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‘Filming’ excited state structural dynamics in photosynthesis and organic semiconductors

Final Report Summary - STRUCTDYN (‘Filming’ excited state structural dynamics in photosynthesis and organic semiconductors)

The overall goal of this ERC project was to measure molecular structural dynamics. Femtosecond time-resolved spectroscopy (Nobel Prize 1999) probes the changes in electronic structure of molecules on time-scales of chemical reactions, but the technique is not directly sensitive to structural changes. X-ray solution scattering and X-ray crystallography report on the positions of atoms in a molecule and has yielded numerous three-dimensional structures of biomolecules (latest Nobel Prize: 2012). However, the techniques do not have an intrinsic time resolution. The specific focus of this project was to advance time-resolved X-ray solution scattering and time-resolved X-ray crystallography. The technique is a combination of the named approaches and has the potential to probe structural change of molecules on all relevant time scales.

Within this ERC starting project, several scientific and two methodological advances were achieved. The propagation of conformational signals within a light-sensing protein was resolved on millisecond time-scales (Takala, Nature, 2014; Björling et al., Science Advances 2016), the structural change of a blue-light sensing protein was determined (Berntsson et al., Structure, 2017), and time-resolved X-ray solution scattering signals of a photosynthetic protein was demonstrated on femtosecond time scales (Arnlund, Nature Methods, 2014). Further, the femtosecond structural dynamics of photodissociation reactions of small photochemicals were investigated. When addressing femto- or picosecond time scales, short X-ray pulses at free electron lasers were used.
The methodological advances are concerned with the structural interpretation time-resolved X-ray solution scattering data. The data contains relatively little but precious information and we hypothesized that it should be combined with advanced computational molecular modelling (Nobel Prize 2013). Thus, we derived and implemented a method to efficiently compute scattering profiles from coarse-grained protein structures (Niebling et al., J App. Cryst, 2014), and amended an existing molecular simulation package (GROMACS) with a plugin for time-resolved X-ray scattering data (Björling, JCTC, 2015).

The project has demonstrated the potential of time-resolved X-ray based techniques for the study of molecular structural dynamics. Using the technique we were able to enhance knowledge for photoactive proteins and chemical reactivity. We and other research teams will continue to use time-resolved X-ray experiments to study interesting biological and chemical problems.