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Related Concept Videos

¹H NMR of Conformationally Flexible Molecules: Temporal Resolution00:52

¹H NMR of Conformationally Flexible Molecules: Temporal Resolution

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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...
1.4K
¹H NMR of Conformationally Flexible Molecules: Variable-Temperature NMR01:15

¹H NMR of Conformationally Flexible Molecules: Variable-Temperature NMR

1.8K
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.
1.8K
¹H NMR: Interpreting Distorted and Overlapping Signals01:02

¹H NMR: Interpreting Distorted and Overlapping Signals

1.7K
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...
1.7K
Spin–Spin Coupling Constant: Overview01:08

Spin–Spin Coupling Constant: Overview

1.6K
In bromoethane, the three methyl protons are coupled to the two methylene protons that are three bonds away. In accordance with the n+1 rule, the signal from the methyl protons is split into three peaks with 1:2:1 relative intensities. The methylene protons appear as a quartet, with the relative intensities of 1:3:3:1.
Qualitatively, any spin plus-half nucleus polarizes the spins of its electrons to the minus-half state. Consequently, the paired electron in the hydrogen–carbon bond must...
1.6K
NMR Spectroscopy: Spin–Spin Coupling01:08

NMR Spectroscopy: Spin–Spin Coupling

3.6K
The spin state of an NMR-active nucleus can have a slight effect on its immediate electronic environment. This effect propagates through the intervening bonds and affects the electronic environments of NMR-active nuclei up to three bonds away; occasionally, even farther. This phenomenon is called spin–spin coupling or J-coupling. Coupling interactions are mutual and result in small changes in the absorption frequencies of both nuclei involved. While nuclei of the same element are involved...
3.6K
Spin–Spin Coupling: One-Bond Coupling01:17

Spin–Spin Coupling: One-Bond Coupling

1.6K
Coupling interactions are strongest between NMR-active nuclei bonded to each other, where spin information can be transmitted directly through the pair of bonding electrons. While nuclei polarize their electrons to the opposite spins, the bonding electron pair has opposite spins. Configurations with antiparallel nuclear spins are expected to be lower in energy. When coupling makes antiparallel states more favorable, J is considered to have a positive value. The one-bond coupling constant, 1J,...
1.6K

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Related Experiment Video

Updated: Mar 29, 2026

Site Directed Spin Labeling and EPR Spectroscopic Studies of Pentameric Ligand-Gated Ion Channels
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Site Directed Spin Labeling and EPR Spectroscopic Studies of Pentameric Ligand-Gated Ion Channels

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Characterization of Protein Conformational Changes with Sparse Spin-Label Distance Constraints.

G Jeschke1

  • 1Lab. Phys. Chem., ETH Zürich, Wolfgang-Pauli-Strasse 10, CH-8093 Zürich, Switzerland.

Journal of Chemical Theory and Computation
|November 24, 2015
PubMed
Summary
This summary is machine-generated.

Site-directed spin labeling and pulse EPR provide distance constraints for protein conformational changes. This method can identify the type and direction of changes, though amplitude may be uncertain.

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Area of Science:

  • Biophysics
  • Structural Biology
  • Protein Dynamics

Background:

  • Site-directed spin labeling (SDSL) and pulse Electron Paramagnetic Resonance (EPR) spectroscopy are powerful techniques for measuring distances within proteins.
  • These methods provide distance constraints on the nanometer length scale, offering insights into protein structure and function.
  • Understanding protein conformational changes is crucial for deciphering biological mechanisms.

Purpose of the Study:

  • To investigate the extent to which protein conformational changes can be characterized using sparse distance constraints.
  • To adapt existing algorithms for analyzing sparse data in the context of protein structural changes.
  • To evaluate the reliability of identifying conformational changes when structural information is available for only one state.

Main Methods:

  • Utilizing site-directed spin labeling to introduce paramagnetic probes at specific protein sites.
  • Employing pulse EPR spectroscopy for distance measurements between spin labels.
  • Adapting a computational algorithm (Zheng & Brooks, 2006) to model protein structures based on sparse distance constraints.

Main Results:

  • The study demonstrates that the general type and direction of protein conformational changes can be identified even with limited distance data.
  • Analysis revealed that while the overall nature of the conformational shift is discernible, the precise amplitude of the change might remain uncertain.
  • The adapted algorithm proved effective in extracting meaningful information from sparse experimental data.

Conclusions:

  • Sparse distance constraints obtained from SDSL and pulse EPR are valuable for characterizing protein conformational dynamics.
  • The approach allows for the recognition of key aspects of conformational transitions, aiding in structural biology research.
  • Further refinement of algorithms could potentially improve the accuracy of amplitude determination in future studies.