Issue 12, 2020

Inert macrocyclic Eu3+ complex with affirmative paraCEST features


We report on a macrocyclic platform based on an 18-membered macrocycle that forms kinetically highly inert paramagnetic complexes and possesses an excellent outlook for the development of bioresponsive paraCEST (paramagnetic chemical exchange saturation transfer) contrast agents. The investigated europium(III) chelate is non-hydrated and contains four amide groups, each possessing two paramagnetically shifted proton resonances distant from bulk water. The X-ray crystal structure and solution studies indicate that the metal ion is ten-coordinated, being directly bound to the six N atoms of the macrocycle and the four amide O atoms of the pendant arms. The complex presents an excellent inertness with respect to dissociation, being stable under a variety of harsh conditions, including highly acidic and basic media or elevated temperatures. The amide protons are in slow-to-intermediate exchange with bulk water, which gives rise to the generation of a strong CEST effect at low probe concentration and saturation powers (∼25% at 5 mM, B1 = 5 μT, 37 °C). We demonstrate the potential of this platform for mapping pH in its microenvironment and foresee potential for the development of diverse paraCEST probes and sensors.

Graphical abstract: Inert macrocyclic Eu3+ complex with affirmative paraCEST features

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Article information

Article type
Research Article
16 Dec 2019
14 Mar 2020
First published
16 Mar 2020
This article is Open Access
Creative Commons BY license

Inorg. Chem. Front., 2020,7, 2274-2286

Inert macrocyclic Eu3+ complex with affirmative paraCEST features

T. Gambino, L. Valencia, P. Pérez-Lourido, D. Esteban-Gómez, M. Zaiss, C. Platas-Iglesias and G. Angelovski, Inorg. Chem. Front., 2020, 7, 2274 DOI: 10.1039/C9QI01612K

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