本文選題：聚電解質(zhì) + 離子效應(yīng)��； 參考：《武漢大學》2017年博士論文

【摘要】：溶液中的離子對帶電膠體球和核酸分子等聚電解質(zhì)結(jié)構(gòu)、穩(wěn)定性和動力學等起著至關(guān)重要的作用。例如核酸(DNA/RNA)分子帶有高密度負電荷,離子在其結(jié)構(gòu)折疊、凝聚以及結(jié)構(gòu)變化時起到重要的調(diào)節(jié)作用,而核酸分子的結(jié)構(gòu)和柔性對其生物功能有重要的影響。在本文里,針對離子溶液中帶電膠體球和核酸這兩種聚電解質(zhì),我們從不同方面進行了深入研究。本論文的主要研究內(nèi)容如下:1.同種電荷膠體球間相互作用中多體效應(yīng)的研究。我們用蒙特卡羅模擬和非線性泊松-玻爾茲曼理論兩種方法,對廣泛鹽離子條件下同種電荷膠體球間平均力勢的多體效應(yīng)進行了系統(tǒng)的研究。我們的計算表明,在高濃度1:1鹽離子條件下,同種電荷膠體球間平均力勢是弱排斥且具有可加性,而在低濃度1:1鹽離子條件下,可加性則高估了多體膠體球間的排斥相互作用。在低濃度2:2鹽離子條件下,兩個膠體球間平均力勢為微弱排斥,而多個膠體球系統(tǒng)的平均力勢卻是相互吸引的。有趣的是,在高濃度2:2鹽離子條件下,兩膠體球間是顯著的吸引作用,而多體效應(yīng)卻會導致這種吸引減弱。微觀分析顯示,多體效應(yīng)是跟束縛在膠體球周圍的離子密切相關(guān)的,而離子的束縛強烈依賴于離子濃度、價數(shù)、膠體球的帶電荷量以及數(shù)目。2.非對稱鹽溶液中異種電荷膠體球間平均力勢的研究。我們利用蒙特卡羅模擬,研究了三價鹽離子溶液中異種電荷膠體球之間的平均力勢。我們發(fā)現(xiàn),對于高濃度對稱3:3鹽溶液,兩個異種電荷膠體球間平均力勢為長程吸引,而對非對稱3:1鹽溶液,兩個異種電荷膠體球之間可產(chǎn)生長程的有效排斥作用。我們的微觀分析以及建立的理論模型皆顯示此長程排斥來自于高價離子對膠體球的過中和效應(yīng)。3.具有伸縮柔性的半彈性有限長鏈末端距離分布解析公式的導出。我們基于前人描述半彈性鏈末端距離分布的公式,計入鏈伸縮柔性,導出了描述具有伸縮柔性的半彈性短鏈末端距離分布的解析公式。此公式在不同的伸縮模量以及持久長度下的結(jié)果與蒙特卡羅模擬高度吻合;進一步,此公式也與短鏈DNA/RNA的全原子分子動力學模擬吻合很好。此外,我們分析發(fā)現(xiàn),當DNA長度超過～130個堿基對,或者RNA長度超過了～240個堿基對時,伸縮柔性對它們末端距離分布影響可忽略。4.發(fā)展描述高價離子凝聚的緊束縛離子模型�？紤]全原子結(jié)構(gòu)和全原子電荷分布,我們發(fā)展了緊束縛離子模型。此拓展模型既可考慮離子間的關(guān)聯(lián)與漲落,又可處理聚電解質(zhì)分子的全原子結(jié)構(gòu)和全原子的電荷分布。其預(yù)測的兩個同種電荷膠體球間平均力勢與蒙特卡羅模擬結(jié)果吻合很好,其預(yù)測的單價/雙價離子對不同的核酸的競爭凝聚效應(yīng)與實驗測量一致,其預(yù)測的三鏈DNA周圍Mg2+離子徑向密度分布與全原子分子動力學模擬結(jié)果也能很好吻合。此外,此模型可給出聚電解質(zhì)周圍離子的三維密度分布。
[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.
【學位授予單位】：武漢大學
【學位級別】：博士
【學位授予年份】：2017
【分類號】：O646.1

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