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Related Concept Videos

¹H NMR: Interpreting Distorted and Overlapping Signals01:02

¹H NMR: Interpreting Distorted and Overlapping Signals

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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...
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¹H NMR: Complex Splitting01:13

¹H NMR: Complex Splitting

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

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

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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...
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2D NMR: Heteronuclear Single-Quantum Correlation Spectroscopy (HSQC)01:19

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

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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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¹H NMR of Conformationally Flexible Molecules: Temporal Resolution00:52

¹H NMR of Conformationally Flexible Molecules: Temporal Resolution

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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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Two-Dimensional (2D) NMR: Overview01:12

Two-Dimensional (2D) NMR: Overview

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The 1D NMR spectrum of large and complex molecules like natural products has complicated splitting patterns and overlapping signals, which can be easily interpreted using 2-dimensional (2D) NMR. Unlike 1D NMR, 2D NMR has two frequency axes that provide the coupling information between the nucleus A and nucleus B in a molecule. The process from which 2D spectra are obtained has four steps.
The first step is the preparation period, during which nucleus A is excited with a radiofrequency pulse....
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Single-molecule Manipulation of G-quadruplexes by Magnetic Tweezers
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Strategy for modeling higher-order G-quadruplex structures recalcitrant to NMR determination.

T Michael Sabo1, John O Trent1, Jonathan B Chaires1

  • 1UofL Health Brown Cancer Center, University of Louisville, Louisville, KY, United States.

Methods (San Diego, Calif.)
|July 20, 2024
PubMed
Summary
This summary is machine-generated.

Researchers developed an integrated structural biology platform to characterize complex G-quadruplexes (G4s) and higher-order G4s (xG4s). This method enables modeling of biologically relevant xG4 structures for potential therapeutic targeting.

Keywords:
AUCCDDNAG-quadruplexHigher-order G4Integrative structural biologyMolecular modelingNMRSAXS

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Area of Science:

  • Structural Biology
  • Biochemistry
  • Genetics

Background:

  • Guanine-rich nucleic acids form G-quadruplexes (G4s), with research traditionally focusing on simple, short sequences.
  • Longer sequences with multiple G4 repeats, found in proto-oncogene promoters and telomeres, suggest complex higher-order structures (xG4s).
  • These xG4s may offer selective drug-targeting sites for therapeutic development but are challenging to characterize.

Purpose of the Study:

  • To develop and present an integrated structural biology (ISB) platform for characterizing complex higher-order G-quadruplexes (xG4s).
  • To demonstrate the utility and generality of the ISB approach for biologically relevant xG4s.

Main Methods:

  • Development of an integrated structural biology (ISB) platform.
  • Combination of experimental and computational methods.
  • Application of the ISB platform to model extended c-Myc promoter and long human telomere G4 repeats.

Main Results:

  • Successful application of the ISB platform to characterize complex xG4 structures.
  • Generation of self-consistent molecular models for biologically relevant xG4s.
  • Demonstration of the ISB platform's utility and generality.

Conclusions:

  • The ISB platform provides a robust method for structural characterization of complex xG4s.
  • This approach facilitates the study of biologically relevant xG4s, aiding in the identification of potential therapeutic targets.
  • The ISB platform overcomes limitations of traditional high-resolution methods for complex G4 structures.