Life of a Photon in X-ray Spectroscopy

This thesis summarizes the experimental work in which an ultrafastX-ray laser plasma source was combined with variousscalable direct detection schemes to test a novel approach forlab-based time-resolved X-ray absorption spectroscopy. A laserplasma source based on a water jet target was built and commissioned.X-ray and electron emissions of this source were characterizedwith various direct detection schemes. The proceduresfor spectral retrieval with direct detection CCD’s were optimizedwith regard to the laser plasma source. The novel approach of usinga single photon measuring cryogenic microcalorimeter arrayas a high-resolution (DE/E 2000 @ 6 keV) energy-dispersivedetector was investigated. The potentially very high quantumefficiency, large detection angle and straightforward scalabilitymake this device an interesting photon analyzer for low photonyield experiments. In this thesis a prototype version of this detectorwas built (in cooperation), implemented and commissionedinto the laser plasma setup. With this combination of a lab-basedbroad-band source and the free standing microcalorimeter spectrometerhigh resolution X-ray absorption spectra in transmissionmode were achieved. The thesis presents the first hard X-rayabsorption fine structure (XAFS) spectrum taken with this novelapproach and discusses further improvements and applications

Investigating the stability of a laser-based plasma x-ray source

The use of laser based plasma x-ray sources (LPXS) has quickly expanded during the past decades due to rapid development of ultrafast laser systems. These sources are used in many research applications such as emission, absorption and particularly time-resolved spectroscopy. From the LPXS x-ray pulses are generated when an intense laser pulse is focused onto a liquid or solid interface in gas or vacuum. In this thesis we investigate the source stability which we define as the x-ray flux and spectrum reproducibility from each generated x-ray pulse. Understanding the stability is of great importance for its research applications. A basic theory of the LPXS is introduced describing relevant parameters for the source stability. Two parameters of relevance for the LPXS stability were investigated: The laser pointing and pulse energy fluctuations. These were experimentally determined using a beam profiler, capturing the beam profile of each laser pulse at 1 kHz. The relevance of these parameter fluctuations to the source stability is discussed based on these measurements. An existing LPXS setup was reconstructed in preparation for shot to shot stability measurements. A synchronized chopper system was built to decrease the laser pulse frequency for single pulsed mode and a program was developed for analyzing the x-ray photons captured by an x-ray CCD camera. Problems with the laser system prevented successful gathering of data within the time of the project. Future measurements based on these preparations will reveal the stability of the LPXS.Det mänskliga ögat observerar världen i formen av synligt ljus med olika färger. Allt ljus kan beskrivas som elektromagnetiska vågor med en viss våglängd, längre våglängder ger rött och kortare ger violett ljus. Utanför det för ögat synliga ljuset finner man röntgenstrålning med våglängder mycket kortare än både violett och ultraviolett ljus. Ända sedan dess upptäckt för över 100 år sedan har man funnit mängder av användningsområden för denna typen av ljus. Röntgenstrålning passerar oförhindrat genom många fasta material och används därför inom sjukvården för att se inuti kroppen. Den korta våglängden gör det även möjligt att studera mycket små saker som annars är osynliga med vanligt ljus. Röntgenstrålning är därför ett utmärkt verktyg inom forskning för att undersöka egenskaper hos molekyler och atomer. Det finns många olika metoder idag för att producera röntgenstrålning. I detta arbete har en mycket speciell typ av röntgenkälla undersökts, nämligen en s.k.laser-plasma-röntgenkälla. Denna röntgenkälla genererar korta intensiva röntgenpulser likt en stark kamera blixt. Röntgenkällan fungerar genom att fokusera en stark laserpuls med en enorm effekt på 1.5 biljoner watt och en kortvarighet på 40 femtosekunder (femtonde decimalen av en sekund). Laserpulsen fokuseras på en vattenstråle inte mycket bredare än ett hårstrå. Då den intensiva laserpulsen träffar vattenytan värms ytan upp så pass kraftigt att molekylerna och atomerna slits isär, vilket bildar ett plasma likt solen, bestående utav fria joner och elektroner. Under den kortvariga, men mycket våldsamma interaktionen accelereras och kolliderar elektroner, vilket resulterar i en skarp blixt av röntgenstrålning. Denna skarpa röntgenblixt kan riktas mot ett material som skall undersökas. När röntgenblixten interagerar med materialet kan ljuset som sänds ut från materialet detekteras av en mycket känslig detektor, likt den i en digitalkamera, där bilden kan återskapas. Den informationen som sensorn fångar in kan då analyseras för att ta reda på egenskaper hos materialet. Ju snabbare och intensivare röntgenblixten är destu bättre blir bildkvaliteten. Den extremt kortvariga röntgenblixten gör det möjligt att observera egenskaper hos molekyler och atomer med en mycket god upplösning. Likt en digitalkamera är det mycket viktigt att bildkvaliten är stabil och inte ändras mellan varje bild. I detta arbete undersöks stabiliteten hos denna röntgenkällan genom att bestämma laserpulsens träffsäkerhet och styrka på den hårtunna vattenstrålen. Information om dess stabilitet kan användas för att i slutändan förbättra stabiliteten hos röngenkällan och på så vis förbättra bildkvaliteten med denna speciella kamera för framtida forskning

