(647b) Carbamate-Dendrimer Directed Synthesis and Characterization of Uniform-Size Shell Cross-Linked Nanocages with Hydrophobic Interior Walls and Functionalized Cores

Hollow nanocage enclosed by a porous shell can function as a molecular cage for encapsulation and storage of guest species. The porous shell offers molecular size-selectivity for access into the cavity, as well as protection or isolation of the active species inside the cavity from the environment or other species. The potential applications of such shell cross-linked nanocages include drug delivery, as nanoreactors for controlled chemical reactions, chemical sensors, and fluorescence microscopy, etc.

We have previously reported a method for the preparation of a 2 nm diameter siloxane nanocage, derived from shell cross-linked micelle (SCM) templates (ref 1). These nanocages possess amine functional groups tethered to the interior surface of the shells. The method, however, does not permit easy control of the size or attaining a high degree of size uniformity. We describe here a new, dendrimer-directed method to prepare uniform, molecular-size nanocages with cross-linked siloxane shells. The method also permits fine tuning of the cage size in the range from 2 to 5 nm.

The synthesis involves first the preparation of a carbamate dendron by reacting 1,3-diamino-2-propanol, as a linker for carbamate linkage, with PNP chloroformate. The number of generation of the dendron is chosen such that a nearly spherical dendrimer would be formed for shell cross-linking after attaching the dendrons to an amine-functionalized core. After forming the desired carbamate-dendrimer, its olefinic groups on the dendrimer surface are converted to alkoxysilanes via hydrosilylation, followed by their hydrolysis to silanols and condensation to form the cross-linked shell. Finally, the cage cavity is formed by cleavage of the interior carbamate linkages. Depending on the size of the starting core molecule, it is possible to design the procedure to leave the starting core molecule trapped inside the cavity.

The preparation procedure and the intermediate and final products of the synthesis are characterized with 1H, 13C and 29Si NMR, MALDI-TOF mass spectrometry, dynamic light scattering (DLS), and transmission electron microscopy. These results will be presented, together with the properties of the nanocages for binding of metal ions.

Ref. 1: “Size-Selective Shell Cross-Linked Interior Functionalized Siloxane Nanocages,” Young-Woong Suh, Mayfair C. Kung, Yingmin Wang, Harold H. Kung, J. Amer. Chem. Soc. 128 (2006) 2776.