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Monica Olvera de la Cruz

Department of Materials Science and Engineering, Northwestern University


Electrostatic Interactions in Mixtures of Cationic and Anionic Biomolecules: Bulk Structures and Induced Surface Pattern Formation

DNA and other biological and synthetic Polyelectrolytes undergo two structural transitions upon increasing the concentration of oppositely charged polyions. In low monovalent salt solutions, mixtures of oppositely charged linear polyelectrolytes collapse into nearly neutral compact structures. With further addition of salt and or of polyelectrolytes the chains dissolve acquiring coiled conformations. The transitions are analyzed using an ionic glass type model for the structure of condensed polyelectrolytes where the cohesive energy of collapse state is dominated by the attractive Coulombic interaction between oppositely charged polyions. In the case of hetergoneous molecules, such as mixtures of basic and acidic polypetide amphiphiles or of cationic-anionic surfactants, stable nano-aggregates form at low salt concentrations even when the components are strongly incompatible. We analyze here the structure of incompatible positively and negatively charged components confined to interfaces. We determine the structure in flat surfaces and in cylindrical micelle surfaces as a function of salt concentration in the medium.