Gadolinium(III) 1,2-Hydroxypyridonate-Based Complexes:  Toward MRI Contrast Agents of High Relaxivity<sup>1</sup>

Xu, Jide; Churchill, David G.; Botta, Maurizio; Raymond, Kenneth N.

doi:10.1021/ic049028s

Cited by 63 publications

(85 citation statements)

References 12 publications

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“…23 Similarly, the synthesis of 5LIO-1,2-HOPO (H 2 1) and its' Eu(III) complex as the pyridinium salt, C 5 H 6 N[Eu(1) 2 ], have been previously reported. 18 A detailed synthesis of 5LI-1,2-HOPO (H 2 2) and its Eu(III) complex, C 5 H 6 N[Eu(2) 2 ], is described below, and corresponding complexes of Sm(III) and Gd(III) were prepared using the same procedure.…”

Section: Synthesismentioning

confidence: 90%

Highly Luminescent Lanthanide Complexes of 1-Hydroxy-2-pyridinones

et al. 2008

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The synthesis, X-ray structure, stability, and photophysical properties of several trivalent lanthanide complexes formed from two differing bis-bidentate ligands incorporating either alkyl or alkyl ether linkages and featuring the 1-hydroxy-2-pyridinone (1,2-HOPO) chelate group in complex with Eu(III), Sm(III) and Gd(III) are reported. The Eu(III) complexes are among some of the best examples, pairing highly efficient emission ( Eu tot Φ ~ 21.5 %,) with high stability (pEu ~ 18.6) in aqueous solution, and are excellent candidates for use in biological assays. A comparison of the observed behavior of the complexes with differing backbone linkages shows remarkable similarities, both in stability and photophysical properties. Low temperature photophysical measurements for a Gd(III) complex were also used to gain insight into the electronic structure, and were found to agree with corresponding TD-DFT calculations for a model complex. A comparison of the high resolution Eu(III) emission spectra in solution and from single crystals also revealed a more symmetric coordination geometry about the metal ion in solution due to dynamic rotation of the observed solid state structure.

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Section: Synthesismentioning

confidence: 90%

Highly Luminescent Lanthanide Complexes of 1-Hydroxy-2-pyridinones

et al. 2008

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“…The favorable electronic relaxation times of 1,2-HOPO chelates versus 3,2-HOPO have been recognized previously for hexadentate TREN-1,2-HOPO (2). 4 However, the relatively low selectivity of 2 for Gd(III) over Zn(II) may represent a problem utilizing this compound as MRI-CA. 5 For this reason relaxometric and solution thermodynamic properties of [Gd(1)] − have been investigated.…”

Section: Introductionmentioning

confidence: 99%

Optimized Relaxivity and Stability of [Gd(H(2,2)-1,2-HOPO)(H₂O)]^- for Use as an MRI Contrast Agent¹

et al. 2007

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Relaxometry and solution thermodynamic measurements show that Gd-H(2,2)-1,2-HOPO is a good candidate as a contrast agent for Magnetic Resonance Imaging (MRI-CA). Acidic, octadentate H(2,2)-1,2-HOPO forms a very stable Gd(III) complex [pGd 21.2 (2)]. The coordination sphere at the Gd(III) center is completed by one water molecule that is not replaced by common physiological anions. In addition, this ligand is highly selective for Gd(III) binding in the presence of Zn(II) or Ca(II).The symmetric charge distribution of the 1,2-HOPO chelates is associated with favorably long electronic relaxation time T 1,2e comparable to those of GdDOTA. This, in addition to the fast water exchange rate typical of HOPO chelates improves relaxivity to r 1p = 8.2 mM −1 s −1 (0.47 T). This remarkably high value is unprecedented for small molecule, q = 1 MRI-CA.

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“…The o-Phen-1,2-HOPO ligand is readily prepared by reaction of the benzyl-protected 1,2-HOPO-6-carboxylic acid intermediate prepared 10 from commercially available 6-bromopicolinic acid with the terminal primary aryl amines of o-aminoaniline (o-Phen), yielding the protected ligand (Scheme S1, Supp. Info).…”

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Aryl-Bridged 1-Hydroxypyridin-2-one: Sensitizer Ligands for Eu(III)

D’Aléo

Moore

et al. 2008

Inorg. Chem.

