Structural dynamics and photoinduced electron transfer

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Our life closely depends on light: vision provides us with information on the world around us while photosynthesis supplies us with food, as well as energy that was deposited over millions of years in fossil fuels. Photosynthesis employs a flow of electrons through proteins driven by sunlight and many researchers are trying to replicate it and produce fuels from abundant clean sources in artificial systems. Electron transfer also underlies many enzymatic reactions as well as respiration. Sequential transfer of electrons through chains of aromatic amino acids (tryptophan, tyrosine) was recently suggested to play a protective role in enzymes that use molecular oxygen to oxidize organic compounds in our bodies.Chemical reactions, including electron transfer, are too often explained in terms of static molecular or protein structures. However, life and chemistry are highly dynamic; molecules as well as their environment are perpetually in motion. Indeed, Richard Feynman famously wrote "everything that is living can be understood in terms of the jiggling and wiggling of atoms". In our work, we will focus on this aspect and try to understand the relation between structural fluctuations and electron transfer. We will study proteins bearing photoactive groups that are capable of inducing transfer of electrons across the protein upon irradiation with visible or ultraviolet light. We will measure how such photoactive assemblies and surrounding water molecules fluctuate in time and relate these structural dynamics with the rates, yields, and directionality of phototriggered electron transfer. Among several protein systems, we will also study proteins (azurins) with several aromatic amino acid groups that can themselves undergo electron transfer, while their mutual distance and orientation fluctuate in time. These investigations will tell us how to design photocatalytic systems for artificial photosynthesis to generate fuels or specialty chemicals, as green plants do. In particular, engineering aromatic amino acid chains into proteins is a promising way to strongly accelerate electron transfer in the desired direction.Time resolved vibrational spectroscopy methods are perfectly suited for such dynamics studies. Infrared or Raman spectra, which report on molecular vibrational motions, are measured as a function of time after irradiation with short laser pulses of light that trigger both structural relaxation and electron transfer. Shifts and intensity changes of spectral features, together with the emergence of new ones, will simultaneously reveal the nature and rates of structural changes and electron transfer processes. Sophisticated data analysis and theoretical calculations will enable interpretation of experimental results and building up a unifying mechanistic picture of interrelated electron transfer and structural dynamics. UK operates a world leading facility in the field of time resolved vibrational spectroscopy at the Rutherford Appleton Laboratory in Oxfordshire, providing a unique opportunity to carry out the proposed research at the highest experimental level.