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Frías JC, Soriano J, Blasco S, García-España E, Rodríguez-Rodríguez A, Esteban-Gómez D, Carniato F, Botta M, Platas-Iglesias C, Albelda MT. Macrocyclic Pyclen-Based Gd 3+ Complex with High Relaxivity and pH Response. Inorg Chem 2020; 59:7306-7317. [PMID: 32379437 DOI: 10.1021/acs.inorgchem.0c00690] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
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.
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Affiliation(s)
- Juan C Frías
- Departamento de Ciencias Biomédicas, Universidad CEU-Cardenal Herrera, CEU Universities, C/Ramón y Cajal, s/n, 46115 Alfara del Patriarca, Valencia, Spain
| | - José Soriano
- Departamento de Quı́mica Inorgánica, Instituto de Ciencia Molecular, Universidad de Valencia, Edificio de Institutos de Paterna, Apdo 22085, 46071 Valencia, Spain
| | - Salvador Blasco
- Departamento de Quı́mica Inorgánica, Instituto de Ciencia Molecular, Universidad de Valencia, Edificio de Institutos de Paterna, Apdo 22085, 46071 Valencia, Spain
| | - Enrique García-España
- Departamento de Quı́mica Inorgánica, Instituto de Ciencia Molecular, Universidad de Valencia, Edificio de Institutos de Paterna, Apdo 22085, 46071 Valencia, Spain
| | - Aurora Rodríguez-Rodríguez
- Centro de Investigacións Cientı́ficas Avanzadas (CICA) and Departamento de Quı́mica, Universidade da Coruña, Campus da Zapateira-Rúa da Fraga 10, 15008 A Coruña, Spain
| | - David Esteban-Gómez
- Centro de Investigacións Cientı́ficas Avanzadas (CICA) and Departamento de Quı́mica, Universidade da Coruña, Campus da Zapateira-Rúa da Fraga 10, 15008 A Coruña, Spain
| | - Fabio Carniato
- Dipartimento di Scienze e Innovazione Tecnologica, Università del Piemonte Orientale "A. Avogadro", Viale T. Michel 11, 15121 Alessandria, Italy
| | - Mauro Botta
- Dipartimento di Scienze e Innovazione Tecnologica, Università del Piemonte Orientale "A. Avogadro", Viale T. Michel 11, 15121 Alessandria, Italy
| | - Carlos Platas-Iglesias
- Centro de Investigacións Cientı́ficas Avanzadas (CICA) and Departamento de Quı́mica, Universidade da Coruña, Campus da Zapateira-Rúa da Fraga 10, 15008 A Coruña, Spain
| | - M Teresa Albelda
- Departamento de Quı́mica Inorgánica, Universidad de Valencia, C/Dr. Moliner 50, 46100 Burjasot, Valencia, Spain
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