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  Unexpected Trends in the Stability and Dissociation Kinetics of Lanthanide(III) Complexes with Cyclen-Based Ligands across the Lanthanide Series

Garda, Z., Nagy, V., Rodríguez-Rodríguez, A., Pujales-Paradela, R., Patinec, V., Angelovski, G., et al. (2020). Unexpected Trends in the Stability and Dissociation Kinetics of Lanthanide(III) Complexes with Cyclen-Based Ligands across the Lanthanide Series. Inorganic Chemistry, 59(12), 8184-8195. doi:10.1021/acs.inorgchem.0c00520.

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Item Permalink: http://hdl.handle.net/21.11116/0000-0006-5022-9 Version Permalink: http://hdl.handle.net/21.11116/0000-0006-905A-2
Genre: Journal Article

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Garda, Z, Author
Nagy, V, Author
Rodríguez-Rodríguez, A, Author
Pujales-Paradela, R, Author
Patinec, V, Author
Angelovski, G1, 2, Author              
Tóth, E, Author
Kálmán, FK, Author
Esteban-Gómez, D, Author
Tripier, R, Author
Platas-Iglesias, C, Author
Tircsó, G, Author
Affiliations:
1Research Group MR Neuroimaging Agents, Max Planck Institute for Biological Cybernetics, Max Planck Society, ou_2528691              
2Max Planck Institute for Biological Cybernetics, Max Planck Society, Spemannstrasse 38, 72076 Tübingen, DE, ou_1497794              

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 Abstract: We report a detailed study of the thermodynamic stability and dissociation kinetics of lanthanide complexes with two ligands containing a cyclen unit, a methyl group, a picolinate arm, and two acetate pendant arms linked to two nitrogen atoms of the macrocycle in either cis (1,4-H3DO2APA) or trans (1,7-H3DO2APA) positions. The stability constants of the Gd3+ complexes with these two ligands are very similar, with log KGdL values of 16.98 and 16.33 for the complexes of 1,4-H3DO2APA and 1,7-H3DO2APA, respectively. The stability constants of complexes with 1,4-H3DO2APA follow the usual trend, increasing from log KLaL = 15.96 to log KLuL = 19.21. However, the stability of [Ln(1,7-DO2APA)] complexes decreases from log K = 16.33 for Gd3+ to 14.24 for Lu3+. The acid-catalyzed dissociation rates of the Gd3+ complexes differ by a factor of ∼15, with rate constants (k1) of 1.42 and 23.5 M-1 s-1 for [Gd(1,4-DO2APA)] and [Gd(1,7-DO2APA)], respectively. This difference is magnified across the lanthanide series to reach a 5 orders of magnitude higher k1 for [Yb(1,7-DO2APA)] (1475 M-1 s-1) than for [Yb(1,4-DO2APA)] (5.79 × 10-3 M-1 s-1). The acid-catalyzed mechanism involves the protonation of a carboxylate group, followed by a cascade of proton-transfer events that result in the protonation of a nitrogen atom of the cyclen unit. Density functional theory calculations suggest a correlation between the strength of the Ln-Ocarboxylate bonds and the kinetic inertness of the complex, with stronger bonds providing more inert complexes. The 1H NMR resonance of the coordinated water molecule in the [Yb(1,7-DO2APA)] complex at 176 ppm provides a sizable chemical exchange saturation transfer effect thanks to a slow water exchange rate of (15.9 ± 1.6) × 103 s-1.

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 Dates: 2020-052020-06
 Publication Status: Published in print
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 Identifiers: DOI: 10.1021/acs.inorgchem.0c00520
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Title: Inorganic Chemistry
  Abbreviation : Inorg. Chem.
Source Genre: Journal
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Publ. Info: Washington, DC : American Chemical Society
Pages: - Volume / Issue: 59 (12) Sequence Number: - Start / End Page: 8184 - 8195 Identifier: ISSN: 0020-1669
CoNE: https://pure.mpg.de/cone/journals/resource/0020-1669