A Macrocyclic Chelator with Unprecedented Th⁴⁺ Affinity

A novel macrocyclic octadentate ligand incorporating terephthalamide binding units has been synthesized and evaluated for the chelation of Th⁴⁺. The thorium complex was structurally characterized by X-ray diffraction and in solution with kinetic studies and spectrophotometric titrations. Dye displacement kinetic studies show that the ligand is a much more rapid chelator of Th⁴⁺ than prevailing ligands (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid and diethylenetriaminepentaacetic acid). Furthermore, the resulting complex was found to have a remarkably high thermodynamic stability, with a formation constant of 10⁵⁴. These data support potential radiotherapeutic applications

Evaluation of macrocyclic hydroxyisophthalamide ligands as chelators for zirconium-89

<div><p>The development of bifunctional chelators (BFCs) for zirconium-89 immuno-PET applications is an area of active research. Herein we report the synthesis and evaluation of octadentate hydroxyisophthalamide ligands (<b>1</b> and <b>2</b>) as zirconium-89 chelators. While both radiometal complexes could be prepared quantitatively and with excellent specific activity, preparation of ⁸⁹Zr-<b>1</b> required elevated temperature and an increased reaction time. ⁸⁹Zr-<b>1</b> was more stable than ⁸⁹Zr-<b>2</b> when challenged <i>in vitro</i> by excess DTPA or serum proteins and <i>in vivo</i> during acute biodistribution studies. Differences in radiometal complex stability arise from structural changes between the two ligand systems, and suggest further ligand optimization is necessary to enhance ⁸⁹Zr chelation.</p></div

Biodistribution and clearance of ⁸⁹Zr-DFO, ⁸⁹Zr-1, and ⁸⁹Zr-2 from selected tissues.

<p>⁸⁹Zr-<b>DFO</b> demonstrated a more favorable biodistribution than ⁸⁹Zr-<b>1</b> and ⁸⁹Zr-<b>2</b>. ⁸⁹Zr-<b>DFO</b> data is taken from reference <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0178767#pone.0178767.ref019" target="_blank">19</a>.</p

Effects of Ligand Geometry on the Photophysical Properties of Photoluminescent Eu(III) and Sm(III) 1‑Hydroxypyridin-2-one Complexes in Aqueous Solution

A series of 10 tetradentate 1-hydroxy-pyridin-2-one (1,2-HOPO) ligands and corresponding eight-coordinated photoluminescent Eu­(III) and Sm­(III) complexes were prepared. Generally, the ligands differ by the linear (nLI) aliphatic linker length, from 2 to 8 methylene units between the bidentate 1,2-HOPO chelator units. The photoluminescent quantum yields (Φ_tot) were found to vary with the linker length, and the same trend was observed for the Eu­(III) and Sm­(III) complexes. The 2LI and 5LI bridged complexes are the brightest (Φ_totxε). The change in ligand wrapping pattern between 2LI and 5LI complexes observed by X-ray diffraction (XRD) is further supported by density functional theory (DFT) calculations. The bimodal Φ_tot trends of the Eu­(III) and Sm­(III) complexes are rationalized by the change in ligand wrapping pattern as the bridge (<i>n</i>LI) is increased in length

Effects of Ligand Geometry on the Photophysical Properties of Photoluminescent Eu(III) and Sm(III) 1‑Hydroxypyridin-2-one Complexes in Aqueous Solution

A series of 10 tetradentate 1-hydroxy-pyridin-2-one (1,2-HOPO) ligands and corresponding eight-coordinated photoluminescent Eu­(III) and Sm­(III) complexes were prepared. Generally, the ligands differ by the linear (nLI) aliphatic linker length, from 2 to 8 methylene units between the bidentate 1,2-HOPO chelator units. The photoluminescent quantum yields (Φ_tot) were found to vary with the linker length, and the same trend was observed for the Eu­(III) and Sm­(III) complexes. The 2LI and 5LI bridged complexes are the brightest (Φ_totxε). The change in ligand wrapping pattern between 2LI and 5LI complexes observed by X-ray diffraction (XRD) is further supported by density functional theory (DFT) calculations. The bimodal Φ_tot trends of the Eu­(III) and Sm­(III) complexes are rationalized by the change in ligand wrapping pattern as the bridge (<i>n</i>LI) is increased in length

