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相关概念视频

Phase Transitions: Melting and Freezing02:39

Phase Transitions: Melting and Freezing

Heating a crystalline solid increases the average energy of its atoms, molecules, or ions, and the solid gets hotter. At some point, the added energy becomes large enough to partially overcome the forces holding the molecules or ions of the solid in their fixed positions, and the solid begins the process of transitioning to the liquid state or melting. At this point, the temperature of the solid stops rising, despite the continual input of heat, and it remains constant until all of the solid is...
Carbon-13 (¹³C) NMR: Overview01:10

Carbon-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...
NMR Spectroscopy and Mass Spectrometry of Aldehydes and Ketones01:15

NMR Spectroscopy and Mass Spectrometry of Aldehydes and Ketones

In aldehydes, the hydrogen atom connected to the carbonyl carbon helps distinguish aldehydes from other carbonyl compounds using ¹H NMR spectroscopy. The closeness of aldehydic hydrogen to the electrophilic carbonyl carbon highly deshields the hydrogen atom causing its signal to appear around 10 ppm in the ¹H NMR spectra. α hydrogens split the aldehydic proton signal, which helps identify the number of α hydrogens in the molecule. For instance, one α hydrogen creates a doublet for an aldehydic...
NMR and Mass Spectroscopy of Carboxylic Acids01:30

NMR and Mass Spectroscopy of Carboxylic Acids

In ¹H NMR spectroscopy, acidic protons (–COOH) of carboxylic acids are highly deshielded and absorb far downfield, at around 9–12 ppm. The chemical shift value depends on the concentration and solvent used.
While α protons of carboxylic acids absorb at 2–2.5 ppm, β protons absorb further upfield.
Carboxylic acids are easily identified by dissolving them in deuterium oxide, which results in a rapid exchange of the acidic protons with deuterium. This leads to the disappearance of the acidic...
¹³C NMR: ¹H–¹³C Decoupling01:04

¹³C 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...
NMR Spectroscopy Of Amines01:19

NMR Spectroscopy Of Amines

In proton NMR spectroscopy, primary amines and secondary amines showcase their N–H protons as a broad signal in the chemical shift range between δ 0.5 and 5 ppm. The exact position in this range depends on several factors, including sample concentration, hydrogen bonding, and the type of solvent used. Since amine protons undergo fast proton exchange in solution, the protons are labile and therefore do not participate in any splitting with adjacent protons. Thus, the observed peak is broad and...

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Methods to Identify the NMR Resonances of the 13C-Dimethyl N-terminal Amine on Reductively Methylated Proteins
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Methods to Identify the NMR Resonances of the 13C-Dimethyl N-terminal Amine on Reductively Methylated Proteins

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酸在和蛋白质中的化学转变:固态碳-13核磁共振光谱和量子化学调查.

Haihong Sun1, Eric Oldfield

  • 1Department of Biophysics, University of Illinois at Urbana-Champaign, 600 South Mathews Avenue, Urbana, Illinois 61801, USA.

Journal of the American Chemical Society
|April 9, 2004
PubMed
概括
此摘要是机器生成的。

这项研究准确地预测了使用量子化学在蛋白质中的托残留物中的碳-13 NMR化学转移. 这些发现解决了长期存在的芳香碳不等价问题,并有助于蛋白质结构的确定.

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Methods to Identify the NMR Resonances of the 13C-Dimethyl N-terminal Amine on Reductively Methylated Proteins
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Methods to Identify the NMR Resonances of the 13C-Dimethyl N-terminal Amine on Reductively Methylated Proteins

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Nuclear Magnetic Resonance Spectroscopy for the Identification of Multiple Phosphorylations of Intrinsically Disordered Proteins
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科学领域:

  • 生物物理化学 生物物理化学
  • 结构生物学 结构生物学
  • 计算化学计算化学

背景情况:

  • 托残留物对蛋白质结构和功能至关重要.
  • 预测托中无质子芳香碳的化学转移一直是具有挑战性的.
  • 了解这些转变是解释蛋白质NMR数据的关键.

研究的目的:

  • 开发和验证一种量子化学方法,用于预测碳-13 NMR中托中非质子化芳香碳的化学转移.
  • 为了研究影响这些化学变化的因素.
  • 为了解决长期存在的蛋白质化学转移不等价问题的问题.

主要方法:

  • 获得了含酸和模型系统的碳-13核磁共振 (NMR) 光谱.
  • 使用X射线晶体结构用于实验数据.
  • 应用了量子化学方法来预测 (13) C NMR 转移的C ,C ,delta 2和C ,epsilon 2) 碳.
  • 分析了化学转移和侧链扭转角度之间的相关性.

主要成果:

  • 在预测和实验 (13) C NMR 转移之间观察到良好的一致性.
  • 准确预测了几个蛋白质中Trp C ((gamma) 的化学转移 (rms误差为1.4 ppm,R=0.86).
  • 甲C (gamma) 转移与侧链扭转角度 (chi (1),chi (2)) 和-左相互作用相关.

结论:

  • 量子化学计算提供了对托芳香碳NMR转移的可靠预测.
  • 侧链扭转角度和马左边相互作用是这些转移的关键决定因素.
  • 这种方法可以帮助解决化学转移不等价问题,并使用NMR数据增强蛋白质结构的确定.