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  Stable and inert macrocyclic cobalt(II) and nickel(II) complexes with paraCEST response

Pérez-Lourido, P., Madarasi, E., Antal, F., Esteban-Gómez, D., Wang, G., Angelovski, G., et al. (2022). Stable and inert macrocyclic cobalt(II) and nickel(II) complexes with paraCEST response. Dalton Transactions, 51(4), 1580-1593. doi:10.1039/d1dt03217h.

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Pérez-Lourido, P, Author
Madarasi, E, Author
Antal, F, Author
Esteban-Gómez, D, Author
Wang, G1, 2, Author              
Angelovski, G1, 2, Author              
Platas-Iglesias, C, Author
Tircsó, G, Author
Valencia, L, 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, ou_1497794              

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 Abstract: We report the synthesis of the macrocyclic ligands 3,9-PC2AMH (2,2'-(3,6,9-triaza-1(2,6)-pyridinacyclodecaphane-3,9-diyl)diacetamide) and 3,9-PC2AMtBu (2,2'-(3,6,9-triaza-1(2,6)-pyridinacyclodecaphane-3,9-diyl)bis(N-tert-butyl)acetamide) which contain a pyclen platform functionalized with acetamide or tert-butylacetamide pendant arms at positions 3 and 9 of the macrocyclic unit. The corresponding Co(II) and Ni(II) complexes were prepared, isolated and characterised as potential paramagnetic chemical exchange saturation transfer (paraCEST) agents. The X-ray structures of the Ni(II) complexes reveal six-coordination of the ligands to the metal ion. The Co(II) complex with 3,9-PC2AMtBu shows a similar six-coordinate structure in the solid state, while the Co(II) complex with 3,9-PC2AMH contains a seven-coordinate metal ion, seventh coordination being completed by the presence of an inner-sphere water molecule. The structure of the Co(II) complexes was investigated using 1H NMR spectroscopy and computational methods. The complexes present a seven-coordinate structure in solution, as demonstrated by the analysis of the paramagnetic shifts using density functional theory. Ligand protonation constants and stability constants of the complexes with 3,9-PC2AMH were determined using potentiometric titrations (I = 0,15 M NaCl). The Co(II) complex was found to be more stable than the Ni(II) analogue (log KCoL = 14.46(5) and log KNiL = 13.15(3)). However, the Ni(II) and Co(II) complexes display similar rate constants characterizing the proton-assisted dissociation mechanism. The presence of highly shifted 1H NMR signals due to the amide protons in slow exchange with bulk water results in sizeable CEST signals, which are observed at +67 and +15 ppm for the Co(II) complex with 3,9-PC2AMH and +42 and +7 ppm for the Ni(II) analogue at 25 °C.

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 Dates: 2022-01
 Publication Status: Published in print
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 Identifiers: DOI: 10.1039/d1dt03217h
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Title: Dalton Transactions
  Abbreviation : Dalton Trans.
Source Genre: Journal
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Publ. Info: Cambridge, UK : Royal Society of Chemistry
Pages: - Volume / Issue: 51 (4) Sequence Number: - Start / End Page: 1580 - 1593 Identifier: ISSN: 1477-9226
CoNE: https://pure.mpg.de/cone/journals/resource/954925269323