A new type of guest has been designed and synthesized for the exo-type supramolecular functionalization of adamantyl-urea-terminated poly(propylene imine) dendrimers. This new type of guest motif features a uriedo methane sulfonic acid moiety that binds very selectively to the surfaces of dendrimers via a combination of noncovalent interactions forming well-defined complexes. The guest-host properties have been examined for a fifth-generation adamantyl-urea-functionalized poly(propylene imine) dendrimer capable of binding 32 guest molecules and for a model host molecule that can bind only one guest molecule. The guest-host chemistry has been studied with H-1 NMR spectroscopy, nuclear Overhauser enhancement spectroscopy NMR spectroscopy, T-1-relaxation NMR experiments, and IR spectroscopy. The 1:32 ratio with the dendrimer has been confirmed unambiguously from H-1 NMR spectra of the complex after size exclusion chromatography. Competition experiments with guests bearing a carboxylic acid instead of a sulfonic acid in the binding motif have demonstrated that the sulfonic acid has superior binding strength. Also, the importance of a combination of noncovalent interactions has been shown via competition experiments with a guest lacking the uriedo moiety. (C) 2004 Wiley Periodicals, Inc.