Prof. Dr. Metin Tolan

Experimental Physics
TU Dortmund University


  • Process characteristics, particle behavior and coating properties during HVOF spraying of conventional, fine and nanostructured WC-12Co powders
    Baumann, I. and Hagen, L. and Tillmann, W. and Hollingsworth, P. and Stangier, D. and Schmidtmann, G. and Tolan, M. and Paulus, M. and Sternemann, C.
    Surface and Coatings Technology 405 (2021)
    In recent years, great effort has been taken in science and industry to find novel material-related solutions, which provide improved properties for future technological applications. One of these approaches is the use of fine structured and nanostructured materials. Within the field of wear protection, the use of fine or nanostructured WC-Co powder feedstock in the thermal spray process enables the application of highly wear resistant, thin near net-shape coatings on parts with complex geometries. In this study, the processing of WC-12Co powders by means of High Velocity Oxy-Fuel (HVOF) flame spraying is fundamentally investigated and the results are compared to those obtained with conventional powders. The influence of process parameter and scaling effects on the spray process and the thermo-kinetic particle behavior in the flame, the heating of the substrate as well as on the coating properties, the microstructure, the behavior of elements and phases and the residual stress is discussed comprehensively. The investigations of this work have shown that HVOF spraying of fine and nanostructured WC-12Co powders instead of conventional ones leads to a significant alteration of the thermo-kinetic spray conditions. Under optimized spray conditions, achieved by the use of special spray equipment and statistical design of experiments (DoE), improvements in terms of the economy of the spray process (higher deposition efficiencies) and the mechanical properties (higher microhardness and fracture toughness, lower porosity and roughness) can be achieved. © 2020
    view abstract10.1016/j.surfcoat.2020.126716
  • A portable on-Axis laser-heating system for near-90° X-ray spectroscopy: Application to ferropericlase and iron silicide
    Spiekermann, G. and Kupenko, I. and Petitgirard, S. and Harder, M. and Nyrow, A. and Weis, C. and Albers, C. and Biedermann, N. and Libon, L. and Sahle, C.J. and Cerantola, V. and Glazyrin, K. and Konopkova, Z. and Sinmyo, R. and Morgenroth, W. and Sergueev, I. and Yavas, H. and Dubrovinsky, L. and Tolan, M. and Sternemann, C. and Wilke, M.
    Journal of Synchrotron Radiation 27 (2020)
    A portable IR fiber laser-heating system, optimized for X-ray emission spectroscopy (XES) and nuclear inelastic scattering (NIS) spectroscopy with signal collection through the radial opening of diamond anvil cells near 90°with respect to the incident X-ray beam, is presented. The system offers double-sided on-Axis heating by a single laser source and zero attenuation of incoming X-rays other than by the high-pressure environment. A description of the system, which has been tested for pressures above 100GPa and temperatures up to 3000K, is given. The XES spectra of laser-heated Mg0.67Fe0.33O demonstrate the potential to map the iron spin state in the pressure-Temperature range of the Earth's lower mantle, and the NIS spectra of laser-heated FeSi give access to the sound velocity of this candidate of a phase inside the Earth's core. This portable system represents one of the few bridges across the gap between laser heating and high-resolution X-ray spectroscopies with signal collection near 90°. © 2020 Journal of Synchrotron Radiation.
    view abstract10.1107/S1600577519017041
  • Pressure stability of the first hydration shell of yttrium in aqueous YCl3 solution
    Elbers, M. and Sternemann, C. and Julius, K. and Paulus, M. and Surmeier, G. and König, N. and Nase, J. and Bolle, J. and Wagner, R. and Irifune, T. and Tolan, M.
    High Pressure Research (2020)
    The pressure stability of the first hydration shell of Y3+ ions in aqueous solution has been investigated by means of extended x-ray absorption fine-structure spectroscopy at the yttrium K-edge for hydrostatic pressures up to 4.5 kbar and concentrations between 1 M and 2.5 M. We find approximately 8.4 water molecules surrounding the yttrium cation at a mean distance of 2.370 Å at ambient conditions, independent on the concentration. The yttrium hydration shell has a low compressibility in the order of (-3.8 ± 0.7)×10-4 Å kbar-1 emphasizing its pressure stability in the kbar range. At the studied conditions, no indication for chloride complexation was observed. © 2020, © 2020 Informa UK Limited, trading as Taylor & Francis Group.
    view abstract10.1080/08957959.2020.1724998
  • Combining X-ray Kβ 1,3 , valence-to-core, and X-ray Raman spectroscopy for studying Earth materials at high pressure and temperature: The case of siderite
    Weis, C. and Spiekermann, G. and Sternemann, C. and Harder, M. and Vankó, G. and Cerantola, V. and Sahle, C.J. and Forov, Y. and Sakrowski, R. and Kupenko, I. and Petitgirard, S. and Yavaş, H. and Bressler, C. and Gawelda, W. and Tolan, M. and Wilke, M.
