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. Author manuscript; available in PMC: 2012 Feb 2.
Published in final edited form as: Chem Rev. 2004 Aug;104(8):3587–3606. doi: 10.1021/cr0304121

Figure 7.

Figure 7

Principles of PISA wheels. (A) Helical wheel showing the 100° arc between adjacent residues that is a consequence of the periodicity of 3.6 residues per turn in an α-helix. (B) Orientations of the principal elements of the spin interaction tensors associated with 15N in a peptide bond. σ11, σ22, and σ33 are the principal elements of the 15N chemical shift interaction tensor, and the 1H–15N dipolar coupling interaction is along the NH bond. σ33 is in the peptide plane and makes an angle of 17° with the NH bond. (C) PISA wheel for an ideal α-helix. (D) Dipolar wave for an ideal α-helix.