发表机构
National Institute of Standards and Technology; Wesleyan University（美国国家标准与技术研究院; 卫斯理安大学）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
通过分子动力学模拟研究模型聚两性电解质链，发现无盐时呈自缔合构象，加盐后链膨胀（抗聚电解质效应），构象更似随机支化聚合物，且温度依赖性增强。
AI 中文摘要
聚两性电解质（PZ）单体中正负电荷基团邻近所产生的竞争性相互作用，使得这类聚合物在某些方面具有与 intrinsically disordered proteins（固有无序蛋白）相似的性质。为了深入理解这类重要的水溶性聚合物，我们对一个带有显式溶剂的模型PZ链进行了分子动力学（MD）模拟，以研究在无盐和有盐条件下其构象状态。我们发现，在无盐条件下，孤立的PZ链呈现自缔合状态，且对温度的依赖性较弱。添加大量NaCl会削弱链内缔合，导致链膨胀，这一转变类似于球状蛋白的变性过程。特别地，在无盐条件下，PZ链的流体力学穿透函数（即流体力学半径与回转半径之比）更符合随机支化聚合物或单链纳米颗粒的特征，而非无规线团聚合物，其中链内的物理交联源于链内的偶极相互作用。链的构象不仅随盐的加入而趋于变大，而且其平均尺寸对温度的依赖性也变得更加显著。PZ分子随盐添加而膨胀的趋势，有时被称为 anti-polyelectrolyte effect（抗聚电解质效应），这与普通聚电解质的常规趋势不同，后者通常随盐的添加而收缩。我们还考察了有无盐条件下PZ链动态水化层的空间范围，以及温度和盐浓度对该层内水分子迁移率的影响，并研究了PZ侧链的迁移率，其动力学显然与周围水分子强烈耦合。
英文摘要
The competitive interactions arising from the proximity of positive and negatively charged groups in the monomers in polyzwitterions (PZ) makes these polymers have properties similar in some ways to intrinsically disordered proteins. To gain qualitative insights into this important class of water-soluble polymers, we performed molecular dynamics (MD) simulations of a model PZ chain with an explicit solvent to understand the conformational state in the absence and presence of added salt. We find that isolated PZ chains under salt-free conditions adopt a self-associated state having a weak dependence on temperature. The addition of an appreciable amount of NaCl leads to a weakening of the intrachain associations, resulting in chain expansion, a transition reminiscent of the denaturation of globular proteins. In particular, the hydrodynamic penetration function, the ratio of hydrodynamic radius to the radius of gyration, of the PZ chains under salt free conditions, is found to be more consistent with a randomly branched polymer or single chain nanoparticle than a random coil polymer where the physical cross-links within the chain arise from the dipoles within the chain. The chain conformation not only tends to become larger with the addition of salt but also acquires a more appreciable temperature dependence of its average size with temperature. This swelling trend of PZ molecules with added salt, sometimes referred to as the anti-polyelectrolyte effect, is distinct from the normal trend polyelectrolytes, which typically become more contracted with the addition of salt. We also examined the spatial extent of the dynamic hydration layer the PZ chain, both with and without added salt, and the effect of temperature and salt concentration on the water mobility within this layer, and PZ side-chain mobility, whose dynamics is apparently strongly coupled to the surrounding water molecules.
Comments29 pages, 9 figures
