Remarkable Tuning of the Photophysical Properties of Bifunctional Lanthanide tris(Dipicolinates) and its Consequence on the Design of Bioprobes

Abstract

Derivatives of dipicolinic acid with a polyoxyethylene pendant arm at the pyridine 4-position have been functionalized for potential grafting with biological material. Four ligands with different terminal functions (alcohol, methoxy, phtalimide and amine) have been synthesized, which react with trivalent lanthanide ions Ln (III) to yield triple helical [Ln(L) 3] (3-) complexes, as shown by NMR and UV-vis titrations. The tris chelates display large thermodynamic stability with log beta 13 approximately 19-20 for all Eu (III) complexes for instance. Photophysical measurements reveal adequate sensitization of the metal-centered luminescence in the europium (eta sens = 33-72%) and terbium complexes, which is modulated by the nature of the terminal function. The lifetimes of the metal-centered excited states are long, up to 1.4 ms for [Eu(L) 3] (3-) and 1.6 ms for [Tb(L) 3] (3-) at room temperature, in line with hydration numbers essentially equal to zero. Quantum yields are as high as 29% for the [Eu( L ( NH2 )) 3] (3-) and 18% for the [Tb( L ( OH )) 3] (3-) tris chelates in water at physiological pH. These series of complexes demonstrate the extent of fine-tuning achievable for lanthanide luminescent probes and are simple models for investigating the effect of binding to biological molecules on the metal-centered luminescent properties.

Synthesis and cell localization of self-assembled dinuclear lanthanide bioprobes

“…Therefore, we may conclude that the functional groups at the end of the polyoxyethylene arms do not interfere with the formation of the helical complex and do not substantially modify its stability, as reported for tris(dipicolinates) bearing the same substituents [26].…”

“…The replacement of the methoxy function in L C2 with an alcohol leads to a sizeable decrease in quantum yield, from 21 to 14.8 per cent for Eu III but to an increase for Tb III , from 11 to 14.8 per cent. The amine function has a highly detrimental effect on the quantum yields of both Eu III and Tb III helicates, which go down to 2.3 per cent (Eu) and 1.6 per cent (Tb), a tendency opposite to the one reported for the tris(dipicolinates) [26]. Finally, the terminal carboxylate induces a 36-37% decrease in the quantum yields of both Eu III and Tb III helicates.…”

“…Compared with H 2 L C2 , the presence of more hydrophilic end functions can induce different changes in the ligand properties: (i) we have demonstrated that the photophysical properties of tris(dipicolinate) derivatives can be fine-tuned depending on the nature of this group [26] and (ii) potentially, the different polarities of the resulting chelates may lead to different behaviours with respect to cell permeability. Therefore, differently substituted arms have been grafted on the Et 2 L C2OH precursor as follows.…”

The btp [2,6-bis(1,2,3-triazol-4-yl)pyridine] binding motif: a new versatile terdentate ligand for supramolecular and coordination chemistry

“…Of these, the dpa ligand and its derivatives have been well studied over the years, particularly for their use in the formation of luminescent supramolecular self-assemblies with Ln(III) ions, by researchers such as Bünzli, Piguet and Chauvin and their co-workers. [1][2][3][4][5][6][7] Chauvin et al have proposed the use of Cs 3 [Ln(dpa) 3 ] complexes as secondary standards for luminescent quantum yield determination. 8,9 Dpa ligands have also been studied for their interactions with transition metal ions, 10 and in particular amide derivatives of dpa have been studied extensively, including for use in the formation of transition metal-containing interlocked systems, [11][12][13] as a ligand in Cu(II)-promoted hydroxylation of THF 14 as well as coordination chemistry with Ln(III) ions.…”

“…These complexes displayed only ligandcentred emission in solution at room temperature, but in CH 3 CN glasses at 77 K showed behaviour similar to that of terpy analogues, resulting in emission due to Pt(II)-Pt(II) stacking interactions as well as interactions between the aromatic ligands. 61,121 Yam and co-workers reported the synthesis of a series of chloroplatinum(II) complexes [Pt(btp)Cl]X (X = Cl À , PF 6 À , CF 3 SO 3 À ) with ligands 1, 3a, 5, 7 and 32a-c, as well as a range of related luminescent alkynylplatinum(II) complexes. The chloroplatinum(II) complexes were found to be non-luminescent in solution at room temperature, however, the alkynylplatinum(II) complexes were observed to be luminescent, displaying large Stokes shifts, , the only Pd(II) complex of a discrete btp system in the literature, of which a crystal structure was also obtained.…”