Fig. 4.
Pulse programs (XY and Z) to evaluate the amount of HR and HN polarization present at different points in the sequence used to determine 15N R1 relaxation rates. A 90° readout pulse followed by a Watergate block (boxed) was applied in either point (i), (ii) or (iii). Δ corresponds to the recycle delay used in R1 measurements. Therefore, point (iii) corresponds to the start of the scans under steady-state conditions. The first t1 increment (12 μs) was acquired in the 1D versions of the pulse program. In the XY-pulse scheme the aliphatic protons magnetization remains in the transverse plane and is saturated by the PFG G1 applied before the T period. In the Z-pulse sequence the aliphatic protons magnetization is aligned along the z-axis at the start of this period. The same pulses, delays and PFG as those described in Fig. 1 were used. Phase cycling: Φ1 = 4(x), 4(−x); Φ2 = y, −y; Φ3 = 2(x), 2(−x); Φ4 = 2(x), 2(−x); Φ5 = 2(y), 2(−y); Φ6 = x, −x; Φ7 = 2(x), 2(y), 2(−x), 2(−y); Φ8 = 2(−x), 2(−y), 2(x), 2(y); Φrec = x, −x, x, x