Electron spin-nuclear spin cross-correlation effects on multiplet splittings in paramagnetic proteins

The effects of cross-correlation between Curie spin-nuclear dipole and nuclear dipole-nuclear dipole interactions on the line-widths and resonance frequencies of the individual lines of an AX multiplet in paramagnetic systems have been calculated. The implication of the relaxation-induced frequency shift of the lines (dynamic frequency shift) for the accurate measurement of residual dipolar couplings in field-oriented systems has been discussed. Our simulations indicate that these effects may play a role in the precise measurement of residual dipolar couplings in systems which belong to the small and intermediate tumbling regime, i.e., correlation times less than 5 ns. (C) 1997 Academic Press.