8 research outputs found
A Macrocyclic Chelator with Unprecedented Th<sup>4+</sup> Affinity
A novel macrocyclic octadentate ligand
incorporating terephthalamide
binding units has been synthesized and evaluated for the chelation
of Th<sup>4+</sup>. 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 Th<sup>4+</sup> 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 10<sup>54</sup>. 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 <sup>89</sup>Zr-<b>1</b> required elevated temperature and an increased reaction time. <sup>89</sup>Zr-<b>1</b> was more stable than <sup>89</sup>Zr-<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 <sup>89</sup>Zr chelation.</p></div
Biodistribution and clearance of <sup>89</sup>Zr-DFO, <sup>89</sup>Zr-1, and <sup>89</sup>Zr-2 from selected tissues.
<p><sup>89</sup>Zr-<b>DFO</b> demonstrated a more favorable biodistribution than <sup>89</sup>Zr-<b>1</b> and <sup>89</sup>Zr-<b>2</b>. <sup>89</sup>Zr-<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) 1âHydroxypyridin-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 EuÂ(III)
and SmÂ(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 (ÎŚ<sub>tot</sub>) were found to vary with the
linker length, and the same trend was observed for the EuÂ(III) and
SmÂ(III) complexes. The 2LI and 5LI bridged complexes are the brightest (ÎŚ<sub>tot</sub>xÎľ).
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 ÎŚ<sub>tot</sub> trends of the EuÂ(III) and SmÂ(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) 1âHydroxypyridin-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 EuÂ(III)
and SmÂ(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 (ÎŚ<sub>tot</sub>) were found to vary with the
linker length, and the same trend was observed for the EuÂ(III) and
SmÂ(III) complexes. The 2LI and 5LI bridged complexes are the brightest (ÎŚ<sub>tot</sub>xÎľ).
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 ÎŚ<sub>tot</sub> trends of the EuÂ(III) and SmÂ(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 curiumÂ(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>â˛-Bis(1-phenylethyl)-2,6-pyridinedicarboxamide
The enantiomers of <i>N</i>,<i>N</i>â˛-bisÂ(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<sup>III</sup> ions to give stable [Ln<b>L</b><sub>3</sub>]<sup>3+</sup> 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><sub>3</sub>]<sup>3+</sup> complexes [Ln<sup>III</sup> = 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<sup>III</sup>-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<sup>III</sup> 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>â˛-Bis(1-phenylethyl)-2,6-pyridinedicarboxamide
The enantiomers of <i>N</i>,<i>N</i>â˛-bisÂ(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<sup>III</sup> ions to give stable [Ln<b>L</b><sub>3</sub>]<sup>3+</sup> 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><sub>3</sub>]<sup>3+</sup> complexes [Ln<sup>III</sup> = 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<sup>III</sup>-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<sup>III</sup> 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)