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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.
Note that the electron spin magnetic moment is opposite to the electron spin while the proton spin magnetic moment is in the direction of the proton spin. The electron spin or proton spin will tend to precess around the magnetic field with a frequency traditionally called the Larmor frequency. For a 1 Tesla magnetic field this Larmor frequency would be
The Larmor frequency can be visualized classically in terms of the precession of the magnetic moment around the magnetic field, analogous to the precession of a spinning top around the gravity field. It can also be visualized quantum mechanically in terms of the quantum energy of transition between the two possible spin states for spin 1/2
Applications 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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