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Magnetic dipole–dipole interaction, also called dipolar coupling, refers to the direct interaction between two magnetic dipoles. Suppose and are two magnetic moments in space. The potential energy of the interaction is then given by: :: where is the magnetic constant, is a unit vector parallel to the line joining the centers of the two dipoles, and || is the distance between the centers of and . Alternatively, suppose and are gyromagnetic ratios of two spins. Then: :: where is a unit vector in the direction of the line joining the two spins, and || is the distance between them. The force arising from the interaction between and is given by: : == Dipolar coupling and NMR spectroscopy == 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, or additionally also on intermolecular distances in the solid state leading to NMR crystallography notably in amorphous materials. 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) occurs 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 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Magnetic dipole–dipole interaction」の詳細全文を読む スポンサード リンク
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