Fig. 1. Protein dynamics into the hundreds of nanosecond to microsecond range accessible to NP-assisted solution NMR.

(A) Protein molecules are in fast exchange between their rapidly tumbling free state and a slowly tumbling NP-bound state giving rise to effective transverse spin relaxation rates $R_2^{\text{NP}}$ versus $R_2^{\text{free}}$in the absence of NPs. (B) Simulated dependence of $R_2^{\text{free}}$ in the absence of NPs (blue) and $\mathrm{\Delta }{R}_2=R_2^{\text{NP}}-R_2^{\text{free}}$ in the presence and absence of NPs (red) on the internal correlation time τ_i and motional restriction (S² order parameter), which demonstrates the wide range of time scales sensitively probed by ΔR₂. The blue and red curves were normalized by setting their maximal values to 1.0.