Hydrodynamic effects on electrophoresis of biopolymers

一个结合理论、模拟和实验的创新研究项目，旨在研究水动力相互作用在DNA等聚电解质电泳中的作用。在DNA的毛细管电泳中，分子平均为球形，DNA各片段之间的水动力相互作用被指数筛选——主链电荷和周围反离子产生的流场相互抵消。然而，如果DNA被拉伸，例如通过与电场一起施加的压力驱动流，那么在实验中可以观察到流和电场线的横向迁移。人们普遍认为电场不会在带电分子周围的流体中产生任何长程流动，这一假设与德拜的理论工作相矛盾；事实上，电场作用下电荷密度的极化产生了偶极流。尽管与电泳速度相比，这种流动是微弱的，但它的方向依赖性为细长的聚电解质垂直于流动和场线的迁移提供了一种手段。我们的研究是由这样一个假设驱动的，即这种极化流是导致几种现象的原因，如果没有远距离的、流体介导的聚电解质之间的相互作用，这些现象是无法解释的。其中一些现象尚未在实验中观察到，例如细长聚电解质的长度依赖的电泳迁移率，但它们可以通过模拟来预测。通过在实验室实验中确认这些效应的存在来检验潜在的假设是该项目的主要目标。智力优势：最简单的极化流模型预测了电场中带电聚合物的远段之间的偶极流体动力学相互作用。最近基于该模型的数值模拟表明，在有限的盐浓度、电场和流速范围内，人们可以半定量地解释从DNA实验中收集的数据。在这项工作的过程中，发现了几个没有在实验中观察到的新现象。正在进行的研究检验了基础模型的有效性，并探索了这种机制在微通道中操纵聚电解质分布的潜力。更广泛的影响：研究：这项工作增强了我们对聚电解质的理论认识，改变了关于聚电解质动力学中流体动力学筛选的普遍观点。该研究还影响了广泛的技术，这些技术需要控制和定位微通道内带电生物聚合物的能力，为操纵聚电解质创造了额外的可能性，这可能有利于诸如增强吸附在？DNA芯片?另一个潜在的应用是利用迁移速度随链长度的变化作为按长度分离DNA链的手段。教育：研究项目与我们的教育活动相结合，重点是培养学生在一个日益依赖国际合作以有效推进科学和开发新技术的世界中工作。活动包括增加学生参与国际合作和会议。我们鼓励各个层次的学生参与我们实验室的高级研究；我们一直并将继续与该大学现有的高中生项目合作。在所有这些活动中，我们强调代表性不足的群体的参与，积极寻求他们的参与。

Award 1067072PIs: ButlerAn innovative research program combining theory, simulations, and experiments is pursued to investigate the role of hydrodynamic interactions in the electrophoresis of polyelectrolytes such as DNA. In capillaryelectrophoresis of DNA, the molecules are spherical on average and the hydrodynamic interactions among various segments of DNA are exponentially screened - the flow fields generated by the backbone charges and surrounding counterions cancel. However if the DNA is stretched, for example by a pressure driven flow applied in conjunction with the electric field, then a migration transverse to the flow and field lines is observed experimentally.The commonly held assumption that electric fields do not generate any long-range flow in the fluid surrounding a charged molecule is contradicted by theoretical work dating back to Debye; there is infact a dipolar flow generated by the polarization of the charge density by the electric field. Although this flow is weak in comparison to the electrophoretic velocity, its orientational dependence provides a means for elongated polyelectrolytes to migrate perpendicular to the flow and field lines. Our research is driven by the hypothesis that this polarization flow is responsible for several phenomena that cannot be explained without a long-range, fluid-mediated interaction between distant segments of the polyelectrolyte. Some of these phenomena have not yet been observed experimentally, such as a length-dependent electrophoretic mobility of an elongated polyelectrolyte, but they are predicted by simulations. Testing the underlying hypothesis by confirming the existence of these effects in laboratory experiments is a primary goal of the project.Intellectual Merit: The simplest model of the polarization flow predicts a dipolar hydrodynamic interaction between distant segments of a charged polymer in an electric field. Recent numerical simulations based on this model showed that one can semi-quantitatively account for data collected from DNA experiments over a limited range of salt concentration, electric field, and flow rate. In the course of this work several new phenomena were discovered that have not been observed experimentally. The ongoing research examines the validity of the underlying model and explores the potential of this mechanism for manipulating the distribution of polyelectrolytes in microchannels.Broader Impacts:Research: This work is enhancing our theoretical understanding of polyelectrolytes and altering prevailing views regarding hydrodynamic screening in polyelectrolyte dynamics. The research also impacts a wide range of technologies that require the ability to control and position charged biopolymers within microchannels by creating additional possibilities for manipulation of polyelectrolytes that may be advantageous for applications such as enhancing adsorption in ?DNA biochips?. Another potential application uses the variation in migration velocity with chain length as a means for separating DNA strands by length.Education: The program of research is integrated with our educational activities, which focus on preparing students to work in a world that increasingly depends upon international collaborations to efficiently advance science and develop new technologies. Activities include increasing the participation of students in international collaborations and meetings. Students of all levels are encouraged to become involved in advanced research within our laboratories; we have been, and continue, to work with an existing program for high school students at the University. In all of these activities, we emphasize the participation of underrepresented groups by actively seeking their involvement.