Issue 10, 2018

Mn2+ complexes of open-chain ligands with a pyridine backbone: less donor atoms lead to higher kinetic inertness

Abstract

The kinetic inertness of Mn2+ complexes is an important parameter for the in vivo safety of potential MRI contrast agents. Rigidifying the ligand structure typically leads to reinforced kinetic inertness. In this context, we studied the Mn2+ complexes of three linear poly(amino carboxylate) ligands containing a pyridine moiety in their skeleton and bearing four (L1, L2) or three carboxylates (L3). The thermodynamic stability constants of the complexes formed with Mn2+, Ca2+, Mg2+, Zn2+ and Cu2+ have been determined using pH-potentiometry, 1H relaxometry and UV/Vis spectrophotometry and are close to those of the EDTA analogues. In contrast, and despite the presence of the pyridine in the ligand backbone, the dissociation rates of the complexes are several orders of magnitude higher than that of [Mn(EDTA)]2−, resulting from a very efficient dissociation pathway catalyzed by the direct attack of Cu2+ or Cu(OH)+. Due to the fewer carboxylate functions, ligand L3 is less favorable for metal-assisted dissociation and provides higher kinetic inertness for its Mn2+ chelate than the L1 and L2 analogues. The water exchange of the monohydrated MnL3 complex has been studied in a variable temperature 17O NMR study. The exchange rate is very high, k298ex = 2.8 × 109 s−1, which is among the highest values reported for a Mn2+ complex. The NMRD profiles are typical of small molecular weight Mn2+ chelates (r1p = 2.44 mM−1 s−1 at 25 °C and 20 MHz).

Graphical abstract: Mn2+ complexes of open-chain ligands with a pyridine backbone: less donor atoms lead to higher kinetic inertness

Supplementary files

Article information

Article type
Paper
Submitted
06 Febr. 2018
Accepted
04 Marts 2018
First published
05 Marts 2018

New J. Chem., 2018,42, 8012-8020

Mn2+ complexes of open-chain ligands with a pyridine backbone: less donor atoms lead to higher kinetic inertness

S. Laine, C. S. Bonnet, F. K. Kálmán, Z. Garda, A. Pallier, F. Caillé, F. Suzenet, G. Tircsó and É. Tóth, New J. Chem., 2018, 42, 8012 DOI: 10.1039/C8NJ00648B

To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page.

If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given.

If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page.

Read more about how to correctly acknowledge RSC content.

Social activity

Spotlight

Advertisements