Quantum chemical methods for studying photoinitiated processes in biological systems

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Spiridoula Matsika of Temple University is supported by an award from the Chemical Theory, Models and Computational Methods program in the Chemistry division to develop and use theoretical models to understand photo-initiated phenomena in biological systems. Matsika and her research group develop efficient quantum chemical methods for excited states and conical intersections, which are essential in studying photo-initiated processes. The proposed methods enhance the efficiency of multireference configuration interaction (MRCI) by using natural orbitals obtained from a high multiplicity state instead of the traditional multi-configurational orbitals. Initial results show that this approach reduces the computational cost significantly compared to traditional MRCI without loss of accuracy. Gradients are also being developed for this method. The effect of the environment is taken into account by a hybrid quantum mechanics/ molecular mechanics (QM/MM) method. When developed, the developed methods will be used to study photophysical and photochemical events in pi-stacked nucleobases. This work contributes to our understanding of how DNA interacts with UV radiation. Photo-initiated processes, a primary focus of this work, play an important role in photosynthesis, vision, and photochemical damage and repair in DNA. Matsika's research is very useful in studying photo-initiated processes in biological systems. The methodology will be implemented in publicly available computational software. Students from groups that are under-represented in the physical sciences and undergraduate students are an integral part of the PI's research team.