Figure 4.

A) Motional model for the fluctuations of the phenylalanine side chains. The motions around the χ₂ dihedral angle consist of large-angle ring-flips and small-angle fluctuations, parameterized by angle α. The diagram displays sites' connectivities according to the strong collision model, illustrated for one of the C^δ-D bonds. The motion around the χ₁ dihedral angle is modeled via the restricted diffusion of the C^β – C^γ axis along an arc and is approximated by small nearest neighbor jumps. B) Potential corresponding to the model of motions around the χ₂ angle, in which $E_a^{l\text{arg}e}$ and $E_a^{\mathit{small}}$ are the activation energies for the large-angle ring-flips and small-angle fluctuations, respectively.