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Related Concept Videos

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: 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...
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...
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...
UV–Vis Spectroscopy of Conjugated Systems01:32

UV–Vis Spectroscopy of Conjugated Systems

Organic compounds with conjugated double bonds show strong absorption features in the UV–visible region of the electromagnetic spectrum attributed to π → π* electronic excitations. Generally, a UV–vis absorption spectrum is recorded as a plot of absorbance vs wavelength. The wavelength of maximum absorbance, which manifests as a peak in the absorption spectrum, is denoted as λmax.
One of the factors influencing λmax is the extent of conjugation in the...
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.

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Related Experiment Video

Updated: May 20, 2026

In Vitro Chemical Mapping of G-Quadruplex DNA Structures by Bis-3-Chloropiperidines
05:32

In Vitro Chemical Mapping of G-Quadruplex DNA Structures by Bis-3-Chloropiperidines

Published on: May 12, 2023

Circular dichroism of quadruplex structures.

Antonio Randazzo1, Gian Piero Spada, Mateus Webba da Silva

  • 1Dipartimento di Chimica Farmaceutica e Tossicologica, Università degli Studi di Napoli "Federico II", via D. Montesano 49, 80131, Napoli, Italy, antranda@unina.it.

Topics in Current Chemistry
|July 4, 2012
PubMed
Summary

Circular dichroism (CD) spectroscopy reveals G-quadruplex DNA folding topologies by analyzing the syn or anti glycosidic bond angle (GBA) sequence. This approach predicts CD spectral features based on GBA sequence, aiding G-quadruplex structure determination.

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Single-Molecule Fluorescence Visualization of DNA Polymerase Dynamics at G-Quadruplexes

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Last Updated: May 20, 2026

In Vitro Chemical Mapping of G-Quadruplex DNA Structures by Bis-3-Chloropiperidines
05:32

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Published on: May 12, 2023

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Single-Molecule Fluorescence Visualization of DNA Polymerase Dynamics at G-Quadruplexes
05:37

Single-Molecule Fluorescence Visualization of DNA Polymerase Dynamics at G-Quadruplexes

Published on: April 4, 2025

Area of Science:

  • Biophysical Chemistry
  • Structural Biology
  • Genetics

Background:

  • Circular dichroism (CD) is a key technique for investigating G-quadruplex (G4) DNA polymorphism.
  • G-quadruplexes exhibit diverse folding topologies, influencing their biological functions.
  • Understanding these topologies is crucial for developing G4-targeting therapeutics.

Purpose of the Study:

  • To analyze CD spectral features associated with different G4-DNA folding topologies.
  • To establish a correlation between GBA sequence and CD spectral characteristics.
  • To demonstrate the predictive power of CD spectroscopy in G4-DNA structure elucidation.

Main Methods:

  • Analysis of CD spectral features in relation to the syn or anti glycosidic bond angle (GBA) sequence within G4-DNA stems.
  • Examination of the chiral disposition of stacked guanines based on GBA sequence.
  • Illustration of CD spectra for prototypal G-quadruplex structures.

Main Results:

  • Different GBA sequences result in distinct chiral arrangements of stacked guanines.
  • These arrangements predictably contribute to the overall CD spectrum of G4-DNA.
  • CD spectral analysis accurately reflects various G4-DNA folding patterns.

Conclusions:

  • The GBA sequence is a critical determinant of G4-DNA folding topology and CD spectral signature.
  • CD spectroscopy provides a powerful and predictive tool for characterizing G-quadruplex structures.
  • This approach is validated by studies on chemically modified G4-DNA and altered strand polarities.