    Journal of Analytical Atomic Spectrometry 34 (2019)
    X-ray emission and X-ray Raman scattering spectroscopy are powerful tools to investigate the local electronic and atomic structure of high and low Z elements in situ. Notably, these methods can be applied for in situ spectroscopy at high pressure and high temperature using resistively or laser-heated diamond anvil cells in order to achieve thermodynamic conditions which appear in the Earth's interior. We present a setup for combined X-ray emission and X-ray Raman scattering studies at beamline P01 of PETRA III using a portable wavelength-dispersive von Hamos spectrometer together with the permanently installed multiple-analyzer Johann-type spectrometer. The capabilities of this setup are exemplified by investigating the iron spin crossover of siderite FeCO 3 up to 49.3 GPa by measuring the Fe M 2,3 -edge and the Fe Kβ 1,3 emission line simultaneously. With this setup, the Fe valence-to-core emission can be detected together with the Kβ 1,3 emission line providing complementary information on the sample's electronic structure. By implementing a laser-heating device, we demonstrate the strength 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 application in geoscience that are accessible with the Johann-type XRS spectrometer. With this setup new insights into the spin transition and compression mechanisms of Earth's mantle materials can be obtained of importance for comprehension of the macroscopic physical and chemical properties of the Earth's interior. © 2019 The Royal Society of Chemistry.
    view abstract10.1039/c8ja00247a
  • Impact of Macromolecular Crowding and Compression on Protein-Protein Interactions and Liquid-Liquid Phase Separation Phenomena
    Julius, K. and Weine, J. and Gao, M. and Latarius, J. and Elbers, M. and Paulus, M. and Tolan, M. and Winter, R.
    Macromolecules 52 (2019)
    We determined the intermolecular interaction potential, V(r), of dense lysozyme solutions, which governs the spatial distribution of the protein molecules and the location of its liquid-liquid phase separation (LLPS) region, in various crowding environments applying small-angle X-ray scattering in combination with liquid-state theory. We explored the effect of polyethylene glycol (PEG) on V(r) and the protein's phase behavior over a wide range of temperatures and pressures, crossing from the dilute to the semidilute polymer regime, thereby mimicking all crowding scenarios encountered in the heterogeneous biological cell. V(r) and hence the protein-protein distances and the phase boundary of the LLPS region strongly depend on the polymer-to-protein size ratio and the polymer concentration. The strongest effect is observed for small-sized PEG molecules, leading to a marked decrease of the mean intermolecular spacing of the protein molecules with increasing crowder concentration. The effect levels off at intermolecular distances where the proteins' second hydration shells start to penetrate each other. Strong repulsive forces like hydration-shell repulsion and/or soft enthalpic protein-PEG interactions must be operative at short distances which stabilize the protein against depletion-induced aggregation, also at pressures as high as encountered in the deep sea, where pressures up to the kbar-level are encountered. © 2019 American Chemical Society.
    view abstract10.1021/acs.macromol.8b02476
  • Microstructural characteristics of high-feed milled HVOF sprayed WC-Co coatings
    Tillmann, W. and Hagen, L. and Stangier, D. and Paulus, M. and Tolan, M. and Sakrowski, R. and Biermann, D. and Freiburg, D.
    Surface and Coatings Technology 374 (2019)
    Over the last decade, great efforts have been undertaken in science and industry to provide WC-Co feedstock with nano-sized WC particles that significantly improves tribo-mechanical coating properties. For tribologically stressed surfaces, superior surface characteristics can be achieved by applying tailored surfaces, using novel technologies in the field of production engineering such as High-Feed Milling (HFM). For the first time, textured surface patterns were produced onto HVOF sprayed WC-Co coatings with nano-sized WC particles by implementing a HFM post process. In dependence to two different textures resulting from the HFM, the microstructural characteristics of the produced surfaces are analyzed. Confocal microscopy revealed the machinability of textured patterns onto a HVOF-sprayed WC-12Co hard coating, which comprise of nano-sized WC particles, by means of HFM technology. X-ray diffraction analyses confirmed the insertion of macro- and micro-scale residual stresses. The experiments showed a significant insertion of compressive residual stresses transverse to the feed direction, whereas the insertion of compresses residual stresses with its feed direction being less pronounced. It was found that the HFM post process leads to a refinement of the WC crystallite size and a distinct increase of its internal strain, which both can be attributed to plastic deformations during HFM. © 2019 Elsevier B.V.
    view abstract10.1016/j.surfcoat.2019.06.012
  • New Approach to Structure–Property Correlations of Different Films of Sorbitan Esters and Their Self-Assembly into Viscoelastic Monolayers
    Demand, S. and Egger, S. and Degen, P. and Salmen, P. and Paulus, M. and Tolan, M. and Rehage, H.
    Journal of Surfactants and Detergents 22 (2019)
    This publication is focused on the structural origin of viscoelasticity in Langmuir monolayers. To improve the understanding of the structural origin of viscoelasticity of surfactant films, we systematically studied interfacial films of different sorbitan esters with saturated (Span 60 and 65) and unsaturated (Span 80 and 85) paraffin chains by means of surface rheology, Langmuir isotherms, X-ray reflectometry (XRR), and Brewster angle microscopy (BAM). The results of two-dimensional shear rheological measurements revealed the existence of temporarily cross-linked networks. In dynamic BAM experiments, we observed a swinging motion of the monolayers as a result of a sudden externally initiated mechanical perturbation. The viscoelastic film response, which relaxed with time as the external force vanished, could be traced back to the presence of foam-like supramolecular structures that interlinked solid-condensed domains. The temperature dependence of the elastic response implied that the solid domains decomposed at temperatures close to the bulk melting point of Span 60 and Span 65. We concluded that insoluble surfactants formed solid domains at the interface, which were linked with each other by nonsolid areas, giving viscoelastic films. These newly discovered insights into coherent film formations could provide new opportunities for designing mechanically stable surfactant interfaces. © 2019 AOCS
    view abstract10.1002/jsde.12261
  • Structure and mechanical properties of hafnium nitride films deposited by direct current, mid-frequency, and high-power impulse magnetron sputtering
    Tillmann, W. and Lopes Dias, N.F. and Stangier, D. and Tolan, M. and Paulus, M.
