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Organic & Biomolecular Chemistry


Complex coacervation is a widely utilized technique for effecting phase separation, though predictive understanding of molecular-level details remains underdeveloped. Here, we couple coarse-grained Monte Carlo simulations with experimental efforts using a polypeptide-based model system to investigate how a comb-like architecture affects complex coacervation and coacervate stability. Specifically, the phase separation behavior of linear polycation-linear polyanion pairs was compared to that of comb polycation-linear polyanion and comb polycation-comb polyanion pairs. The comb architecture was found to mitigate cooperative interactions between oppositely charged polymers, as no discernible phase separation was observed for comb-comb pairs and complex coacervation of linear-linear pairs yielded stable coacervates at higher salt concentration than linear-comb pairs. This behavior was attributed to differences in counterion release by linear vs. comb polymers during polyeletrolyte complexation. Additionally, the comb polycation formed coacervates with both stereoregular poly(L-glutamate) and racemic poly(D,L-glutamate), whereas the linear polycation formed coacervates only with the racemic polyanion. In contrast, solid precipitates were obtained from mixtures of stereoregular poly(L-lysine) and poly(L-glutamate). Moreover, the formation of coacervates from cationic comb polymers incorporating up to ~90% pendant zwitterionic groups demonstrated the potential for inclusion of comonomers to modulate the hydrophilicity and/or other properties of a coacervate-forming polymer. These results provide the first detailed investigation into the role of polymer architecture on complex coacervation using a chemically and architecturally well-defined model system, and highlight the need for additional research on this topic.




Org. Biomol. Chem., 2017, Accepted Manuscript


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B.M.J. acknowledges support from the University of Massachusetts, Amherst Commonwealth Honors College Fellowship, C.E.S. acknowledges support from NSF CAREER Award DMR-1654158 and use of the Extreme Science and Engineering Discovery Environment (XSEDE), which is supported by National Science Foundation Grant ACI-1053575. R.A.L. and T.E. acknowledge financial support from the National Science Foundation (NSF CBET 1403742) and facilities support from the Materials Research Science and Engineering Center (MRSEC DMR-0820506) on Polymers at the University of Massachusetts.

Combs SI - Final.pdf (555 kB)
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