Following the stability of amphiphilic nanoaggregates by using intermolecular energy transfer

Amphiphilic Nanoaggregates with Bimodal MRI and Optical Properties Exhibiting Magnetic Field Dependent Switching from Positive to Negative Contrast Enhancement

Mixed micelles based on amphiphilic gadolinium(III)-DOTA and europium(III)-DTPA complexes were synthesized and evaluated for their paramagnetic and optical properties as potential bimodal contrast agents. Amphiphilic folate molecule for targeting the folate receptor protein, which is commonly expressed on the surface of many human cancer cells, was used in the self-assembly process in order to create nanoaggregates with targeting properties. Both targeted and nontargeted nanoaggregates formed monodisperse micelles having distribution maxima of 10 nm. The micelles show characteristic europium(III) emission with quantum yields of 2% and 1.1% for the nontargeted and targeted micelles, respectively. Fluorescence microscopy using excitation at 405 nm and emission at 575-675 nm was employed to visualize the nanoaggregates in cultured HeLa cells. The uptake of folate-targeted and nontargeted micelles is already visible after 5 h of incubation and was characterized with the europium(III) emission, which is clearly observable in the cytoplasm of the cells. The very fast longitudinal relaxivity r₁ of ca. 26 s^-1 mM^-1 per gadolinium(III) ion was observed for both micelles at 60 MHz and 310 K. Upon increasing the magnetic field to 300 MHz, the nanoaggregates exhibited a large switching to transversal relaxivity with r₂ value of ca. 52 s^-1 mM^-1 at 310 K. Theoretical fitting of the ¹H NMRD profiles indicate that the efficient T₁ and T₂ relaxations are sustained by the favorable magnetic and electron-configuration properties of the gadolinium(III) ion, rotational correlation time, and coordinated water molecule. These nanoaggregates could have versatile application as a positive contrast agent at the currently used magnetic imaging field strengths and a negative contrast agent in higher field applications, while at the same time offering the possibility for the loading of hydrophobic therapeutics or targeting molecules.

Drawing on biology to inspire molecular design: a redox-responsive MRI probe based on Gd(iii)-nicotinamide

A novel, reversible redox-active MRI probe, GdNR1, has been developed for the study of redox changes associated with diseased states. This system exhibits switching in relaxivity upon reduction and oxidation of the appended nicotinimidium. Relaxivity studies and cyclic voltammetry confirmed the impressive reversibility of this system, at a biologically-relevant reduction potential. A 2.5-fold increase in relaxivity was observed upon reduction of the complex, which corresponds to a change in the number of inner-sphere water molecules, as confirmed by luminescence lifetimes of the Eu(iii) analogue and NMRD studies. This is the first example of a redox-responsive MRI probe utilising the biologically-inspired nicotinimidium redox switch. In the future this strategy could enable the non-invasive identification of hypoxic tissue and related cardiovascular disease.

Amphiphilic complexes of Ho(iii), Dy(iii), Tb(iii) and Eu(iii) for optical and high field magnetic resonance imaging

Amphiphilic lanthanide(iii) complexes self-assemble into monodisperse micelles with favourable properties for optical and high field magnetic resonance imaging.