Spin-state selection for increased confidence in cross-correlation rates measurements.

A new approach is described for measuring chemical shift anisotropy (CSA)/dipolar cross-correlated relaxation (CCR) rates based on the selection of the individual 15N doublet components prior to the relaxation period. The method uses the spin-state-selective element (S3E) of Sørensen and co-authors [Meissner et al. (1997) J. Mag. Reson., 128, 92-97]. The main advantage of the new method compared to other J-resolved experiments is that it does not create problems of additional signal overlap encountered in coupled spectra. At the same time, this approach allows a simpler control of magnetization pathways than the indirect methods. The method is demonstrated for the B3 domain of protein G.