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Nuclear Overhauser Enhancement (NOE)

Nuclear Overhauser Enhancement (NOE)

Irradiation of a spin-active nucleus causes an increase or decrease in the signal intensity of neighboring nuclei that are not necessarily chemically bonded or involved in J-coupling. This phenomenon, called the Nuclear Overhauser Enhancement (NOE), results from through-space interactions between the nuclear spins. The NOE effect decreases with increasing internuclear distance and is generally not observed beyond 4 angstroms. In NOE, dipole-dipole interactions between neighboring...

Spin–Spin Coupling: Two-Bond Coupling (Geminal Coupling)

Spin–Spin Coupling: Two-Bond Coupling (Geminal Coupling)

Two NMR-active nuclei bonded to a central atom can be involved in geminal or two-bond coupling. Geminal coupling is commonly seen between diastereotopic protons in chiral molecules and unsymmetrical alkenes, among others.
The central atom need not be NMR-active because its electrons are affected by the electron polarization of the spin-active atoms. However, spin information is transmitted less effectively than in one-bond coupling, and 2J values are usually weaker than 1J values. The energy of...

Spin–Spin Coupling Constant: Overview

Spin–Spin Coupling Constant: Overview

In bromoethane, the three methyl protons are coupled to the two methylene protons that are three bonds away. In accordance with the n+1 rule, the signal from the methyl protons is split into three peaks with 1:2:1 relative intensities. The methylene protons appear as a quartet, with the relative intensities of 1:3:3:1.
Qualitatively, any spin plus-half nucleus polarizes the spins of its electrons to the minus-half state. Consequently, the paired electron in the hydrogen–carbon bond must...

Spin–Spin Coupling: Three-Bond Coupling (Vicinal Coupling)

Spin–Spin Coupling: Three-Bond Coupling (Vicinal Coupling)

Vicinal or three-bond coupling is commonly observed between protons attached to adjacent carbons. Here, nuclear spin information is primarily transferred via electron spin interactions between adjacent C‑H bond orbitals. This generally favors the antiparallel arrangement of spins, so 3J values are usually positive.
The extent of coupling depends on the C‑C bond length, the two H‑C‑C angles, any electron-withdrawing substituents, and the dihedral angle between the...

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Related Experiment Video

Updated: Jul 17, 2025

Site Directed Spin Labeling and EPR Spectroscopic Studies of Pentameric Ligand-Gated Ion Channels

Site Directed Spin Labeling and EPR Spectroscopic Studies of Pentameric Ligand-Gated Ion Channels

Published on: July 4, 2016

Cucurbit[7]uril Enhances Distance Measurements of Spin-Labeled Proteins.

Zhimin Yang¹, Richard A Stein², Maren Pink³

¹Department of Chemistry, University of Nebraska, Lincoln, Nebraska 68588-0304, United States.

Biorxiv : the Preprint Server for Biology

|September 4, 2023

Summary

Cucurbit[7]uril (CB-7) forms strong complexes with a novel nitroxide radical (ClA-DZD), enhancing immobilization and enabling sensitive, long-distance electron spin measurements in biomolecules like T4 Lysozyme.

Keywords:

Biophysics Cucurbiturils EPR spectroscopy Host-guest systems Organic Radicals

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Last Updated: Jul 17, 2025

Site Directed Spin Labeling and EPR Spectroscopic Studies of Pentameric Ligand-Gated Ion Channels

Site Directed Spin Labeling and EPR Spectroscopic Studies of Pentameric Ligand-Gated Ion Channels

Published on: July 4, 2016

Paramagnetic Relaxation Enhancement for Detecting and Characterizing Self-Associations of Intrinsically Disordered Proteins

Paramagnetic Relaxation Enhancement for Detecting and Characterizing Self-Associations of Intrinsically Disordered Proteins

Published on: September 23, 2021

Measuring the Spin-Lattice Relaxation Magnetic Field Dependence of Hyperpolarized [1-13C]pyruvate

Measuring the Spin-Lattice Relaxation Magnetic Field Dependence of Hyperpolarized [1-13C]pyruvate

Published on: September 13, 2019

Area of Science:

Supramolecular Chemistry
Biophysical Chemistry
Electron Paramagnetic Resonance Spectroscopy

Background:

Organic radicals are crucial spin labels for probing molecular dynamics and structure.
Cucurbiturils (CBs) are macrocyclic hosts with potential applications in molecular recognition and stabilization.
Previous studies have explored radical-host interactions, but high-affinity systems for advanced EPR applications are limited.

Conclusions:

CB-7 forms a highly stable complex with the ClA-DZD radical, significantly altering its dynamics.
CB-7 complexation enhances the sensitivity and temperature range of DEER measurements on spin-labeled proteins.
This supramolecular approach offers a promising strategy for long-distance EPR measurements under near-physiological conditions.