Figure 1.

(a) Plot of the relative magnetization transfer efficiencies using optimal transfer delays T (see Eqs. 1– 7) for CRIPT, INEPT, and CRINEPT at 750-MHz proton frequency versus molecular size represented by the isotropic rotational correlation time τ_c. The CRIPT graph is shown with a broken line for small τ_c values, to indicate that the optimal transfer time T would be unreasonably long. (b) Plot of the maximal polarization transfer obtainable with CRIPT versus the static magnetic field B_o represented by the corresponding ¹H frequency. The curves were calculated by using Eqs. 1-7 for a ¹⁵N—¹H-moiety located in a β-sheet of a fully ¹⁵N,²H-labeled protein. The following parameters were used (8): r_HN = 1.04 Å, Δσ_H = 15 ppm, and Θ_H = 10°. Remote protons considered are ¹H^N(i − 1), ¹H^N(i + 1), and ¹H^N(j) at distances of 4.3, 4.3, and 3.3 Å, respectively. These are typical values for a β-sheet in a ¹⁵N,²H-labeled protein, where i is the observed residue, (i − 1) and (i + 1) are the sequential neighbors, and j indicates a long-range contact across the β-sheet (1).