温度変数17O NMRの研究は,有機固体の分子動態の定量的な評価を可能にします
Xianqi Kong1, Luke A O'Dell, Victor Terskikh
1Department of Chemistry, Queen's University, 90 Bader Lane, Kingston, Ontario K7L 3N6, Canada.
Journal of the American Chemical Society
|August 11, 2012
まとめ
固体 (17) O NMRは,結晶硫酸の硫酸群の動的3倍回転ジャンプを明らかにした. この研究では,水素結合エネルギーと回転障壁を定量化して,NMRを実証した.
科学分野:
- 固体NMRスペクトロスコーピー 固体NMRスペクトロスコーピー
- 物理化学 物理化学
- マテリアルサイエンス 材料科学
背景:
- 硫酸は固体状態でズウィテリオンとして存在します.
- これらのズウィテリオンには,水素結合に関与する硫酸塩基が特徴です.
- 固体における分子ダイナミクスを理解することは極めて重要です.
研究 の 目的:
- 結晶硫酸の硫酸酸群の回転ダイナミクスを研究する.
- 固体 (17) O NMRを用いて水素結合エネルギーと回転障壁を定量化する.
- 有機固体におけるダイナミックなプロセスを研究するために,17O NMRの有用性を実証する.
主な方法:
- 温度変数固体 (17) O NMRスペクトロスコーピーは21.1T.
- マジック・アングル・スピニング (MAS) と静的なNMR技術.
- スペクトル割り当てのための密度関数理論 (DFT) 計算.
主要な成果:
- タウリン,ホモタウリン,ABSAの完全な (17) O NMRテンソールパラメータを測定した.
- 硫酸塩基の3倍回転ジャンプメカニズムが確認されました.
- 回転ジャンプ速度 (10^210^5 s−1) と活性化エネルギー (Ea ≈ 4248 kJ mol−1) を決定した.
- 実験的なEa値は,量的に評価された水素結合エネルギーである.
結論:
- 固体 (17) O NMRは,硫酸塩群動態を直接探知する.
- アクティベーションエネルギーは,計算された回転障壁と相関する.
- この方法は,有機固体および潜在的にバイオ分子におけるダイナミックなプロセスを定量化するのに有効です.
関連する概念動画
¹H NMR of Conformationally Flexible Molecules: Variable-Temperature NMR
The axial and equatorial protons in cyclohexane can be distinguished by performing a variable-temperature NMR experiment. In this process, except for one proton, the remaining eleven protons are replaced by deuterium. The deuterium substitution avoids the possible peak splitting caused by the spin-spin coupling between the adjacent protons. The remaining proton flips between the axial and equatorial positions.
¹H NMR of Conformationally Flexible Molecules: Temporal Resolution
At room temperature, the chair conformer of cyclohexane undergoes rapid ring flipping between two equivalent chair conformers at a rate of approximately 105 times per second. These two chair conformers are in equilibrium. The rapid ring flipping results in the interconversion of the axial proton to an equatorial proton and an equatorial to the axial proton. Such interconversions are too rapid and cannot be detected on the NMR timescale. Hence, the NMR spectrometer cannot distinguish between the...
¹H NMR of Labile Protons: Temporal Resolution
Protons bonded to heteroatoms such as nitrogen and oxygen exhibit a range of chemical shift values. This is due to the varying degree of hydrogen bonding between the proton and the heteroatom in other molecules. The extent of hydrogen bonding affects the electron density around the proton, thereby giving different chemical shift values for the protons in the proton NMR spectrum.
The –OH proton in alcohols typically appears in the range of δ 2 to 5 ppm but can vary depending on the specific...
The –OH proton in alcohols typically appears in the range of δ 2 to 5 ppm but can vary depending on the specific...
NMR Spectroscopy of Aromatic Compounds
Aromatic compounds can be identified or analyzed using proton NMR and carbon‐13 NMR. Typically, aromatic hydrogens or hydrogens directly bonded to the aromatic rings are strongly deshielded by the aromatic ring current. Therefore, they absorb in the range of 6.5–8.0 ppm in proton NMR spectra. For instance, aromatic hydrogens directly bonded to the benzene ring absorb at 7.3 ppm. However, aromatic hydrogens of larger rings absorb farther upfield or downfield than the ideal range. Consider...
Chemical Shift: Internal References and Solvent Effects
In an NMR sample, precise measurement of the absolute absorption frequencies of nuclei is difficult. A standard internal reference compound is added, and the frequency difference between the reference signal and sample signals is measured.
The internal reference compound generally used in NMR spectroscopy is tetramethylsilane (TMS). TMS is preferred because it is chemically inert, soluble in NMR solvents, and easily removable. Also, the highly shielded methyl protons in TMS yield an intense...
The internal reference compound generally used in NMR spectroscopy is tetramethylsilane (TMS). TMS is preferred because it is chemically inert, soluble in NMR solvents, and easily removable. Also, the highly shielded methyl protons in TMS yield an intense...
¹H NMR: Interpreting Distorted and Overlapping Signals
Spin systems where the difference in chemical shifts of the coupled nuclei is greater than ten times J are called first-order spin systems. These nuclei are weakly coupled, and their chemical shifts and coupling constant can generally be estimated from the well-separated signals in the spectrum.
As Δν decreases and the signals move closer, the doublets appear increasingly distorted. The intensities of the inner lines increase at the cost of those of the outer lines as the signals are slanted or...
As Δν decreases and the signals move closer, the doublets appear increasingly distorted. The intensities of the inner lines increase at the cost of those of the outer lines as the signals are slanted or...


