Partitioning of poly(amidoamine) dendrimers between n-octanol and water

Dendritic nanomaterials are emerging as key building blocks for a variety of nanoscale materials and technologies. Poly(amidoamine) (PAMAM) dendrimers were the first class of dendritic nanomaterials to be commercialized. Despite numerous investigations, the environmental fate, transport, and toxicity of PAMAM dendrimers is still not well understood. As a first step toward the characterization of the environmental behavior of dendrimers in aquatic systems,wemeasured the octanol-water partition coefficients (logK_ow) of a homologous series of PAMAM dendrimers as a function of dendrimer generation (size), terminal group and core chemistry. We find that the logK_ow of PAMAM dendrimers depend primarily on their size and terminal group chemistry. For G1-G5 PAMAM dendrimers with terminal NH₂ groups, the negative values of their logK_ow indicate that they prefer to remain in the water phase. Conversely, the formation of stable emulsions at the octanol-water (O/W) interface in the presence of G6-NH₂ and G8-NH₂ PAMAM dendrimers suggest they prefer to partition at the O/W interface. In all cases, published studies of the cytotoxicity of Gx-NH₂ PAMAM dendrimers show they strongly interact with the lipid bilayers of cells. These results suggest that the logK_ow of a PAMAM dendrimer may not be a good predictor of its affinity with natural organic media such as the lipid bilayers of cell membranes.