Temperature dependence of the hydrogen bond network in Trimethylamine N-oxide and guanidine hydrochloride - water solutions

We present an X-ray Compton scattering study on aqueous Trimethylamine N-oxide (TMAO) and guanidine hydrochloride solutions (GdnHCl) as a function of temperature. Independent from the concentration of the solvent, Compton profiles almost resemble results for liquid water as a function of temperature. However, The number of hydrogen bonds per water molecule extracted from the Compton profiles suggests a decrease of hydrogen bonds with rising temperatures for all studied samples, the differences between water and the solutions are weak. Nevertheless, the data indicate a reduced bond weakening with rising TMAO concentration up to 5M of 7.2% compared to 8 % for pure water. In contrast, the addition of GdnHCl appears to behave differently for concentrations up to 3.1 M with a weaker impact on the temperature response of the hydrogen bond structure

Intramolecular structure and energetics in supercooled water down to 255 K

We studied the structure and energetics of supercooled water by means of X-ray Raman and Compton scattering. Under supercooled conditions down to 255 K, the oxygen K-edge measured by X-ray Raman scattering suggests an increase of tetrahedral order similar to the conventional temperature effect observed in non-supercooled water. Compton profile differences indicate contributions beyond the theoretically predicted temperature effect and provide a deeper insight into local structural changes. These contributions suggest a decrease of the electron mean kinetic energy by 3.3 +/- 0.7 kJ (mol K)(-1) that cannot be modeled within established water models. Our surprising results emphasize the need for water models that capture in detail the intramolecular structural changes and quantum effects to explain this complex liquid.Peer reviewe

X-ray studies on adsorption processes at solid-liquid interfaces and ultrafast dynamics in water

Wasser und wässrige Systeme spielen in der Natur und Technik eine signifikante Rolle, da die meisten biologischen und chemischen Prozesse in wässriger Umgebung stattfinden. Tritt eine wässrige Lösung in Kontakt zu einem Festkörper, entsteht eine fest-flüssig-Grenzfläche, an welcher in Wasser gelöste Moleküle bevorzugt adsorbieren können. Im Rahmen dieser Arbeit wurden mittels Röntgenreflektivität (X-ray Reflectivity, XRR) in-situ Einflüsse diverser Parameter auf den Adsorptionsprozess an der fest-flüssig-Grenzfläche erforscht. Hierzu zählen thermodynamische Eigenschaften, elektrostatische Wechselwirkungen zwischen Oberfläche und Solvat, Oberflächenbeschaffenheit und Eigenschaften des Solvats. Dafür wurde im ersten Abschnitt der Arbeit das Adsorptionsverhalten des Proteins Lysozym auf einem mit Titanoxid beschichteten Siliziumwafer, also einer hydrophilen Oberfläche, untersucht. Hier wurden jeweils einzeln die Temperatur (20°C – 80°C), der Druck (50 bar – 5000 bar), der pH-Wert (2 -12) und die Schichtdicke der Titanoxidbeschichtung (50 Å – 115 Å) variiert, um den Einfluss dieser Parameter auf den Adsorptionsprozess zu untersuchen. Eine Erhöhung der Temperatur, des pH-Wertes und der Titanoxidschichtdicke führte dabei zu größerer Adsorption von Lysozym auf der Oberfläche, während eine Erhöhung des Drucks zur Desorption führte. Des Weiteren wurde das Adsorptionsverhalten von Ionen auf einem mit Oktadecyltrichlorosilan (OTS) beschichteten Siliziumwafer, also einer hydrophoben Oberfläche, erforscht. Dabei wurden jeweils der Ionenradius und die Konzentration der Ionen variiert. Es wurde festgestellt, dass Ionen sowohl auf dem OTS als auch zwischen den einzelnen OTS Molekülen adsorbieren, wobei die Adsorption von Ionen größen- und konzentrationsabhängig ist. Im zweiten Abschnitt der Arbeit wurden mittels inelastischer Röntgenstreuung Elektronendichtestörungen in Wasser auf Zeitskalen von Attosekunden bei drei unterschiedlichen Wassertemperaturen erforscht. Die Elektronendichtestörung spiegelt sich in einer zeitlich und räumlich gedämpften Oszillation der Elektronendichte wider. Diese breitet sich bei 90°C auf kürzeren Zeitskalen im Vergleich zu 4°C und 20°C warmen Wasser aus. Ab 600 as relaxiert das System in einen ungestörten Zustand.Water and aqueous solutions play a significant role in nature and technical applications. Many biological and chemical processes that are of great importance in everyday life take place within a liquid environment. When an aqueous solution comes in contact with a solid, a solid-liquid interface is formed at which solvated molecules adsorb preferably. In the framework of this thesis the influence of different parameters, such as thermodynamic properties, electrostatic interactions as well as surface and solvate properties, on the adsorption process at solid-liquid interfaces was investigated. Therefore, in the first part of this thesis, the adsorption of lysozyme on a titanium oxide coated silicon wafer was studied under variation of temperature (20°C – 80°C), pressure (50 bar – 5000 bar), pH value (2 -12) and titanium oxide layer thickness (50 Å – 115 Å), respectively. With increasing temperature, pH value and titanium oxide layer thickness, the adsorption of lysozyme on the surface increases, while rising pressure leads to a desorption of lysozyme. In opposite to this hydrophilic surface also a hydrophobic surface was studied by investigating the adsorption of ions at a silicon wafer with octadecyltrichlorosilane (OTS) coating. Here, ion size as well as ion concentration were varied, respectively. The ions adsorb both in-between as well as on top of the OTS molecules. The adsorbed ion amount increases with rising ion concentration independent of the ion size. The second part of this thesis deals with water as solvent. Here, electron density disturbances in water were investigated on attosecond time scales by means of Inelastic X-ray Scattering (IXS) at three different water temperatures. The electron density disturbance is represented by a damped oscillation of the electron density in space and time, which propagates at 90°C on shorter time scales compared to 4°C and 20°C. Finally, on time scales above 600 as, the system reverts to an undisturbed state

