Structural origins of diamagnetic anisotropy in proteins.

Magnetic anisotropy in proteins and polypeptides can be attributed to the diamagnetic anisotropy of the planar peptide bonds. The alpha helix in particular has large anisotropy due to the axial alignment of the peptide bonds. The regular arrangements of the peptide bonds in beta pleated sheet and collagen structures also produce substantial anisotropy, but less than for alpha helix. The anisotropy permits orientation of small structures of these types in magnetic fields of several kilogauss.