{"doi":"10.1063/4.0000130","title":"Effects of x-ray free-electron laser pulse intensity on the Mn K<b><i>β</i></b><sub>1,3</sub> x-ray emission spectrum in photosystem II—A case study for metalloprotein crystals and solutions","abstract":"In the last ten years, x-ray free-electron lasers (XFELs) have been successfully employed to characterize metalloproteins at room temperature using various techniques including x-ray diffraction, scattering, and spectroscopy. The approach has been to outrun the radiation damage by using femtosecond (fs) x-ray pulses. An example of an important and damage sensitive active metal center is the Mn 4 CaO 5 cluster in photosystem II (PS II), the catalytic site of photosynthetic water oxidation. The combination of serial femtosecond x-ray crystallography and Kb x-ray emission spectroscopy (XES) has proven to be a powerful multimodal approach for simultaneously probing the overall protein structure and the electronic state of the Mn 4 CaO 5 cluster throughout the catalytic (Kok) cycle. As the observed spectral changes in the Mn 4 CaO 5 cluster are very subtle, it is critical to consider the potential effects of the intense XFEL pulses on the Kb XES signal. We report here a systematic study of the effects of XFEL peak power, beam focus, and dose on the Mn Kb 1,3 XES spectra in PS II over a wide range of pulse parameters collected over seven different experimental runs using both microcrystal and solution PS II samples. Our findings show that for beam intensities ranging from $5 10 15 to 5 10 17 W/cm 2 at a pulse length of $35 fs, the spectral effects are small compared to those observed between S-states in the Kok cycle. Our results provide a benchmark for other XFEL-based XES studies on metalloproteins, confirming the viability of this approach.","journal":"Structural Dynamics","year":2021,"id":178974,"datarank":0.0,"base_score":0.0,"endowment":0.0,"self_citation_contribution":0.0,"citation_network_contribution":0.0,"self_endowment_contribution":0.0,"citer_contribution":0.0,"corpus_percentile":null,"corpus_rank":null,"citation_count":19,"citer_count":0,"citers_with_citation_signal":0,"citers_with_endowment":0,"datacite_reuse_total":0,"is_dataset":false,"is_dataset_confidence":0.9542,"is_data_producer":false,"deposit_databanks":null,"is_oa":true,"file_count":0,"downloads":0,"has_version_chain":false,"published_date":"2021-01-01","fair_score":null,"fair_percentile":null,"algorithm_id":"datarank_citation_only_1hop_v6","ranking_scope":"data_only","authors":[{"id":240879,"name":"Roberto Alonso‐Mori","orcid":"0000-0002-5357-0934","position":1,"is_corresponding":false},{"id":240863,"name":"Ruchira Chatterjee","orcid":"0000-0002-0865-061X","position":2,"is_corresponding":false},{"id":240864,"name":"Mun Hon Cheah","orcid":"0000-0001-5732-1524","position":3,"is_corresponding":false},{"id":240861,"name":"Mohamed Ibrahim","orcid":"0000-0002-1431-9755","position":4,"is_corresponding":false},{"id":240865,"name":"Rana Hussein","orcid":"0000-0001-6292-2375","position":5,"is_corresponding":false},{"id":725618,"name":"Miao Zhang","orcid":"0000-0003-4022-7093","position":6,"is_corresponding":false},{"id":240867,"name":"Franklin D. 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