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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”.

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Interaction between Astramol poly(propylene imine) dendrimers of five generations, DAB-dendr-(NH2) x (where x is equal to 4, 8, 16, 32, or 64) and linear poly(sodium acrylate), poly(acrylic) acid, poly(sodium styrenesulfonate), or native DNA was studied in salt-free solutions by means of potentiometric, argentometric, and turbidimetric titrations. In addition to x outer primary amine groups the dendrimer molecule contains x − 2 inner tertiary amine groups. It is found that the pH-controlled interpolyelectrolyte coupling reaction resulting in formation of the corresponding interpolyelectrolyte complexes occurs on mixing of the dendrimer and the polyanion solutions. A peculiar finding was that all dendrimer amine groups being protonated can form ion pairs with carboxylate or sulfonate groups of the polyanions. In other words DAB-dendr-(NH2) x molecules are fully penetrable for rather flexible oppositely charged polyelectrolyte chains. However, this is not the case for rigid negatively charged DNA double helixes which apparently bind only to the dendrimer shell. The complexes of dendrimers, with polyanions containing equal amounts of cationic and anionic groups mostly ion-paired (stoichiometric complexes), are insoluble in water. At the same time water soluble nonstoichiometric interpolyelectrolyte complexes can be obtained if the dendrimer is a deficient component of the complex species. This behavior is similar to that of complexes formed by oppositely charged linear polyions.

This paper describes the application of the numerical solution of the Percus–Yevick approximation for a multicomponent system of sticky hard spheres to small angle x-ray scattering experiments. The effect of polydispersity on the pair correlation function is quantitatively described, thus enabling the analysis of experimental data. In this way quantitative estimates of the size distribution width, interaction radii and the measure of attraction between particles can be obtained. The attractive interaction in a system of sticky spheres is known to give rise to a transition analogous to a gas–liquid phase transition. The effect of polydispersity on this transition is discussed. Finally it is shown how the model can be used to describe small angle x-ray scattering from an AOT microemulsion system.

Small-angle neutron scattering has been applied for structural investigations of amine-terminated poly(propylene imine) dendrimer (Astramol) solutions in D2O as a function of concentration and acidity. The forward scattering, dΣ/dΩ(Q = 0), decreases progressively by increasing dendrimer concentration due to interdendrimer interference, giving rise to a well-defined interference peak. Upon increasing dendrimer concentration, a shift is observed in the peak position, Q max, with the empirical scaling relation Q max ∼ φ0.55±0.05, which is significantly larger than that of a simple packing argument Q max ∼ φ1/3. At high Q values, all data sets collapse to a single curve, indicating that the internal structure of the dendrimers are unaffected by interactions between neighboring molecules. Upon addition of acid, the dendrimers become charged, giving rise to a pronounced interference peak. These Coulomb interactions can be screened by addition of either excess acid or salts.

Abstract:As a part of a study of the colloidal structures present in nonionic ointments, the interaction between polyoxyethylene and water is investigated. A series of mixtures of polyoxyethylene 1550 and water is studied using differential scanning calorimetry. Heating as well as cooling experiments are performed. The effects of the heat of mixing, supercooling and melting point depression on the measured enthalpy changes are discussed. From the non-freezing water fraction it is concluded that 2 water molecules per oxyethylene unit are tightly bound to the polymer chain. The observed differences between the cooling and the heating curves lead to a possible explanation for the alterations in the samples occurring at low temperatures. A hydrate structure of polyoxyethylene at low temperatures is proposed. Finally, comment is made on the phase diagram of the system polyoxyethylene/water.

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