(413b) Length Effects on Polyelectrolyte Complexation: How ‘Poly’ Must a Polyelectrolyte be? | AIChE

(413b) Length Effects on Polyelectrolyte Complexation: How ‘Poly’ Must a Polyelectrolyte be?

Authors 

Vieregg, J. - Presenter, University of Chicago
Lueckheide, M., University of Chicago
Tirrell, M. V., University of Chicago
The term ‘polyelectrolyte complexation’ describes the associative phase separation that occurs when oppositely charged polymers are mixed in aqueous solution, resulting in formation of liquid coacervates or solid precipitates. Measurements indicate that the free energy gain of polyelectrolyte complexation is primarily due to increase in entropy upon mixing, and this is usually described in terms of counterion release: by directly neutralizing each other, the polyelectrolytes release their screening counterions into solution. Consistent with this picture, complexation is found to be inhibited by high concentrations of salt. Similar physics drives the condensation of genomic DNA into compact structures in vitro and in vivo: low valence cations are displaced by binding of multivalent ions and cationic proteins. Theoretical treatments of both problems also typically assume the polyelectrolytes are quite long. Recent measurements aimed at understanding polyelectrolyte complexes as delivery vehicles for therapeutic oligonucleotides and as protocells in early life scenarios challenge this understanding, however: coacervation is observed for mixtures of short oligomers and even singly-charged nucleotide monophosphates. These molecules are not polyelectrolytes by conventional description, raising the question of what drives complexation when the translational entropy of all the constituent molecules is similar. In order to address this question, we measured the complexation properties of oligonucleotides and mononucleotides by short peptides and polyamines. I will present results of these studies, including phase diagrams and thermodynamic measurements that compare the effect of counterion release to other molecular interactions such as base stacking, in order to define the length scale at which our conventional understanding of polyelectrolyte physics begins to operate.

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