Dendritic polyelectrolytes with monovalent and divalent counterions: Charge regulation effect and counterion release
Dendritic polyelectrolytes with monovalent and divalent counterions: Charge regulation effect and counterion release
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具有一价和二价抗衡离子的树枝状聚电解质：电荷调节效应和抗衡离子释放
DOI：
10.1039/d1sm01392k
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发表时间：
2021
期刊：
影响因子：
3.4
通讯作者：
Yuejun Zhang
中科院分区：
文献类型：
--
作者：
Xiao Xu;Xu Jia;Yuejun Zhang
电荷调节和反离子的释放在决定聚电解质的电荷状态和聚电解质与蛋白质的相互作用中是极其重要的。除了一价阳离子到多价阳离子之外，众所周知，离子的影响在性质上是不同的。因此，基于单价离子的电荷调节和反离子释放的公认描述并不立即适用于具有多价离子的系统。在这里，我们研究的关键结构和静电功能的带电树枝状聚合物在手的药学上重要的树枝状聚甘油硫酸酯（dPGS）的大分子平衡与单价和二价盐的分子动力学（MD）模拟。遵循一个简单但准确的方案来确定其有效半径，dPGS的反离子凝聚层以高精度确定，并且我们观察到凝聚的一价阳离子（MC）到二价阳离子（DC）的顺序替换，从而使dPGS的有效电荷与DC浓度相比更小。我们解析并追踪dPGS上的抗衡离子的释放，该抗衡离子沿着其与血浆蛋白人血清白蛋白（HSA）的结合途径。我们发现，MC的释放仍然有利于络合，导致相当数量的释放熵作为络合的驱动力。DC的释放仅在高于一定DC浓度时发生，释放的离子数量比MC少得多。其对结合自由能的贡献很小，表明在释放DC中的熵增益和从树枝状聚合物解离DC的焓罚之间的微妙抵消。
The charge regulation and the release of counterions are extremely important and substantial in determining the charge state of polyelectrolytes and the interaction between polyelectrolytes and proteins. Going beyond monovalent to multivalent cations, it is well-known that the effects of ions are qualitatively different. Therefore, the well-accepted descriptions of the charge regulation and the counterion release based on monovalent ions do not immediately apply to systems with multivalent ions. Here, we study the key structural and electrostatic features of charged dendrimers at hand of the pharmaceutically important dendritic polyglycerol sulfate (dPGS) macromolecule equilibrated with monovalent and divalent salts by molecular dynamics (MD) simulations. Following a simple but accurate scheme to determine its effective radius, the counterion condensed layer of the dPGS is determined with high accuracy and we observe the sequential replacement of condensed monovalent cations (MCs) to divalent cations (DCs) rendering a smaller dPGS effective charge versus the DC concentration. We resolve and track the release of counterions on the dPGS along its binding pathway with the plasma protein Human Serum Albumin (HSA). We find that the release of MCs remains favorable for the complexation leading to a considerable amount of release entropy as the driving force for complexation. The release of DCs only occurs above a certain DC concentration with a comparably smaller number of released ions than MCs. Its contribution to the binding free energy is small indicating a subtle cancellation between the entropy gain in releasing DCs and the enthalpy penalty from dissociating DCs from the dendrimer.