Figure 3.

Polarization transfer in the 2D R2_n^v-driven (n, v = 1 and 2) spin diffusion experiments as a function of the mixing time for (a) C_α-C_β of Leu residue and (b) C_α-C′ of Met residue in [U-¹³C,¹⁵N] N-formyl-Met-Leu-Phe (MLF) tripeptide. The sample was spun at a MAS frequency of 16 kHz. The cross-peak intensities in each spectrum were normalized to those of the corresponding diagonal peaks in the following way: $I_{norm}=\frac{2I_{AB}}{I_{AA}+I_{BB}}$, where I_norm is the normalized cross peak intensity, I_AB is the non-normalized cross peak intensity, I_AAand I_BB are the non-normalized intensities of the corresponding diagonal peaks. The build-up curves corresponding to the different recoupling sequences are color coded as follows: R2₁¹, black; R2₁², blue; R2₂¹, red; R2₂², green; and POST-R2₂¹, purple.