High resolution NMR alignment studies on biomolecules

It is well established that aromatic molecules possessing magnetic susceptibility anisotropies (Δ/sub X/) are aligned by strong magnetic fields (1,2). Although the alignment is counteracted by thermal motion, at high enough fields a net alignment results. Two anisotropic interactions resulting from this alignment have been investigated, namely the dipolar interaction between nuclear spins and the interaction of a nuclear quadrupole with the local electric field gradient caused by its surroundings. These anisotropic nuclear interactions are manifested in the NMR spectra as extra splittings in the NMR lines. A new application of these alignment studies involves the investigation of biomolecules. The nucleotides of DNA, namely adenosine, guanosine, cytidine and thymidine were studied to yield basic Δ/sub X/ values. These basic Δ/sub X/ values are presently being used in studying being synthesized, sequence-specific minihelices (hexamers, octamers and decamers). Stacking of base pairs approximately perpendicular to the major axis of a DNA helix results in a measurable total susceptibility anisotropy of the molecule; the total is expected be an effective sum of the component base susceptibility anisotropies