Macrocyclic Pyclen-Based Gd3+ Complex with High Relaxivity and pH Response
- 7 May 2020
- journal article
- research article
- Published by American Chemical Society (ACS) in Inorganic Chemistry
- Vol. 59 (10), 7306-7317
- https://doi.org/10.1021/acs.inorgchem.0c00690
Abstract
We report the synthesis and characterization of the macrocyclic ligand 2,2′-((2-(3,9-bis(carboxymethyl)-3,6,9-triaza-1(2,6)-pyridinacyclodecaphane-6-yl)ethyl)azanediyl)diacetic acid (H4L) and several of its complexes with lanthanide ions. The structure of the free ligand was determined using X-ray diffraction measurements. Two N atoms of the pyclen moiety in the trans position are protonated in the solid state, together with the exocyclic N atom and one of the carboxylate groups of the ligand. The relaxivity of the Gd3+ complex was found to increase from 6.7 mM–1 s–1 at pH 8.6 to 8.5 mM–1 s–1 below pH ≈ 6.0. Luminescence lifetime measurements recorded from H2O and D2O solutions of the Eu3+ complex evidence the presence of a single complex species in solution at low pH (∼5.0) that contains two inner-sphere water molecules. DFT calculations suggest that the coordination environment of the Ln3+ ion is fulfilled by the four N atoms of the pyclen unit, two oxygen atoms of the macrocyclic acetate groups, and an oxygen atom of an exocyclic carboxylate group. The two inner-sphere water molecules complete coordination number nine around the metal ion. At high pH (∼9.3), the lifetime of the excited 5D0 level of Eu3+ displays a biexponential behavior that can be attributed to the presence of two species in solution with hydration numbers of q = 0 and q = 1. The 1H NMR and DOSY spectra recorded from solutions of the Eu3+ and Y3+ complexes reveal a structural change triggered by pH and the formation of small aggregates at high pH values.Keywords
Funding Information
- Ministerio de Ciencia e Innovaci?n
- European Regional Development Fund
- Ministerio de Econom?a y Competitividad (CTQ2016-76756-P, CTQ2016-78499-C6-1-R, CTQ2017-90852-REDC)
- Xunta de Galicia (ED431B 2017/59, ED431D 2017/01)
- Universit? degli Studi del Piemonte Orientale (FAR 2019)
This publication has 107 references indexed in Scilit:
- Self‐Aggregated Dinuclear Lanthanide(III) Complexes as Potential Bimodal Probes for Magnetic Resonance and Optical ImagingChemistry – A European Journal, 2013
- Lower Ligand Denticity Leading to Improved Thermodynamic and Kinetic Stability of the Gd3+ Complex: The Strange Case of OBETAChemistry – A European Journal, 2012
- Europium(III) DOTA-tetraamide Complexes as Redox-Active MRI SensorsJournal of the American Chemical Society, 2012
- A New Gadolinium-Based MRI Zinc SensorJournal of the American Chemical Society, 2009
- OLEX2: a complete structure solution, refinement and analysis programJournal of Applied Crystallography, 2009
- Equilibrium and Formation/Dissociation Kinetics of Some LnIIIPCTA ComplexesInorganic Chemistry, 2006
- Can the Theoretical Fitting of the Proton‐Nuclear‐Magnetic‐Relaxation‐Dispersion (Proton NMRD) Curves of Paramagnetic Complexes Be Improved by Independent Measurement of Their Self‐Diffusion Coefficients?Helvetica Chimica Acta, 2005
- Contrast Agents for Magnetic Resonance Imaging: A Novel Route to Enhanced Relaxivities Based on the Interaction of a GdIII Chelate with Poly-β-cyclodextrinsChemistry – A European Journal, 1999
- Structural and Dynamic Parameters Obtained from 17O NMR, EPR, and NMRD Studies of Monomeric and Dimeric Gd3+ Complexes of Interest in Magnetic Resonance Imaging: An Integrated and Theoretically Self-Consistent Approach1Journal of the American Chemical Society, 1996
- Synthesis, Crystal Structure, and Potentiometry of Pyridine-Containing Tetraaza Macrocyclic Ligands with Acetate Pendant ArmsInorganic Chemistry, 1995