Transition metal complexes of the (2,2,2-trifluoroethyl)phosphinate NOTA analogue as potential contrast agents for F magnetic resonance imaging
A new hexadentate 1,4,7-triazacyclononane-based ligand bearing three coordinating methylene-(2,2,2-trifluoroethyl)phosphinate pendant arms was synthesized and its coordination behaviour towards selected divalent (Mg 2+ , Ca 2+ , Mn 2+ , Fe 2+ , Co 2+ , Ni 2+ , Cu 2+ , Zn 2+ ) and trivalent (Cr 3+ ,...
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| Published in | Dalton transactions : an international journal of inorganic chemistry Vol. 53; no. 22; pp. 9267 - 9285 |
|---|---|
| Main Authors | , , , , , , , |
| Format | Journal Article |
| Published |
04.06.2024
|
| Online Access | Get full text |
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| Summary: | A new hexadentate 1,4,7-triazacyclononane-based ligand bearing three coordinating methylene-(2,2,2-trifluoroethyl)phosphinate pendant arms was synthesized and its coordination behaviour towards selected divalent (Mg
2+
, Ca
2+
, Mn
2+
, Fe
2+
, Co
2+
, Ni
2+
, Cu
2+
, Zn
2+
) and trivalent (Cr
3+
, Fe
3+
, Co
3+
) transition metal ions was studied. The ligand forms stable complexes with late divalent transition metal ions (from Co
2+
to Zn
2+
) and the complexes of these metal ions are formed above pH ∼3. A number of complexes with divalent metal ions were structurally characterized by means of single-crystal X-ray diffraction. The complex of the larger Mn
2+
ion adopts a twisted trigonally antiprismatic geometry with a larger coordination cavity and smaller torsion of the pendant arms, whereas the smaller ions Ni
2+
, Cu
2+
and Zn
2+
form octahedral species with a smaller cavity and larger pendant arm torsion. In the case of the Co
2+
complexes, both coordination arrangements were observed. The complexes with paramagnetic metal ions were studied from the point of view of potential utilization in
19
F magnetic resonance imaging. A significant shortening of the
19
F NMR longitudinal relaxation times was observed: a sub-millisecond range for complexes of Cr
3+
, Mn
2+
and Fe
3+
with symmetric electronic states (
t
2g
3
and HS-
d
5
), the millisecond range for the Ni
2+
and Cu
2+
complexes and tens of milliseconds for the Co
2+
complex. Such short relaxation times are consistent with a short distance between the paramagnetic metal ion and the fluorine atoms (∼5.5-6.5 Å). Among the redox-active complexes (Mn
3+
/Mn
2+
, Fe
3+
/Fe
2+
, Co
3+
/Co
2+
, Cu
2+
/Cu
+
), the cobalt complexes show sufficient stability and a paramagnetic-diamagnetic changeover with the redox potential lying in a physiologically relevant range. Thus, the Co
3+
/Co
2+
complex pair can be potentially used as a smart redox-responsive contrast agent for
19
F MRI.
A new hexadentate 1,4,7-triazacyclononane-based ligand bearing methylene-(2,2,2-trifluoroethyl)phosphinate pendant arms was synthesized and its complexes with selected metal ions were studied. |
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| Bibliography: | 2327147-2327158 For ESI and crystallographic data in CIF or other electronic format see DOI Electronic supplementary information (ESI) available: HPLC data, details on refinement of the crystal structures, discussion of the crystal structures of organic intermediates, molecular structures found in the crystal structures, selected geometric parameters, NMR spectra of the prepared compounds, UV-Vis spectra of selected complexes, distribution diagrams of the studied systems, and visualization of spectro-electrochemical experiments. CCDC https://doi.org/10.1039/d4dt00507d |
| ISSN: | 1477-9226 1477-9234 |
| DOI: | 10.1039/d4dt00507d |