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 res onance frequencies of the individual lines of an AX multiplet in param agnetic systems have been calculated. The implication of the relaxatio n-induced frequency shift of the lines (dynamic frequency shift) for t he accurate measurement of residual dipolar couplings in field-oriente d systems has been discussed. Our simulations indicate that these effe cts may play a role in the precise measurement of residual dipolar cou plings in systems which belong to the small and intermediate tumbling regime, i.e., correlation times less than 5 ns. (C) 1997 Academic Pres s.