Highly Luminescent and Stable Hydroxypyridinonate Complexes: A Step Towards New Curium Decontamination Strategies

Abstract

The photophysical properties, solution thermodynamics, and in vivo complex stabilities of Cm(III) complexes formed with multidentate hydroxypyridinonate ligands, 3,4,3-LI(1,2-HOPO) and 5-LIO(Me-3,2-HOPO), are reported. Both chelators were investigated for their ability to act as antenna chromophores for Cm(III), leading to highly sensitized luminescence emission of the metal upon complexation, with long lifetimes (383 and 196 μs for 3,4,3-LI(1,2-HOPO) and 5-LIO(Me-3,2-HOPO), respectively) and remarkable quantum yields (45 % and 16 %, respectively) in aqueous solution. The bright emission peaks were used to probe the electronic structure of the 5f complexes and gain insight into ligand field effects; they were also exploited to determine the high (and proton-independent) stabilities of the corresponding Cm(III) complexes (log β110 = 21.8(4) for 3,4,3-LI(1,2-HOPO) and log β120 = 24.5(5) for 5-LIO(Me-3,2-HOPO)). The in vivo complex stability for both ligands was assessed by using (248) Cm as a tracer in a rodent model, which provided a direct comparison with the in vitro thermodynamic results and demonstrated the great potential of 3,4,3-LI(1,2-HOPO) as a therapeutic Cm(III) decontamination agent.

Intramolecular sensitization of americium luminescence in solution: shining light on short-lived forbidden 5f transitions

“…As expected the maxima of the electronic UV-visible absorption of the Am III complexes, due to π → π* transitions, are located in the UV part of the spectrum, spanning from 315 to 345 nm ( Fig. 2 and Table 1), at the same energies as those observed for the corresponding lanthanide and Cm III complexes ( previously published results 25,28 in the case of 1 and 3 and new data on Eu III and Cm III complexes of 2, ESI Fig. S1 and Table S1 †).…”

“…[16][17][18][19][20][21][22] In contrast, most of our recent work has focused on the indirect modulation of actinide luminescence through the use of sensitizing antenna chelators. [23][24][25] In this process, luminescence of the metal ion is prompted by the excitation of the ligand and subsequent intramolecular energy transfer from a triplet excited state or a singlet intra-ligand charge-transfer excited state of the ligand to the metal ion. 12,26 Using the so-called "antenna" effect therefore leverages the much larger molar absorption coefficients of organic chromophores as compared to those of the weakly absorbing f-f transitions of actinide and lanthanide ions.…”

Siderocalin-mediated recognition, sensitization, and cellular uptake of actinides

“…Emission spectra were recorded on a HORIBA Jobin Yvon IBH FluoroLog-3 spectrofluorimeter, used in steady state mode and luminescence lifetimes were determined with time-correlated single photon counting and multichannel scaling measurements (details provided in SI Appendix). Quantum yields and kinetic parameters were determined as previously described (26,39). The brightness was calculated as the product of the molar absorption coefficient and the luminescence quantum yield.…”

“…We therefore investigated the affinity of Scn for lanthanide and actinide complexes of Ent and of the synthetic octadentate hydroxypyridinonate siderophore analog, 3,4,3-LI(1,2-HOPO) ("HOPO"; Fig. 1A), reported to form some of the most stable, fully coordinated f-element complexes (25,26). Further X-ray diffraction and spectroscopic characterization of the resulting Scn adducts formed with chelated f elements provided crystal structures of protein complexes with four actinide elements (Th, Pu, Am, and Cm), and revealed the protein as an antenna that sensitizes metal luminescence through highly efficient intramolecular energy transfer processes.…”

Investigating subtle 4f vs. 5f coordination differences using kinetically inert Eu(iii), Tb(iii), and Cm(iii) complexes of a coumarin-appended 1,4,7,10-tetraazacyclododecane-1,4,7-triacetate (DO3A) ligand

“…As a stronger competing ligand was needed, series of experiments were conducted using 3,4,3-LI(1,2-HOPO); a synthetic chelator whose solution thermodynamics with Eu(III), Tb(III), and Cm(III) were previously characterized and reported in the literature. [68][69][70] Upon addition of a 2-fold excess of 3,4,3-LI(1,2-HOPO), treatment at 60°C for four days, and 25°C for three days, the three DO3A-coumarin complexes could finally be challenged. In divided into separate aliquots and the competing 3,4,3-LI(1,2-HOPO) ligand were added to reach concentrations varying from 0 to 15 μM.…”