Cation Hydration in Supercritical NaOH and HCl Aqueous Solutions

We present a study of the local atomic environment of the oxygen atoms in the aqueous solutions of NaOH and HCl under simultaneous high-temperature and high-pressure conditions. Experimental nonresonant X-ray Raman scattering core-level spectra at the oxygen K-edge show systematic changes as a function of temperature and pressure. These systematic changes are distinct for the two different solutes and are described well by calculations within the Bethe- Salpeter formalism for snapshots from ab initio molecular dynamics simulations. The agreement between experimental and simulation results allows us to use the computations for a detailed fingerprinting analysis in an effort to elucidate the local atomic structure and hydrogen-bonding topology in these relevant solutions. We observe that both electrolytes, especially NaOH, enhance hydrogen bonding and tetrahedrality in the water structure at supercritical conditions, in particular in the vicinity of the hydration shells. This effect is accompanied with the association of the HCl and NaOH molecules at elevated temperatures

Human Apolipoprotein A1 at Solid/Liquid and Liquid/Gas Interfaces

An X-ray reflectivity study on the adsorption behavior of human apolipoprotein A1 (apoA1) at hydrophilic and hydrophobic interfaces is presented. It is shown that the protein interacts via electrostatic and hydrophobic interactions with the interfaces, resulting in the absorption of the protein. pH dependent measurements at the solid/liquid interface between silicon dioxide and aqueous protein solution show that in a small pH range between pH 4 and 6, adsorption is increased due to electrostatic attraction. Here, the native shape of the protein seems to be conserved. In contrast, the adsorption at the liquid/gas interface is mainly driven by hydrophobic effects, presumably by extending the hydrophobic regions of the amphipathic helices, and results in a conformational change of the protein during adsorption. However, the addition of differently charged membrane-forming lipids at the liquid/gas interface illustrates the ability of apoA1 to include lipids, resulting in a depletion of the lipids from the interface

Formation of CaB6\mathrm{CaB_6} in the thermal decomposition of the hydrogen storage material Ca(BH4\mathrm{Ca(BH_{4}})2\mathrm{_{2}}

Using a combination of high resolution X-ray powder diffraction and X-ray Raman scattering spectroscopyat the B K- and Ca L$_{2,3}$-edges, we analyzed the reaction products of Ca(BH$_{4}$)$_{2}$ after annealing at 350 $\circ$C and 400 $\circ$Cunder vacuum conditions. We observed the formation of nanocrystalline/amorphous CaB$_6$ mainly and found only small contributions from amorphous B for annealing times larger than 2 h. For short annealing times of 0.5 h at 400 $\circ$C we observed neither Ca(BH$_{4}$)$_{2}$nor CaB$_6$. The results indicate a reaction pathway in which Ca(BH$_{4}$)$_{2}$ decomposes to B and CaH$_2$ and finally reacts to form CaB$_6$.These findings confirm the potential of using Ca(BH$_{4}$)$_{2}$ as a hydrogen storage medium and imply the desiredcycling capabilities for achieving high-density hydrogen storage materials

