Well-defined assemblies of adamantyl-terminated poly(propylene imine) dendrimers and beta-cyclodextrin in water

Adamantyl-terminated poly(propylene imine) dendrimers 1-5 were dissolved in water in the presence of beta-cyclodextrin through strong non-covalent int eraction between the beta-cyclodextrin and adamantyl groups. The solubiliza tion of the dendrimer by beta-cyclodextrin is most effective at pH=2, becau se at this pH there is complete protonation of the tertiary amino groups pr esent in the dendritic cores, which causes the dendrimers to adopt a stretc hed conformation. The dendrimers remain in solution at pH less than or equa l to 7, but precipitate under basic conditions, except for 1, which remains in solution. The stoichiometries of the beta-cyclodextrin complexes of 1-4 at pH=2 are 1.(beta-CD)(4), 2.(beta-CD)(8), 3.(beta-CD)(16), and 4.(beta-C D)(32), respectively. For steric reasons not all 64 adamantyl groups of 5 c an be complexed by beta-cyclodextrin. The stoichiometry of the 5.(beta-CD)( n) complex is about 1:40 (pH=2). Steric arguments confirm that the outer su rface area of 5 is too small to allow complete coverage by beta-cyclodextri ns. Qualitative fluorescence measurements at pH=1 using 8-anilinonaphthalen e-1-sulfonate (ANS) as a probe showed that the assemblies of 2-5 with beta- cyclodextrin act as supramolecular hosts for ANS in water. The binding of A NS is electrostatically driven and increases for higher generations.