TY - JOUR
T1 - Mono-, Bi-, and Trinuclear Bis-Hydrated Mn2+ Complexes as Potential MRI Contrast Agents
AU - Forgács, Attila
AU - Regueiro-Figueroa, Martín
AU - Barriada, José Luis
AU - Esteban-Gómez, David
AU - De Blas, Andrés
AU - Rodríguez-Blas, Teresa
AU - Botta, Mauro
AU - Platas-Iglesias, Carlos
N1 - Publisher Copyright:
© 2015 American Chemical Society.
PY - 2015/9/23
Y1 - 2015/9/23
N2 - 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.
AB - 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.
UR - http://www.scopus.com/inward/record.url?scp=84942934285&partnerID=8YFLogxK
U2 - 10.1021/acs.inorgchem.5b01677
DO - 10.1021/acs.inorgchem.5b01677
M3 - Article
SN - 0020-1669
VL - 54
SP - 9576
EP - 9587
JO - Inorganic Chemistry
JF - Inorganic Chemistry
IS - 19
ER -