Proteins and peptides undergo internal motions over a wide range of time scales from picoseconds to milliseconds and longer. Fast motions falling in the picosecond to nanosecond range generally arise from motions of individual bonds or small groups of atoms that are faster than the overall tumbling of the molecule. These fast motions contribute to NMR relaxation parameters, such as, for instance: Internal motions of larger groups of atoms, correlated motions of several residues, segmental motions, and the like usually occurs on the nanosecond to microsecond time scales, whereas conformational reorganization of the entire molecule, like folding-unfolding, occurs on the slower time scale of microseconds to milliseconds. These motions contribute primarily to transverse magnetization as chemical exchange.
Interesting revision articles: 01NAT912 , 01NAT932 , and 01COP555 .
