The molecular characteristics of the first five generations of poly(propyleneimine) dendrimers with two different types of end groups have been investigated using small-angle neutron scattering (SANS), viscosimetry, and molecular dynamics simulations. The dimension of the poly(propyleneimine) dendrimers, as measured by both SANS and viscosimetry, increases linearly with the generation number and roughly as M 1/3 , where M is the molar mass of the dendrimer. This relationship proves to be independent of the character of the end group and the solvent used and is indicative of a compact (space-filling) structure with a fractal dimensionality of approximately 3. The distinct maximum in the Kratky representation of the scattering data and the observed relation (i.e., R η = (5/3)R g ) between the hydrodynamic radius Rη and the radius of gyration Rg are consistent with such a structure. Molecular dynamics simulations for two different solvent qualities are in good accordance with the acquired experimental results. The probability distributions of the amine end groups, based on these simulations, exhibit a substantial degree of backfolding. The corresponding radial density distributions show a constant density plateau and a monotonic decrease of the density toward the exterior of the molecule. The above results indicate that the poly(propyleneimine) dendrimers can be considered as flexible molecules with a relatively homogeneous radial density distribution. This view clearly deviates from both the dense shell and dense core models.

No abstract

Investigations have been carried out to clarify the binding interactions between two kinds of native DNA:  one from salmon sperm (300−500 bp) and another from bacteriophage T4dC (166 kbp) and amine-terminated, diaminobutane core, poly(propylene imine) dendrimers (Astramol) of five generations (G1, G2, G3, G4, and G5). All dendrimers interacting with DNA at an equal concentration of amine and phosphate groups form electroneutral water-insoluble interpolyelectrolyte complexes (IPECs). However, G4 and G5 added to DNA solution in excess form positively charged water-soluble IPECs representing perfect objects to investigate the state of DNA molecules incorporated into IPEC. Using UV spectroscopy and CD spectroscopy combined with ultracentrifugation, it is shown that complexed DNA compacts, revealing a wound double-helical structure. Using fluorescence microscopy, we observed compaction of individual ultrahigh molecular mass DNA interacting with excess of G4 to form water-soluble positively charged IPECs “unimers”.