In recent years, electronic structure calculations have located numerous photochemical reactions in the condensed phase that are predicted to proceed through conical intersections; while some kinetic data exist to bolster theses claims, direct evidence for the presence of conical intersections in the condensed phase is scarce. Our research focuses on leveraging precise theoretical predictions for conical intersection structures to predict, identify, and characterize these structures with the ultimate goal of rationally controlling photoreactivity. We intend first to employ laser spectroscopy to watch the reactions, then to invoke theoretical modeling to understand the data and to locate new substrates. As we move into the spectroscopy of branching reactions, we intend to manipulate macromolecular chaperones to attempt to steer and control the photochemistry.
Our theoretical efforts are very closely tied to the experimental efforts; neither can be successful without the other. The Hamiltonian, being a Hermitian operator, can only support state crossings in N-2 dimensions; therefore, the conical intersection must have a two dimensional branching space. Further, the conical intersection necessarily permits access to multiple product wells. In conjunction with our experimental effort, we intend to map this branching space and observe which nuclear modes are most active in steering the reaction through the branching space. To read this information from the experimental data, we must model the nonlinear response of this system including evolution along the reaction coordinate during the coherence and rephrasing times.
As our experimental efforts advance, we intend to employ macromolecular chaperones to steer the reaction through the branching space that determines products. Such development of photoenzymatic activity falls into a different class completely from evolution of novel enzymes using ground state reactivity. Rather than requiring wholesale changes to the ground state potentials to stabilize transition states, we only require slight steric effects to steer a reaction that already progresses under kinetic control. Using simple selection techniques, we hope to evolve novel photoenzymes to control the yields and products of reactions.
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C. Wang*, M.L. Flanagan*, R.D. McGillicuddy, H. Zheng, A.R. Ginzburg, X. Yang, K. Moffat, and G.S. Engel, "Bacteriophytochrome Photoisomerization Proceeds Homogeneously Despite Heterogeneity in Ground State" Biophysical Journal 111, 2125–2134 2016.