离子与聚电解质间的相互作用：从带电颗粒到核酸

发布时间：2018-04-27 07:15

本文选题：聚电解质 + 离子效应　；参考：《武汉大学》2017年博士论文

【摘要】：溶液中的离子对带电胶体球和核酸分子等聚电解质结构、稳定性和动力学等起着至关重要的作用。例如核酸(DNA/RNA)分子带有高密度负电荷,离子在其结构折叠、凝聚以及结构变化时起到重要的调节作用,而核酸分子的结构和柔性对其生物功能有重要的影响。在本文里,针对离子溶液中带电胶体球和核酸这两种聚电解质,我们从不同方面进行了深入研究。本论文的主要研究内容如下:1.同种电荷胶体球间相互作用中多体效应的研究。我们用蒙特卡罗模拟和非线性泊松-玻尔兹曼理论两种方法,对广泛盐离子条件下同种电荷胶体球间平均力势的多体效应进行了系统的研究。我们的计算表明,在高浓度1:1盐离子条件下,同种电荷胶体球间平均力势是弱排斥且具有可加性,而在低浓度1:1盐离子条件下,可加性则高估了多体胶体球间的排斥相互作用。在低浓度2:2盐离子条件下,两个胶体球间平均力势为微弱排斥,而多个胶体球系统的平均力势却是相互吸引的。有趣的是,在高浓度2:2盐离子条件下,两胶体球间是显著的吸引作用,而多体效应却会导致这种吸引减弱。微观分析显示,多体效应是跟束缚在胶体球周围的离子密切相关的,而离子的束缚强烈依赖于离子浓度、价数、胶体球的带电荷量以及数目。2.非对称盐溶液中异种电荷胶体球间平均力势的研究。我们利用蒙特卡罗模拟,研究了三价盐离子溶液中异种电荷胶体球之间的平均力势。我们发现,对于高浓度对称3:3盐溶液,两个异种电荷胶体球间平均力势为长程吸引,而对非对称3:1盐溶液,两个异种电荷胶体球之间可产生长程的有效排斥作用。我们的微观分析以及建立的理论模型皆显示此长程排斥来自于高价离子对胶体球的过中和效应。3.具有伸缩柔性的半弹性有限长链末端距离分布解析公式的导出。我们基于前人描述半弹性链末端距离分布的公式,计入链伸缩柔性,导出了描述具有伸缩柔性的半弹性短链末端距离分布的解析公式。此公式在不同的伸缩模量以及持久长度下的结果与蒙特卡罗模拟高度吻合;进一步,此公式也与短链DNA/RNA的全原子分子动力学模拟吻合很好。此外,我们分析发现,当DNA长度超过～130个碱基对,或者RNA长度超过了～240个碱基对时,伸缩柔性对它们末端距离分布影响可忽略。4.发展描述高价离子凝聚的紧束缚离子模型。考虑全原子结构和全原子电荷分布,我们发展了紧束缚离子模型。此拓展模型既可考虑离子间的关联与涨落,又可处理聚电解质分子的全原子结构和全原子的电荷分布。其预测的两个同种电荷胶体球间平均力势与蒙特卡罗模拟结果吻合很好,其预测的单价/双价离子对不同的核酸的竞争凝聚效应与实验测量一致,其预测的三链DNA周围Mg2+离子径向密度分布与全原子分子动力学模拟结果也能很好吻合。此外,此模型可给出聚电解质周围离子的三维密度分布。
[Abstract]:The ions in the solution play an important role in the structure, stability and kinetics of polyelectrolyte such as charged colloidal spheres and nucleic acid molecules. For example, nucleic acid DNA rRNA RNAs have high density negative charge, ions play an important role in the structure folding, condensation and structural changes, while the structure and flexibility of nucleic acid molecules have an important impact on their biological functions. In this paper, we have studied the charged colloidal spheres and nucleic acid polyelectrolytes in ionic solutions from different aspects. The main contents of this thesis are as follows: 1. Study on the multibody effect in the interaction between the same charge colloidal spheres. Monte Carlo simulation and nonlinear Poisson Boltzmann theory are used to study the multibody effect of the average force potential between the same charge colloids under the condition of a wide range of salt ions. Our calculations show that the average force potential between the same charge colloidal spheres is weakly repulsive and additive under the condition of high concentration of 1:1 salt ions, while the additivity overestimates the repulsive interaction between the multibody colloidal spheres at low 1:1 salt ion concentration. Under the condition of low concentration of 2:2 salt ions, the average force potential between the two colloidal spheres is weak repulsive, but the average force potential of many colloidal spheres systems is attractive to each other. Interestingly, under the condition of high concentration of 2:2 salt, the attraction between the two colloidal spheres is significant, but the multi-body effect leads to the weakening of the attraction. Microscopic analysis shows that the multibody effect is closely related to the ions bound around the colloidal sphere, and the binding of ions is strongly dependent on the concentration of ions, the number of valence, the amount of charge and the number of the colloidal spheres. Study on the average force potential between different charge colloids in asymmetric salt solution. The average force potential between dissimilar charge colloidal spheres in trivalent salt ion solution has been studied by Monte Carlo simulation. It is found that for high concentration symmetric 3:3 salt solution, the average force potential between two dissimilar charge colloids is a long range attraction, while for asymmetric 3:1 salt solution, there is a long range effective repulsive effect between the two dissimilar charge colloidal spheres. Our microscopic analysis and established theoretical models show that this long range exclusion is due to the over neutralization effect of the colloidal sphere of high valence ions. The derivation of the analytic formula for the end distance distribution of a semi-elastic finite long chain with telescopic flexibility. Based on the formula used to describe the distance distribution of the end of a semi-elastic chain, an analytical formula for describing the distance distribution of the end of a semi-elastic short chain with extensibility is derived by taking into account the flexibility of the chain. The results of this formula are in good agreement with the Monte Carlo simulation under different modulus of expansion and durative length, and the formula is in good agreement with the full atomic molecular dynamics simulation of short chain DNA/RNA. In addition, we find that when the length of DNA exceeds 130 base pairs or the length of RNA exceeds 240 base pairs, the effect of stretching flexibility on the distance distribution of their ends is negligible. A tight-binding ion model describing the condensation of high valence ions was developed. Considering the total atomic structure and the total atomic charge distribution, we developed a tight-binding ion model. The extended model can not only consider the correlation and fluctuation of ions, but also deal with the whole atomic structure and charge distribution of polyelectrolyte molecules. The predicted average force potential between two same charge colloidal spheres is in good agreement with the Monte Carlo simulation results. The predicted competitive coacervation effect of univalent / bivalent ions on different nucleic acids is consistent with the experimental measurements. The predicted radial density distribution of Mg2 ions around triplex DNA is in good agreement with the results of full atomic molecular dynamics simulation. In addition, the three dimensional density distribution of ions around polyelectrolyte can be obtained by this model.
【学位授予单位】：武汉大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：O646.1

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