The complexation of siRNA (small interfering RNA) with cationic micelles was studied by time dependent synchrotron SAXS. Micelles were formed by two types of divalent cationic surfactants, i.e. Gemini bis (quaternary ammonium) bromide with variable spacer length (12-3-12, 12-6-12, 12-12-12) and a weak electrolyte surfactant (SH14) with triazine head. Immediately after mixing (t < 50 ms), new large aggregates appeared in solution and the scattering intensity at low q increased. Concomitantly, the presence of a quasi-Bragg peak at q ~ 1.5〖 nm〗^(-1) indicated core structuring within the complexes. We hypothesize that siRNA and micelles are alternately arranged into “sandwiches”, forming domains with internal structural coherence. The process of complex reorganization followed a first-order kinetics and was completed in less than about 5 minutes, after which a steady state was reached. Aggregates containing Geminis were compact globular structures whose gyration radii Rg depended on the spacer length and was in the order of 7-27 nm. Complexes containing SH14 (Rg =14-16 nm) were less ordered and possessed a loser internal arrangement. The obtained data, joint to previous structural investigation by Dynamic Light Scattering, Zeta potential and Small Angle Neutron Scattering, are encouraging evidence for using these systems in biological trials. In fact we showed that transfection agents can be obtained by simple mixing a micelle solution of the cationic surfactant and a siRNA solution, both of which are easily prepared and stable.

We have generated closed-cell microcellular foams from gliadin, an abundantly available wheat storage protein. The extraction procedure of gliadin from wheat gluten, which involves only the natural solvents water and ethanol, respectively, is described with emphasis on the precipitation step of gliadin which results in a fine dispersion of mostly spherical, submicron gliadin particles composed of myriad of protein molecules. A dense packing of these particles was hydrated and subjected to an atmosphere of carbon dioxide or nitrogen in a high-pressure cell at 250 bar. Subsequent heating to temperatures close to but still below 100 A degrees C followed by sudden expansion and simultaneous cooling resulted in closed-cell microcellular foam. The spherical gliadin templates along with the resulting foam have been analyzed by scanning electron microscope (SEM) pictures. The size distribution of the primary particles shows diameters peaked around 0.54 mu m, and the final foam cell size peaks around 1.2 mu m, at a porosity of about 80 %. These are the smallest foam cell sizes ever reported for gliadin. Interestingly, the cell walls of these microcellular foams are remarkably thin with thicknesses in the lower nanometer range, thus nourishing the hope to be able to reach gliadin nanofoam.

The shape and interactions between model microemulsion droplets (R = 8.2 nm, polydispersity 20%) either decorated with hydrophilic-hydrophobic diblock (PEO-m: C12H25-(EO)n, MPEO = 5.2 kg/mol), or with telechelic triblock copolymers (PEO-2m: C12H25-(EO)2n-C12H25 , MPEO = 10.4 kg/mol) have been studied by small angle neutron scattering (SANS). The results as a function of droplet and copolymer concentration have been compared to the reference case of the bare microemulsion. Using Porod representations, the average bare droplet size was found to be independent of microemulsion concentration in the range studied here, up to some 13%v. Upon addition of copolymer (from r=0 to 30 hydrophobic stickers per droplet), the average droplet radius was unaffected. The interactions between bare and decorated droplets have been analyzed using the structure factor S(q), at first in a model-free way based on its low-q limit S(q→0). This analysis provides clear evidence on the concentration-dependent repulsive or attractive nature of the contributions to the pair droplet-droplet pair potential of the copolymers. Model pair potentials describing the steric repulsions and attractions by copolymer bridging are used to describe the low-q behavior of the structure factor based on an integral equation approach, giving a quantitative estimate of the range and amplitude of the potentials. Moreover, they provide an explanation for the observed transient clustering in terms of a shallow minimum of the total potential.