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. Author manuscript; available in PMC: 2010 May 1.
Published in final edited form as: J Magn Reson. 2008 Dec 14;198(1):1–7. doi: 10.1016/j.jmr.2008.12.007

Figure 3.

Figure 3

Illustration of an α-helix with attached TOAC spin label and applied magnetic field. φ represents the helical tilt angle, ζ, (equal to ψ in the parallel orientation) is the director tilt angle, which is directly measured in the EPR spectrum. ZD is the director axis of the spin label and to the axis directed along the π-orbital, perpendicular to the N-O bond of the TOAC spin label (not shown). αD is the rotation of the spin label around the helix and depends on the residue number, while βD is the angle between the director axis and the helical axis.