Do dendritic amphiphiles self-assemble in water? A Fourier transform pulse-gradient spin-echo NMR study

Amphiphilic poly(amidoamine) (PAMAM) dendrimers were synthesized having an average of 7-46 hydrophobic chains of varying lengths (C-10-C-14) attached to the periphery of 64 amine groups. The synthesis was performed in three steps: (1) protection of a desired number of amines with BOC groups; (2) reaction of the remaining amine groups with long-chain acid chlorides; and (3) deprotection from the BOC groups to produce the amphiphilic dendrimers as HCl salts. The behavior of the dendrimers in aqueous media was examined by pulse-gradient spin-echo (FT-PGSE) NMR and dynamic light scattering. Self-diffusion data on dendrimers with 22 or fewer chains, along with dynamic light scattering on concentrations of less than or equal to 16 wt%, gave no indication of dendrimer-dendrimer self-assembly via hydrocarbon chains exposed on the dendrimer surface. It is concluded that dendrimers with 7-22 chains, each having 10-14 carbons, behave as unimolecular entities with chains coiled largely within the dendrimer periphery, Only when the number of chains becomes very large (ca greater than or equal to 34) are chains forced externally where they can promote hydrophobically induced self-assembly. Monomeric dendrimers possessing the full range of functional polarity have great potential in enzyme modeling. Copyright (C) 2001 John Wiley & Sons, Ltd.