The phase separation of oppositely-charged polyelectrolytes in solution is of current interest . In this work we study the driving force for polyelectrolyte complexation using molecular dynamics simulations. We calculate the potential of mean force between poly(lysine) and poly(glutamate) oligomers using three different forcfields , an atomistic forcefield and two coarse-grained forcefields . There is excellent qualitative agreement between all forcefields  which suggests that the molecular nature of water does not play a significant role. We find that the driving force for association is entropic in all cases when small ions either neutralize the poly-ions, or are in excess. The removal of all counterions switches the driving force, making complexation energetic. This is an important finding, that suggests that the entropy of complexation is dominated by the counterions , although we see no evidence of counterion condensation . The simulations shed insight into the mechanism of complex coacervation and question several of the approximations currently used in theoretical studies of the phenomena .
The phase separation of oppositely-charged polyelectrolytes in solution is of current interest . In this work we study the driving force for polyelectrolyte complexation using molecular dynamics simulations. We calculate the potential of mean force between poly(lysine) and poly(glutamate) oligomers using three different forcefields , an atomistic force field and two coarse-grained force fields . There is qualitative agreement between all forcefields , i.e., the sign and magnitude of the free energy and the nature of the driving force are similar, which suggests that the molecular nature of water does not play a significant role. For fully charged peptides, we find that the driving force for association is entropic in all cases when small ions either neutralize the poly-ions, or are in excess. The removal of all counterions switches the driving force, making complexation energetic. This suggests that the entropy of complexation is dominated by the counterions . When only 6 residues of a 11-mer are charged, however, the driving force is enthalpic in salt-free conditions . The simulations shed insight into the mechanism of complex coacervation and the importance of realistic models for the polyions .
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forcfields
forcefields
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forcefield
force field
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forcefields
force fields
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excellent
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, i.e., the sign and magnitude of the free energy and the nature of the driving force are similar,
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We
For fully charged peptides, we
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is an important finding, that
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, although we see no evidence of counterion condensation
. When only 6 residues of a 11-mer are charged, however, the driving force is enthalpic in salt-free conditions
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question several of the approximations currently used in theoretical studies of
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phenomena
importance of realistic models for the polyions