The CSA of 15N induces motion-influenced time-dependent magnetic field BCSA(t) on spin 15N which couples to the precessional motion of the nuclear spin and leads to transverse relaxation and line broadening. Chemical Shift Anisotropy (CSA) is defined as the chemical shift difference between the isotropic and anisotropic states. Thus, chemical shifts can provide useful structural information due to their anisotropy. Nuclei which are part of a specific functional group resonate at different frequencies depending on shielding by the local electronic environment and its orientation. Thus, the chemical shift anisotropy (CSA) contributes to nuclear spin relaxation and the interpretation of relaxation data often requires the accurate knowledge of CSA tensors that can be determined from 15N NMR relaxation studies. However, recently several approaches have been proposed to the direct determination of protein dynamics from 15N relaxation data which require no assumption about 15N CSA. Thus, 15N CSA can be directly determined from such relaxation data ( 99JACS8577, 01JACS4567 and 01METH109-339).
