Experimental and theoretical determination of nucleic acid magnetic susceptibility: Importance for the study of dynamics by field-induced residual dipolar couplings

Magnetic susceptibility anisotropies (Δχ) are determined for the nucleic acid bases on the basis of a combined NMR spectroscopic and DFT study. Magnetic field-induced residual dipolar couplings (RDC) measured for the Dickerson dodecamer allow for the determination of a precise value of Δχ for this DNA. A tensor summation employing the results of DFT calculations of the individual base magnetic susceptibility tensors and the known structure of the dodecamer provides a value of Δχ which is in excellent agreement with experiment. The DFT results are shown to provide superior agreement with experiment for the dodecamer and a protein-DNA complex when compared with other sets of values in common use in the literature. The marked discrepancy between our Δχ values and existing sets of values has a direct and significant impact on the interpretation of field-induced anisotropic interactions in terms of biomolecular structure and dynamics. Copyright © 2003 American Chemical Society.