Guest speaker in Polymers & Materials group: Pol Besenius

Room 170.048, Adolphe Merkle Institute, Marly

Friday, February 5th, 2010  13:00 h

Supramolecular MRI Contrast Agents

Dr. Pol Besenius

Eindhoven University of Technology, The Netherlands

A challenging target in the non-covalent synthesis of nanostructured functional materials is the formation of uniform features having well-defined properties, e.g. a precise control over the size, spatial resolution and the degree of functionalisation.

Helical columnar aggregates of preferred handedness are obtained in aqueous environments via one dimensional stacking of optically active discotic amphiphiles. We have developed a strategy based on Coulombic interactions that enables us to control the stack length and shape of the ordered selfassemblies. By balancing out attractive forces within the hydrophobic fluorinated core of the molecular building blocks with electrostatic repulsive interactions on the hydrophilic periphery we managed to switch from elongated rod like assemblies (building block 1, picture A) to small and discrete objects (building block 2, picture B). Intriguingly this rod-to-sphere transition is expressed in a loss of cooperativity in the temperature dependent self-assembly. The aggregates were characterized using circular dichroism, UV and electron microscopy. In analogy to many systems found in biology mechanistic details have emphasized the importance of cooperativity as a key feature that dictates the physical properties of the produced supramolecular polymers.

Equipping the discotics with paramagnetic Gd(III) complexes has allowed us to develop a new class of supramolecular magnetic resonance imaging (MRI) contrast agents. By controlling the size of one dimensional columnar assemblies with diameters in the range of 6 nm we obtained the supramolecular equivalent of a dendritic polymer. These paramagnetic objects exhibit excellent ionic relaxivities and high stability upon dilution or in the presence of hydrophobic proteins. In comparison to the covalent macromolecular scaffolds it is the reversible nature of the supramolecular stacks that will ultimately increase the control over scope of the self-assembled objects by aiming to develop multimodal and target-specific MRI contrast agents. 1H-NMR spectroscopy, small angle X-ray scattering and cryotransmissionin vivo excretion rates of the MRI contrast agents. We are now expanding the scope of the self-assembled objects by aiming to develop multimodal and target-specific MRI contrast agents.