    Thin Solid Films 669 (2019)
    The structural properties of hafnium nitride films are mainly influenced by the deposition conditions, which are affected by the sputtering technique. A suitable use of the different sputtering modes allows to control the structural development of the films and thus to adjust the profile of the properties. NaCl-type hafnium nitride films were deposited using direct current magnetron sputtering (dcMS), mid-frequency magnetron sputtering (mfMS), and high-power impulse magnetron sputtering (HiPIMS). dcMS produces films with a columnar microstructure, whereas a fully-dense morphology is achieved by mfMS and HiPIMS. X-ray diffraction patterns show that films sputtered in dcMS mode have a (200) orientation, whereas mfMS and HiPIMS favor an orientation with the (111) plane parallel to the samples’ surface. mfMS leads to films with the largest crystal sizes and lowest stresses, which is ascribed to recrystallization mechanisms during the film growth. Hafnium films with an overstoichiometric composition show the highest hardness values. In this context, the dcMS-Hf49.8N50.2, mfMS-Hf50.4N49.6, and HiPIMS-Hf49.0N51.0 have a hardness of 28.2 ± 2.1, 32.4 ± 3.4, and 30.4 ± 3.1 GPa, respectively. In summary, the sputtering technique has a crucial role on the properties of the film and can be suitable used to adjust the structure and hardness of HfN films. © 2018 Elsevier B.V.
    view abstract10.1016/j.tsf.2018.10.035
  • Surfactant-mediated formation of alginate layers at the water-air interface
    Degen, P. and Paulus, M. and Zwar, E. and Jakobi, V. and Dogan, S. and Tolan, M. and Rehage, H.
    Surface and Interface Analysis 51 (2019)
    The self-organization process of polysaccharide alginate with different cationic surfactants at the water-air interface was investigated over a wide concentration regime. The changes of surface properties determined by surface tension measurements, surface rheology, and X-ray reflectivity are correlated with changes of bulk properties measured by turbidity, light scattering, and zeta potential measurements. We demonstrate that the interactions between the alginate and cationic surfactants result in significant changes of bulk and interfacial properties. The results of surface shear experiments point to the existence of highly viscoelastic interfacial films. In combination with X-ray reflectivity, we demonstrate that these rheological features are related to polymer-surfactant associations at the interface. In the regime of high surfactant concentrations, we observed the existence of multilayer structures. © 2019 The Authors. Surface and Interface Analysis published by John Wiley & Sons Ltd
    view abstract10.1002/sia.6691
  • Temperature-induced formation of lubricous oxides in vanadium containing iron-based arc sprayed coatings
    Tillmann, W. and Hagen, L. and Kokalj, D. and Paulus, M. and Tolan, M.
    Coatings 9 (2019)
    In the field of surface engineering, the use of self-lubricous coatings with the incorporation of vanadium represent a promising approach to reduce friction, thus contributing to the wear behavior. For vanadium containing hard coatings produced by means of thin film technology, the reduction in friction at elevated temperatures was repeatedly attributed to temperature-induced and tribo-oxidatively formed oxides which act as solid lubricant. Only very few studies focused on the tribological characteristics of vanadium containing arc sprayed coatings. In this study, the tribological characteristics of a vanadium containing iron-based arc sprayed deposit were investigated in dry sliding experiments under ambient conditions and different temperatures. Types of wear at the worn surfaces and counterparts were examined by means of electron microscopy and energy dispersive X-ray (EDX) spectroscopy. The speciation of vanadium in the superficial layer was determined using X-ray absorption near edge structure (XANES) spectroscopy. It was found that the vanadium-containing coating exhibited a distinctly reduction of the coefficient of friction above 450 °C which further decreased with increasing temperature. XANES spectroscopy indicated an increased oxidation state for the V component on the coating surface, suggesting the prevalence of specific vanadium oxides which promote a self-lubricating ability of the coating. © 2018 by the authors.
    view abstract10.3390/coatings9010018
  • Adsorption Behavior of Lysozyme at Titanium Oxide-Water Interfaces
    Forov, Y. and Paulus, M. and Dogan, S. and Salmen, P. and Weis, C. and Gahlmann, T. and Behrendt, A. and Albers, C. and Elbers, M. and Schnettger, W. and Egger, S. and Zwar, E. and Rehage, H. and Kiesel, I. and Riedl, T. and Tolan, M.
    Langmuir 34 (2018)
    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. © 2018 American Chemical Society.
    view abstract10.1021/acs.langmuir.8b00280
  • Human Apolipoprotein A1 at Solid/Liquid and Liquid/Gas Interfaces
    Dogan, S. and Paulus, M. and Forov, Y. and Weis, C. and Kampmann, M. and Cewe, C. and Kiesel, I. and Degen, P. and Salmen, P. and Rehage, H. and Tolan, M.
    Journal of Physical Chemistry B 122 (2018)
    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. © 2018 American Chemical Society.
    view abstract10.1021/acs.jpcb.7b12481
  • Investigation on the oxidation behavior of AlCrVxN thin films by means of synchrotron radiation and influence on the high temperature friction
    Tillmann, W. and Kokalj, D. and Stangier, D. and Paulus, M. and Sternemann, C. and Tolan, M.
