Figure 1.

Pulse sequences considered in this work to highlight quadrupolar nuclei S bound to labile ¹Hs on the water resonance. a) Spin echo (SE) scheme based on the work of Ronen et al., ^[23] in which S‐decoupling is/is not applied during an echo time TE and the difference on water is observed. b) D‐REX, a FLEX‐inspired scheme in which the S‐spin is/is not highlighted with either hard pulses or with S‐decoupling, and the whole module is repeated N times to port the S‐encoding thus imparted from the S‐bound proton to the water, as driven by exchanges happening during a mixing time t _mix. S‐encoding modes were based on either SEDOR, that is, on applying a series of π pulses i=1 times (as in BIRD ^[51] ), and i=4 or i=8 times using xy‐4 or xy‐8 phase cyclings. ^[52] The S‐effects were also introduced by using a continuous decoupling (CW) scheme; this included an i=0 case representing a jump−return (JR) sequence ^[53] in which τ comprises the full time in between π/2 pulses. c) D‐REST, a saturation transfer scheme in which an RF pulse is applied on protons for a selective saturation, while an S‐decoupling sequence is/is not applied on the S‐spin.