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Related Concept Videos

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: 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.
Interpreting ¹H NMR Signal Splitting: The (n + 1) Rule01:10

Interpreting ¹H NMR Signal Splitting: The (n + 1) Rule

In the AX proton spin system, proton A can sense the two spin states of a coupled proton X, resulting in a doublet NMR signal with two peaks of equal (1:1) intensity. When proton A is coupled to two equivalent protons (AX2 spin system), the spin states of each X can be aligned with or against the external field, creating three possible scenarios. This results in a 1:2:1  triplet signal, where the central peak corresponds to the chemical shift of A and is twice as large or intense as the others.
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...
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...
IR Spectrum Peak Splitting: Symmetric vs Asymmetric Vibrations01:08

IR Spectrum Peak Splitting: Symmetric vs Asymmetric Vibrations

Identical bonds within a polyatomic group can stretch symmetrically (in-phase) or asymmetrically (out-of-phase). Similar to hydrogen bonding, these vibrations also influence the shape of the IR peak. Generally, asymmetric stretching frequencies are higher than symmetric stretching frequencies. For example, primary amines exhibit two distinct IR peaks between 3300–3500 cm−1 corresponding to the symmetric and asymmetric N-H stretching, while secondary amines exhibit a single stretching vibration...

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Related Experiment Video

Updated: Jul 18, 2026

Line Shape Analysis of Dynamic NMR Spectra for Characterizing Coordination Sphere Rearrangements at a Chiral Rhenium Polyhydride Complex
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Line Shape Analysis of Dynamic NMR Spectra for Characterizing Coordination Sphere Rearrangements at a Chiral Rhenium Polyhydride Complex

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1H NMR study on equilibrium between parallel G-quartet structures.

Kenji Kanaori1, Ami Yasumura, Kunihiko Tajima

  • 1Department of Applied Biology, Kyoto Institute of Technology, Matsugasaki, Sakyo-ku, Kyoto 606-8585, Japan.

Nucleic Acids Symposium Series (2004)
|December 8, 2006
PubMed
Summary

Monovalent cations like potassium (K+) induce a single structure in parallel G-quartets. Sodium ions (Na+) however, result in multiple G-quartet conformations, revealing cation-specific structural dynamics.

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

Published on: May 12, 2023

Area of Science:

  • Biochemistry
  • Structural Biology
  • Molecular Biophysics

Background:

  • G-quartets are nucleic acid secondary structures crucial in various biological processes.
  • The structural plasticity of G-quartets is influenced by cation binding.
  • Understanding G-quartet conformation is vital for drug design and gene regulation studies.

Purpose of the Study:

  • To investigate the impact of different monovalent cations on the structural transitions of parallel G-quartets.
  • To elucidate the distinct conformational outcomes induced by potassium (K+) versus sodium (Na+) ions.

Main Methods:

  • Synthesis of the d(TG4T) DNA sequence.
  • Spectroscopic analysis (e.g., UV-Vis, CD) to monitor structural changes.
  • Ion titration experiments to observe cation-induced G-quartet formation.

Main Results:

  • Potassium ions (K+) stabilize the parallel G-quartet into a single, defined conformation.
  • Sodium ions (Na+) induce an equilibrium between at least three distinct G-quartet conformations.
  • Differential cation binding leads to divergent structural pathways for the d(TG4T) G-quartet.

Conclusions:

  • Monovalent cations exert distinct control over parallel G-quartet structure.
  • The choice of cation (K+ vs. Na+) dictates the conformational heterogeneity of G-quartets.
  • These findings highlight the cation-dependent nature of G-quartet structural dynamics.