Looping Dynamics of Semiflexible Polymers

ID：MPS/dmr/bmat(7623)1006485 PI：Todd，Brian ORG：普渡大学标题：半柔性聚合物的环路动力学电子优点：只要聚合物链包含一个以上的反应部位，就会形成分子内环路。这一过程背后的物理基础是两个远端聚合物链段的扩散传输到一个共同的位置(“环”)。大多数聚合物理论预测聚合物环化反应不遵循传统的动力学模型，但这些预测还没有得到充分的实验验证。这项研究的目标是以DNA为模型实验系统，表征半柔性聚合物的成环动力学。特别是，PI将检验最近的一项理论预测，即半柔性聚合物环服从基于Kramers速率理论的简单描述。这种简单的描述将极大地促进在实际生物聚合物设计应用中对环化动力学的预测，例如用于非病毒基因治疗的DNA纳米颗粒的动力学确定的加工。提出了两种测量聚合物结圈率的独立方法。在第一种方法中，聚合物的一端将连接一个荧光团，另一端将连接一个猝灭剂。然后，可以通过荧光相关光谱(FCS)测量环介导的荧光团猝灭来确定环化动力学。第二种方法使用环路和二级封顶反应之间的动力学竞争。拟议的研究将表征半柔性聚合物环，最终建立一个模型，详细说明聚合物结构对环化率的影响。这加深了我们对半柔性聚合物中链段运动的理解，并将广泛使用的生物聚合物模型扩展到涉及环的应用中。BROADER Impact：本项目的主要目标是培训学生思考如何将聚合物物理应用于生物材料设计和分子生物学等跨学科应用。PI已经向实验室招收了两名有才华的研究生，预计实验室很快就会有不同级别的学生。这位PI是普渡大学针对高危学生的“地平线计划”的导师，希望能吸引一些他的学员到他的实验室来。他还将继续通过指导、实验室参观和普渡大学科学学院支持的项目来招募和留住代表不足的少数族裔。过去，PI是俄亥俄州东克利夫兰一所100%少数族裔公立中学的导师项目的负责人。他计划继续接触印第安纳州西拉斐特的中学生。国际学生联合会目前正在开发一个推广实验室，旨在向中学生介绍“自下而上”材料设计的概念。我们的想法是挑战学生设计出宏观磁性和非磁性“单体”的“共聚序列”，这些单体能够自组装成环状、纽结和立方体等结构。预算中包括了少量资金，用于购买制作这些演示套件的材料。在不使用时，示范教材会透过教育署的物理外展资源室提供给幼稚园至12年级的教师。

ID: MPS/DMR/BMAT(7623) 1006485 PI: Todd, Brian ORG: Purdue UniversityTitle: Looping Dynamics of Semiflexible PolymersINTELLECTUAL MERIT: Intramolecular loops can form whenever a polymer chain contains more than one reactive site. The physics underlying this process is the diffusive transport of two distal polymer segments to a common location ("looping"). Most polymer theories predict that polymer looping reactions do not follow traditional kinetic models, but these predictions have not been fully tested experimentally. The goal of the proposed research is to characterize semiflexible polymer looping dynamics, using DNA as a model experimental system. In particular, the PI will test a recent theoretical prediction that semiflexible polymer looping is amenable to a simple description based on Kramers rate theory. This simple description would greatly facilitate predictions of looping kinetics in practical biopolymer design applications, such as the kinetically-determined processing of DNA nanoparticles for non-viral gene therapy. Two independent methods of measuring polymer looping rates are proposed. In the first, a fluorophore will be attached to one end of the polymer and a quencher to the other. Looping kinetics can then be determined from loop-mediated fluorophore quenching, measured via fluorescence correlation spectroscopy (FCS). The second method uses kinetic competition between looping and a second-order capping reaction. The proposed research will characterize semiflexible polymer looping, culminating in a model that details the influence of polymer structure on the looping rate. This deepens our understanding of segmental motion in semiflexible polymers and extends a widely used biopolymer model into applications involving looping.BROADER IMPACTS: A major goal of this project is to train students to think about how polymer physics can be used in interdisciplinary applications such as biomaterials design and molecular biology. The PI has recruited two talented graduate students into the laboratory, and it is expected that the laboratory will soon contain a mix of students at different levels. The PI is a mentor in the "Horizons Program" for at-risk students at Purdue and hopes to attract some of his mentees into his lab. He will also continue to recruit and retain underrepresented minorities through mentoring, lab tours, and programs supported by the College of Sciences at Purdue University. In the past, the PI was a director of a mentoring program in a 100% minority public middle school in East Cleveland, Ohio. He plans to continue outreach with middle school-aged students in West Lafayette, Indiana. The PI is currently developing an outreach laboratory designed to introduce concepts of "bottom-up" materials design to middle school-aged students. The idea is to challenge the students to design "co-polymer sequences" out of macroscopic magnetic and non-magnetic "monomers" that are capable of self-assembling into structures, such as loops, knots, and cubes. Modest funding is included in the budget to purchase the materials to make these demonstration kits. When not in use, the demonstration materials will be made available to K-12 teachers through the department's Physics Outreach Resource Room.