Ln(iii)-complexes of a DOTA analogue with an ethylenediamine pendant arm as pH-responsive PARACEST contrast agents

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Abstract

A novel macrocyclic DO3A derivative containing a linear diamine pendant arm, H3do3aNN, was prepared and its protonation and complexation properties were studied by means of potentiometry. It determined ligand consecutive protonation constants logKAn = 12.62, 10.28, 9.67, 8.30, 3.30 and 1.58 and stability constants of selected lanthanide (Eu(iii), Yb(iii)) complexes logKEuL = 23.16 and logKYbL = 22.76. The complexes could be protonated on the pendant amino group(s) with logK(HLM) ≈ 5.6 and logK(H2LM) ≈ 4.8. Solution structures of both complexes were studied by NMR spectroscopy. The study revealed that the complex species exist exclusively in the form of twisted-square-antiprismatic (TSA) isomers. The complexes show significant pH dependence of the Chemical Exchange Saturation Transfer (CEST) between their amino groups and the bulk water molecules in the pH range of 5-8. Thus, the pH dependence of the magnetization transfer ratio of CEST signals can be used for pH determination using magnetic resonance imaging techniques in a pH range relevant for in vivo conditions.

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Krchová, T., Gálisová, A., Jirák, D., Hermann, P., & Kotek, J. (2016). Ln(iii)-complexes of a DOTA analogue with an ethylenediamine pendant arm as pH-responsive PARACEST contrast agents. Dalton Transactions, 45(8), 3486–3496. https://doi.org/10.1039/c5dt04443j

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