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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...
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...
¹H NMR Chemical Shift Equivalence: Enantiotopic and Diastereotopic Protons00:58

¹H NMR Chemical Shift Equivalence: Enantiotopic and Diastereotopic Protons

Replacing each alpha-hydrogen in chloroethane by bromine (or a different functional group) yields a pair of enantiomers. Such protons are called prochiral or enantiotopic and are related by a mirror plane. Enantiotopic protons are chemically equivalent in an achiral environment. Because most proton NMR spectra are recorded using achiral solvents, enantiotopic hydrogens yield a single signal.
In chiral compounds such as 2-butanol, replacing the methylene hydrogens at C3 produces a pair of...
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 Chemical Shift Equivalence: Homotopic and Heterotopic Protons01:03

¹H NMR Chemical Shift Equivalence: Homotopic and Heterotopic Protons

Protons in identical electronic environments within a molecule are chemically equivalent and have the same chemical shift. The replacement test is a useful tool to identify chemical equivalence and predict NMR spectra. A substituent replaces each of the protons being examined and the resulting molecules are compared. If the same molecule is obtained, the protons are equivalent or homotopic. Replacement of any hydrogens in ethane by chlorine yields chloroethane because all six protons are...
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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Chemical shift optimization in multidimensional NMR spectra by AUREMOL-SHIFTOPT.

Kumaran Baskaran1, Renate Kirchhöfer, Fritz Huber

  • 1Department of Biophysics and Physical Biochemistry, University of Regensburg, Postfach, 93040, Regensburg, Federal Republic of Germany.

Journal of Biomolecular NMR
|February 24, 2009
PubMed
Summary

Two new algorithms, AUREMOL-SHIFTOPT1 and AUREMOL-SHIFTOPT2, optimize protein chemical shift assignments for multidimensional NMR spectroscopy. These methods improve spectral analysis for complex datasets, aiding researchers in accurate protein structure determination.

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Area of Science:

  • Biochemistry
  • Structural Biology
  • Spectroscopy

Background:

  • Accurate assignment of multidimensional NMR spectra is crucial for protein structure determination.
  • Existing chemical shift lists often do not perfectly match experimental spectra, hindering reliable assignment, especially for temperature or pressure series.
  • Automated evaluation of n-dimensional NMR spectra requires robust methods for handling spectral variations.

Purpose of the Study:

  • To introduce and evaluate two novel algorithms, AUREMOL-SHIFTOPT1 and AUREMOL-SHIFTOPT2, for optimizing chemical shift assignments in multidimensional NMR spectroscopy.
  • To assess the performance of these algorithms using both simulated and experimental 2D and 3D NMR spectra from three different proteins.
  • To develop a new z-score metric for weighting chemical shift contributions across different dimensions.

Main Methods:

  • Development of two algorithms: AUREMOL-SHIFTOPT1 and AUREMOL-SHIFTOPT2.
  • Analysis of simulated and experimental 2D and 3D NMR spectra from three distinct proteins.
  • Introduction of a novel z-score based on atom and amino acid specific chemical shift distributions.

Main Results:

  • Demonstration of the effectiveness of AUREMOL-SHIFTOPT1 and AUREMOL-SHIFTOPT2 in improving chemical shift assignments.
  • Validation of algorithm performance across diverse spectral datasets (simulated and experimental, 2D and 3D).
  • Successful application of the new z-score for accurate weighting of chemical shift contributions.

Conclusions:

  • AUREMOL-SHIFTOPT1 and AUREMOL-SHIFTOPT2 provide effective solutions for optimizing chemical shift assignments in challenging multidimensional NMR datasets.
  • The developed algorithms enhance the reliability of automated spectral assignment and analysis, particularly for variable condition studies.
  • The novel z-score metric contributes to more accurate and robust spectral interpretation in protein NMR research.