3D-printed sheet jet for stable megahertz liquid sample delivery at X-ray free-electron lasers.

X-ray free-electron lasers (XFELs) can probe chemical and biological reactions as they unfold with unprecedented spatial and temporal resolution. A principal challenge in this pursuit involves the delivery of samples to the X-ray interaction point in such a way that produces data of the highest possible quality and with maximal efficiency. This is hampered by intrinsic constraints posed by the light source and operation within a beamline environment. For liquid samples, the solution typically involves some form of high-speed liquid jet, capable of keeping up with the rate of X-ray pulses. However, conventional jets are not ideal because of radiation-induced explosions of the jet, as well as their cylindrical geometry combined with the X-ray pointing instability of many beamlines which causes the interaction volume to differ for every pulse. This complicates data analysis and contributes to measurement errors. An alternative geometry is a liquid sheet jet which, with its constant thickness over large areas, eliminates the problems related to X-ray pointing. Since liquid sheets can be made very thin, the radiation-induced explosion is reduced, boosting their stability. These are especially attractive for experiments which benefit from small interaction volumes such as fluctuation X-ray scattering and several types of spectroscopy. Although their use has increased for soft X-ray applications in recent years, there has not yet been wide-scale adoption at XFELs. Here, gas-accelerated liquid sheet jet sample injection is demonstrated at the European XFEL SPB/SFX nano focus beamline. Its performance relative to a conventional liquid jet is evaluated and superior performance across several key factors has been found. This includes a thickness profile ranging from hundreds of nanometres to 60 nm, a fourfold increase in background stability and favorable radiation-induced explosion dynamics at high repetition rates up to 1.13 MHz. Its minute thickness also suggests that ultrafast single-particle solution scattering is a possibility.

Investigation of Intestinal Absorption and Excretion of Paracetamol in Streptozotocin-Induced Hyperglycemia.

The phenolic drug molecules can be metabolized, among others, by the small intestine's enterocytes. The conjugation reactions (glucuronidation and sulfation) show great importance in these transformations, although the oxidation reactions can be significant. These processes are dependent on the substituents of the phenolic compounds or the reacting functional groups (hydroxyl or carboxyl). Pathologic conditions, e.g., permanent hyperglycemia and diabetes, can alter the activities of the conjugative and possibly the oxidative enzymes, thus forming a change in the metabolic pattern and eventually provoking oxidative stress. A rat intestinal perfusion model was used to investigate the way in which experimental hyperglycemia affects the paracetamol's intestinal elimination and metabolism. Hyperglycemia was induced by the administration of streptozotocin. Two hundred and fifty µM paracetamol was used in the intestinal perfusion solution. For the quantitation of the paracetamol and its major metabolites in the intestinal perfusate, an isocratic high-performance liquid chromatography method with UV-Vis detection was developed. The results revealed that quantities of all of the measured metabolites (glucuronide, sulfate, cysteine, and mercapturic acid conjugates) increased as the effect of the streptozotocin-induced hyperglycemia also did. In the small intestine's homogenate, the glutathione levels showed that there was a decrease in the hyperglycemia levels after the paracetamol administration. In contrast, the tissue levels of the cysteine were lower in the streptozotocin-induced hyperglycemia and increased after the administration of the paracetamol. The changes in the activity of the intestinal CYP 3A4, CYP 2E1, and cyclooxygenase (COX) enzymes were determined in the control and the hyperglycemic cases. Still, there was a significant observable enzyme activity elevation in the intestinal COX enzymes, but there was a decrease in the amount of activity of the intestinal CYP3A4 enzymes, and the CYP2E1 enzyme activity was practically changeless. The results on the cysteine levels in the intestinal homogenate, at least partly, can be explained by the regulation function of the cysteine during the occurrence of oxidative stress.

Protein motions visualized by femtosecond time-resolved crystallography: The case of photosensory vs photosynthetic proteins.

Proteins are dynamic objects and undergo conformational changes when functioning. These changes range from interconversion between states in equilibrium to ultrafast and coherent structural motions within one perturbed state. Time-resolved serial femtosecond crystallography at free-electron X-ray lasers can unravel structural changes with atomic resolution and down to femtosecond time scales. In this review, we summarize recent advances on detecting structural changes for phytochrome photosensor proteins and a bacterial photosynthetic reaction center. In the phytochrome structural changes are extensive and involve major rearrangements of many amino acids and water molecules, accompanying the regulation of its biochemical activity, whereas in the photosynthetic reaction center protein the structural changes are smaller, more localized, and are optimized to facilitate electron transfer along the chromophores. The detected structural motions underpin the proteins' function, providing a showcase for the importance of detecting ultrafast protein structural dynamics.