3,4,3-LI(1,2-HOPO): In Vitro Formation of Highly Stable Lanthanide Complexes Translates into Efficacious In Vivo Europium Decorporation Page: 6 of 11
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100
60
' 40
020
0
0 2 4 6 8
pH* 5000-6000 4000-5000
* 3000-4000 2000-3000
1000-2000 0-1000:5 pH
1.9
1.6
I 1.4
550 570 590 609 629 648 667
A(nm)
Fig. 3 Re-determination of the stability constants of the [Eu"'(3,4,3-LI(1,2-HOPO))]- complex through direct spectrofluorimetric titration ([Eu"] =
[3,4,3-LI(1,2-HOPO)] = 0.05 mM, 0.1 M KCl, 10 mM MES, 10 mM acetic acid, 25 0C, Xexc= 325 nm, pH 1.3 to 10). Emission spectra shown for the pH
range of 1.4 - 4.5; the luminescence signal increases with the pH, which allows the determination of the stability constants.' Inset. Eu species distribution
in the titration conditions: dotted line = free Eu; dashed line = EuLH; solid line = EuL.
Table 2. Protonation and Eu" Complex Formation Constants for 3,4,3-LI(1,2-HOPO).species
LH
LH2
LH3
LH4
EuL
EuLH
pEu"'m. 1, h
0,1,1
0, 1, 2
0, 1,3
0, 1, 4
1, 1, 0
1,1,1log Pm/h
6.64(1) "]
12.32(1) "]
17.33(1) "]
21.20(1)"]
20.2(2)"I3
21.4(2)"I3
21.1(2)"I3"Previously determined and reported.9
[b]Values experimentally determined in this work, following a previously reported method9 with modified additional titrant increments for more accurate
measurements.
10
As only two lanthanides other than Eul" are sensitized by 3,4,3-LI(1,2-HOPO) to emit luminescence in the visible, with very low
quantum yields, a systematic determination of the stability constants of each complex was not possible through the direct titration
method. However, proton-independent stability constants (Ku = P110) and corresponding conditional stability constants (calculated and
reported as pM values): for the lanthanide series could be determined indirectly through metal competition titrations (Table 1), using
is Eu"I as a reference because of its central position in the series and the remarkable luminescence properties of the corresponding 3,4,3-
LI(1,2-HOPO) complex. In these competition titrations, solutions containing an equimolar ratio of Eul" and 3,4,3-LI(1,2-HOPO) ([Eu"']
= [3,4,3-LI(1,2-Gd(III)/E
Gd(III)/570
620
u(III) 0:1
I
Eu(III) 10:1670
720
XA(nm)
Fig. 4 Spectrofluorimetric competition titration of [Eu"'(3,4,3-LI(1,2-HOPO))]- against Gd(III). [Eu"] = [3,4,3-LI(1,2-HOPO)] = 5 pM, [Gd"] = 0-
20 0.05 mM, 0.1 M KCl, 0.1 M HEPES, pH = 7.4, 25.0 0C, A_ = 325 inn. The luminescence signal resulting from the sensitization of Eu" by 3,4,3-LI(1,2-
HOPO) decreases while the Gd"' concentration increases
HOPO)] = 5 pM, [KCl] = 0.1 M, [HEPES] = 0.1 M, pH 7.4, 25.0 0C) were divided into separate aliquots and the studied lanthanide was
added to reach concentrations varying from 0 to 5 mM. The solutions were allowed to reach equilibrium (when no luminescence change
25 was observed) and the emission spectra recorded (A = 325 nm). The intensity of the [Eu"'(3,4,3-LI(1,2-HOPO))]- emission decreases
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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/m1/6/: accessed July 17, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.