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. Author manuscript; available in PMC: 2019 Jun 26.
Published in final edited form as: Acta Radiol. 2010 Oct;51(8):910–923. doi: 10.3109/02841851.2010.502126

Fig. 6.

Fig. 6

Illustrations of different ligand design concepts for “responsive” PARACEST agents. (a) Introduction of electron-withdrawing or electron-donating substituents into a single aromatic amide side-chain ligand alters water exchange and hence CEST. (b) At physiological pH the binding of Zn2+ to a site above the Eu3+-bound water molecule results in catalysis of proton exchange and “turns off “ CEST. (c) Binding of glucose over the Eu3+-bound water molecule slows water exchange and “turns on” CEST.