Dynamics of Excited Electronic States in DNA

蒙大拿州立大学的Bern Kohler教授将与他的研究生和本科生一起，在化学系化学结构、动力学和机制项目的资助下，对单链和双链DNA吸收紫外线产生的激发态进行自下而上的研究。这些激发态是生物体中破坏性光化学反应的来源。广泛可调谐飞秒激光器将用于测量各种DNA模型系统的瞬态电子和振动谱，以确定电子能量的演化如何被碱基堆叠和碱基配对所改变。实验将对修饰寡核苷酸进行，以了解结构紊乱对非辐射衰变途径的影响。电荷转移激发将通过包含修饰核碱基和天然核碱基的DNA模型系统的时间分辨振动谱来表征，并通过将实验结果与合作者进行的电子结构计算进行比较。通过探测对氢键敏感的振动模式，将有针对性地了解双链DNA中质子耦合电子转移的机制。除了具有生物学意义外，DNA是研究光在复杂分子结构中沉积的能量如何随时间演化和耗散的重要模型系统。通过了解DNA双螺旋结构对紫外光的反应与更小的DNA构建块的反应有何不同，这项研究将有助于预测和定制其他光活性组分的复杂组合的光学特性，包括纳米材料。科勒教授还将参与一个向蒙大拿州农村学童提供高质量科学教育的试点项目。互动科学工具包将被开发并邮寄给蒙大拿州服务不足地区的选定教师。目标是通过身临其境的实践活动，为教师和学生提供更丰富的学习体验，并培养与蒙大拿州科学家榜样的关系。透过互动视像会议与美国赠地大学沟通。

In this project, funded by the Chemical Structure, Dynamics, and Mechanisms Program of the Division of Chemistry, Professor Bern Kohler of Montana State University, together with his graduate and undergraduate students, will conduct a bottom-up investigation of excited electronic states created in single- and double-stranded DNA by the absorption of UV light. These excited states are the source of damaging photochemical reactions in living organisms. Widely tunable femtosecond lasers will be used to measure transient electronic and vibrational spectra of various DNA model systems in order to determine how the evolution of electronic energy is modified by base stacking and base pairing. Experiments will be performed on modified oligonucleotides in order to understand the effects of structural disorder on nonradiative decay pathways. Charge transfer excitations will be characterized by time-resolved vibrational spectra of DNA model systems containing modified and natural nucleobases and by comparison of experimental results with electronic structure calculations to be performed by collaborators. By probing vibrational modes that are sensitive to hydrogen bonding, mechanistic understanding of proton-coupled electron transfer in double-stranded DNA will be targeted.Apart from its biological significance, DNA is an important model system for studying how energy deposited by light in a complex molecular structure evolves in time and is dissipated. By understanding how the response of the DNA double helix to UV light differs from the response of much smaller DNA building blocks, the research will benefit efforts that seek to predict and tailor the optical properties of other complex assemblies of light-active components, including nanomaterials. Prof. Kohler will also participate in a pilot project to deliver top-quality science education to rural Montana school children. Interactive science kits will be developed and mailed to select Montana teachers in underserved areas of the state. The goal is to give teachers and their students a richer learning experience through immersive, hands-on activities and to foster relationships with scientist role models from Montana?s land grant university through interactive videoconferencing.