FIXED: Fluorescent Incoherent X-ray Emission and Diffraction to determine protein structures

Project title: FIXED: Fluorescent Incoherent X-ray Emission and Diffraction to determine protein structures
Main applicant: Nicusor Timneanu, Division of Molecular and Condensed Matter Physics
Grant amount: 3 200 000 SEK for the period 2020-2023
Funder: Project grant from the Swedish Research Council

The project studies the feasibility of incoherent diffractive imaging – a brand new method to determine atomic and electronic structure of condensed matter and molecules. It uses ultrashort and intense pulses of X-ray lasers to probe the structure of samples, like protein crystals, before these would turn into plasma due to the extreme radiation dose. Elastically scattered X-rays have been successfully used for coherent diffractive imaging – here we propose to use the X-ray fluorescence from specific atoms to gain further structural information. Emission from different atoms will be incoherent, however if the photons are indistinguishable they will interfere. We plan to investigate intensity interferometry of X-ray fluorescence from transient metals to gain fundamental insights into quantum optics and ultrafast X-ray physics, to understand high-order coherence of X-ray emission from complex plasma environments. We will do theoretical modeling to gain knowledge about the practical realisation of experiments, and optimise conditions to extract novel structural and spectroscopic information. This study is interdisciplinary between physics and biology, and builds upon our experience in Uppsala in ultrafast X-ray imaging of proteins, paired with the local expertise in X-ray spectroscopy. We envision this as a complementary method suited to study biological systems, in particular proteins with metallic clusters that catalyse some of the most fundamental chemical reactions on Earth.