Figure 2.

Illustration of dynamics of CH bond fluctuations. (A) Example of (top) autocorrelation function $G_{\mathrm{0,2}}^{\left(9\right)}\left(t\right)$ and (bottom) spectral density function $J_{\mathrm{0,2}}^{\left(9\right)}\left(\omega \right)$ for carbon C9 of the sn-2 chain of DMPC. The results correspond to fluctuations of the CH bonds as described by the Wigner $D_{00}^{\left(2\right)}(\Omega )$ function. Simulation data are shown in gray and best power-law fit to the simulation results in black. Insets show expansion of the data from the highlighted region from 0 to 1000 MHz but in a log-log plot. Shown for comparison are sample functions of the form $a{x}^{-1}$ (purple) and $a{x}^{-1/2}$ (red). (B) Power exponents of best fits to the spectral densities $J_{0,s}^{\left(n\right)}\left(\omega \right)$ for carbons C2–C14 on the sn-1 (red) and sn-2 (blue) chains of DMPC with 0, 20, 33, and 50 mol % cholesterol. The power exponents of all carbons in all simulated bilayers are close to −1/2, consistent with collective segmental dynamics. All simulations were performed at 44°C. See text for details. To see this figure in color, go online.