Using pseudo-symmetrization to overcome dendrimer surface steric crowding: a birth of l-lysine-β-alanine architecture.

A synthetic approach to overcoming the surface crowding of polylysine dendrimers is reported. The introduction of a β-alanine unit on the α-amine of l-lysine creates a pseudo-symmetry between the two amino groups, which is found to reduce the steric bias when used as a dendrimer building block, compared with the parent l-lysine. Our findings show that this approach allows the unhindered growth of the l-lysine-β-alanine dendrimers until generation 8, thus significantly increasing the generation at which de Gennes' critical dense state of surface functional groups is reached, compared with traditional polylysine dendrimers. Highly uniform high molecular weight nanostructures have been isolated, purified, and characterized by NMR spectroscopy, matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectroscopy, and gel-permeation chromatography (GPC).