Combined influence of ectoine and salt: spectroscopic and numerical evidence for compensating effects on aqueous solutions

Ectoine is an important osmolyte, which allows microorganisms to survive in extreme environmental salinity. The hygroscopic effects of ectoine in pure water can be explained by a strong water binding behavior whereas a study on the effects of ectoine in salty solution is yet missing. We provide Raman spectroscopic evidence that the influence of ectoine and NaCl are opposing and completely independent of each other. The effect can be explained by the formation of strongly hydrogen-bonded water molecules around ectoine which compensate the influence of the salt on the water dynamics. The mechanism is corroborated by first principles calculations and broadens our understanding of zwitterionic osmolytes in aqueous solution. Our findings allow us to provide a possible explanation for the relatively high osmolyte concentrations in halotolerant bacteria

Gadolinium-based Contrast Agents for Cardiac MRI:Use of Linear and Macrocyclic Agents with Associated Safety Profile from 154 779 European Patients

Purpose: To assess current use and acute safety profiles of gadolinium-based contrast agents (GBCAs) in cardiac MRI given recent suspensions of GBCA approval. Materials and Methods: Patients were retrospectively included from the multinational multicenter European Society of Cardiovascular Radiology (ESCR) MR/CT Registry collected between January 2013 and October 2019. GBCA-associated acute adverse events (AAEs) were classified as mild (self-limiting), moderate (pronounced AAE requiring medical management), and severe (life threatening). Multivariable generalized linear mixed-effect models were used to assess AAE likelihood. Results: A total of 154 779 patients (average age, 53 years ± 19 [standard deviation]; 99 106 men) who underwent cardiac MRI were included, the majority of whom underwent administration of GBCAs (94.2% [n = 145 855]). While linear GBCAs were used in 15.2% of examinations through 2011, their use decreased to less than 1% in 2018 and 2019. Overall, 0.36% (n = 556) of AAEs were documented (mild, 0.12% [n = 178]; moderate, 0.21% [n = 331]; severe, 0.03% [n = 47]). For nonenhanced cardiac MRI, examination-related events were reported in 2.59% (231 of 8924) of cases, the majority of which were anxiety (0.98% [n = 87]) and dyspnea (0.93% [n = 83]). AAE rates varied significantly by pharmacologic stressor, GBCA molecular structure (macrocyclic vs linear GBCA: multivariable odds ratio, 0.634; 95% confidence interval: 0.452, 0.888; P = .008), GBCA subtype, and imaging indication. Conclusion: Gadolinium-based contrast agent administration changed according to recent regulatory decisions, with use of macrocyclic agents almost exclusively in 2018 and 2019; these agents also demonstrated a favorable acute safety profile.Supplemental material is available for this article.© RSNA, 2020

Implications for the Binding of the Protein G5P to DNA

Microorganisms accumulate molar concentrations of compatible solutes like ectoine to prevent proteins from denaturation. Direct structural or spectroscopic information on the mechanism and about the hydration shell around ectoine are scarce. We combined surface plasmon resonance (SPR), confocal Raman spectroscopy, molecular dynamics simulations, and density functional theory (DFT) calculations to study the local hydration shell around ectoine and its influence on the binding of a gene-S-protein (G5P) to a single-stranded DNA (dT(25)). Due to the very high hygroscopicity of ectoine, it was possible to analyze the highly stable hydration shell by confocal Raman spectroscopy. Corresponding molecular dynamics simulation results revealed a significant change of the water dielectric constant in the presence of a high molar ectoine concentration as compared to pure water. The SPR data showed that the amount of protein bound to DNA decreases in the presence of ectoine, and hence, the protein-DNA dissociation constant increases in a concentration- dependent manner. Concomitantly, the Raman spectra in terms of the amide I region revealed large changes in the protein secondary structure. Our results indicate that ectoine strongly affects the molecular recognition between the protein and the oligonudeotide, which has important consequences for osmotic regulation mechanisms