Figure 2.

(A) MQ-CEST profiles recorded at four temperatures (−15 to 2.4 °C) on a 50 mM sample of [¹³C₆, ¹⁵N₄]-l-arginine dissolved in 50/50% vol H₂O/MeOH at a static magnetic field of 14.1 T and using a 10 Hz B₁ CEST saturation pulse for T_CEST = 250 ms. (B) Corresponding longitudinal exchange, zz-EXSY, data recorded on the same sample. (C) Correlation plot of symmetrical exchange rates obtained from MQ-CEST (abscissa) and from longitudinal exchange (ordinate). The excellent linear correlation between the rates shows that accurate rotational exchange rates, k_ex, can be derived from the MQ-CEST experiment.