A Self‐Assembled Complex with a Titanium(IV) Catecholate Core as a Potential Bimodal Contrast Agent

Abstract

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.

Zn2+‐Responsive Bimodal Magnetic Resonance Imaging and Fluorescence Imaging Agents and Their Interaction with Human Serum Albumin

“…Thus, the formation of the (GdL2) 2 Zn species with one Zn 2+ ion bound to two GdL2 chelates results in a correspondingly longer rotational correlation time and a higher relaxivity value. [29][30][31][32] T 1 -weighted images were recorded by using a commercial 0.55 T (23 MHz) magnet. As depicted in Figure 1, the imaging contrast of GdL2 (0.1 mm) is clearly improved by the addition of 0.5 equiv.…”

Catechol‐Based Biomimetic Functional Materials

“…Using a different supramolecular approach, Parac‐Vogt and co‐workers prepared a ditopic chelating ligand bearing both catechol and carboxylic acids groups that was shown to specifically bind trivalent lanthanide ions through the carboxylic acid moieties, and Ti IV via catechol groups. The resulting Gd‐“metallostar” showed magnetic relaxivities almost an order of magnitude higher than a currently commercial MRI contrast agent 403…”

Magnetofluorescent Nanoaggregates Incorporating Terbium(III) Complexes as Potential Bimodal Agents for Magnetic Resonance and Optical Imaging

“…The use of bioconjugates led to significant improvements of MRI and optical properties; however, practical applications are limited by the short luminescence lifetimes (100–300 ns), small Stokes shifts and poor resistance to photobleaching of the organic fluorophores. In a different approach, transition metal complexes have been linked to DTPA or DOTA to produce luminescent CAs 10a,10b,14. However, in terms of their luminescence properties, lanthanides have several advantages as they can exhibit excited‐state lifetimes in the range of milliseconds and, thereby, remove the problem of short‐lifetime autofluorescence.…”