Issue 43, 2017

Toward inert paramagnetic Ni(ii)-based chemical exchange saturation transfer MRI agents

Abstract

The Ni2+ complexes with hexadentate ligands containing two 6-methylpicolinamide groups linked by ethane-1,2-diamine (dedpam) or cyclohexane-1,2-diamine (chxdedpam) spacers were investigated as potential contrast agents in magnetic resonance imaging (MRI). The properties of the complexes were compared to that of the analogues containing 6-methylpicolinate units (dedpa2− and chxdedpa2−). The X-ray structure of the [Ni(dedpam)]2+ complex reveals a six-coordinated metal ion with a distorted octahedral environment. The protonation constants of the dedpa2− and dedpam ligands and the stability constants of their Ni2+ complexes were determined using pH-potentiometry and spectrophotometric titrations (25 °C, 0.15 M NaCl). The [Ni(dedpa)] complex (log KNiL = 20.88(1)) was found to be considerably more stable than the corresponding amide derivative [Ni(dedpam)]2+ (log KNiL = 14.29(2)). However, the amide derivative [Ni(chxdedpam)]2+ was found to be considerably more inert with respect to proton-assisted dissociation than the carboxylate derivative [Ni(chxdedpa)]. A detailed 1H NMR and DFT study was conducted to assign the 1H NMR spectra of the [Ni(chxdedpa)] and [Ni(chxdedpam)]2+ complexes. The observed 1H NMR paramagnetic shifts were found to be dominated by the Fermi contact contribution. The amide resonances of [Ni(chxdedpam)]2+ at 91.5 and 22.2 ppm were found to provide a sizeable chemical exchange saturation transfer effect, paving the way for the development of NiCEST agents based on these rigid non-macrocyclic platforms.

Graphical abstract: Toward inert paramagnetic Ni(ii)-based chemical exchange saturation transfer MRI agents

Supplementary files

Article information

Article type
Paper
Submitted
28 Jul 2017
Accepted
26 Sep 2017
First published
02 Oct 2017

Dalton Trans., 2017,46, 15095-15106

Toward inert paramagnetic Ni(II)-based chemical exchange saturation transfer MRI agents

L. Caneda-Martínez, L. Valencia, I. Fernández-Pérez, M. Regueiro-Figueroa, G. Angelovski, I. Brandariz, D. Esteban-Gómez and C. Platas-Iglesias, Dalton Trans., 2017, 46, 15095 DOI: 10.1039/C7DT02758C

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