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Controlling the Motion of Complex Molecules and Particles

Final Report Summary - COMOTION (Controlling the Motion of Complex Molecules and Particles)

The COMOTION project implemented groundbreaking approaches for the preparation of well-defined samples of complex molecules and nanoparticles ideally suited for the recording of so-called “molecular movies”, i. e., the high-resolution imaging of atomic-scale structures on ultrafast timescales.
We have achieved the observation of molecular structures of molecules with very high resolution, ranging from a few picometers for small molecules, over hundreds of picometers for proteins, to a few nanometers for large nanoparticles. We have also recorded high-fidelity movies of the quantum-dynamics of molecules.
These achievements in the observation of the intrinsic properties of molecules and nanoparticles are rooted in the fundamental progress we made in the preparation of highly controlled samples. This includes the transfer into the gas-phase, for biomolecules in native states requiring minute amounts of aqueous buffer solution to be retained, and the rapid cooling to few-Kelvin temperatures, which creates glassy structures directly resembling the initial warm “correct” structures. These shockfrozen samples enable further control, such as the selection and spatial separation of individual conformers or folding structures, or even individual quantum states. They also enable the efficient transport through fluid-dynamics, electric, and laser fields and the corresponding focusing of particle streams into the interaction point of an imaging setup, such as the focus of an x-ray free-electron laser. The latter enables the atomic-resolution imaging of molecular structure. Furthermore, the ultracold samples enable the triggering of chemical dynamics at well-defined times, through the interrogation with resonant light that excited the molecular system, within femtoseconds, from the static frozen state into states that show chemical dynamics at well defined and reproducible times. This allows for the reproducible time-delayed imaging of these dynamics. The resulting time-delayed high-resolution images can be stitched together into a flipbook to form the envisioned molecular movies.
These methods were combined with approaches to fix the molecules in space, namely laser-alignment, which enables to observe the structure and dynamics in the frame of the molecular system. Otherwise, the permanent and unavoidable ultrafast rotation of the molecules in free space angularly averages the obtained images, effectively washing out most of the structure. Our methods to fix the molecules in space allow to retrieve nearly the full information conceptionally available.
We have already brought many of these novel methods into action, both, in in-house experiments as well as at free-electron-laser beamlines, and have recorded the first images and movies as described above. With the performed and ongoing knowledge and method transfer, this approach will be generally available – also to other scientists, other fields, and any interested colleague or facility user – for the investigation of the structures and dynamics of macromolecules and biological and artificial nanoparticles with highest resolution.
Furthermore, we have made important theoretical and computational improvements related to these experiments and beyond, also shining light on the path ahead. This includes the development of software for the accurate quantum-mechanical description of the rotational dynamics in electric fields, including the effects of internal molecular motions and spin angular momenta. These methods were benchmarked against experimental data, which proved their very high accuracy. Thus, we could confidently use these methods to predict effects due to the interaction of chiral electric fields with molecules, such as the creation, detection, and spatial separation of chiral molecules – with direct relevance to the homochirality of biological molecules and life. We also developed start-to-end-simulation software for the particle-injection pipelines, which provided deep insight into the ongoing fluid-dynamics and laser-focusing processes and enabled their significant improvements and the reliable predictions of optimized experimental setups, which is of utmost importance for the usability at large-scale facilities, such as the European XFEL.