Probing the onset of dense shell packing by measuring the aminolysis rates for a series amine terminated dendrimers

In an effort to probe dendritic structure, the initial rate of an aminolysis reaction was measured for a series of dendrimers with 4, 8, 16, 32 and 64 terminal amine groups (1st -5th generation dendrimers, respectively). From these experiments, a relationship between size and rate was observed. In all cases, the rate was faster than the control experiment using a simple amine (N-acetylethylene diamine), with the 4th generation dendrimer displaying the maximum rate enhancement (28-fold with respect to the control experiment). The observed increase in rates was due to: (i) hydrophobic binding and (ii) transition state stabilization, (dependent on dendrimer generation). These experimental results supported a preliminary surface density analysis, which predicted the onset of a closed shell/globular structure at or around the 4th generation PAMAM dendrimer. (c) 2005 Elsevier B.V. All rights reserved.