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Related Concept Videos

NMR Spectroscopy: Chemical Shift Overview01:15

NMR Spectroscopy: Chemical Shift Overview

The position of the absorption signal of a sample is reported relative to the position of the signal of tetramethylsilane (TMS), which is added as an internal reference while recording spectra. The difference between the absorption frequencies of the sample and TMS (in Hz) is divided by the spectrometer operating frequency (in MHz) to obtain a dimensionless quantity called the chemical shift. It is reported on the δ (delta) scale and expressed in parts per million.
For instance, the proton...
Chemical Shift: Internal References and Solvent Effects01:17

Chemical Shift: Internal References and Solvent Effects

In an NMR sample, precise measurement of the absolute absorption frequencies of nuclei is difficult. A standard internal reference compound is added, and the frequency difference between the reference signal and sample signals is measured.
The internal reference compound generally used in NMR spectroscopy is tetramethylsilane (TMS). TMS is preferred because it is chemically inert, soluble in NMR solvents, and easily removable. Also, the highly shielded methyl protons in TMS yield an intense...
¹H NMR: Interpreting Distorted and Overlapping Signals01:02

¹H NMR: Interpreting Distorted and Overlapping Signals

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 slanted or...
Proton (¹H) NMR: Chemical Shift01:07

Proton (¹H) NMR: Chemical Shift

Organic molecules primarily contain carbon and hydrogen atoms. While all the hydrogen isotopes are NMR-active, protium or hydrogen-1 is the most abundant. It has a significant energy separation between its nuclear spin states due to its large gyromagnetic ratio. As per Boltzmann's distribution, an increase in the energy separation implies a greater excess population of nuclei available for excitation, resulting in a strong NMR absorption signal.
Absorption signals of all the protium nuclei in 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...
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...

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Related Experiment Video

Updated: May 31, 2026

Atomic Scale Structural Studies of Macromolecular Assemblies by Solid-state Nuclear Magnetic Resonance Spectroscopy
14:55

Atomic Scale Structural Studies of Macromolecular Assemblies by Solid-state Nuclear Magnetic Resonance Spectroscopy

Published on: September 17, 2017

Structure determination in "shiftless" solid state NMR of oriented protein samples.

Yuanyuan Yin1, Alexander A Nevzorov

  • 1Department of Chemistry, North Carolina State University, 2620 Yarbrough Drive, Raleigh, NC 27695-8204, USA.

Journal of Magnetic Resonance (San Diego, Calif. : 1997)
|July 12, 2011
PubMed
Summary
This summary is machine-generated.

This study presents a new method for protein structure calculation using solid-state NMR data. The approach utilizes dipolar couplings, enabling accurate structure determination even with experimental uncertainties.

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Area of Science:

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

Background:

  • Protein structure determination is crucial for understanding biological function.
  • Solid-state NMR (ssNMR) spectroscopy offers a powerful tool for analyzing protein structures, especially for insoluble or aggregated proteins.
  • Calculating protein structures from NMR data traditionally relies on various NMR observables, each with its own sensitivities and limitations.

Purpose of the Study:

  • To develop an efficient formalism for calculating protein structures from oriented-sample NMR data in torsion-angle space.
  • To introduce a method that speeds up structural fitting by simplifying the dependence on torsion angles.
  • To enable protein structure calculation using solely "shiftless" solid-state NMR data, overcoming limitations of chemical shift anisotropy.

Main Methods:

  • Utilizing an irreducible spherical basis of rotations to treat angular anisotropies of NMR observables.
  • Introducing an intermediate rotational transformation for diagonalizing torsion angle dependence, accelerating structural fitting.
  • Employing heteronuclear dipolar couplings (1H-15N, 1Hα-13Cα, 13Cα-15N, 13C'-15N) as primary structural restraints.
  • Simulating ssNMR spectra and back-calculating structures with consideration for experimental uncertainties and peptide non-planarity.

Main Results:

  • The developed formalism significantly speeds up structural fitting by rendering torsion angle dependence diagonal.
  • Protein structure calculation using only dipolar couplings, termed "shiftless" NMR, was demonstrated to be feasible.
  • Back-calculation of spectra for protein G and a helical hairpin yielded converged structural solutions, even with simulated experimental uncertainties.
  • The study highlights the sensitivity of structure determination to uncertainties in chemical shift anisotropy (CSA) values.

Conclusions:

  • The presented formalism provides an efficient and robust method for protein structure calculation from oriented-sample NMR data.
  • The use of dipolar couplings as primary restraints allows for accurate structure determination, particularly in "shiftless" ssNMR approaches.
  • Distance restraints are shown to be critical for improving structural convergence, especially when experimental uncertainties are significant.