Weak Alignment of Paramagnetic Proteins Warrants Correction for Residual CSA Effects in Measurements of Pseudocontact Shifts.

The article reports that nonisotropic averaging of the nuclear chemical shift Hamiltonian arising from paramagnetic alignment results in residual anisotropic chemical shifts (RACS) which must be taken into account for an accurate analysis of pseudocontact shift data of heteronuclear spins with pronounced chemical shift anisotropy (CSA). It suggests that CSA tensors of 1HN, 15N, and 13C' nuclei have been determined from ΔδRACS observed in the presence of a liquid crystalline medium, from cross-correlated relaxation,and from density functional theory calculations.