Electrostatics of Macro-Ions

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9708646 Bruinsma This is a grant to conduct theoretical research to develop further a fundamental understanding of the electrostatic interactions in aqueous media between lamellar, cylindrical and spherical macro-ions. The research is funded by the Mathematical and Physical Sciences Office of Multidisciplinary Activities and the Divisions of Materials Research, Chemistry, Molecular and Cellular Biology, and Physics. One aim of the research is to study electrostatic forces between macro-ions of mixed dimensionality, such as interactions between charged spheres and planes, and charged rods and planes. Under conditions of mixed dimensionality and opposite charges on the macro-ions, release of counterions into the solvent by the rod and/or the sphere produces an unusual entropic mechanism for binding in the plane. Adsorption of charged biopolymers onto oppositely charged lipid membranes by counterion release attraction will be studied. A second aim will be to address various deficiencies in Poisson-Boltzmann (PB) theory, the main analytical tool available to describe the electrostatic interactions between macro-ions. Whereas PB theory predicts repulsive interactions between like-charged rods, simulations show that attractive forces can appear due to counterion correlation effects. A theoretical, many-body description of macro-ion attraction between rods by polyvalent counterions and by flexible polyelectrolytes will be undertaken. In the former case, a linear response approach will be used to treat the interacting rods as coupled one- dimension plasmas. In the latter case, the polymer field theory of Edwards will be generalized to include electrostatic effects for this special rod-chain-rod geometry. Brownian dynamics simulations of cylindrical macro-ion interaction with both ordinary polyvalent counterions and with flexible polyelectrolytes will be done by Dr. Gronbech-Jensen of UCLA/LANL. A final aim of the research will be to examine the effects of intra-bilayer fluidity on binding of macro-ions to membranes which consist of non-ionic/ionic lipid mixtures. A new degree of freedom is associated with a variable, and inhomogeneous, surface charge layer. Charged biopolymers bound to such membranes are expected to develop a two- dimensional variant of the well-known Manning condensation of charged rods in bulk solvent. Motivated by experimental studies of condensates of DNA on cationic membranes, either with solid support or in stacks, the self-assembly of ionic amphiphiles in membranes during macro-ion adsorption will be studied. %%% This is a grant to conduct theoretical research to develop further a fundamental understanding of the electrostatic interactions in aqueous media between lamellar, cylindrical and spherical macro-ions. The research is funded by the Mathematical and Physical Sciences Office of Multidisciplinary Activities and the Divisions of Materials Research, Chemistry, Molecular and Cellular Biology, and Physics. The study of the electrostatic interactions between large, macro-ions of various shapes is a challenging problem of fundamental importance. It is also a problem of great practical interest when one realizes that these systems are also comprised of the biopolymers (DNA) and membranes which make up living systems. ***