Quantum energy flow and localization during photochemical reactions in proteins
Many photochemical reactions in proteins occur in vibrationally unrelaxed states, as evident from the coherent, low-frequency oscillations observed during a variety of such reactions. Examples include low frequency oscillations observed in the primary step in vision, light-harvesting complexes, and excited state proton transfer in GFP. The observation of coherent vibrations during reaction is surprising since, as chemists, we are accustomed to equilibration prior to reaction, which we exploit to predict reaction rates. Structures that are highly improbable when energy is thermally distributed may be accessed, structures that could facilitate reaction. In this talk, I will discuss some of the ways in which vibrational relaxation controls the kinetics of simple chemical reactions, and how quantum effects, in particular localization of vibrational states, control vibrational relaxation in molecules and can give rise to long-lived, low-frequency oscillations during photochemical reactions of large molecules. As specific examples I will discuss calculation of lifetimes of vibrational modes of several proteins, then address the relatively long lifetimes of low-frequency chromophore modes.