Frederick D. Lewis, George C. Schatz, Michael R. Wasielewski (all at Northwestern University), Torsten Fiebig (Boston College) and Alexander L. Burin (Tulane University) are jointly supported for research into the electronic structure of DNA. More specific objectives include the investigation of the nuclear and electronic structure of short, well-defined duplex base pair domains in both the ground and electronically excited states; and investigation of the structural and electronic changes which occur upon the oxidation or reduction of duplex domains. The team will study short stable base pair domains in custom-designed hairpin and dumbbell structures. A wide range of state-of-the-art time-resolved spectroscopic, computational, and structural techniques will be used to probe how the structural changes within DNA are coupled to the properties of excited and ion states within it. Experimental approaches include molecular design and synthesis, spectroscopy, time-resolved transient absorption spectroscopy, time-resolved EPR spectroscopy, molecular dynamics, time-resolved circular dichroism, and electronic structure calculations. David Tiede (Argonne National Laboratory) will also collaborate with the team and bring expertise in time-resolved diffraction techniques.
The structural and functional integrity of DNA is critical to its role in biology, so that this project will provide fundamental information on how light and chemical agents introduce reactive sites within DNA, which change its structure and potentially alter its function. The anticipated outcomes of this collaboration include elucidation of the properties of neutral and ionized short DNA base-pair domains, training of undergraduate and graduate students in an important interdisciplinary area, and providing a model for interlocking collaboration among investigators with varying experience and in different research environments. This project is supported by the Collaborative Research in Chemistry Program.
The experimental data for charge transport through DNA hairpins we available only for the times of charge entrance and exits to and from the DNA bridge. We developed the mathematical (kinetics) model that permitted us to describe the life of charge inside the bridge including the calculation of the rate of charge hopping between adjacent identical base pairs (either AT or GC). The main outcome is the estimates of these rates, which are around one hop per nanosecond for AT pairs and around four hops per nanosecond for GC pairs. The special theory has been developed to characterize the temperature dependence of the charge transfer rate in DNA. To hop between two base pairs the charge needs to borrow some energy from its environment. Essential part of energy comes from molecular vibrations. We show that at room temperature they cannot be described classically. Quantum mechanical nature of vibrational dynamics reduces the temperature dependence of charge transfer rate in qualitative agreement with the experiment. This finding is important for other charge transfer reactions where the similar quantum effects should take place. We have participated in the LS LAMP program (www.tulane.edu/~lamp/lamp_and_tulane.html) to provide research opportunities to minority students. Ms. Carmen Dibaya who was undergraduate student in the Berea College has worked with our group on the investigation of the humidity effect on DNA conductance (2009). Ms. Brittany Demas who was undergraduate student in the Xavier University of Louisiana has worked with our group on the investigation of the charge separation and recombination in DNA hairpins (2008, 2010). They both worked hard and contributed to the research articles in leading scientific journals. Thus our research helped to recruit minorities and underrepresented groups into the scientific research.
