Journal
INORGANIC CHEMISTRY
Volume 51, Issue 16, Pages 8775-8783Publisher
AMER CHEMICAL SOC
DOI: 10.1021/ic300537y
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Funding
- IWT Flanders (Belgium)
- FWO-Flanders [G.0412.09]
- ARC (program of Research of the French Community of Belgium) [00/05-258, 05/10-335, AUWB-2010-10/15-UMONS-5]
- FNRS
- ENCITE
- European Network of Excellence EMIL (European Molecular Imaging Laboratories) [LSCH-2004-503569]
- Center for Microscopy and Molecular Imaging (CMMI)
- European Regional Development Fund
- Walloon Region
- [TD1004]
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A novel ditopic ligand DTPA-ph-phen, based on 1,10-phenanthroline and diethylenetriaminepentaacetic acid (DTPA) units, has been designed and fully characterized by H-1, C-13, and 2D-COSY NMR spectroscopy, 1R and electrospray ionization mass spectrometry (ESI-MS) techniques. The DTPA core of the ligand specifically binds Ln(III) ions (Ln = Eu, Gd) resulting in formation of the [Ln{DTPA-ph-phen}(H2O)](-) complex. The photophysical properties of the Eu(III) compound have been investigated, and the complex shows characteristic red luminescence with an overall quantum yield of 2.2%. Reaction of [Gd{DTPA-ph-phen}(H2O)](-) with Ru(II) leads to further self-assembly into a heterobimetallic metallostar complex containing Gd(III) and Ru(11) in a 3:1 ratio. This tetranuclear [(Gd{DTPA-ph-phen})(3)(H2O)(3)Ru](-) complex (Gd3Ru), formed by the coordination of Ru(II) to the 1,10-phenanthroline unit, has been characterized by a range of experimental techniques and evaluated toward its feasibility as a potential bimodal optical/MRI agent. The Gd3Ru metallostar shows intense metal-to-ligand charge transfer (MLCT) transition resulting in intense light absorption in the visible spectral region. Upon irradiation into this MLCT band at 450 nm, the Gd3Ru complex exhibits red broad-band luminescence in the range of 550-800 nm centered at 610 nm with a quantum yield of 4.8%. Proton nuclear magnetic relaxation dispersion (NMRD) measurements indicate that the Gd3Ru complex exhibits an enhanced relaxivity value r(1) of 36.0 s(-1) mMs(-1) per metallostar molecule at 20 MHz and 310 K. The ability of the complex to noncovalently bind to human serum albumin (HSA) was investigated, but no significant interaction was detected.
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