Structure of dendrimer-dye host-guest complexes as revealed by small-angle X-ray scattering

Small angle X-ray scattering (SAXS) expts. were performed on dil. aq. solns. of a new type of water-sol. ethyleneoxy-terminated poly(propyleneimine) dendrimer system. They reveal that the dimensions and d. distributions of the dendrimer are hardly affected by a change in the degree of protonation. This is in contrast to recent predictions regarding the structure of polyelectrolyte dendrimers but in line with the results of recent structural studies on charged PAMAM dendrimers. These dendrimer systems were applied as nanosized containers for guests like xanthene dyes. Structural studies with SAXS provide clear evidence for a complex formation but despite higher molar mass the max. dimensions of the complex are only slightly changed compared to the dendritic host. Since the radius of gyration represents the second moment of the electron d. distribution it appears to be very sensitive to changes in this distribution upon encapsulation of heavy-atom contg. guest mols. These are reflected in a decrease of the radius of gyration upon an increase of the guest-host ratio in the soln., a behavior that strongly indicates an accumulation of guest mols. in the center of the dendritic host. [on SciFinder (R)]