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. Author manuscript; available in PMC: 2017 Jan 13.
Published in final edited form as: Biochim Biophys Acta. 2014 Jun 16;1848(1 Pt B):246–259. doi: 10.1016/j.bbamem.2014.06.004

Fig. 4.

Fig. 4

Illustration of how the orientational distribution function describes average membrane structural properties by travel of the lipid segments. The frame of the CH2 bond is the principal axis system (P) for evaluating the segmental order parameter from solid-state 2H NMR spectroscopy. The main external magnetic field B0 corresponds to the laboratory frame (L). Designations for the Euler angles Ω ≡ (α,β,γ) are: P, principal axis system for 2H nucleus (z-axis parallel to CH2 bond); I, intermediate frame for methylene group motion (z-axis perpendicular to H–C–H plane); M, molecular coordinate system; D, director frame (z-axis is bilayer normal); and L, laboratory system (z-axis along main external magnetic field B0). The closure property from group theory allows the overall rotation of the C–2H bond to the laboratory frame to be expanded or collapsed in terms of various coordinate frames depending on the motional model.