Circularly Polarized Luminescence of Curium: A New Characterization of the 5f Actinide Complexes

A key distinction between the lanthanide (4f) and the actinide (5f) transition elements is the increased role of f-orbital covalent bonding in the latter. Circularly polarized luminescence (CPL) is an uncommon but powerful spectroscopy which probes the electronic structure of chiral, luminescent complexes or molecules. While there are many examples of CPL spectra for the lanthanides, this report is the first for an actinide. Two chiral, octadentate chelating ligands based on orthoamide phenol (IAM) were used to complex curium­(III). While the radioactivity kept the amount of material limited to micromole amounts, spectra of the highly luminescent complexes showed significant emission peak shifts between the different complexes, consistent with ligand field effects previously observed in luminescence spectra

Structural and Photophysical Properties of Visible- and Near-IR-Emitting Tris Lanthanide(III) Complexes Formed with the Enantiomers of <i>N</i>,<i>N</i>′-Bis(1-phenylethyl)-2,6-pyridinedicarboxamide

The enantiomers of <i>N</i>,<i>N</i>′-bis­(1-phenylethyl)-2,6-pyridinedicarboxamide (<b>L</b>), namely, (<i>R</i>,<i>R</i>)-<b>1</b>, and (<i>S</i>,<i>S</i>)-<b>1</b>, react with Ln^III ions to give stable [Ln<b>L</b>₃]³⁺ complexes in an anhydrous acetonitrile solution and in the solid state, as evidenced by electrospray ionization mass spectrometry, NMR, luminescence titrations, and their X-ray crystal structures, respectively. All [Ln<b>L</b>₃]³⁺ complexes [Ln^III = Eu, Gd, Tb, and Yb; <b>L</b> = (<i>R</i>,<i>R</i>)-<b>1</b> and (<i>S</i>,<i>S</i>)-<b>1</b>] are isostructural and crystallize in the cubic space group <i>I</i>23. Although the small quantum yields of the Ln^III-centered luminescence clearly point to the poor efficiency of the luminescence sensitization by the ligand and the intersystem crossing and ligand-to-metal energy transfers, the ligand triplet-excited-state energy seems relatively well suited to sensitize many Ln^III ion's emission for instance, in the visible (Eu and Tb), near-IR (Nd and Yb), or both regions (Pr, Sm, Dy, Er, and Tm)

Structural and Photophysical Properties of Visible- and Near-IR-Emitting Tris Lanthanide(III) Complexes Formed with the Enantiomers of <i>N</i>,<i>N</i>′-Bis(1-phenylethyl)-2,6-pyridinedicarboxamide

The enantiomers of <i>N</i>,<i>N</i>′-bis­(1-phenylethyl)-2,6-pyridinedicarboxamide (<b>L</b>), namely, (<i>R</i>,<i>R</i>)-<b>1</b>, and (<i>S</i>,<i>S</i>)-<b>1</b>, react with Ln^III ions to give stable [Ln<b>L</b>₃]³⁺ complexes in an anhydrous acetonitrile solution and in the solid state, as evidenced by electrospray ionization mass spectrometry, NMR, luminescence titrations, and their X-ray crystal structures, respectively. All [Ln<b>L</b>₃]³⁺ complexes [Ln^III = Eu, Gd, Tb, and Yb; <b>L</b> = (<i>R</i>,<i>R</i>)-<b>1</b> and (<i>S</i>,<i>S</i>)-<b>1</b>] are isostructural and crystallize in the cubic space group <i>I</i>23. Although the small quantum yields of the Ln^III-centered luminescence clearly point to the poor efficiency of the luminescence sensitization by the ligand and the intersystem crossing and ligand-to-metal energy transfers, the ligand triplet-excited-state energy seems relatively well suited to sensitize many Ln^III ion's emission for instance, in the visible (Eu and Tb), near-IR (Nd and Yb), or both regions (Pr, Sm, Dy, Er, and Tm)