Angelini Thomas E, Golestanian Ramin, Coridan Robert H, Butler John C, Beraud Alexandre, Krisch Michael, Sinn Harald, Schweizer Kenneth S, Wong Gerard C L
Department of Physics, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.
Proc Natl Acad Sci U S A. 2006 May 23;103(21):7962-7. doi: 10.1073/pnas.0601435103. Epub 2006 May 11.
Current understanding of electrostatics in water is based on mean-field theories like the Poisson-Boltzmann formalism and its approximations, which are routinely used in colloid science and computational biology. This approach, however, breaks down for highly charged systems, which exhibit counterintuitive phenomena such as overcharging and like-charge attraction. Models of counterion correlations have been proposed as possible explanations, but no experimental comparisons are available. Here, collective dynamics of counterions that mediate like-charge attraction between F-actin filaments have been directly observed in aqueous solution using high-resolution inelastic x-ray scattering down to molecular length-scales. We find a previously undescribed acoustic-like phonon mode associated with correlated counterions. The excitation spectra at high wave-vector Q reveal unexpected dynamics due to ions interacting with their "cages" of nearest neighbors. We examine this behavior in the context of intrinsic charge density variations on F-actin. The measured speed of sound and collective relaxation rates in this liquid agree surprisingly well with simple model calculations.
目前对水中静电学的理解基于诸如泊松-玻尔兹曼形式及其近似等平均场理论，这些理论在胶体科学和计算生物学中经常使用。然而，这种方法对于高电荷系统失效，高电荷系统会表现出诸如过充电和同电荷吸引等违反直觉的现象。已经提出了反离子相关性模型作为可能的解释，但尚无实验比较。在这里，使用高分辨率非弹性X射线散射，直至分子长度尺度，在水溶液中直接观察到介导F-肌动蛋白丝之间同电荷吸引的反离子的集体动力学。我们发现了一种与相关反离子相关的前所未有的类似声子的模式。高波矢Q处的激发光谱揭示了由于离子与其最近邻的“笼”相互作用而产生的意外动力学。我们在F-肌动蛋白上固有电荷密度变化的背景下研究这种行为。在这种液体中测得的声速和集体弛豫率与简单模型计算惊人地吻合。
