トリプル量子マジックアングルスピニング (27) アルミニウム水酸化物のアル NMR
Krishnan Damodaran1, Pattuparambil R Rajamohanan, Debojit Chakrabarty
1National Chemical Laboratory, Pune 411008, India, Unilever Research India, Mumbai 400 099, India.
Journal of the American Chemical Society
|March 28, 2002
まとめ
トリプル量子マジック・アングル・スピニング (3Q-MAS) 実験では,アルミニウム水酸化物中のアルミニウム八面体構造が明らかになりました. このテクニックは,アルミニウム共鳴の割り当てを助け,変形材料の研究を進めます.
科学分野:
- 固体核磁共振 (NMR) スペクトロスコーピーは,固体核磁共振 (NMR) スペクトロスコーピーを用います.
- マテリアルサイエンス 材料科学
- 無機化学 無機化学とは
背景:
- ギブサイト,ベイライト,ボヘミットなどのアルミニウム水酸化物は,広く研究されている材料です.
- (27) AL NMRスペクトルの二次四極拡大は,アルミニウム環境の分析を複雑にする.
研究 の 目的:
- (27) AL三次量子魔法の角度回転 (3Q-MAS) NMRがスペクトル拡大を克服する方法を実証する.
- 主要なアルミニウム水酸化物における非同等のアルミニウム八面体の構造構成単位を解明する.
- 結晶構造内の特定のアルミニウム位置に (27) アル同otropic 共鳴を割り当てます.
主な方法:
- (27) アル三次量子魔法の角度回転 (3Q-MAS) NMRスペクトロスコーピーを利用する.
- 標準的なマジック・アングル・スピニング (MAS) NMR実験を行う.
- 電気場梯度 (EFG) テンソールを決定するために,アビニシオ計算を行う.
主要な成果:
- 3Q-MAS実験は,二次四極拡大を効果的に抑制しました.
- 明確なアルミニウム八面体の環境は,ギブサイト,ベイライト,ボヘミットで解決されました.
- 3Q-MAS/MASの結果とab initio計算を組み合わせることで,X線で決定された構造部位に (27) Al共振を正確に割り当てることができました.
結論:
- 3Q-MAS NMRは,水酸化物中のアルミニウム調整環境を特徴付ける強力な技術です.
- この研究は,より複雑なアルミニウムを含む材料を分析するための基礎を提供します.
- この研究は,基本的なアルミニウム水酸化物から派生した構造的に変換された材料に関する将来の調査を容易にする.
関連する概念動画
01:13¹H NMR: Complex Splitting
A proton M that is coupled to a proton X results in doublet signals for M. However, NMR-active nuclei can be simultaneously coupled to more than one nonequivalent nucleus. When M is coupled to a second proton A, such as in styrene oxide, each peak in the doublet is split into another doublet.
Splitting diagrams or splitting tree diagrams are routinely used to depict such complex couplings. While drawing splitting diagrams, the splitting with the larger coupling constant is usually applied first.
Splitting diagrams or splitting tree diagrams are routinely used to depict such complex couplings. While drawing splitting diagrams, the splitting with the larger coupling constant is usually applied first.
00:52¹H 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...
01:20¹³C NMR: Distortionless Enhancement by Polarization Transfer (DEPT)
When proton-coupled carbon-13 spectra are simplified by a broadband proton decoupling technique, structural information about the coupled protons is lost. Distortionless enhancement by polarization transfer (DEPT) is a technique that provides information on the number of hydrogens attached to each carbon in a molecule. While the DEPT experiment utilizes complex pulse sequences, the pulse delay and flip angle are specifically manipulated. The resulting signals have different phases depending on...
01:15NMR Spectroscopy: Chemical Shift Overview
The position of the absorption signal of a sample is reported relative to the position of the signal of tetramethylsilane (TMS), which is added as an internal reference while recording spectra. The difference between the absorption frequencies of the sample and TMS (in Hz) is divided by the spectrometer operating frequency (in MHz) to obtain a dimensionless quantity called the chemical shift. It is reported on the δ (delta) scale and expressed in parts per million.
For instance, the proton...
For instance, the proton...
01:15¹H 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.
01:04¹³C NMR: ¹H–¹³C Decoupling
The probability of having two carbon-13 atoms next to each other is negligible because of the low natural abundance of carbon-13. Consequently, peak splitting due to carbon-carbon spin-spin coupling is not observed in spectra. However, protons up to three sigma bonds away split the carbon signal according to the n+1 rule, resulting in complicated spectra.
A broadband decoupling technique is used to simplify these complex, sometimes overlapping, signals. Broadband decoupling relies on a...
A broadband decoupling technique is used to simplify these complex, sometimes overlapping, signals. Broadband decoupling relies on a...