Johan F. G. A. Jansen

Encapsulation of guest molecules into a dendritic box

Dendrimers are well-defined, highly branched macromolecules that emanate from a central core and are synthesized through a stepwise, repetitive reaction sequence. The synthesis and characterization of dendritic boxes, based on the construction of a chiral shell of protected amino acids onto poly(propyleneimine) dendrimers with 64 amine end groups, is reported here. Nuclear magnetic resonance-relaxation and optical data show that a dense shell with solid-phase character is formed. Guest molecules were captured within the internal cavities of the boxes when these boxes were constructed in the presence of guest molecules. The diffusion of guest molecules out of the boxes into solution was unmeasurably slow because of the close packing of the shell. These monomolecular dendritic containers of 5-nanometer dimensions with physically locked-in guest molecules were characterized spectroscopically.

The Dendritic Box; Synthesis, Properties, and Applications

A dendritic structure with a densely-packed shell is prepared via modification of the fifth generation poly(propylene imine) dendrimers with N-BOC-L-phenylalanine groups. This so-called dendritic box has a diameter of approximately 4.5 nm, as determined by DLS and SAXS, and has internal cavities which can be used for the encapsulation of guest molecules. Supramolecular encapsulation is achieved by performing the construction of the box in the presence of the guest molecules, followed by dialysis to remove excess and adhered guest. A number of properties of encapsulated guests is critically influenced by the host, like the observation of induced optically activity and a solvent-independent fluorescence of dyes encapsulated as well as the formation of a triplet radical pair of 3-carboxy-proxyl. A shape-selective liberation of encapsulated guests is accomplished by a two-step hydrolysis of the shell. The potentials of these boxes as new supramolecular architectures within the nanometer regime are discussed.