Dendronised Ni(<scp>ii</scp>) porphyrins as photoswitchable contrast agents for MRI

Dommaschk, Marcel; Gröbner, Jens; Wellm, Vanessa; Hövener, Jan‐Bernd; Riedel, Christian; Herges, Rainer

doi:10.1039/c9cp04156g

Cited by 15 publications

(25 citation statements)

References 30 publications

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“…In order to check whether the switching efficiencies would decrease in aqueous environment to a similar extend as in previous cases [ 3 ], switching experiments with the protic record players 1e (R = OH), 1h (SH) and 1j (R = COOH) in acetone/water 1:9 were performed. UV experiments revealed that the switching efficiencies of the protonated species indeed dropped dramatically as compared to those in pure acetone.…”

Section: Resultsmentioning

confidence: 99%

“…3 ). If it comes to medical applications, such as switchable contrast agents [ 3 – 7 ], the new carboxylate substituted system 1j has the distinct advantage of being deprotonated at neutral pH, whereas the previously synthesized hydroxylate system 1e exhibits its highest switching efficiency at unphysiological pH 10.5 [ 14 ]. Hence, further attempts to optimize our molecular spin switches will be based on pyridine-4-carboxylate-substituted systems.…”

Section: Resultsmentioning

confidence: 99%

“…Molecular spin switches operated with visible light in homogeneous solution [ 1 ] or on surfaces [ 2 ], hold promise for a number of hitherto unprecedented applications such as switchable contrast agents [ 3 – 7 ], switchable NMR relaxation agents [ 8 – 10 ], and building blocks for molecular spintroncis [ 11 ]. Our modular design is based on three components: a) a Ni(II)-porphyrin (square planar base complex), b) an azoaryl unit (photoswitchable ligand) and c) a molecular linker or tether (connecting the porphyrin with the switchable ligand).…”

Section: Introductionmentioning

confidence: 99%

“…In previous studies we have shown that methoxy substitution (σ = −0.27) improved the spin switching efficiency in organic solvents to >98% in both directions [ 13 ]. However, the switching efficiency drops in protic solvents, particularly in water [ 3 , 14 ]. We now synthesized sulfur and carboxylic acid substituted record players aiming at the improvement of the switching efficiency.…”

Section: Introductionmentioning

confidence: 99%

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Synthesis of 4-substituted azopyridine-functionalized Ni(II)-porphyrins as molecular spin switches

Ludwig¹,

Moje²,

Röhricht³

et al. 2020

Beilstein J. Org. Chem.

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We present the synthesis and the spin switching efficiencies of Ni(II)-porphyrins substituted with azopyridines as covalently attached photoswitchable ligands. The molecules are designed in such a way that the azopyridines coordinate to the Ni ion if the azo unit is in cis configuration. For steric reasons no intramolecular coordination is possible if the azopyridine unit adopts the trans configuration. Photoisomerization of the azo unit between cis and trans is achieved upon irradiation with 505 nm (trans→cis) and 435 nm (cis→trans). Concurrently with the isomerization and coordination/decoordination, the spin state of the Ni ion switches between singlet (low-spin) and triplet (high-spin). Previous studies have shown that the spin switching efficiency is strongly dependent on the solvent and on the substituent at the 4-position of the pyridine unit. We now introduced thiol, disulfide, thioethers, nitrile and carboxylic acid groups and investigated their spin switching efficiency.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Synthesis of 4-substituted azopyridine-functionalized Ni(II)-porphyrins as molecular spin switches

Ludwig¹,

Moje²,

Röhricht³

et al. 2020

Beilstein J. Org. Chem.

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“…Several light-responsive MRI CAs have been reported in the last decade. For instance, Herges and co-workers reported porphyrin-based nickel(II) complexes, bearing a photoresponsive azobenzene moiety, whose relaxivity can be switched on by irradiation with λ = 505 nm light [ 22 , 23 ]. Even though the authors were able to minimize initial challenges with respect to the low water solubility, the overall very low relaxivity (0.03 s −1 mM −1 at 7T) remains a challenge [ 24 ].…”

Section: Introductionmentioning

confidence: 99%

A Photocleavable Contrast Agent for Light-Responsive MRI

et al. 2020

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Thanks to its innocuousness and high spatiotemporal resolution, light is used in several established and emerging applications in biomedicine. Among them is the modulation of magnetic resonance imaging (MRI) contrast agents’ relaxivity with the aim to increase the sensitivity, selectivity and amount of functional information obtained from this outstanding whole-body medical imaging technique. This approach requires the development of molecular contrast agents that show high relaxivity and strongly pronounced photo-responsiveness. To this end, we report here the design and synthesis of a light-activated MRI contrast agent, together with its evaluation using UV–vis spectroscopy, Fast Field Cycling (FFC) relaxometry and relaxometric measurements on clinical MRI scanners. The high relaxivity of the reported agent changes substantially upon irradiation with light, showing a 17% decrease in relaxivity at 0.23T upon irradiation with λ = 400 nm (violet) light for 60 min. On clinical MRI scanners (1.5T and 3.0T), irradiation leads to a decrease in relaxivity of 9% and 19% after 3 and 60 min, respectively. The molecular design presents an important blueprint for the development of light-activatable MRI contrast agents.

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Molecular Sensors Operating by a Spin‐State Change in Solution: Application to Magnetic Resonance Imaging

et al. 2020

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Recent proposals for molecular switches are reviewed that adopt a different spin state before and after the encounter with an analyte (metabolite) or physical stimulus (light). Spin‐state switching has significant potential to provide molecular MRI with a first line of probes operating by an off/on mode. Past efforts to design MRI sensors relied on strategies other than spin‐switching and thus mostly comprised probes only modulating the signal before and after encounter with the analyte (X%‐on/Y%‐on). The article thus essentially treats small‐molecule metal ion chelates, i.e. coordination compounds. Initially, a comprehensive treatment of design considerations for optimal spin‐state switches is furnished. The article then enters into a treatment of reported examples of spin‐state switches according to three response mechanisms: 1) changes in the redox state of the metal center; 2) changes in coordination geometry; and 3) modification of the surrounding ligand field, either by peripheral interaction with the analyte, or by replacement of a coordinating ligand by another.

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Dendronised Ni(ii) porphyrins as photoswitchable contrast agents for MRI

Abstract: On–off photoswitching of MRI contrast in water and gels with spatial resolution.

Cited by 15 publications

References 30 publications

Synthesis of 4-substituted azopyridine-functionalized Ni(II)-porphyrins as molecular spin switches

Synthesis of 4-substituted azopyridine-functionalized Ni(II)-porphyrins as molecular spin switches

A Photocleavable Contrast Agent for Light-Responsive MRI

Molecular Sensors Operating by a Spin‐State Change in Solution: Application to Magnetic Resonance Imaging

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