3,4,3-LI(1,2-HOPO): In Vitro Formation of Highly Stable Lanthanide Complexes Translates into Efficacious In Vivo Europium Decorporation Page: 7 of 11
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upon addition of the competing lanthanide (Fig. 4), dependent on its affinity for the ligand, and corresponding to the formation of the
new complex. The data consisting of sets of emission spectra (Am = 570-720 nm) with varying concentrations of competing lanthanide
ion were imported into the refinement program HypSpec15 and analyzed by nonlinear least-squares refinements. The equilibration of
3,4,3-LI(1,2-HOPO) between EuII and the competing metal was calculated by including the proton association and Eu"I complex
5 formation constants of the ligand (Table 2), as well as the hydrolysis constants of the competing lanthanide ions16 (See ESIt Table Si),
as fixed parameters in the refinements, with the emission intensity resulting exclusively from the sensitization of Eu"', Sm"', or Tb"' by
3,4,3-LI(1,2-HOPO). The refined complex formation constants and corresponding pM values are reported in Table 1.
Stability Increase Along the Lanthanide Series
The stability of the [Ln"I(3,4,3-LI(1,2-HOPO))]- complexes increases along the lanthanide series (Table 1 and Fig. 5), an effect that can
to be attributed to different reasons: (i) the cation radii size, which decreases along the series,23,24 (ii) the coordination number of the
lanthanide, which can vary from 9 to 8, and thus the number of water molecules in the complex inner sphere,25,26 and (iii) the Lewis
acidity of the metal, which increases along the series.27 The number of inner sphere water molecules in the Eu"I complex was determined
previously as zero,9 using the luminescence-based Horrocks equation,28 which could not be reliably applied to the other lanthanides.
Mass spectrometry was used to characterize the complexes and determine the corresponding coordination number. However, only 8-
1s coordinated complexes could be confirmed in negative ion mode (Fig. 6 and ESIt Table S2).
24 123 -
22 -
n21 -
5.20 -
19-
Q18-
17 -
16 -
15U
f " A A A A
A
A
La Ce Pr Nd PmSm Eu Gd Tb Dy Ho Er Tm Yb Lu
Fig. 5 Comparison of the pM values obtained for the Ln" complexes of 3,4,3-LI(1,2-HOPO) (0) and DTPA6(A).La
Prt#14 Nd
Sm
64 EuTb
Dy***1
880 890 900 910
920 930
m/z
Fig. 6 Mass spectra of 50 pM [Ln"'(3,4,3LI-(1,2-HOPO))]- solutions directly injected in the ESI-MS at pH = 7.4 (solid lines). The diamonds
20 represent the theoretical calculated isotope patterns for the complexes.I: C
Er
Tm
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Sturzbecher-Hoehne, Manuel; Ng Pak Leung, Clara; Daleo, Anthony; Kullgren, Birgitta; Prigent, Anne-Laure; Shuh, David K. et al. 3,4,3-LI(1,2-HOPO): In Vitro Formation of Highly Stable Lanthanide Complexes Translates into Efficacious In Vivo Europium Decorporation, article, July 13, 2011; Berkeley, California. (https://digital.library.unt.edu/ark:/67531/metadc827667/m1/7/: accessed July 17, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.