Trinuclear heterobimetallic Ln(III)-Ru(II) complexes (Ln = Eu, Gd) based on a 1,10-phenanthroline ligand bearing a diethylenetriaminepentaacetic acid (DTPA) core have been synthesized and fully characterized by a range of experimental techniques. The (17)O NMR and proton nuclear magnetic relaxation dispersion (NMRD) measurements of Gd(III)-Ru(II) show that, in comparison to the parent Gd-DTPA, this complex exhibits improved relaxivity, which is the result of an increase of the rotational correlation time. Relaxometry and ultrafiltration experiments indicate that the 1,10-phenanthroline ligand has a high affinity for noncovalent binding to human serum albumin, which results in a high relaxivity r(1) of 14.3 s(-1) mM(-1) at 20 MHz and 37 °C. Furthermore, the Ln(III)-Ru(II) complexes (Ln = Eu, Gd) show an intense light absorption in the visible spectral region due to metal-to-ligand charge transfer (MLCT) transitions. Upon excitation into the MLCT band at 440 nm, the complexes exhibit a bright-red luminescence centered at 610 nm, with a quantum yield of 4.7%. The luminescence lifetime equals 540 ns and is therefore long enough to exceed the fluorescent background. Monometallic lanthanide complexes have also been synthesized, and the Eu(III) analogue shows a characteristic red luminescence with a quantum yield of 0.8%. Taking into account the relaxometric and luminescent properties, the developed Gd(III)-Ru(II) complex can be considered as a potential in vitro bimodal imaging agent.

A ditopic chelating ligand (H(6)4) that bears catechol and diethylenetriamine-N,N,N',N'',N''-pentaacetate (DTPA) has been designed and shown to specifically bind lanthanide(III) ions at the DTPA core ([Ln(H(2)4)(H(2)O)](-)) and further self-assemble with titanium(IV), thereby giving rise to the formation of a supramolecular metallostar complex with a lanthanide(III)-to-titanium(IV) ratio of 3:1, [(Ln4)(3)Ti(H(2)O)(3)](5-) (Ln=La, Eu, Gd). The efficacy of the metallostar complex as a potential bimodal optical/magnetic resonance imaging (MRI) agent has been evaluated. Nuclear magnetic relaxation dispersion (NMRD) measurements for the [(Gd4)(3)Ti(H(2)O)(3)](5-) complex have demonstrated an enhanced r(1) relaxivity that corresponds to 36.9 s(-1) mM(-1) per metallostar molecule at 20 MHz and 310 K, which is a result of a decreased tumbling rate. The ability of the complex to bind to human serum albumin (HSA) was also examined by relaxometric measurements. In addition, upon UV irradiation the [(Gd4)(3)Ti(H(2)O)(3)](5-) complex exhibits broad-band green emission in the range 400-750 nm with a maximum at 490 nm. Taking into account the high relaxivity and luminescence properties, the [(Gd4)(3)Ti(H(2)O)(3)](5-) complex is a good lead compound for the development of efficient bimodal contrast agents.

In this paper, a modular pathway towards the synthesis of new specific MRI contrast agents and their luminescent analogues is described. Using two azide‐bearing probes, 3β‐deoxycholic acid and cRGDfK(N3), we performed a “click” reaction with an alkyne‐bearing 1,4,7,10‐tetraazacyclododecane‐1,4,7,10‐tetraacetic acid (DOTA) analogue, yielding a possible blood‐pool contrast agent, as well as a contrast agent with a high affinity for cells expressing αvβ3 integrin. The nuclear magnetic relaxation dispersion (NMRD) profiles and human serum albumin (HSA) titration of the contrast agent bearing deoxycholic acid show that this contrast agent interacts with HSA. T1 measurements of Jurkat T cells in the presence of the contrast agent proved the retention of the integrin‐binding property of the RGD‐bearing contrast agent.

