Figure 4.

2D ¹⁵N-¹³C selective correlation experiment focused on the Arg-¹³C_γ-¹⁵N_ε of bR. The sequence described in Figure 1 was employed with a 1.98 ms Gaussian refocusing pulse, and TPPM decoupling optimized to reduce transverse dephasing. The REDOR mixing time of 4 ms was chosen to favor short distances (~2.4–2.5 Å). The spinning frequency was 7.576 kHz, and all DNP experiments were conducted in dark-adapted bacteriorhodopsin (90 K), as described elsewhere.