带电多肽络合的驱动力
The Driving Force for the Complexation of Charged Polypeptides
摘要：
带相反电荷的聚电解质在溶液中的相分离是当前的研究热点。在这项工作中，我们研究的驱动力，利用分子动力学模拟双络合。我们使用三种不同的力场，一个原子力场和两个粗粒力场计算了聚（赖氨酸）和聚（谷氨酸）寡聚体之间的平均力的潜力。所有力场之间存在定性一致性，即，自由能的符号和大小以及驱动力的性质是相似的，这表明水的分子性质并不起重要作用。对于完全带电的肽，我们发现，在所有情况下，当小离子中和聚离子，或过量的驱动力协会是熵。所有反离子的去除转换了驱动力，使络合充满活力。这表明络合的熵是由抗衡离子主导的。然而，当11聚体中只有6个残基带电时，驱动力在无盐条件下是可逆的。模拟揭示了复杂凝聚的机制和现实的聚离子模型的重要性。
英文摘要：
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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