    Applied Surface Science 427 (2018)
    Friction minimization is an important topic which is pursued in research and industry. In addition to the use of lubricants, friction-reducing oxide phases can be utilized which occur during. These oxides are called Magnéli phases and especially vanadium oxides exhibit good friction reducing properties. Thereby, the lubrication effect can be traced back to oxygen deficiencies. AlCrN thin films are being used as coatings for tools which have to withstand high temperatures. A further improvement of AlCrN thin films concerning their friction properties is possible by incorporation of vanadium. This study analyzes the temperature dependent oxidation behavior of magnetron sputtered AlCrVN thin films with different vanadium contents up to 13.5 at.-% by means of X-ray diffraction and X-ray absorption near-edge spectroscopy. Up to 400 °C the coatings show no oxidation. A higher temperature of 700 °C leads to an oxidation and formation of Magnéli phases of the coatings with vanadium contents above 10.7 at.-%. Friction coefficients, measured by ball-on-disk test are correlated with the oxide formation in order to figure out the effect of vanadium oxides. At 700 °C a decrease of the friction coefficient with increasing vanadium content can be observed, due to the formation of VO2, V2O3 and the Magnéli phase V4O7. © 2017 Elsevier B.V.
    view abstract10.1016/j.apsusc.2017.09.029
  • The effects of osmolytes and crowding on the pressure-induced dissociation and inactivation of dimeric LADH
    Julius, K. and Al-Ayoubi, S.R. and Paulus, M. and Tolan, M. and Winter, R.
    Physical Chemistry Chemical Physics 20 (2018)
    Investigating the correlation between structure and activity of oligomeric enzymes at high pressure is essential for understanding intermolecular interactions and reactivity of proteins in cellulo of organisms thriving at extreme environmental conditions as well as for biotechnological applications, such as high-pressure enzymology. In a combined experimental effort employing small-angle X-ray scattering, FT-IR and fluorescence spectroscopy as well as stopped-flow enzyme kinetics in concert with high-pressure techniques, we reveal the pressure-induced conformational changes of the dimeric enzyme horse liver alcohol dehydrogenase (LADH) on the quaternary, secondary and tertiary structural level. Moreover, the effects of cosolutes and crowding agents, mimicking intracellular conditions, have been addressed. Our results show that beyond an increase of enzymatic activity at low pressures, loss of enzyme activity occurs around 600-800 bar, i.e. in a pressure regime where small conformational changes take place in the coenzyme's binding pocket, only. Whereas higher-order oligomers dissociate at low pressures, subunit dissociation of dimeric LADH takes place, depending on the solution conditions, between 2000 and 4000 bar, only. Oligomerization and subunit dissociation are modulated by cosolvents such as urea or trimethylamine-N-oxide as well as by the crowding agent polyethylene glycol, based on their tendency to bind to the protein's interface or act via their excluded volume effect, respectively. © the Owner Societies 2018.
    view abstract10.1039/c7cp08242h
  • Water-Mediated Protein-Protein Interactions at High Pressures are Controlled by a Deep-Sea Osmolyte
    Julius, K. and Weine, J. and Berghaus, M. and König, N. and Gao, M. and Latarius, J. and Paulus, M. and Schroer, M.A. and Tolan, M. and Winter, R.
    Physical Review Letters 121 (2018)
    The influence of natural cosolvent mixtures on the pressure-dependent structure and protein-protein interaction potential of dense protein solutions is studied and analyzed using small-angle X-ray scattering in combination with a liquid-state theoretical approach. The deep-sea osmolyte trimethylamine-N-oxide is shown to play a crucial and singular role in its ability to not only guarantee sustainability of the native protein's folded state under harsh environmental conditions, but it also controls water-mediated intermolecular interactions at high pressure, thereby preventing contact formation and hence aggregation of proteins. © 2018 American Physical Society.
    view abstract10.1103/PhysRevLett.121.038101
  • A Study on the Tribological Behavior of Vanadium-Doped Arc Sprayed Coatings
    Tillmann, W. and Hagen, L. and Kokalj, D. and Paulus, M. and Tolan, M.
    Journal of Thermal Spray Technology 26 (2017)
    The formation of thin reactive films in sliding contacts under elevated temperature provides enhanced tribological properties since the formation of Magnéli phases leads to the ability of self-lubricating behavior. This phenomenon was studied for vanadium-doped coating systems which were produced using CVD and PVD technology. Vanadium-containing arc sprayed coatings were not widely examined so far. The aim of this study was to characterize Fe-V coatings deposited by the Twin Wire Arc Spraying process with respect to their oxidation behavior at elevated temperatures and to correlate the formation of oxides to the tribological properties. Dry sliding experiments were performed in the temperature range between 25 and 750 °C. The Fe-V coating possesses a reduced coefficient of friction and wear coefficient (k) at 650 and 750 °C, which were significant lower when compared to conventional Fe-based coatings. The evolution of oxide phases was identified in situ by x-ray diffraction for the investigated temperature range. Further oxidation of (pre-oxidized) arc sprayed Fe-V coatings, as verified by differential thermal analysis and thermo-gravimetric analysis, starts at about 500 °C. © 2017 ASM International
    view abstract10.1007/s11666-017-0524-y
  • Antibodies under pressure: A Small-Angle X-ray Scattering study of Immunoglobulin G under high hydrostatic pressure
    König, N. and Paulus, M. and Julius, K. and Schulze, J. and Voetz, M. and Tolan, M.
