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.