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This nuclear magnetic resonance (NMR) causes the spin of the nucleus to flip.The analogy for Earth spinning on its axis would be if Earth flipped so that the north and south poles interchanged and Earth were suddenly spinning in the opposite direction. Just as it would take considerable energy to flip Earth's spinning motion, the nucleus absorbs and emits energy as it flips its spin. With the correct electronic equipment physicists can measure the spectrum of absorbed and emitted energy.
When the nuclear magnetic moment associated with a nuclear spin is placed in an external magnetic field, the different spin states are given different magnetic potential energies. In the presence of the static magnetic field which produces a small amount of spin polarization, a radio frequency signal of the proper frequency can induce a transition between spin states. This "spin flip" places some of the spins in their higher energy state. If the radio frequency signal is then switched off, the relaxation of the spins back to the lower state produces a measurable amount of RF signal at the resonant frequency associated with the spin flip.
A magnetic dipole moment (usually just called "magnetic moment") in a magnetic field will have a potential energy related to its orientation with respect to that field.
Application of NMR
- Solution structure The only method for atomic-resolution structure determination of biomacromolecules in aqueous solutions under near physiological conditions or membrane mimeric environments.
- Molecular dynamics The most powerful technique for quantifying motional properties of biomacromolecules.
- Protein folding The most powerful tool for determining the residual structures of unfolded proteins and the structures of folding intermediates.
- Ionization state The most powerful tool for determining the chemical properties of functional groups in biomacromolecules, such as the ionization states of ionizable groups at the active sites of enzymes.
- Weak intermolecular interactions Allowing weak functional interactions between macrobiomolecules (e.g., those with dissociation constants in the micromolar to millimolar range) to be studied, which is not possible with other technologies.
- Protein hydration A power tool for the detection of interior water and its interaction with biomacromolecules.
- Hydrogen bonding A unique technique for the DIRECT detection of hydrogen bonding interactions.
- Drug screening and design Particularly useful for identifying drug leads and determining the conformations of the compounds bound to enzymes, receptors, and other proteins.
- Native membrane protein Solid state NMR has the potential for determining atomic-resolution structures of domains of membrane proteins in their native membrane environments, including those with bound ligands.
- Metabolite analysis A very powerful technology for metabolite analysis.
- Chemical analysis A matured technique for chemical identification and conformational analysis of chemicals whether synthetic or natural.
- Material science A powerful tool in the research of polymer chemistry and physics.
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