A hydrothermal apparatus for x-ray absorption spectroscopy of hydrothermal fluids at DESY

We present a new autoclave that enables in situ characterization of hydrothermal fluids at high pressures and high temperatures at synchrotron x-ray radiation sources. The autoclave has been specifically designed to enable x-ray absorption spectroscopy in fluids with applications to mineral solubility and element speciation analysis in hydrothermal fluids in complex compositions. However, other applications, such as Raman spectroscopy, in high-pressure fluids are also possible with the autoclave. First experiments were run at pressures between 100 and 600 bars and at temperatures between 25 °C and 550 °C, and preliminary results on scheelite dissolution in fluids of different compositions show that the autoclave is well suited to study the behavior of ore-forming metals at P-T conditions relevant to the Earth's crust.

Copper(I) targeting in the Alzheimer's disease context: a first example using the biocompatible PTA ligand

Copper(I) coordinating ligands in the Alzheimer's disease context have remained unexplored, despite the biological relevance of this redox state of the copper ion. Here, we show that the PTA ligand can remove copper from Aβ, prevent reactive oxygen species production and oligomer formation, two deleterious events in the disease's etiology.

Random alloy-like local structure of Fe(Se, S)(1-x)Te(x) superconductors revealed by extended x-ray absorption fine structure

The local structure of Fe(Se, S)(1-x)Te(x) ternary (11-type) chalcogenides has been studied by temperature dependent Fe K-edge extended x-ray absorption fine structure measurements. We find that the Fe-Se and Fe-Te distances in ternary FeSe(1-x)Te(x) are closer to the respective distances in the binary systems, revealing significant divergence of the local structure from the average one. The mean square relative displacements show a systematic change with Te content, consistent with bond relaxation in the inhomogeneous ternary phases. Also, the Fe-Te and Fe-S distances in the FeS(0.2)Te(0.8) ternary system are found to be different in the crystallographically homogeneous structure. The observed features are characteristic of ternary random alloys, suggesting that a proper consideration should be given to the atomic distribution for describing the complex electronic structure of these multi-band Fe-based chalcogenides.

Monitoring microbial redox transformations of metal and metalloid elements under high pressure using in situ X-ray absorption spectroscopy

X-ray absorption spectroscopy is a well-established method for probing local structural and electronic atomic environments in a variety of systems. We used X-ray absorption near-edge structure (XANES) spectroscopy for monitoring in real-time conditions selenium reduction in situ in live cultures of Shewanella oneidensis MR-1 under high hydrostatic pressure. High-quality XANES data show that Shewanella oneidensis MR-1 reduces selenite Se(IV) to red elemental selenium Se(0) up to 150 MPa without any intermediate redox state. MR-1 reduces all selenite provided (5-10 mM) between 0.1 and 60 MPa. Above 60 MPa the selenite reduction yield decreases linearly with pressure and the activity is calculated to stop at 155 ± 5 MPa. The analysis of cultures recovered after in situ measurements showed that the decrease in activity is linked to a decrease in viability. This study emphasizes the promising potential of XANES spectroscopy for real-time probing in situ microbial redox transformations of a broad range of metal and metalloid elements in live samples, including under high hydrostatic pressure.

New insight into the contributions of thermogenic processes and biogenic sources to the generation of organic compounds in hydrothermal fluids

Experiments on hydrothermal degradation of Pyrococcus abyssi biomass were conducted at elevated pressure (40 MPa) over a 200-450 °C temperature range in sapphire reaction cells. Few organic compounds could be detected in the 200 °C experiment. This lack was attributed to an incomplete degradation of P. abyssi cells. On the contrary, a wide range of soluble organic molecules were generated at temperatures ≥ 350 °C including toluene, styrene, C₈-C₁₆ alkyl-benzenes, naphthalene, C₁₁-C₁₆ alkyl-naphthalenes, even carbon number C₁₂-C₁₈ polycyclic aromatic hydrocarbons, C₁₅-C₁₈ alkyl-phenanthrenes and C₈:₀-C₁₆:₀ n-carboxylic acids. The effect of time on the final organic composition of the degraded P. abyssi solutions at 350 °C was also investigated. For that purpose the biomass was exposed for 10, 20, 60, 90, 270 and 720 min at 350 °C. We observed a similar effect of temperature and time on the chemical diversity obtained. In addition, temperature and time increased the degree of alkylation of alkyl-benzenes. This study offers additional evidence that a portion of the aliphatic hydrocarbons present in the fluids from the Rainbow ultramafic-hosted hydrothermal field may be abiogenic whereas a portion of the aromatic hydrocarbons and n-carboxylic acids may have a biogenic origin. We suggest that aromatic hydrocarbons and linear fatty acids at the Rainbow site may be derived directly from thermogenic alteration of material from the sub-seafloor biosphere. Yet we infer that the formation and dissolution of carboxylic acids in hydrothermal fluids may be controlled by other processes than in our experiments.

Structural characterization of the active form of PerR: insights into the metal-induced activation of PerR and Fur proteins for DNA binding

In Bacillus subtilis, the transcription factor PerR is an iron dependant sensor of H(2)O(2). The sensing mechanism relies on a selective metal catalysed oxidation of two histidine residues of the regulatory site. Here we present the first crystal structure of the active PerR protein in complex with a Mn(2+) ion. In addition, X-ray absorption spectroscopy experiments were performed to characterize the corresponding iron form of the protein. Both studies reveal a penta-coordinate arrangement of the regulatory site that involves three histidines and two aspartates. One of the histidine ligand belongs to the N-terminal domain. Binding of this residue to the regulatory metal allows the protein to adopt a caliper-like conformation suited to DNA binding. Since this histidine is conserved in all PerR and a vast majority of Fur proteins, it is likely that the allosteric switch induced by the regulatory metal is general for this family of metalloregulators.

Spectroscopic characterization of microscopic hydrogen-bonding disparities in supercritical water

The local hydrogen-bonding environment in supercritical water (380 degrees C, 300 bars, density 0.54 gcm3) was studied by x-ray Raman scattering at the oxygen K edge. The spectra are compared to those of the gas phase, liquid surface, bulk liquid, and bulk ice, as well as to calculated spectra. The experimental model systems are used to assign spectral features and to quantify specific local hydrogen-bonding situations in supercritical water. The first coordination shell of the molecules is characterized in more detail with the aid of the calculations. Our analysis suggests that approximately 65% of the molecules in supercritical water are hydrogen bonded in configurations that are distinctly different from those in liquid water and ice. In contrast to liquid water the bonded molecules in supercritical water have four intact hydrogen bonds and in contrast to ice large variations of bond angles and distances are observed. The remaining approximately 35% of the molecules exhibit two free O-H bonds and are thus either not involved in hydrogen bonding at all or have one or two hydrogen bonds on the oxygen side. We determine an average O-O distance of 3.1+/-0.1 A in supercritical water for the H bonded molecules at the conditions studied here. This and the corresponding hydrogen bond lengths are shown to agree with neutron- and x-ray-diffraction data at similar conditions. Our results on the local hydrogen-bonding environment with mainly two disparate hydrogen-bonding configurations are consistent with an extended structural model of supercritical water as a heterogeneous system with small patches of bonded molecules in various tetrahedral configurations and surrounding nonbonded gas-phase-like molecules.