Synthesis of Clickable Water-Soluble Poly(amidoamine) Fullerodendrimers and Their Use for Surface Functionalization of Azido-Coated Polymer Nanoparticles

In this study, the synthesis of water-soluble fullerene derivatives bearing on one side a poly(amidoamine) (PAMAM) dendron with peripheral carboxylic groups and an alkyne moiety on the other side is presented. Fullerodendrimers with tert-butyl ester groups at the periphery were first prepared by treating C60 with unsymmetrical malonates through the use of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU)/I2 or DBU/CBr4 conditions. The latter led to an unexpected addition of dibromocarbene on C60. The tert-butyl esters were then cleaved using formic acid and gave the corresponding carboxyfullerene derivatives. The second generation with eight carboxylic groups at the periphery was easily dissolved in water, whereas the first generation with its four carboxylic groups can only be solubilized in a basic medium. These compounds self-assemble into micelle-like aggregates probably composed of a cluster of C60 surrounded by a PAMAM shell. The alkyne moiety was then used as a chemical anchor to immobilize in water fullerodendrimers on the surface of azido-coated polymer nanoparticles by means of the copper(I)-catalyzed azide and alkyne cycloaddition reaction. At room temperature, this reaction is competing with azido cycloaddition onto the fullerene core. Given the high density of azide anchoring groups on the nanoparticle surface and the size of the fullerodendrimers, unreacted azides are still active and are available for subsequent functional arrangements. This strategy paves the way for the design of functional fullerene-rich nanomaterials that could be of interest in the field of materials science.