Electrostatics of Macro-Ions

这是一笔用于开展理论研究的基金，目的是进一步了解水介质中层状、圆柱形和球形大离子之间的静电相互作用。这项研究是由多学科活动的数学和物理科学办公室以及材料研究、化学、分子和细胞生物学以及物理学部门资助的。本研究的目的之一是研究混合维宏观离子之间的静电力，如带电球体与平面、带电棒与平面之间的相互作用。在混合维数和大离子电荷相反的条件下，棒状和/或球体将反离子释放到溶剂中会产生一种不寻常的在平面上结合的熵机制。带电荷的生物聚合物通过反离子释放吸引吸附在带相反电荷的脂质膜上。第二个目标将是解决泊松-玻尔兹曼（PB）理论的各种缺陷，该理论是描述宏观离子之间静电相互作用的主要分析工具。虽然PB理论预测了类电荷棒之间的排斥相互作用，但模拟表明，由于反离子相关效应，引力可能会出现。将对多价反离子和柔性聚电解质在棒之间的大离子吸引进行理论的多体描述。在前一种情况下，将使用线性响应方法将相互作用的杆视为耦合的一维等离子体。在后一种情况下，Edwards的聚合物场理论将被推广到包括这种特殊的棒-链-棒几何结构的静电效应。圆柱形巨离子与普通多价反离子和柔性聚电解质相互作用的布朗动力学模拟将由UCLA/LANL的Gronbech-Jensen博士完成。研究的最终目的将是检查双层内流动性对大离子与由非离子/离子脂质混合物组成的膜结合的影响。一个新的自由度与一个可变的、不均匀的表面电荷层有关。与这种膜结合的带电生物聚合物有望发展出一种众所周知的曼宁在散装溶剂中带电棒冷凝的二维变体。基于对DNA在阳离子膜上凝聚体的实验研究，我们将研究离子两亲体在膜上吸附大离子过程中的自组装。这是一笔进行理论研究的基金，以进一步了解水介质中层状、圆柱形和球形大离子之间的静电相互作用。这项研究是由多学科活动的数学和物理科学办公室以及材料研究、化学、分子和细胞生物学以及物理学部门资助的。研究不同形状的大型宏观离子之间的静电相互作用是一个具有挑战性的基础性问题。当人们意识到这些系统也是由构成生命系统的生物聚合物（DNA）和膜组成时，这也是一个具有重大实际意义的问题。＊＊＊

9708646 Bruinsma This is a grant to conduct theoretical research to develop further a fundamental understanding of the electrostatic interactions in aqueous media between lamellar, cylindrical and spherical macro-ions. The research is funded by the Mathematical and Physical Sciences Office of Multidisciplinary Activities and the Divisions of Materials Research, Chemistry, Molecular and Cellular Biology, and Physics. One aim of the research is to study electrostatic forces between macro-ions of mixed dimensionality, such as interactions between charged spheres and planes, and charged rods and planes. Under conditions of mixed dimensionality and opposite charges on the macro-ions, release of counterions into the solvent by the rod and/or the sphere produces an unusual entropic mechanism for binding in the plane. Adsorption of charged biopolymers onto oppositely charged lipid membranes by counterion release attraction will be studied. A second aim will be to address various deficiencies in Poisson-Boltzmann (PB) theory, the main analytical tool available to describe the electrostatic interactions between macro-ions. Whereas PB theory predicts repulsive interactions between like-charged rods, simulations show that attractive forces can appear due to counterion correlation effects. A theoretical, many-body description of macro-ion attraction between rods by polyvalent counterions and by flexible polyelectrolytes will be undertaken. In the former case, a linear response approach will be used to treat the interacting rods as coupled one- dimension plasmas. In the latter case, the polymer field theory of Edwards will be generalized to include electrostatic effects for this special rod-chain-rod geometry. Brownian dynamics simulations of cylindrical macro-ion interaction with both ordinary polyvalent counterions and with flexible polyelectrolytes will be done by Dr. Gronbech-Jensen of UCLA/LANL. A final aim of the research will be to examine the effects of intra-bilayer fluidity on binding of macro-ions to membranes which consist of non-ionic/ionic lipid mixtures. A new degree of freedom is associated with a variable, and inhomogeneous, surface charge layer. Charged biopolymers bound to such membranes are expected to develop a two- dimensional variant of the well-known Manning condensation of charged rods in bulk solvent. Motivated by experimental studies of condensates of DNA on cationic membranes, either with solid support or in stacks, the self-assembly of ionic amphiphiles in membranes during macro-ion adsorption will be studied. %%% This is a grant to conduct theoretical research to develop further a fundamental understanding of the electrostatic interactions in aqueous media between lamellar, cylindrical and spherical macro-ions. The research is funded by the Mathematical and Physical Sciences Office of Multidisciplinary Activities and the Divisions of Materials Research, Chemistry, Molecular and Cellular Biology, and Physics. The study of the electrostatic interactions between large, macro-ions of various shapes is a challenging problem of fundamental importance. It is also a problem of great practical interest when one realizes that these systems are also comprised of the biopolymers (DNA) and membranes which make up living systems. ***