Pressure driven spin transition in siderite and magnesiosiderite single crystals

Iron-bearing carbonates are candidate phases for carbon storage in the deep Earth and may play an important role for the Earth’s carbon cycle. To elucidate the properties of carbonates at conditions of the deep Earth, we investigated the pressure driven magnetic high spin to low spin transition of synthetic siderite FeCO$_3$ and magnesiosiderite (Mg$_{0.74}$Fe$_{0.26}$)CO$_3$ single crystals for pressures up to 57 GPa using diamond anvil cells and x-ray Raman scattering spectroscopy to directly probe the iron 3d electron configuration. An extremely sharp transition for siderite single crystal occurs at a notably low pressure of 40.4 ± 0.1 GPa with a transition width of 0.7 GPa when using the very soft pressure medium helium. In contrast, we observe a broadening of the transition width to 4.4 GPa for siderite with a surprising additional shift of the transition pressure to 44.3 ± 0.4 GPa when argon is used as pressure medium. The difference is assigned to larger pressure gradients in case of argon. For magnesiosiderite loaded with argon, the transition occurs at 44.8 ± 0.8 GPa showing similar width as siderite. Hence, no compositional effect on the spin transition pressure is observed. The spectra measured within the spin crossover regime indicate coexistence of regions of pure high- and low-spin configuration within the single crystal

Combining X-ray Kβ1,3β_{1,3}, valence-to-core, and X-ray Raman spectroscopy for studying Earth materials at high pressure and temperature: the case of siderite

X-ray emission and x-ray Raman scattering spectroscopy are powerful tools to investigate thelocal electronic and atomic structure of high and low Z elements in-situ. Notably, these methodscan be applied for in-situ spectroscopy at high pressure and high temperature using resistively orlaser-heated diamond anvil cells in order to achieve thermodynamic conditions which are presentin the Earth’s interior. We developed a setup for combined x-ray emission and x-ray Raman scatteringstudies at beamline P01 of PETRA III using a portable wavelength-dispersive von Hamosspectrometer together with the permanently installed multiple-analyzer Johann-type spectrometer.The capabilities of this setup discussed through the investigation of are exemplified by investigatingthe iron spin crossover of siderite FeCO$_3$ up to 49.3GPa by measuring the Fe M$_{2,3}$-edgeand Fe Kβ$_{1,3}$ emission line simultaneously. With this setup, the Fe valence-to-core emission canbe detected simultaneously with the Kβ$_{1,3}$ emission line providing complementary information onthe sample’s electronic structure. By implementing a laser-heating device, we demonstrate thestrength of using a von Hamos type spectrometer for spin state mapping at extreme conditions.Finally, we give different examples of low Z elements’ absorption edges relevant for applicationin geoscience that are accessible with the Johann-type XRS spectrometer. This setup providesa unique combination to gain new insights of the spin transition and compression mechanismsof Earth’s mantle materials of importance for comprehension of the macroscopic physical andchemical properties of the Earth’s interior

Human Apolipoprotein A1 at Solid/Liquid and Liquid/Gas Interfaces

An X-ray reflectivity study on the adsorption behavior of human apolipoprotein A1 (apoA1) at hydrophilic and hydrophobic interfaces is presented. It is shown that the protein interacts via electrostatic and hydrophobic interactions with the interfaces, resulting in the absorption of the protein. pH dependent measurements at the solid/liquid interface between silicon dioxide and aqueous protein solution show that in a small pH range between pH 4 and 6, adsorption is increased due to electrostatic attraction. Here, the native shape of the protein seems to be conserved. In contrast, the adsorption at the liquid/gas interface is mainly driven by hydrophobic effects, presumably by extending the hydrophobic regions of the amphipathic helices, and results in a conformational change of the protein during adsorption. However, the addition of differently charged membrane-forming lipids at the liquid/gas interface illustrates the ability of apoA1 to include lipids, resulting in a depletion of the lipids from the interface

Adsorption Behavior of Lysozyme at Titanium Oxide–Water Interfaces

We present an in situ X-ray reflectivity study of the adsorption behavior of the protein lysozyme on titanium oxide layers under variation of different thermodynamic parameters, such as temperature, hydrostatic pressure, and pH value. Moreover, by varying the layer thickness of the titanium oxide layer on a silicon wafer, changes in the adsorption behavior of lysozyme were studied. In total, we determined less adsorption on titanium oxide compared with silicon dioxide, while increasing the titanium oxide layer thickness causes stronger adsorption. Furthermore, the variation of temperature from 20 to 80 °C yields an increase in the amount of adsorbed lysozyme at the interface. Additional measurements with variation of the pH value of the system in a region between pH 2 and 12 show that the surface charge of both protein and titanium oxide has a crucial role in the adsorption process. Further pressure-dependent experiments between 50 and 5000 bar show a reduction of the amount of adsorbed lysozyme with increasing pressure