simulation. The structure dependent part of the observable chemical shift was modeled by ring current effect, magnetic anisotropy effect from the nearby groups, whereas the structure independent part was replaced with the random coil shift. A new harmonic function derived from the differences between the observed and calculated chemical shifts was added into physical force field as an pseudo potential energy term with force constant of 250 kJmol-1 ppm-2. During the 1.5 ns molecular dynamics simulation with chemical shift restraints BPTI has accessed different conformation space compared to crystal and NOE driven structure.

• Bulletin of the Korean Chemical Society
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• 제24권7호
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• pp.981-985
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• 2003

Fluorine-19 NMR solution measurements have been made for various phenyl-fluorinated iron porphyrin complexes. Large chemical shifts for phenyl fluorine signals of iron(III) and iron(II) are observed, and these signals are sensitive to electronic structure. The chemical shift differences in ortho-phenyl fluorine signals between high-spin ferric and low-spin ferric tetrakis(pentafluorophenyl)porphyrins are approximately 40 ppm, whereas the differences are approximately 7 ppm between high- and low-spin states of ferrous tetrakis(pentafluorophenyl)porphyrin complexes. Analysis of fluorine-19 isotropic shifts for the iron(III) tetrakis(pentafluorophenyl) porphyrin using fluorine-19 NMR indicates there is a sizable contact contribution at the ortho-phenyl fluorine ring position. Large phenyl fluorine-19 NMR chemical shift values, which are sensitive to the oxidation and spin states, can be utilized for identification of the solution electronic structures of iron(III) and iron(II) porphyrin complexes.

• Bulletin of the Korean Chemical Society
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• 제7권3호
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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.

• 대한전자공학회논문지SD
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• 제42권6호
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• pp.17-22
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• 2005

유무기 하이브리드 SiOC 박막은 차세대 유력한 저유전상수를 갖는 박막이다. SiOC 박막의 결합구조는 FTIR 분석기를 이용하여 화학적 이동이 일어나는 것을 확인하여 분석하였다. 유기화학분야에서의 일반적인 화학적 이동은 red shift에 해당하지만, 하이브리드 타입의 SiOC 박막은 red shift 뿐만 아니라 특이한 경우에 해당하는 blue shift도 관찰되었다. 화학적 이동의 원인은 전기음성도가 큰 원소가 주변에 존재하는 수소결합사이의 상호작용 때문인데, SiOC 박막에서 blue shift는 전자를 많이 포함하는 메틸그룹이 증가함으로 생기는 기공을 만드는 원인을 제공한다. SiOC 박막의 결합구조 역시 2가지 유형의 화학적 이동에 따라서 cross-link 구조와 case-link 구조의 두 가지 유형으로 나타난다. 유량비와 증착할 때 주어지는 열에너지에 따라서 두 가지 결합구조를 나타낸다. cross-link 구조와 cross-link breakage 구조는 박막의 유전상수가 낮아지는 원인 서로 다르며 화학적 물리적인 특성 또한 다르게 나타나는 것을 증명하고 있다. Si-O-C cross-link 구조는 red shift의 원인이 된 수소결합에 의한 원자사이의 길이가 길어지는 효과에 의해 표면접착력이 개선되며, 유전상수 역시 감소하였다.

• Bulletin of the Korean Chemical Society
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• 제6권2호
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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.

• Bulletin of the Korean Chemical Society
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• 제17권1호
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• pp.69-72
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• 1996

The NMR dipolar shift in tetrahedral and tetragonally-distorted tetrahedral complexes for Cu(Ⅱ) has been calculated adopting nonmultipole expansion method. The exact solution of ΔB/B(ppm) is exactly in agreement with multipolar results when R, the distance between the paramagnetic ion and the nucleus, is larger than 0.2 nm. The major contribution to the dipolar shift arises from 1/R3 term but the other terms, 1/R5 and 1/R7, contribute significantly to the pseudocontact shift when R is shorter than 0.5 nm. The shift is mainly due to the 3d orbitals and sensitive to distortion parameters at short range of R.