Tuning the Redox Sensitivity of MnII/MnIII-Bispidine MRI Probes by the Introduction of a Phenolate Donor

Abstract

In the objective of exploiting the MnII/III redox couple combined with the bispidine scaffold for the development of redox-responsive magnetic resonance imaging (MRI) probes, we have designed and synthesized H3L1 ligand, featuring a phenol pendant arm. This novel ligand is hypothesized to lower the MnII/III redox potential relative to previously reported derivatives, while retaining the high kinetic inertness and good relaxivity properties characteristic of MnII bispidine complexes. The [MnIIL1(H2O)]- complex exhibits high thermodynamic stability (log KMnIIL1 = 14.2), notable kinetic inertness (dissociation half-life, t1/2 = 20.4 h at pH 6 in the presence of 50 equiv of ZnII), and high relaxivity (r1 = 3.91 mM–1s–1 at 60 MHz, 25 °C, pH 7), highlighting the suitability of the MnII complex as a platform for MRI probe development. Electrochemical studies revealed a significantly lower oxidation potential (E1/2 = 306 mV vs SCE) compared to other Mn-bispidine chelates, enabling successful synthesis of the oxidized [MnIIIL1] form in methanol. Although the aqueous stability of the +III oxidation state remains limited and highly dependent on water content, these results demonstrate that the incorporation of a phenolate donor effectively tunes the MnII/III redox properties of the bispidine scaffold.

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BibTeX RIS

BibTeX

@article{mahamoud2026tuning,
  title = {{Tuning the Redox Sensitivity of MnII/MnIII-Bispidine MRI Probes by the Introduction of a Phenolate Donor}},
  author = {Anli Mahamoud and Zoltán Garda and Jean Bouvet and Daouda Ndiaye and Clotilde Policar and Mourad Elhabiri and Éva Tóth and Aline Nonat},
  journal = {Inorganic Chemistry},
  year = {2026},
  month = jul,
  doi = {10.1021/acs.inorgchem.6c01966},
  url = {https://hal.science/hal-05843456v1},
  note = {CC BY-NC-ND 4.0},
}

RIS

TY  - JOUR
TI  - Tuning the Redox Sensitivity of MnII/MnIII-Bispidine MRI Probes by the Introduction of a Phenolate Donor
AU  - Anli Mahamoud
AU  - Zoltán Garda
AU  - Jean Bouvet
AU  - Daouda Ndiaye
AU  - Clotilde Policar
AU  - Mourad Elhabiri
AU  - Éva Tóth
AU  - Aline Nonat
PY  - 2026
DA  - 2026/07/22
JO  - Inorganic Chemistry
DO  - 10.1021/acs.inorgchem.6c01966
UR  - https://hal.science/hal-05843456v1
AB  - In the objective of exploiting the MnII/III redox couple combined with the bispidine scaffold for the development of redox-responsive magnetic resonance imaging (MRI) probes, we have designed and synthesized H3L1 ligand, featuring a phenol pendant arm. This novel ligand is hypothesized to lower the MnII/III redox potential relative to previously reported derivatives, while retaining the high kinetic inertness and good relaxivity properties characteristic of MnII bispidine complexes. The [MnIIL1(H2O)]- complex exhibits high thermodynamic stability (log KMnIIL1 = 14.2), notable kinetic inertness (dissociation half-life, t1/2 = 20.4 h at pH 6 in the presence of 50 equiv of ZnII), and high relaxivity (r1 = 3.91 mM–1s–1 at 60 MHz, 25 °C, pH 7), highlighting the suitability of the MnII complex as a platform for MRI probe development. Electrochemical studies revealed a significantly lower oxidation potential (E1/2 = 306 mV vs SCE) compared to other Mn-bispidine chelates, enabling successful synthesis of the oxidized [MnIIIL1] form in methanol. Although the aqueous stability of the +III oxidation state remains limited and highly dependent on water content, these results demonstrate that the incorporation of a phenolate donor effectively tunes the MnII/III redox properties of the bispidine scaffold.
SN  - 0020-1669
SN  - 1520-510X
ER  -

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