(13) C NMRスペクトロスコーピーと計算研究によるグルコースにおける適合均衡同位体効果 (13)
1Department of Biochemistry, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, New York 10461, USA.
Journal of the American Chemical Society
|July 18, 2001
まとめ
この研究は,デュテリウム同位体効果が水中のD-グルコピラノースのアノメリック均衡にどのように影響するか明らかにしています. 内分子効果,特にハイパー結合とステリック反発は,これらの同位体波動の主要な原動力である.
科学分野:
- 生物物理化学 生物物理化学
- イソトープ効果とは
- 炭水化物化学 炭水化物の化学
背景:
- 糖の同位体効果を理解することは,酵素結合分子にとって極めて重要です.
- 水中のD-グルコピラノースのアノメリック均衡が調査されています.
- デュテリウムの構成均衡同位体効果 (CEIE) が採用されています.
研究 の 目的:
- 水中のアルファ-およびベータ-D-グルコピラノース異常の完全な分子研究を行う.
- デウテリウムイソトープがアノメリック均衡常数に及ぼす影響を定量化するために.
- これらの同位体効果の背後にあるメカニズムを解明する.
主な方法:
- 1D (13) C NMRスペクトロスコピーは,デウテリウム同位体効果を測定するために使用されました.
- 計算的研究 (半経験的および初期) が実施されました.
- ナチュラル・ボンド・オービタル (NBO) 分析を用いた.
主要な成果:
- D-グルコピラノースの様々な標識位置について,特定のデュテリウム同位体効果が定量化されました.
- 計算の結果は実験データとよく相関していた.
- H1とH2での同位体効果について,ハイパーコンジュガティブメカニズムが特定されました.
結論:
- ハイパーコンジュガーションとステリック反発を含む分子内効果は,アノメリック均衡の同位体の乱れに大きく影響する.
- H1における同位体効果は,β-グルコースにおけるハイパーコンジュガティブ・トランスファーに起因する.
- H2における同位体効果は,回転制限とハイパー結合に関連しています.
関連する概念動画
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...
01:10Carbon-13 (¹³C) NMR: Overview
Carbon-13 is a naturally occurring NMR-active isotope of carbon with a low natural abundance of 1.1%. In contrast, carbon-12 is the most abundant isotope of carbon with zero nuclear spin. Therefore, it is NMR inactive. The gyromagnetic ratio of carbon-13 is smaller than that of protons. As a result, carbon-13 resonance is about 6000 times weaker than proton resonance. For a given magnetic field strength, the resonance frequency of carbon-13 is about one-fourth of the resonance frequency for...
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...
00:58¹H NMR Signal Integration: Overview
The intensity of a signal, which can be represented by the area under the peak, depends on the number of protons contributing to that signal. The area under each peak is shown as a vertical line called an integral, with the integral value listed under it, as seen in the proton NMR spectrum of benzyl acetate. Each integral value is divided by the smallest integral value to obtain the ratio of the number of protons producing each signal. The ratio reveals the relative number of protons and not...
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...