    Biophysical Chemistry 231 (2017)
    In the present work two subclasses of the human antibody Immunoglobulin G (IgG) have been investigated by Small-Angle X-ray Scattering under high hydrostatic pressures up to 5kbar. It is shown that IgG adopts a symmetric T-shape in solution which differs significantly from available crystal structures. Moreover, high-pressure experiments verify the high stability of the IgG molecule. It is not unfolded by hydrostatic pressures of up to 5kbar but a slight increase of the radius of gyration was observed at elevated pressures. © 2017 Elsevier B.V.
    view abstract10.1016/j.bpc.2017.05.016
  • Compositional fingerprint of soy sauces via hydrophobic surface interaction
    Jakobi, V. and Salmen, P. and Paulus, M. and Tolan, M. and Rosenhahn, A.
    Food Chemistry 218 (2017)
    In this work, the interaction of soy sauces with hydrophobic surfaces has been analyzed. Hydrophobic self-assembled monolayers on gold or silicon dioxide were used to harvest conditioning layers from soy sauce products with varying amounts of additives. The data was compared to adsorption of soy protein and glutamic acid as common ingredients. Spectral ellipsometry revealed that all tested sauces led to the formation of thin overlayers on hydrophobic surfaces. Products with less additives yielded adlayers in the same thickness range as pure soy protein. In contrast, sauces with more ingredients create distinctly thicker films. Using water contact angle goniometry, it is shown that all adlayers render the substrate more hydrophilic. Infrared spectroscopy provided a deeper insight into the adlayer chemistry and revealed that the adlayer composition is dominated by protein rich components. X-ray reflectivity on selected films provided further insight into the density profiles within the adlayers on the molecular scale. © 2016 Elsevier Ltd
    view abstract10.1016/j.foodchem.2016.09.045
  • Connecting structurally and dynamically detected signatures of supramolecular Debye liquids
    Büning, T. and Lueg, J. and Bolle, J. and Sternemann, C. and Gainaru, C. and Tolan, M. and Böhmer, R.
    Journal of Chemical Physics 147 (2017)
    The monohydroxy alcohol 2-ethyl-1-hexanol mixed with the halogen-substituted alkyl halides 2-ethyl-1-hexyl chloride and 2-ethyl-1-hexyl bromide was studied using synchrotron-based x-ray scattering. In the diffraction patterns, an oxygen-related prepeak appears. The concentration dependence of its intensity, shape, and position indicates that the formation of the hydrogen-bonded associates of monohydroxy alcohols is largely hindered by the halogen alkane admixture. Using dielectric spectroscopy and high-resolution rheology on the same liquid mixtures, it is shown that these structural features are correlated with the relaxation mechanisms giving rise to supramolecular low-frequency dynamics. © 2017 Author(s).
    view abstract10.1063/1.4986866
  • Investigation of the influence of the vanadium content on the high temperature tribo-mechanical properties of DC magnetron sputtered AlCrVN thin films
    Tillmann, W. and Kokalj, D. and Stangier, D. and Paulus, M. and Sternemann, C. and Tolan, M.
    Surface and Coatings Technology 328 (2017)
    The forming of high-strength steels or new aluminum alloys leads to a steady increase of the load of tools and coatings. One approach is to positively influence the manufacturing process by using thin solid films with self-lubricating features, provided by oxides at high temperatures with low decohesion energies. For the purpose of this study, AlCrN provides the matrix, while vanadium oxides are used to enhance the frictional and wear properties. However, it is not yet clear which minimum amount of vanadium has to be incorporated in DC magnetron sputtered AlCrN coatings to improve the tribological behavior. Therefore, in this study, AlCrVN coatings are synthesized with an increasing vanadium content by means of reactive DC magnetron sputtering. Additionally, a vanadium-free AlCrN coating is used as reference for the tribo-mechanical investigations. The coatings were synthesized up to a vanadium content of 13.5 at.-% and no phase change could be detected by means of x-ray diffraction. Moreover, no hexagonal AlN phase, which reduces the mechanical properties and the oxidation resistance, was formed. In contrast to the vanadium-free coating, the hardness of the coatings containing vanadium is slightly reduced. The coating with the smallest vanadium content shows the highest hardness of all analyzed coatings. A heat treatment at 400 °C does not lead to any significant changes with respect to mechanical properties, but at 700 °C hardness, modulus of elasticity and critical load decreased for all coatings, indicating a significant change in mechanical properties. The ball-on-disc test at room-temperature, 400 °C, and 700 °C shows the highest wear coefficient for the coating with the lowest vanadium content, due to the poor adhesion of the coating, although this coating shows the highest H/E-ratio. © 2017 Elsevier B.V.
    view abstract10.1016/j.surfcoat.2017.08.046
  • Pressure driven spin transition in siderite and magnesiosiderite single crystals
    Weis, C. and Sternemann, C. and Cerantola, V. and Sahle, C.J. and Spiekermann, G. and Harder, M. and Forov, Y. and Kononov, A. and Sakrowski, R. and Yavaş, H. and Tolan, M. and Wilke, M.
    Scientific Reports 7 (2017)
    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 FeCO3 and magnesiosiderite (Mg0.74Fe0.26)CO3 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. © 2017 The Author(s).
    view abstract10.1038/s41598-017-16733-3
  • The Hydrophobic Gap at High Hydrostatic Pressures
    Wirkert, F.J. and Hölzl, C. and Paulus, M. and Salmen, P. and Tolan, M. and Horinek, D. and Nase, J.
