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Related Concept Videos

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...
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...
Inductive Effects on Chemical Shift: Overview01:27

Inductive Effects on Chemical Shift: Overview

The protons in unsubstituted alkanes are strongly shielded with chemical shifts below 1.8 ppm. Methine, methylene, and methyl protons appear at approximately 1.7, 1.2 and 0.7 ppm, while the proton signal from methane appears at 0.23 ppm. An electronegative substituent, such as chlorine, withdraws the electron density from the protons, increasing their chemical shift. Progressive substitution of the hydrogens in methane by chlorine shifts the proton signals increasingly downfield, to 3.05 ppm in...
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...
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...
2D NMR: Heteronuclear Single-Quantum Correlation Spectroscopy (HSQC)01:19

2D NMR: Heteronuclear Single-Quantum Correlation Spectroscopy (HSQC)

Heteronuclear single-quantum correlation spectroscopy (HSQC) is a 2D NMR technique that reveals one-bond correlations between hydrogen and a heteronucleus. The HSQC experiment is similar to the heteronuclear correlation experiment (HETCOR) but is more sensitive. In the HSQC spectrum, the proton chemical shift is plotted on the horizontal F2 axis, while the 13C chemical shift is plotted on the vertical F1 axis. The corresponding proton and 13C spectra are also shown. The HSQC contour plot does...

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Related Experiment Video

Updated: Jun 21, 2026

High-Accuracy Correction of 3D Chromatic Shifts in the Age of Super-Resolution Biological Imaging Using Chromagnon
08:18

High-Accuracy Correction of 3D Chromatic Shifts in the Age of Super-Resolution Biological Imaging Using Chromagnon

Published on: June 16, 2020

CheckShift improved: fast chemical shift reference correction with high accuracy.

Simon W Ginzinger1, Marko Skocibusić, Volker Heun

  • 1Department of Molecular Biology Division of Bioinformatics, Center of Applied Molecular Engineering, University of Salzburg, Hellbrunnerstr. 34/3.OG, Salzburg 5020, Osterreich. simon@came.sbg.ac.at

Journal of Biomolecular NMR
|July 4, 2009
PubMed
Summary
This summary is machine-generated.

CheckShift, a protein chemical shift referencing tool, has been significantly optimized. Its running time decreased by 90% while maintaining accuracy, improving protein structural studies.

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Last Updated: Jun 21, 2026

High-Accuracy Correction of 3D Chromatic Shifts in the Age of Super-Resolution Biological Imaging Using Chromagnon
08:18

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Published on: June 16, 2020

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14:55

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NMR-Based Fragment Screening in a Minimum Sample but Maximum Automation Mode
09:19

NMR-Based Fragment Screening in a Minimum Sample but Maximum Automation Mode

Published on: June 4, 2021

Area of Science:

  • Biochemistry
  • Structural Biology
  • Bioinformatics

Background:

  • Protein chemical shift data is crucial for structural studies but hampered by referencing inaccuracies.
  • Automated preprocessing is needed to correct errors in chemical shift referencing.
  • Previous work developed CheckShift for automatic referencing error detection and correction.

Purpose of the Study:

  • To significantly improve the running time of the CheckShift algorithm.
  • To maintain or improve the accuracy of CheckShift's referencing error correction.
  • To evaluate alternative secondary structure prediction programs for CheckShift integration.

Main Methods:

  • Optimized the algorithm for searching the optimal re-referencing offset.
  • Evaluated various secondary structure prediction programs for compatibility and speed.
  • Compared the new CheckShift version's performance against RefDB and LACS for outlier detection.

Main Results:

  • Achieved a 90% reduction in CheckShift's running time.
  • Demonstrated that faster secondary structure prediction programs can be used without compromising accuracy.
  • The new CheckShift version resolves previously identified outliers, aligning with other databases.

Conclusions:

  • The optimized CheckShift algorithm offers a substantial speed improvement for processing protein chemical shift data.
  • Faster secondary structure prediction tools can be integrated into CheckShift, enhancing its efficiency.
  • The enhanced CheckShift is a more robust and accurate tool for building consistent protein chemical shift databases.