METRICS · Element-selective impulsive electronic and vibrational spectroscopy of iron-sulfur clusters

The catalytic activity of metalloproteins and cofactors is at the heart of biological systems’ functioning. Biological reactions occur under physiological conditions in stunning contrast with the extreme temperatures and pressures demanded by industrial processes. The evolutionary “optimal design” of enzymatic reactions led to the ubiquitous presence of key molecular motifs in several metabolic pathways, among which the iron-sulfur (FeS) clusters. Understanding how these multimetallic clusters act in Nature requires mapping their electronic and structural configuration, a challenging task that calls for new investigation methods.In this project, the main issues of conventional spectroscopies for the characterization of FeS clusters are circumvented harnessing the potential of novel atto- and femtosecond sources, implementing element-selective impulsive vibrational spectroscopy (ES-IVS) and element-selective impulsive electronic spectroscopy (ES-IES). The impulsive excitation of FeS clusters with few-cycle pumps in the nearinfrared (for ES-IVS) and visible (for ES-IES) spectral ranges triggers their vibrational and electronic wavepacket dynamics, respectively. Using ultrashort soft X-ray pulses, the clusters’ time-domain response is monitored with element selectivity at the Fe M2,3-edge and S L2,3-edge, retrieving characteristic oscillation frequencies upon Fourier transform of the time traces. ES-IVS will provide direct structural information of FeS clusters measuring Fe and S low-frequency vibrational spectra inaccessible with other approaches. ES-IES will map the Fe electronic states that are at the hearth of FeS catalytic activity and whose experimental observation has proven impractical. This project will establish these techniques as advanced X-ray spectroscopic tools for the investigation of FeS clusters, providing a better understanding of their role in crucial biological processes such as oxidative phosphorylation, photosynthesis and nitrogen fixation.