CEST spectra of A) [Fe(STHP)]2+ (○) and [Fe(TCMC)]2+ (▲); B) [Ni(CCRM)]2+ (◇) and [Ni(NOPE)]2+ (○); C) [Co(NOPE)]2+ (○) and [Co(TCMC)]2+ (▲); D) [Ni(TCMT)]2+ (▲), [Fe(TCMT)]2+ (⋄), and [Co(TCMT)]2+ (○). All samples contained 10 mM complex, 20 mM HEPES buffer pH ~7.4, and 100 mM NaCl B1 = 24 μT (1000 Hz) presaturation for 2 s at 37 ºC,. CEST spectra modified from references [22, 23, 25, 26].