Mono-, Bi-, and Trinuclear Bis-Hydrated Mn2+ Complexes as Potential MRI Contrast Agents

Attila Forgács, Martín Regueiro-Figueroa, José Luis Barriada, David Esteban-Gómez, Andrés De Blas, Teresa Rodríguez-Blas, Mauro Botta, Carlos Platas-Iglesias

Risultato della ricerca: Contributo su rivistaArticolo in rivistapeer review

Abstract

We report a series of ligands containing pentadentate 6,6′-((methylazanediyl)bis(methylene))dipicolinic acid binding units that form mono- (H2dpama), di- (mX(H2dpama)2), and trinuclear (mX(H2dpama)3) complexes with Mn2+ containing two coordinated water molecules per metal ion, which results in pentagonal bipyramidal coordination around the metal ions. In contrast, the hexadentate ligand 6,6′-((ethane-1,2-diylbis(azanediyl))bis(methylene))dipicolinic acid (H2bcpe) forms a complex with distorted octahedral coordination around Mn2+ that lacks coordinated water molecules. The protonation constants of the ligands and the stability constants of the Mn2+, Cu2+, and Zn2+ complexes were determined using potentiometric and spectrophotometric titrations in 0.15 M NaCl. The pentadentate dpama2- ligand and the di- and trinucleating mX(dpama)24- and mX(dpama)36- ligands provide metal complexes with stabilities that are very similar to that of the complex with the hexadentate ligand bcpe2-, with log β101 values in the range 10.1-11.6. Cyclic voltammetry experiments on aqueous solutions of the [Mn(bcpe)] complex reveal a quasireversible system with a half-wave potential of +595 mV versus Ag/AgCl. However, [Mn(dpama)] did not suffer oxidation in the range 0.0-1.0 V, revealing a higher resistance toward oxidation. A detailed 1H NMRD and 17O NMR study provided insight into the parameters that govern the relaxivity for these systems. The exchange rate of the coordinated water molecules in [Mn(dpama)] is relatively fast, (Formula presented.) = (3.06 ± 0.16) × 108 s-1. The trinuclear [mX(Mn(dpama)(H2O)2)3] complex was found to bind human serum albumin with an association constant of 1286 ± 55 M-1 and a relaxivity of the adduct of 45.2 ± 0.6 mM-1 s-1 at 310 K and 20 MHz.

Lingua originaleInglese
pagine (da-a)9576-9587
Numero di pagine12
RivistaInorganic Chemistry
Volume54
Numero di pubblicazione19
DOI
Stato di pubblicazionePubblicato - 23 set 2015

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