    Angewandte Chemie - International Edition 56 (2017)
    We have gained new insight into the so-called hydrophobic gap, a molecularly thin region of decreased electron density at the interface between water and a solid hydrophobic surface, by X-ray reflectivity experiments and molecular dynamics simulations at different hydrostatic pressures. Pressure variations show that the hydrophobic gap persists up to a pressure of 5 kbar. The electron depletion in the interfacial region strongly decreases with an increase in pressure, indicating that the interfacial region is compressed more strongly than bulk water. The decrease is most significant up to 2 kbar; beyond that, the pressure response of the depletion is less pronounced. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstract10.1002/anie.201706662
  • Bulk sensitive determination of the Fe3+/FeTot-ratio in minerals by Fe L2/3-edge X-ray Raman scattering
    Nyrow, A. and Sternemann, C. and Tse, J.S. and Weis, C. and Sahle, C.J. and Mende, K. and Wieland, D.C.F. and Cerantola, V. and Gordon, R.A. and Spiekermann, G. and Regier, T. and Wilke, M. and Tolan, M.
    Journal of Analytical Atomic Spectrometry 31 (2016)
    We present the first measurements of the iron L2/3-edge of the compounds FeO, Fe2O3, and Fe3O4 at ambient pressure and of FeCO3 at high pressures of 2.4 and 40 GPa using a diamond anvil cell by X-ray Raman scattering spectroscopy, a bulk sensitive probe of soft X-ray absorption edges making use of hard X-rays. We show that the spectral shape of the Fe L2/3-edge can be analyzed quantitatively to reveal the oxidation state of iron in matter. Consequently, in situ X-ray Raman scattering spectroscopy at the iron L-edge at high pressure and temperature opens exciting perspectives to characterize the local coordination, oxidation, and spin state of iron at high pressure and temperature, conditions that are of relevance for e.g. geological sciences or chemical processing. © The Royal Society of Chemistry 2016.
    view abstract10.1039/c5ja00261c
  • Formation of CaB6 in the thermal decomposition of the hydrogen storage material Ca(BH4)2
    Sahle, C.J. and Sternemann, C. and Giacobbe, C. and Yan, Y. and Weis, C. and Harder, M. and Forov, Y. and Spiekermann, G. and Tolan, M. and Krisch, M. and Remhof, A.
    Physical Chemistry Chemical Physics 18 (2016)
    Using a combination of high resolution X-ray powder diffraction and X-ray Raman scattering spectroscopy at the B K- and Ca L2,3-edges, we analyzed the reaction products of Ca(BH4)2 after annealing at 350 °C and 400 °C under vacuum conditions. We observed the formation of nanocrystalline/amorphous CaB6 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 °C we observed neither CaB12H12 nor CaB6. The results indicate a reaction pathway in which Ca(BH4)2 decomposes to B and CaH2 and finally reacts to form CaB6. These findings confirm the potential of using Ca(BH4)2 as a hydrogen storage medium and imply the desired cycling capabilities for achieving high-density hydrogen storage materials. © the Owner Societies 2016.
    view abstract10.1039/c6cp02495e
  • In situ characterization of the decomposition behavior of Mg(BH4)2 by X-ray Raman scattering spectroscopy
    Sahle, C.J. and Kujawski, S. and Remhof, A. and Yan, Y. and Stadie, N.P. and Al-Zein, A. and Tolan, M. and Huotari, S. and Krisch, M. and Sternemann, C.
    Physical Chemistry Chemical Physics 18 (2016)
    We present an in situ study of the thermal decomposition of Mg(BH4)2 in a hydrogen atmosphere of up to 4 bar and up to 500 °C using X-ray Raman scattering spectroscopy at the boron K-edge and the magnesium L2,3-edges. The combination of the fingerprinting analysis of both edges yields detailed quantitative information on the reaction products during decomposition, an issue of crucial importance in determining whether Mg(BH4)2 can be used as a next-generation hydrogen storage material. This work reveals the formation of reaction intermediate(s) at 300 °C, accompanied by a significant hydrogen release without the occurrence of stable boron compounds such as amorphous boron or MgB12H12. At temperatures between 300 °C and 400 °C, further hydrogen release proceeds via the formation of higher boranes and crystalline MgH2. Above 400 °C, decomposition into the constituting elements takes place. Therefore, at moderate temperatures, Mg(BH4)2 is shown to be a promising high-density hydrogen storage material with great potential for reversible energy storage applications. © 2016 the Owner Societies.
    view abstract10.1039/c5cp06571b
  • Intramolecular structure and energetics in supercooled water down to 255 K
    Lehmkühler, F. and Forov, Y. and Büning, T. and Sahle, C.J. and Steinke, I. and Julius, K. and Buslaps, T. and Tolan, M. and Hakala, M. and Sternemann, C.
    Physical Chemistry Chemical Physics 18 (2016)
    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. © the Owner Societies 2016.
    view abstract10.1039/c5cp07721d
  • Near-Surface and Bulk Behavior of Bicontinuous Microemulsions under High-Pressure Conditions
    Berghaus, M. and Paulus, M. and Salmen, P. and Al-Ayoubi, S. and Tolan, M. and Winter, R.
