Chemical Sciences: A Manual for CSIR-UGC National Eligibility Test for Lectureship and JRF/Magnetic dipole–dipole interaction

From Wikibooks, open books for an open world
Jump to navigation Jump to search

Magnetic dipole–dipole interaction, also called dipolar coupling, refers to the direct interaction between two magnetic dipoles. The energy of the interaction is as follows:

where ejk is a unit vector parallel to the line joining the centers of the two dipoles. rjk is the distance between two dipoles, mk and mj.

For two interacting nuclear spins:

, and rjk are gyromagnetic ratios of two spins and spin-spin distance respectively.

Dipolar coupling and NMR spectroscopy[edit | edit source]

The direct dipole-dipole coupling is very useful for molecular structural studies, since it depends only on known physical constants and the inverse cube of internuclear distance. Estimation of this coupling provides a direct spectroscopic route to the distance between nuclei and hence the geometrical form of the molecule. Although internuclear magnetic dipole couplings contain a great deal of structural information, in isotropic solution, they average to zero as a result of rotational diffusion. However, their effect on nuclear spin relaxation results in measurable nuclear Overhauser effects (NOEs).

The residual dipolar coupling (RDC) occur if the molecules in solution exhibit a partial alignment leading to an incomplete averaging of spatially anisotropic magnetic interactions i.e. dipolar couplings. RDC measurement provides information on the global folding of the protein-long distance structural information. It also provides information about "slow" dynamics in molecules.

References[edit | edit source]

  • Malcolm H. Levitt , Spin Dynamics: Basics of Nuclear Magnetic Resonance. ISBN 0-471-48922-0.