Fig. 1.

L-optimized pulse sequences for measuring aromatic ¹³C relaxation parameters. The pulse sequence of the R ₁ relaxation experiment shown in the top panel is divided into two blocks that encode: a polarization transfer from ¹H to ¹³C and the relaxation period; and d the ¹³C evolution period followed by polarization transfer back to ¹H. The R ₂ experiment is obtained by replacing block a with block b, and similarly the {¹H}–¹³C NOE experiment is given by block c. The TROSY transfer sequence of block d can be substituted for the PEP-HSQC sequence given in block e. Each of the three relaxation experiments specified by blocks a–c can be combined with either of blocks d or e. Narrow (wide) filled bars represent 90° (180°) rectangular high power pulses. Grey wide bars in block b represent 180° rectangular CPMG pulses attenuated by 6 dB compared to the other hard pulses. Filled bell-shaped bars represent shaped pulses. Narrow bell-shaped bars on ¹H represent EBURP2 shapes (bandwidth of 6.6 ppm, shifted 2.8 ppm upfield), while wide bell-shaped bars are i-SNOB-5 pulses (bandwidth of 2.7 ppm, shifted 2.5 ppm downfield). Wide bell-shaped pulses on ¹³C represent REBURP shapes (bandwidth 40 ppm). Pulsed field gradients (PFG) are indicated as grey open bars. Phases are x unless otherwise indicated. In all sequences τ_a = 1.5 ms and τ_b = 1.623 ms. The delay δ varies between blocks: in a, δ = 25 ms; in b, δ = 4 ms; and in c, δ = 10 ms. In all experiments echo/anti-echo selection were made during t₁ by reversing ϕ₃, GC, and the even-numbered increments of ϕ_rec. For every second t₁ increment ϕ₂ and ϕ_rec were incremented. Durations and strengths of the gradients are G1 = (1 ms, 10 G/cm); G2 = (0.5 ms, 8 G/cm); G3 = (0.5 ms, 12 G/cm); G4 = (0.5 ms, 16 G/cm), G5 = (0.5 ms, 18 G/cm), GC = (1 ms, −50 G/cm), GH = (0.5 ms, 25 G/cm). The phase cycling for the different experiments is: a + d and b + d, ϕ₁ = (x, x, x, x, −x, −x, −x, −x), ϕ₂ = (y, x, −y, −x), ϕ_rec = (x, −y, −x, y, −x, y, x, −y); c + d, ϕ₂ = (y, x, −y, −x), ϕ_rec = (x, −y, −x, y); a + e and b + e, ϕ₁ = (x, x, −x, −x), ϕ₂ = (y, −y), ϕ_rec = (x, −x, −x, x); c + e, ϕ₂ = (y, −y), ϕ_rec = (x, −x). The phase cycling within the CPMG block is (x, x, y, −y, x, x, −y, y) in b + e, and (y, y, −x, x, y, y, x, −x) in b + d. The phase of the shaped ¹H pulse in middle of the CPMG block is x for CPMG block n and −x for n + 1