Bimodal System (Luminophore and Paramagnetic Contrastophore) Derived from Ln(III) Complexes Based on a Bipyridine-Containing Macrocyclic Ligand

Abstract

The synthesis of a new 15-membered polyaza-macrocyclic ligand L3H3, which is based on a 2,2'-bipyridine moiety and a diethylenetriaminetriacetic acid core, is reported. The lanthanide chelates of this octadentate ligand were programmed for bimodal probes, luminescent agents (Sm, Eu, Tb, Dy), and magnetic resonance imaging agents (Gd3+). The neutral 1:1 complexes with these Ln3+ ions were prepared and studied in aqueous solution by luminescence and NMR techniques. The main photophysical characteristics of these complexes (i.e., the absorption and luminescence spectra, the metal-centered lifetimes, and the overall luminescence yields, Phi) were measured. In addition, the role played by nonradiative pathways (vibrational energy transfer involving coordinated water molecules, involvement of ligand-to-metal charge-transfer excited states, or metal --> ligand back transfer) is discussed. The L3.Eu and L3.Tb complexes show very bright luminescence when photoexcited from the lowest-energy absorption band of the bipyridine chromophore. The luminescence quantum yields in an air-equilibrated water solution at room temperature are 0.10 and 0.21, respectively, despite the presence of one water molecule in the first coordination sphere of the metal ion. NMR data show that L3.Gd contains also one H2O molecule in the inner sphere. The proton longitudinal relaxivity, r1, of this complex is 3.4 s(-1) mM(-1) (0.47 T, 310 K) and the rotational correlation time, tau(R), is 57 ps (310 K). These values are comparable to those of the clinically used Gd-DTPA. Interestingly, the water exchange rate between the coordination site and the bulk solvent is slow (tau(M) = 3.5 micros at 310 K). The presence of water molecules in the second sphere and in rapid exchange with the solvent is discussed. Finally, it was found by luminescence and NMR experiments that these lanthanide complexes are stable versus transmetalation by several cations (especially Ca2+ and Zn2+) at physiological pH and have no interaction with blood proteins.

A Versatile Ditopic Ligand System for Sensitizing the Luminescence of Bimetallic Lanthanide Bio‐Imaging Probes

“…Keywords: helical structures · heterometallic complexes · imaging agents · lanthanides · luminescence dine-based cryptands, [16] cyclen derivatives containing coordinating and sensitizing groups, [17] aza-macrocycles incorporating a pyridine, bipyridine or terpyridine unit [18,19] and b-diketonates [20] ), which often have in common the simultaneous use of carboxylate (or amide) and amine coordinating groups.…”

“…This can be done by attaching an organic luminophore onto a contrast agent [35,36] or by developing receptors that are able to bind Gd III and luminescent Ln III ions while preserving the specific physical properties of the metal ions. [19,37,38] Some of these systems bear a targeting vector for cell internalization. [39] Alternatively, the attachment of two magnetic or two luminescent lanthanide ions onto a biologically relevant molecule, such as a protein, brings definitive advantages, as demonstrated recently by the generation of peptide-linked double lanthanide binding tags, which proved to be superior to single tags with respect to luminescence output [40] and X-ray scattering power.…”

Synthesis and Luminescence Properties of Lanthanide Complexes of a Novel Polyaminopolycarboxylate Ligand

“…But the ions' poor ability to absorb light makes it necessary to dress them up with an organic ligand as a skin in the form of a complex. 1 The complexes have become increasingly significant in the last few years due to the wide variety of potential applications in many important areas of chemistry, [2][3][4] biology, [5][6] medicine [7][8] and imaging. [9][10][11][12] The design of the organic part of such complexes is thus paramount in achieving the required circumstances for the complex to be efficiently luminescent.…”

A Water‐Stable and Strongly Luminescent Terbium(III) Macrocyclic Complex Incorporating an Intracyclic Pyrazolylpyridine Chromophore

“…Moreover, in such system, the antenna-to-cation sensitization step occurs between partners in a rigid conformation that can improve the energy-transfer rates. It is worth noting that only a few reports are based on lanthanide binding by macrocyclic compounds incorporating both an intracyclic chromophoric unit and pendant carboxylate groups, [11] whereas numerous examples of photoactive Ln III complexes based on cyclen-derivatived ligands (cyclen is 1,4,7,10-tetraazacyclododecane) where a chromophoric unit is located on the dangling arms are described in the literature. [12] Although the N,C-pyrazolylpyridine unit has been the focus of much less attention than the 2,2Ј-bipyridine moiety, it exhibits promising properties for photon collection and transfer to terbium cations.…”