Guest-host chemistry with dendrimers : stable polymer assemblies by rational design

A new type of guest has been designed and synthesized for the exo-type supramol. 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 examd. for a fifth-generation adamantyl-urea-functionalized poly(propylene imine) dendrimer capable of binding 32 guest mols. and for a model host mol. that can bind only one guest mol. The guest-host chem. has been studied with 1H NMR spectroscopy, nuclear Overhauser enhancement spectroscopy NMR spectroscopy, T1-relaxation NMR expts., and IR spectroscopy. The 1:32 ratio with the dendrimer has been confirmed unambiguously from 1H NMR spectra of the complex after size exclusion chromatog. Competition expts. 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 expts. with a guest lacking the uriedo moiety.