    Journal of Physical Chemistry B 120 (2016)
    The effect of hydrostatic pressure on the structure of a bicontinuous microemulsion in the presence of a solid interface has been studied by X-ray reflectometry and compared to the bulk behavior determined by small-angle X-ray scattering. Surface-induced lamellar ordering is observed close to the hydrophilic interface, which persists upon compression. The lamellar domains are compressed, but the correlation length of lamellar order does not change with pressure. SAXS measurements on the bulk microemulsion revealed an increased order upon pressurization. Although pressure can cause the formation of highly ordered lamellar phases from ordered bicontinuous cubic phases, such a scenario is not observed for the disordered analogue studied here. High pressure increases the stiffness of the interfacial surfactant layer, but this is not sufficient to overcome the loss in conformational entropy that would result from a transition to an ordered lamellar phase. Possible technological and biological implications of our results are briefly discussed. © 2016 American Chemical Society.
    view abstract10.1021/acs.jpcb.6b05639
  • Phase behavior of lysozyme solutions in the liquid-liquid phase coexistence region at high hydrostatic pressures
    Schulze, J. and Möller, J. and Weine, J. and Julius, K. and König, N. and Nase, J. and Paulus, M. and Tolan, M. and Winter, R.
    Physical Chemistry Chemical Physics 18 (2016)
    We present results from small-angle X-ray scattering and turbidity measurements on the effect of high hydrostatic pressure on the phase behavior of dense lysozyme solutions in the liquid-liquid phase separation region, and characterize the underlying intermolecular protein-protein interactions as a function of temperature and pressure under charge-screening conditions (0.5 M NaCl). A reentrant liquid-liquid phase separation region is observed at elevated pressures, which may originate in the pressure dependence of the solvent-mediated protein-protein interaction. A temperature-pressure-concentration phase diagram was constructed for highly concentrated lysozyme solutions over a wide range of temperatures, pressures and protein concentrations including the critical region of the liquid-liquid miscibility gap. © the Owner Societies 2016.
    view abstract10.1039/c6cp01791f
  • Polaron-induced lattice distortion of (In,Ga)As/GaAs quantum dots by optically excited carriers
    Tiemeyer, S. and Bombeck, M. and Göhring, H. and Paulus, M. and Sternemann, C. and Nase, J. and Wirkert, F.J. and Möller, J. and Büning, T. and Seeck, O.H. and Reuter, D. and Wieck, A.D. and Bayer, M. and Tolan, M.
    Nanotechnology 27 (2016)
    We report on a high resolution x-ray diffraction study unveiling the effect of carriers optically injected into (In,Ga)As quantum dots on the surrounding GaAs crystal matrix. We find a tetragonal lattice expansion with enhanced elongation along the [001] crystal axis that is superimposed on an isotropic lattice extension. The isotropic contribution arises from excitation induced lattice heating as confirmed by temperature dependent reference studies. The tetragonal expansion on the femtometer scale is tentatively attributed to polaron formation by carriers trapped in the quantum dots. © 2016 IOP Publishing Ltd.
    view abstract10.1088/0957-4484/27/42/425702
  • Solid-Supported Lipid Multilayers under High Hydrostatic Pressure
    Nowak, B. and Paulus, M. and Nase, J. and Salmen, P. and Degen, P. and Wirkert, F.J. and Honkimäki, V. and Tolan, M.
    Langmuir 32 (2016)
    In this work, the structure of solid-supported lipid multilayers exposed to increased hydrostatic pressure was studied in situ by X-ray reflectometry at the solid-liquid interface between silicon and an aqueous buffer solution. The layers' vertical structure was analyzed up to a maximum pressure of 4500 bar. The multilayers showed phase transitions from the fluid into different gel phases. With increasing pressure, a gradual filling of the sublayers between the hydrophilic head groups with water was observed. This process was inverted when the pressure was decreased, yielding finally smaller water layers than those in the initial state. As is commonly known, water has an abrasive effect on lipid multilayers by the formation of vesicles. We show that increasing pressure can reverse this process so that a controlled switching between multi- and bilayers is possible. © 2016 American Chemical Society.
    view abstract10.1021/acs.langmuir.5b04554
  • The interaction between stearic acid monolayers and butane under elevated pressures
    Giebel, F. and Paulus, M. and Nase, J. and Kiesel, I. and Bieder, S. and Tolan, M.
    Colloids and Surfaces A: Physicochemical and Engineering Aspects 504 (2016)
    A study on the interaction between butane and lipid membranes is presented. Monomolecular films of stearic acid were prepared on a water surface and were exposed to dense gas phases of n-butane and isobutane. From X-ray reflectivity measurements and grazing incidence X-ray diffraction, the accumulation of gas molecules at the liquid-gas interface was analyzed. We show that the gas molecules penetrate into the lipid membrane and accumulate between the head group and tail group of the lipids. This process goes in hand with an increase of the long-range lateral crystallographic order within the lipid film. This and the formation of multilayer islands points to an expulsion of lipids by the gas molecules. At higher pressures close to the condensation pressure of the studied gases, the vertical and lateral order is lost, indicating an adsorbed liquid film in which the lipids are dissolved. © 2016 Elsevier B.V.
    view abstract10.1016/j.colsurfa.2016.05.067
  • X-ray diffraction (XRD)-studies on the temperature dependent interface reactions on hafnium, zirconium, and nickel coated monocrystalline diamonds used in grinding segments for stone and concrete machining
    Tillmann, W. and Tolan, M. and Pinho Ferreira, M. and Paulus, M. and Becke, M. and Stangier, D.
