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Related Concept Videos

Electron Paramagnetic Resonance (EPR) Spectroscopy: Organic Radicals01:17

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Ideally, an unpaired electron shows a single peak in the EPR spectrum due to the transition between the two spin energy states. However, coupling interactions can occur between the spins of the unpaired electron and any neighboring spin-active nuclei. This hyperfine coupling results in hyperfine splitting, where the EPR signal is split into multiplets. The signals split into 2nI + 1 peaks, where n is the number of equivalent nuclei and I is the nuclear spin. These splitting patterns provide...
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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.
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NMR Spectroscopy: Spin–Spin Coupling01:08

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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...
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¹³C NMR: Distortionless Enhancement by Polarization Transfer (DEPT)01:20

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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...
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NMR Spectrometers: Resolution and Error Correction01:14

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When magnetic nuclei in a sample achieve resonance and undergo relaxation, the signal detected in NMR is an approximately exponential free induction decay. Fourier transform of an exponential decay yields a Lorentzian peak in the frequency domain. Lorentzian peaks in an NMR spectrum are defined by their amplitude, full width at half maximum, and position, where the peak width is governed by the spin-spin relaxation time alone. In real experiments, however, the applied magnetic field is rendered...
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¹³C NMR: ¹H–¹³C Decoupling01:04

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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.
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Site Directed Spin Labeling and EPR Spectroscopic Studies of Pentameric Ligand-Gated Ion Channels
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EPR moments for site-directed spin-labelling.

Derek Marsh1

  • 1Max-Planck-Institut für biophysikalische Chemie, 37070 Göttingen, Germany.

Journal of Magnetic Resonance (San Diego, Calif. : 1997)
|October 15, 2014
PubMed
Summary

This study analyzes moments of nitroxide Electron Paramagnetic Resonance (EPR) spectra for site-directed spin labeling. The findings calibrate spectral moments for assessing spin probe dynamics, aiding in structural biology research.

Keywords:
EPR momentsOrder parameterRotational diffusionSDSLSpin label

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Area of Science:

  • Biophysics
  • Spectroscopy
  • Structural Biology

Background:

  • Electron Paramagnetic Resonance (EPR) spectroscopy is crucial for studying molecular dynamics.
  • Site-directed spin labeling (SDSL) utilizes nitroxide probes to report on local environments.
  • Analyzing EPR spectral moments offers quantitative insights into molecular motion.

Purpose of the Study:

  • To systematically analyze the absolute-value first and second moments of nitroxide EPR spectra.
  • To calibrate these spectral moments against spin probe rotational mobility and motional amplitude.
  • To establish their utility in site-directed spin labeling applications.

Main Methods:

  • Utilized spectral simulations based on the stochastic Liouville equation.
  • Performed calibrations of spectral moments as a function of rotational correlation time (τR) and order parameter (Szz).
  • Investigated the behavior of moments for multicomponent spectra, including those with multiple conformations.

Main Results:

  • Established comprehensive calibrations for spectral moments across a wide range of motional parameters.
  • Demonstrated that both first and second moments are additive for complex spectral systems.
  • Showcased the advantage of the absolute-value first moment over line width for avoiding overemphasis on fast motions.

Conclusions:

  • The analyzed spectral moments provide a robust framework for quantitative analysis in SDSL.
  • The absolute-value first moment offers improved robustness against spectral noise and baseline artifacts compared to the second moment.
  • These findings enhance the application of EPR spectroscopy in determining molecular dynamics and structure.