Impact of ligands structure on formation of hydrophilic colloids from their Gd(III) complexes with high magnetic relaxivity
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The present paper introduces specific structure of thiacalixarenes derivatives adopting 1,3-alternate conformation with alkyl-carboxyl substituents as ligands for conversion of their complexes with Gd(III) ions into hydrophilic colloids with longitudinal (r1) and transverse relaxivities (r2) higher than that of Gd(III)-based commercial contrast agents (r1 = 20.53 and r2 = 23.46 mM−1 s−1 at 0.47 T). pH-dependent coordination of Gd(III) ions via carboxyl substituents of the thiacalixarenes is the driving force for the complex formation, while the precipitation of the complexes is the basis for the colloids formation. Tert-butyl and butyl substituents of thiacalixarenes were found to be of crucial impact on the complex precipitation. The specific inner- and outer-sphere ligand environment provided by the thiacalixarene ligands was revealed as the optimal for high r1 and r2 values of the colloids. High relaxivities along with negligible cytotoxicity open up the possibility of their further use as positive contrast agents in magnetic resonance imaging (MRI).
KeywordsCarboxylated thiacalixarenes Longitudinal relaxivity Paramagnetic colloids Hydrophilic colloids Gd(III) ions
We are grateful to RSF (Grant Number 17-13-01013) for financial support of this work.
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