Through this award, funded by the Chemical Structure, Dynamics, and Mechanisms - A Program of the Division of Chemistry, Prof. Mattanjah S. de Vries from the University California Santa Barbara and his team, will measure photochemical properties in clusters of stacked, hydrogen bonded, and microsolvated nucleobases. These studies will constitute a new step in the reductionist approach to understanding nucleobase photodynamics. Gas phase spectroscopy will be compared with quantum computations in collaboration with Dr. Nachtigallová at the Academy of Sciences of the Czech Republic. This approach, so far applied to isolated nucleobases, suggests a general process in which, following absorption of UV light, DNA bases can avoid chemical transformation by very rapidly diffusing the excitation energy to heat (in a process called internal conversion) which can safely be transferred to the environment. This process strongly depends on molecular structure and is remarkably prevalent in the specific forms in which nucleobases occur in biological contexts. However, intermolecular interactions also affect these processes. Compared to single bases, pi-stacking opens new possible excited state decay pathways, involving exciplex states, which will be studied in the picosecond time domain, as a function of precise intermolecular structure. Understanding the precise role of these interactions, which is the objective of this study, is crucial for fully understanding the way light interacts with biological molecules.
Understanding the response of DNA bases to ultraviolet (UV) radiation is critical for both practical and fundamental reasons. Nucleobase photochemistry following UV absorption constitutes a fundamental step in radiation-induced DNA damage. It appears that DNA bases are especially stable against damage caused by UV light. This unique property may have played a role in the selection of the building blocks of life four billion year ago. The bases that make up today's DNA may be the molecules that were most suited to survive harsh UV radiation on an early earth. This work will study the details of the molecular properties that make our genetic material so robust against photochemical damage. The work employs techniques of ultrafast laser spectroscopy, mass spectrometry and computational chemistry. In addition to training graduate students in these advanced methods, undergraduate students and high school students will also be exposed to this work as part of a number of outreach programs, including an ongoing collaboration with Jackson State University.
