PAMAM dendrimers undergo pH responsive conformational changes without swelling

Evidence for relative radius of gyration as the criterion for selective diffusion behavior of polymer brushes

When exposed to a dilute solution of free species, the polymer brush functions as a selective barrier to diffusion. Experiments with linear polymer chains and dendrimers of various sizes demonstrated that the selection criterion is relative size, i.e., radius of the free species (radius of gyration for linear chains and simple radius for dendrimers) relative to the radius of gyration of the chains composing the brush. This suggests that linear chains do not necessarily assume extended conformations as they diffuse into a brush but have conformations similar to those of nanoscale spherical inclusions.

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, we measured 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.