Nap Rikkert J, Szleifer Igal
Department of Biomedical Engineering, Northwestern University, Evanston, Illinois, USA.
Biophys J. 2008 Nov 15;95(10):4570-83. doi: 10.1529/biophysj.108.133801. Epub 2008 Aug 8.
Weak polyelectrolytes tethered to cylindrical surfaces are investigated using a molecular theory. These polymers form a model system to describe the properties of aggrecan molecules, which is one of the main components of cartilage. We have studied the structural and thermodynamical properties of two interacting aggrecans with a molecular density functional theory that incorporates the acid-base equilibrium as well as the molecular properties: including conformations, size, shape, and charge distribution of all molecular species. The effect of acidity and salt concentration on the behavior is explored in detail. The repulsive interactions between two cylindrical-shaped aggrecans are strongly influenced by both the salt concentration and the pH. With increasing acidity, the polyelectrolytes of the aggrecan acquire charge and with decreasing salt concentration those charges become less screened. Consequently the interactions increase in size and range with increasing acidity and decreasing salt concentration. The size and range of the forces offers a possible explanation to the aggregation behavior of aggrecans and for their ability to resist compressive forces in cartilage. Likewise, the interdigitation of two aggrecan molecules is strongly affected by the salt concentration as well as the pH. With increasing pH, the number of charges increases, causing the repulsions between the polymers to increase, leading to a lower interdigitation of the two cylindrical polymer layers of the aggrecan molecules. The low interdigitation in charged polyelectrolytes layers provides an explanation for the good lubrication properties of polyelectrolyte layers in general and cartilage in particular.
利用分子理论研究了附着在圆柱表面的弱聚电解质。这些聚合物构成了一个模型系统，用于描述聚集蛋白聚糖分子的性质，聚集蛋白聚糖是软骨的主要成分之一。我们用分子密度泛函理论研究了两个相互作用的聚集蛋白聚糖的结构和热力学性质，该理论纳入了酸碱平衡以及分子性质，包括所有分子种类的构象、大小、形状和电荷分布。详细探讨了酸度和盐浓度对其行为的影响。两个圆柱状聚集蛋白聚糖之间的排斥相互作用受到盐浓度和pH值的强烈影响。随着酸度增加，聚集蛋白聚糖的聚电解质获得电荷，随着盐浓度降低，这些电荷的屏蔽作用减弱。因此，随着酸度增加和盐浓度降低，相互作用的大小和范围都会增加。这些力的大小和范围为聚集蛋白聚糖的聚集行为及其在软骨中抵抗压缩力的能力提供了一种可能的解释。同样，两个聚集蛋白聚糖分子的相互交错也受到盐浓度和pH值的强烈影响。随着pH值增加，电荷数量增加，导致聚合物之间的排斥力增加，从而使聚集蛋白聚糖分子的两个圆柱状聚合物层的相互交错程度降低。带电聚电解质层中较低的相互交错程度总体上解释了聚电解质层尤其是软骨具有良好润滑性能的原因。
