Chandrasekhar Hall

Dipole-driven Self-assembly of Charged Macromolecules

Murugappan Muthukumar

University of Massachusetts Amherst

Control of self-assembled structures of charged macromolecules in aqueous solutions is vital in myriads of natural phenomena that includes the liquid-liquid phase separation of intrinsically disordered proteins. In the simplest situation, uniformly charged polyelectrolyte chains in electrolyte solutions are homogeneously distributed due to their electrostatic repulsion. In stark contrast with this well-established result, we find that the same system exhibits rich phase behavior consisting of precipitation, interlude of self-assembled mesomorphic structures that can self-poison, and homogeneous solution, in the presence of a small organic anion. Using theory and experiments on model systems, we find that this phenomenon originates from dipole-dipole interactions overwhelming charge-charge repulsion. The discovered principle of dipole-directed assembly appears to be essential to understand and control macromolecular structures in the broader context of polyzwitterions, complex coacervation, and membrane-less organelles.