DSIDMO · Dendrimers and supramolecular interactions for the design of multivalent objects

Final Activity Report Summary - DSIDMO (Dendrimers and supramolecular interactions for the design of multivalent objects)

Supramolecular chemistry makes use of noncovalent interactions, such as pi?pi stacking, hydrogen bonding, metal coordination and solvophobic interactions, to build materials and objects. A characteristic of these interactions is that they are reversible under certain conditions, which is desirable for many biomedical applications such as drug delivery or gene transfection. Dendrimers are in our view excellent building blocks for those applications. They are monodisperse, have a highly branched and regular structure with different regions with defined properties. The branched structure allows the use of multivalency to tune the robustness of the system. In this project, we aimed at taking to water a dendrimer-based supramolecular system in chloroform developed in the Eindhoven University of Technology, so that the system could be used for the applications mentioned above. The morphology of the system in solution is studied by cryo-TEM (cryogenic transmission electron microscopy) using a Vitrobot blotting apparatus. This enables us to make a very thin layer (<200 nm) of solution on a carbon coated TEM grid and freeze this layer instantly, using liquid ethane. The water of the solution doesn't have time to crystallise and therefore stays transparent for the electron beam. It is assumed that the structures present in solution are conserved in the frozen sample. Hydrogen bonding and ionic interactions maintain the supramolecular system in chloroform as desired single dendrimers surrounded by guest molecules but in water they are partially overcome by hydrophobic interactions. Upon dissolution of the single-host complexes in water, mainly small dendrimer-based assemblies are formed with a diameter of 4.1 +- 0.45 nm. The core of these new assemblies in water consists of on average three dendrimers, no matter the concentration of the solution. This concentration independence indicates that the core of the dendrimer-based assemblies is kinetically trapped upon dissolution in water. Apparently, hydrophobic forces and shielding of the host by the hydrophilic guest molecules are optimal at these distinct numbers of host molecules in the core of the assembly. The corona of the dendrimer-based assemblies in water, consisting of multiple guest molecules, is dynamic as proved by AFM experiments. When concentration of guest molecules is twice the stoichiometric, novel and reproducible worm-like structures are obtained. Our results point to lateral interactions (hydrophobic and hydrogen bonding) between guest being also responsible for this morphology. Surprisingly the use of multivalent guests does not lead to an increase of stability of the complex formed. Our work evidences the importance of solvent in supramolecular chemistry and has lead to the discovery of novel supramolecular architectures using dendrimers.

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