Lanthanide-Based T2ex and CEST Complexes Provide Insights into the Design of pH Sensitive MRI Agents

Lei Zhang, André F. Martins, Piyu Zhao, Yunkou Wu, Gyula Tircsó, A. Dean Sherry

Research output: Contribution to journalArticlepeer-review

13 Scopus citations


The CEST and T1/T2 relaxation properties of a series of Eu3+ and Dy3+ DOTA-tetraamide complexes with four appended primary amine groups are measured as a function of pH. The CEST signals in the Eu3+ complexes show a strong CEST signal after the pH was reduced from 8 to 5. The opposite trend was observed for the Dy3+ complexes where the r2ex of bulk water protons increased dramatically from ca. 1.5 mm−1 s−1 to 13 mm−1 s−1 between pH 5 and 9 while r1 remained unchanged. A fit of the CEST data (Eu3+ complexes) to Bloch theory and the T2ex data (Dy3+ complexes) to Swift–Connick theory provided the proton-exchange rates as a function of pH. These data showed that the four amine groups contribute significantly to proton-catalyzed exchange of the Ln3+-bound water protons even though their pKa’s are much higher than the observed CEST or T2ex effects. This demonstrated the utility of using appended acidic/basic groups to catalyze prototropic exchange for imaging tissue pH by MRI.

Original languageEnglish (US)
Pages (from-to)16626-16630
Number of pages5
JournalAngewandte Chemie - International Edition
Issue number52
StatePublished - Dec 22 2017
Externally publishedYes


  • MRI contrast agents
  • amide ligands
  • chemical exchange saturation transfer (CEST)
  • lanthanide complexes
  • pH responsive

ASJC Scopus subject areas

  • Catalysis
  • General Chemistry


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