Dynamics of local director (LD) vectors connecting two carbons (or a carbon and the phosphate) of a lipid. (A) Plotted are the b-exponents of the best power-law fits to the spectral densities of LD vectors originating from C7 (yellow), C9 (red), and C11 (blue) carbons on the sn-2 chain of DMPC in the cholesterol-free bilayer. The LD vectors are from two (2C) to ten (10C) carbon segments in length or extend all the way to the phosphorus atom (P). Shown for comparison are the exponents of the best power-law fits to the spectral densities of the CH bonds at C7, C9, and C11 carbons (dashed lines). (B) Schematic of all analyzed LD vectors. The CH bond fluctuations correspond most closely to LD vectors of lengths 3–4 carbons, illustrating the segmental nature of the CH bond dynamics. See text for details. To see this figure in color, go online.