CEST properties of 10 – 16. a) Z-spectra and MTRasym for 10 – 12 at 25 mM, pH = 7.2, tsat = 3 s and B1 = 3.6 µT; b) CEST contrast of 12 at 7.5 ppm as a function of concentration, using B1 = 3.6 µT; c) QUESP data of 12 at 25 mM, pH = 7.1, with ksw =0.6 kHz; d) pH dependence of % contrast for 12; e) Analogues of 12 with different CEST peak frequencies from 6 – 8 ppm.