Supramolecular assemblies based on amphiphilic Mn2+-complexes as high relaxivity MRI probes??

Dalton Transactions Pub Date: 2018-05-18 DOI: 10.1039/C8DT01250D

Abstract

In the research field of MRI contrast agents (CAs), amphiphilic paramagnetic complexes are typically sought for the increased plasmatic half-life and high relaxivity values, but limited examples of amphiphilic Mn2+-based CAs have been reported to date. In this work the Mn2+-complexes of six original amphiphilic ligands (three EDTA-like ligands and three 1,4-DO2A derivatives) embodying one or two aliphatic chains were evaluated as potential MRI contrast agents and compared. Strong self-association into micelles resulted in a relaxivity (r1) enhancement (ca. 80% with respect to MnEDTA) as a consequence of the increased molecular tumbling rate of the supramolecular aggregate. In the case of bis-substituted systems the r1 gain is much higher due to the restricted local rotation of the chelates about the pendant aliphatic chains (r1 in the range 12.6–18.4 mM?1 s?1, 2–3 times higher than for the micelles obtained with single-chain EDTA systems). Furthermore, these amphiphilic chelates tightly bind to human serum albumin (HSA) with association constants KA in the range 104–105 M?1. The resulting supramolecular adducts achieve remarkable relaxivity values, in the range 50–60 mM?1 s?1 for the MnEDTA-like chelates and 27–30 mM?1 s?1 for the 1,4-DO2A-like systems (at 298 K and 20 MHz), thanks to their fast water exchange rate.

Graphical abstract: Supramolecular assemblies based on amphiphilic Mn2+-complexes as high relaxivity MRI probes
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