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The synthesis, crystal structure, solution stability and photophysical properties of an aryl group bridging two 1-hydroxypyridin-2-one units complexed to Eu(III) are reported. The results show that this backbone unit increases the rigidity of the ensuing complex, and also the conjugation of the ligand. As a result of the latter, the singlet absorption energy is decreased, along with the energy of the lowest excited triplet state. The resulting efficiency of sensitization for the Eu(III) ion is influenced by these phenomena, yielding an overall quantum yield of 6.2% in aqueous solution. The kinetic parameters arising from the luminescence data reveal an enhanced nonradiative decay rate for this compound when compared to previously reported aliphatic bridges.Due to the Laporte forbidden character and intraconfigurational nature of the 4f transitions, 1 luminescence from lanthanide cations is typically highly monochromatic, exhibits long-lived excited state lifetimes when compared to organic compounds, and is usually insensitive to quenching by molecular oxygen, making these metal ions ideal for applications as fluorescent probes, 2 optical signal amplifiers 3 or light emitting diodes. 4 Unfortunately, for the same reason, the molar absorption coefficient of lanthanide transitions is very small (less than 10 M −1 .cm −1 ). 5 To obviate this problem, organic ligands having a large molar absorption coefficient can be coordinated to the lanthanide ion, resulting in sensitized emission through the so-called antenna effect. The mechanism of antenna sensitization is comprised of three differing steps: the initial excitation of the ligand, followed by intersystem crossing to give an excited triplet state, then subsequent energy transfer to yield the metal centered excited state which emits light. 1,[5][6][7] For this mechanism, the energy of the sensitizing triplet state relative to the 5 D 0 or 5 D 1 excited states of Eu(III) is one of the critical parameters which can be tuned in order to optimize the system. Furthermore, the rate of intersystem crossing, energy transfer and radiative vs. non-radiative decay of the metal must be considered, and these rates may all be influenced by the geometry and chemical structure of the sensitizing ligand. We report here the synthesis, crystal structure, solution stability and photophysical properties of a new 1-hydroxypyridin-2-one (1,2-HOPO) based chelator, o-Phen-1,2-HOPO (Chart 1), acting as a tetradentate ligand to form an ML 2 complex with Eu(III). This ligand bridges two 1,2-HOPO units via an aryl group, yielding a higher degree of conjugation when compared to previously reported alkyl linkages. [8,9] The resultant stability constants and optical properties of this new ligand architecture are compared to the parent 5LI-8 and 5LIO-1,2-HOPO 9 compounds.* To whom correspondence should be addressed. raymond@socrates.berkeley.edu. Fax: +1 (510) The o-Phen-1,2-HOPO ligand is readily prepared by reaction of the benzyl-protected 1,2-HOPO-6-carboxylic acid intermediate prepare...

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Gadolinium(III) 1,2-Hydroxypyridonate-Based Complexes: Toward MRI Contrast Agents of High Relaxivity¹

Cited by 63 publications

References 12 publications

Highly Luminescent Lanthanide Complexes of 1-Hydroxy-2-pyridinones

Highly Luminescent Lanthanide Complexes of 1-Hydroxy-2-pyridinones

Optimized Relaxivity and Stability of [Gd(H(2,2)-1,2-HOPO)(H₂O)]^- for Use as an MRI Contrast Agent¹

Aryl-Bridged 1-Hydroxypyridin-2-one: Sensitizer Ligands for Eu(III)

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Gadolinium(III) 1,2-Hydroxypyridonate-Based Complexes: Toward MRI Contrast Agents of High Relaxivity1

Cited by 63 publications

References 12 publications

Highly Luminescent Lanthanide Complexes of 1-Hydroxy-2-pyridinones

Highly Luminescent Lanthanide Complexes of 1-Hydroxy-2-pyridinones

Optimized Relaxivity and Stability of [Gd(H(2,2)-1,2-HOPO)(H2O)]- for Use as an MRI Contrast Agent1

Aryl-Bridged 1-Hydroxypyridin-2-one: Sensitizer Ligands for Eu(III)

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Gadolinium(III) 1,2-Hydroxypyridonate-Based Complexes: Toward MRI Contrast Agents of High Relaxivity¹

Optimized Relaxivity and Stability of [Gd(H(2,2)-1,2-HOPO)(H₂O)]^- for Use as an MRI Contrast Agent¹