x 10 12 x 10 12 To gain deeper insights into the atomic motions underlying the observed features in the TCFs shown in Figure , the time traces of the χ 1 and χ 2 side chain dihedral angles of ILE61 are plotted in Figure . The χ 1 dihedral angle occupies only one single rotamer state, the gauche(-) conformer at -60°. The restriction of χ 1 limits the motion of the ILE61-C γ,2 methyl group to fast fluctuations inside the single rotamer well, which is linked to the fast singleexponential decay of the TCF on the sub-ns time scale. In contrast, the χ 2 dihedral angle dynamically jumps between several rotamer wells on a nanosecond time scale (Figure and D), explaining the slowly decaying component of the ILE61-C δ TCF. The restricted dynamics of ILE61-C γ,2 and the increased dynamics of ILE61-C δ are supported by the experimental data. 32 MD simulations and NMR experiments are consistent in that ILE61-C γ,2 has a higher CCR rate and methyl axis order parameter than the more flexible ILE61-C δ methyl group (Tables and). This finding is further supported by measured J-couplings, which indicate that the ILE61 χ 1 side chain dihedral angle exclusively populates the gauche(-) rotamer well (Table ). A more comprehensive comparison to the experimental data is given below.