The effect on the lanthanide luminescence of structurally simple Eu(iii) cyclen complexes upon deprotonation of metal bound water molecules and amide based pendant arms

Abstract

A series of substituted 1,4,7,10-tetraazacylcododecane ligands 1-4, possessing sensitizing nitrobenzene or naphthalene antennae, as one of the amide pendant arms, and their complexes with europium(III) were synthesised. The protonation constants and the metal ion stability constants of two of these ligands were determined by potentiometric titration. The pK a of the water molecules coordinated to the complexed metal ion were determined by both luminescent and potentiometric measurements. The luminescence pH dependence of a further three Eu(III) complexes, 5-7, which lack any antennae, were also studied with the aim of gaining a better understanding of the role of the metal bound water molecules in the luminescence properties of such complexes upon direct excitation of the lanthanide ion. The results from these luminescent measurements demonstrate that the Eu(III) emission was significantly modulated as a function of pH for all the complexes, which we assigned to changes occurring in the coordination environment of the ion within the cyclen system, caused by deprotonation of metal bound water molecules and/or deprotonation of pendent amide arms.

Synthesis and Characterisation of First Generation Luminescent Lanthanide Complexes Suitable for Being Adapted for Uptake via the Mannose Receptor

“…It is also improbable that the coordinated -Dmannose residue is responsible for the changes observed in the fluorescent spectra of each complex, as the p a of -Dmannose is 12.08. Therefore, as all of the complexes show evidence of a p a at 7.5 in their fluorescence spectra, but not in the phosphorescent spectra, it is likely that delocalisation centred around the amide bond [25] affects the * band observed at 260 nm in their UV-visible spectra. This effect appears to influence the singlet state of the triazole to a greater extent than the triplet state, resulting in a change in the fluorescent emission whilst the phosphorescence (via energy transfer from the triplet state of the triazole) remains unaffected.…”

Lanthanide luminescence sensing of copper and mercury ions using an iminodiacetate-based Tb(III)-cyclen chemosensor

“…This would enable sensititization of the Tb(III) 5 It was clear from the structure of 1.Tb.Na that possible protonation of the aniline moiety as well as potential deprotonation of the secondary amide (as well as the metal bound water) could perturb the photophysical properties of the Tb(III) complex. 27 In order to quantify the pH dependence of the Tb(III) emission from 1.Tb.Na, we carried out a pH titration, the result of which is shown in Figure 1. Here, the Tb(III) emission corresponding to the 5 D 4 7 F J (J = 6, 5, 4, 3) transition occurring at 490 nm, 545 nm, 586 nm and 622 nm, respectively, showed some change with respect to pH environment, Figure 1.…”

Macrocyclic coordination chemistry

“…A series of tetraamide cyclen chelators were synthesised, including L 44 , with either naphthalene or nitrobenzyl groups to sensitise lanthanide luminescence and the protonation effects on luminescence of the europium(III) complexes determined. 74 Parker and co-workers continued their studies of luminescent lanthanide probes for biological systems by staining the chromosomal DNA of dividing cells using the terbium(III) complex of L 45 . 75 The mechanism of cellular uptake appears to be different from other cell types or complexes, which used macropinocytosis, and certainly warrants further study.…”