A novel ditopic ligand DTPA-ph-phen, based on 1,10-phenanthroline and diethylenetriaminepentaacetic acid (DTPA) units, has been designed and fully characterized by (1)H, (13)C, and 2D-COSY NMR spectroscopy, IR 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}(H(2)O)](-) 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}(H(2)O)](-) with Ru(II) leads to further self-assembly into a heterobimetallic metallostar complex containing Gd(III) and Ru(II) in a 3:1 ratio. This tetranuclear [(Gd{DTPA-ph-phen})(3)(H(2)O)(3)Ru](-) complex (Gd(3)Ru), 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 Gd(3)Ru 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 Gd(3)Ru 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 Gd(3)Ru complex exhibits an enhanced relaxivity value r(1) of 36.0 s(-1) mM(-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.

A ditopic DTPA monoamide derivative containing an 8-hydroxyquinoline moiety was synthesized and the corresponding gadolinium(III) complex ([Gd(H5)(H(2)O)](-)) was prepared. After adding aluminum(III), the 8-hydroxyquinoline part self-assembled into a heteropolymetallic triscomplex [(Gd5)(3)Al(H(2)O)(3)](3-). The magnetic and optical properties of this metallostar compound were investigated in order to classify it as a potential in vitro bimodal contrast agent. The proton nuclear magnetic relaxation dispersion measurements indicated that the relaxivity r(1) of [Gd(H5)(H(2)O)](-) and [(Gd5)(3)Al(H(2)O)(3)](3-) at 20 MHz and 310 K equaled 6.17 s(-1) mM(-1) and 10.9 s(-1) mM(-1) per Gd(III) ion respectively. This corresponds to a relaxivity value of 32.7 s(-1) mM(-1) for the supramolecular complex containing three Gd(III) ions. The high relaxivity value is prominently caused by an increase of the rotational tumbling time τ(R) by a factor of 2.7 and 5.5 respectively, in comparison with the commercially used MRI contrast agent Gd(III)-DTPA (Magnevist®). Furthermore, upon UV irradiation, [(Gd5)(3)Al(H(2)O)(3)](3-) exposes green broad-band emission with a maximum at 543 nm. Regarding the high relaxivity and the photophysical properties of the [(Gd5)(3)Al(H(2)O)(3)](3-) metallostar compound, it can be considered as a lead compound for in vitro bimodal applications.

Dedicated to Professor Jean-Claude Bünzli on the occasion of his 65th birthday Luminescence spectra of aqueous solutions containing a fixed concentration of tetracycline (TC) and increasing concentrations of Eu 3þ were recorded both in the absence and presence of hydrogen peroxide (H 2 O 2 ). In H 2 O 2 -free solutions in which the Eu/TC molar ratio was varied from 1 : 1 to 8 : 1, the 5 D 0 ! 7 F 0 transition consisted of only one peak at 580 nm. In the presence of H 2 O 2 , an extra peak appeared in the spectrum at 578 nm when the Eu/TC molar ratios were above 2.5. A detailed analysis of this spectral region revealed that at lower Eu/TC molar ratios (up to 2 : 1), the 5 D 0 ! 7 F 0 transition experienced a slight blue shift. This indicates that at low Eu/TC molar ratios, the presence of H 2 O 2 leads to two different environments of the trivalent europium ions, which most likely form bridged peroxide complexes with hydrogen peroxide (m-H 2 O 2 ligand). Luminescence spectra measured in the presence of molybdate ions, which catalytically decompose H 2 O 2 , led to the disappearance of the extra europium(III) site that was formed in the presence of H 2 O 2 . The intensity of the hypersensitive 5 D 0 ! 7 F 2 transition did not linearly depend on the H 2 O 2 /TC molar ratio. For H 2 O 2 /TC ratios up to 10, a sharp linear increase of the peak intensity was observed, but with further increase of the H 2 O 2 concentration, the intensity remained nearly constant. For H 2 O 2 /TC ratios above 100, the intensity of this transition even started to decrease, which limits the use of the (tetracycline)europium(III) system to quantify hydrogen peroxide in solution.