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Related Concept Videos

¹H NMR: Complex Splitting01:13

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

¹H 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...
NMR Spectrometers: Resolution and Error Correction01:14

NMR Spectrometers: Resolution and Error Correction

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...
NMR Spectroscopy: Spin–Spin Coupling01:08

NMR Spectroscopy: Spin–Spin Coupling

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

¹H 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.
2D NMR: Overview of Homonuclear Correlation Techniques01:16

2D NMR: Overview of Homonuclear Correlation Techniques

Homonuclear correlation spectroscopy (COSY) is a powerful technique used in Nuclear Magnetic Resonance (NMR) spectroscopy to study the correlations between nuclei of the same type within a molecule. It provides information about scalar couplings between adjacent nuclei, which helps determine connectivity and structural information. There are several COSY variants, each with its unique strengths and experimental parameters.
COSY90 is the standard two-dimensional (2D) COSY experiment that...

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Related Experiment Video

Updated: Jun 21, 2026

Structure and Coordination Determination of Peptide-metal Complexes Using 1D and 2D 1H NMR
14:44

Structure and Coordination Determination of Peptide-metal Complexes Using 1D and 2D 1H NMR

Published on: December 16, 2013

Complete cross-validation and R-factor calculation of a solid-state NMR derived structure.

S Kim1, J R Quine, T A Cross

  • 1Center for Interdisciplinary Magnetic Resonance, National High Magnetic Field Laboratory (NHMFL), Institute of Molecular Biophysics, Department of Chemistry, and Department of Mathematics, Florida State University, Tallahassee, Florida 32310, USA.

Journal of the American Chemical Society
|July 27, 2001
PubMed
Summary

This study validates solid-state Nuclear Magnetic Resonance (NMR) structure determination by employing cross-validation. This method refines membrane polypeptide structures, enhancing accuracy by balancing experimental data with energy functions.

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Area of Science:

  • Biophysics
  • Structural Biology
  • Nuclear Magnetic Resonance (NMR) Spectroscopy

Background:

  • Determining membrane polypeptide structures is crucial for understanding biological functions.
  • Solid-state NMR provides orientational restraints for structural analysis.
  • Refining these structures requires balancing experimental data with theoretical models.

Purpose of the Study:

  • To demonstrate a robust cross-validation method for refining solid-state NMR-derived membrane polypeptide structures.
  • To optimize the weighting factor in the penalty function for improved structural accuracy.
  • To validate the cross-validation approach using experimental data.

Main Methods:

  • Utilized orientational restraints from anisotropic nuclear spin interactions in solid-state NMR.
  • Developed a penalty function combining experimental data and an energy function.
  • Implemented complete cross-validation by partitioning data into working and test sets.
  • Monitored the free R-value during refinement to optimize the weighting factor.

Main Results:

  • Successfully demonstrated cross-validation for solid-state NMR structure determination.
  • The cross-validation method effectively balances experimental restraints and energy functions.
  • Optimizing the weighting factor through cross-validation enhances the quality of the refined structure.
  • Validated the approach using gramicidin A structure in lipid bilayers.

Conclusions:

  • Cross-validation is a critical step for accurate solid-state NMR structure refinement.
  • This method minimizes over-fitting and improves the reliability of structural models.
  • The demonstrated approach offers a significant advancement in determining membrane protein structures using solid-state NMR.