Figure 6. Orientation-selected Q-band Mims-ENDOR spectra of the paramagnetic intermediate with magnetic nuclei (²H7 and ¹⁵N1) from the substrate DTB.

A, Depiction of the intermediate with the incorporated nuclei ²H7 marked in green, and ¹⁵N1 marked in blue. The geometry of the intermediate is adapted from the DFT model given in Figure 7A & Figure 8B. B, Mims-ENDOR spectra of ²H7-DTB-labled intermediate. C, Mims-ENDOR spectra of ¹⁵N1-DTB-labled intermediate.

Experimental parameters: 10 K, microwave pulse π/2 = 12 ns, τ = 240 ns for ²H7 and 300 ns for ¹⁵N1, RF pulse = 20 μs. Simulation parameters: g = [1.993, 1.941, 1.847]; A(¹⁵N1) = [−0.14, −0.25, −0.39] MHz, Euler angle = [0, 10, 0]°; A(²H7) = [0.03, 0.03, 0.09] MHz, P(²H7) = [−0.02, −0.08, 0.10] MHz, Euler angle = [0, 150, 0]°. All the experimental spectra are in black, while the simulated spectra are colored. The BioB enzyme used to generate the intermediate sample is natural abundant and (guanidino-¹⁵N₂)-arginine enriched for ¹⁵N1-DTB-labeled and ²H7-DTB-labeled intermediate, respectively.