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Atomic Nuclei: Nuclear Relaxation Processes

Atomic Nuclei: Nuclear Relaxation Processes

In the absence of an external magnetic field, nuclear spin states are degenerate and randomly oriented. When a magnetic field is applied, the spins begin to precess and orient themselves along (lower energy) or against (higher energy) the direction of the field. At equilibrium, a slight excess population of spins exists in the lower energy state. Because the direction of the magnetic field is fixed as the z-axis, the precessing magnetic moments are randomly oriented around the z-axis. This...

Atomic Nuclei: Nuclear Spin State Population Distribution

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Atomic Nuclei: Nuclear Spin State Overview

Atomic Nuclei: Nuclear Spin State Overview

NMR-active nuclei have energy levels called 'spin states' that are associated with the orientations of their nuclear magnetic moments. In the absence of a magnetic field, the nuclear magnetic moments are randomly oriented, and the spin states are degenerate. When an external magnetic field is applied, the spin states have only 2 + 1 orientations available to them. A proton with = ½ has two available orientations. Similarly, for a quadrupolar nucleus with a nuclear spin value of one, the...

Atomic Nuclei: Magnetic Resonance

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The number of nuclear spins aligned in the lower energy state is slightly greater than those in the higher energy state. In the presence of an external magnetic field, as the spins precess at the Larmor frequency, the excess population results in a net magnetization oriented along the z axis. When a pulse or a short burst of radio waves at the Larmor frequency is applied along the x axis, the coupling of frequencies causes resonance and flips the nuclear spins of the excess population from the...

Atomic Nuclei: Nuclear Spin

Atomic Nuclei: Nuclear Spin

All atomic particles possess an intrinsic angular momentum, or 'spin'. Electrons, protons, and neutrons each have a spin value of ½, although protons and neutrons in nuclei may have higher half-integer spins owing to energetic factors.
Atomic nuclei have a net nuclear spin, , which can have an integer or half-integer value. In atomic nuclei, the spins of protons are paired against each other but not with neutrons, and vice versa. Consequently, an even number of protons does not contribute to...

Diamagnetic Shielding of Nuclei: Local Diamagnetic Current

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An applied magnetic field causes the electrons present in the molecule to circulate, setting up a local diamagnetic current within the molecule. The local diamagnetic current arising from circulating sigma-bonding electrons induces a magnetic field, Blocal that opposes the applied magnetic field, B0. The effective magnetic field experienced by these nuclei is given by the difference between the applied and local magnetic fields in a phenomenon called local diamagnetic shielding. Essentially,...

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Related Experiment Video

Updated: Jun 9, 2026

Magnetic Tweezers for the Measurement of Twist and Torque

Magnetic Tweezers for the Measurement of Twist and Torque

Published on: May 19, 2014

DNA-backbone radio resistivity induced by spin blockade effect.

Ramin M Abolfath¹, Thomas Brabec

¹Department of Radiation Oncology, University of Texas, Southwestern Medical Center, Dallas, Texas 75390, USA. Ramin.Abolfath@utdallas.edu

Journal of Computational Chemistry

|August 27, 2010

Summary

This study demonstrates that controlling the spin-triplet state in DNA can prevent DNA damage by OH free radicals. This spin-blockade effect offers a novel protective mechanism against molecular damage.

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Last Updated: Jun 9, 2026

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Area of Science:

Molecular Biophysics
Quantum Chemistry
Biochemistry

Background:

DNA damage by hydroxyl (OH) free radicals is a significant concern.
Understanding molecular interactions at the quantum level is crucial for developing protective strategies.

Purpose of the Study:

To investigate the coherent control of OH free radicals interacting with DNA's spin-triplet state.
To develop a model Hamiltonian for molecular spin singlet-triplet resonance.
To explore the potential of spin-triplet states in preventing DNA damage.

Main Methods:

Development of a model Hamiltonian for molecular spin singlet-triplet resonance.
Utilizing ab-initio Car-Parrinello molecular dynamics simulations.
Investigating spin-injection rates versus decay rates in organic molecules.

Main Results:

Efficient population of the spin-triplet state in DNA molecules is achievable.
Spin-injection rates can significantly exceed decay rates due to low spin-orbit coupling.
A non-equilibrium free energy barrier, lasting over a microsecond, effectively blocks hydrogen abstraction and DNA damage.

Conclusions:

The spin-triplet state in DNA can be coherently controlled to induce a protective 'spin-blockade' effect.
This mechanism offers a promising avenue for preventing DNA damage from free radicals.
Molecular simulations confirm the feasibility of this spin-blockade strategy.