Branched Polyhedral Oligomeric Silsesquioxane Nanoparticles Prepared via Strain-Promoted 1,3-Dipolar Cycloadditions

Abstract

Conjugation of small organic molecules and polymers to polyhedral oligosilsesquioxane (POSS) cores results in novel hybrid materials with unique physical characteristics. We report here an approach in which star-shaped organic-inorganic scaffolds bearing eight cyclooctyne moieties can be rapidly functionalized via strain-promoted azide-alkyne cycloaddition (SPAAC) to synthesize a series of nearly monodisperse branched core-shell nanoparticles with hydrophobic POSS cores and hydrophilic arms. We established that SPAAC is a robust method for POSS core octafunctionalization with the reaction rate constant of 1.9 × 10-2 M-1 s-1. Functionalization with poly(ethylene glycol) (PEG) azide, fluorescein azide, and unprotected lactose azide gave conjugates which represent different classes of compounds: polymer conjugates, fluorescent dots, and bioconjugates. These resulting hybrid compounds were preliminarily tested for their ability to self-assemble in solution and at the air-water interface. We observed the formation of robust smooth Langmuir monolayers with diverse morphologies. We found that polar lactose moieties are completely submerged into the subphase whereas the relatively hydrophobic fluorescein arms had extended conformation at the interface, and PEG arms were partially submerged. Finally, we observed the formation of stable micelles with sizes between 70 and 160 nm in aqueous solutions with size and morphology of the structures dependent on the molecular weight and the type of the peripheral hydrophilic moieties.