Fig. 4.

Pulse sequence for the 3D J-doubled HNCO experiment. All narrow (wide) pulses are applied with a flip angle of 90° (180°) with a phase of × unless otherwise indicated. ¹H, ¹⁵N and ¹³C carriers are centered at the water resonance, 119 and 175 ppm, respectively. Off-resonance ¹³C^α pulses were centered at 55 ppm. ¹H and ¹⁵N pulses are applied with a pulse width of 9.35 and 38 μs, respectively, except for the rectangular water selective pulses which have a pulse width of 1.12 ms. Rectangular ¹³C 90° pulses are applied with a pulse width of 14 μs, and shaped ¹³C inversion pulses are applied with a g3 profile (225 μs at 800 MHz) (Emsley and Bodenhausen 1990). The delays used are: τ_α = 2.5 ms, T_N = 13 ms, τ_β = 47.79 μs. The following eight step phase cycle is employed: ϕ₁ = x, −x; ϕ₂ = x; ϕ₃ = 4(x), 4(−x); ϕ₄ = 2(x), 2(−x); ϕ_rec = x, 2(−x), x, 2(−x), x, −x, 2(x), −x. Quadrature in F1 and F2 is achieved by the method of States-TPPI on ϕ2 and ϕ₁, respectively. The gradients were set as follows: g1 (0.5 ms, 17.25 G/cm), g2 (5 ms, 4.31 G/cm), g3 (0.2 ms, 4.31 G/cm), g4 (0.2 ms, 5.60 G/cm), g5 (0.5 ms, 4.31 G/cm) and g6 (0.25 ms, 3.24 G/mm)