    Materialwissenschaft und Werkstofftechnik 47 (2016)
    Diamond impregnated metal matrix composites are the state of the art solution for the machining of mineral materials. The type of interface reactions between the metal matrix and diamond surface has an essential influence on the tool performance and durability. To improve the diamond retention, the diamonds can be coated by physical vapour deposition with metallic materials, which enforce interface reactions. Hence, this paper focuses on the investigation of the interfacial area on metal-coated monocrystalline diamonds. Hafnium and zirconium, both known as carbide forming elements, are used as coating materials. The third coating, which is used to determine its catalytic influences when applied as a physical vapour deposition (PVD)-layer, is nickel. Additionally, the coated diamond samples were heat-treated to investigate the starting point of the formation of new phases. X-ray diffraction-analyses revealed the assumed carbide formation on hafnium and zirconium coated samples. The formation temperature was identified between 800 °C and 1000 °C for hafnium and zirconium coatings. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstract10.1002/mawe.201600713
  • Salt induced reduction of lysozyme adsorption at charged interfaces
    Göhring, H. and Paulus, M. and Salmen, P. and Wirkert, F. and Kruse, T. and Degen, P. and Stuhr, S. and Rehage, H. and Tolan, M.
    Journal of Physics Condensed Matter 27 (2015)
    A study of lysozyme adsorption below a behenic acid membrane and at the solid-liquid interface between aqueous lysozyme solution and a silicon wafer in the presence of sodium chloride is presented. The salt concentration was varied between 1 mmol L-1 and 1000 mmol L-1. X-ray reflectivity data show a clear dependence of the protein adsorption on the salt concentration. Increasing salt concentrations result in a decreased protein adsorption at the interface until a complete suppression at high concentrations is reached. This effect can be attributed to a reduced attractive electrostatic interaction between the positively charged proteins and negatively charged surfaces by charge screening. The measurements at the solid-liquid interfaces show a transition from unoriented order of lysozyme in the adsorbed film to an oriented order with the short protein axis perpendicular to the solid-liquid interface with rising salt concentration. © 2015 IOP Publishing Ltd.
    view abstract10.1088/0953-8984/27/23/235103
  • About the role of surfactants on the magnetic control over liquid interfaces
    Degen, P. and Zwar, E. and Paulus, M. and Tolan, M. and Rehage, H.
    Langmuir 30 (2014)
    The behavior of magnetically responsive aqueous Fe(III) surfactant solutions at liquid interfaces is analyzed. Such surfactants attracted much attention, because of the ability to manipulate interfaces by magnetic fields without any use of magnetic nanoparticles. A detailed analysis of the surface properties proves that the mixing of paramagnetic electrolyte solution with anionic, cationic and nonionic surfactants yields the similar magnetic response and no effect of the surfactant charge can be observed. We conclude that the observed magnetic shiftability of interfaces is caused by a combination of the paramagnetic behavior of the bulk liquid and a reduction of the surface tension. Thus, this work gives an alternative interpretation of the properties of 'magnetic surfactants' compared to the ones claimed in the literature. © 2014 American Chemical Society.
    view abstract10.1021/la503142q
  • Intermolecular interactions in highly concentrated protein solutions upon compression and the role of the solvent
    Grobelny, S. and Erlkamp, M. and Möller, J. and Tolan, M. and Winter, R.
    Journal of Chemical Physics 141 (2014)
    The influence of high hydrostatic pressure on the structure and protein-protein interaction potential of highly concentrated lysozyme solutions up to about 370 mg ml1was studied and analyzed using small-angle X-ray scattering in combination with a liquid-state theoretical approach. In the concentration region below 200 mg ml1, the interaction parameters of lysozyme solutions are affected by pressure in a nonlinear way, which is probably due to significant changes in the structural properties of bulk water, i.e., due to a solvent-mediated effect. Conversely, for higher concentrated protein solutions, where hydration layers below ∼4 water molecules are reached, the interaction potential turns rather insensitive to compression. The onset of transient (dynamic) clustering is envisaged in this concentration range. Our results also show that pressure suppresses protein nucleation, aggregation and finally crystallization in supersaturated condensed protein solutions. These findings are of importance for controlling and fine-tuning protein crystallization. Moreover, these results are also important for understanding the high stability of highly concentrated protein solutions (as they occur intracellularly) in organisms thriving under hydrostatic pressure conditions such as in the deep sea, where pressures up to the kbar-level are reached. © 2014 AIP Publishing LLC.
    view abstract10.1063/1.4895542
  • Iron speciation in minerals and glasses probed by M2/3-edge X-ray Raman scattering spectroscopy
    Nyrow, A. and Sternemann, C. and Wilke, M. and Gordon, R.A. and Mende, K. and Yavaş, H. and Simonelli, L. and Hiraoka, N. and Sahle, C.J. and Huotari, S. and Andreozzi, G.B. and Woodland, A.B. and Tolan, M. and Tse, J.S.
    Contributions to Mineralogy and Petrology 167 (2014)
    We present a spectroscopic study of the iron M2/3-edge for several minerals and compounds to reveal information about the oxidation state and the local coordination of iron. We describe a novel approach to probe the iron M2/3-edge bulk sensitively using X-ray Raman scattering. Significant changes in the onset and shape of the Fe M2/3-edge were observed on ferrous and ferric model compounds with Fe in octahedral and tetrahedral coordination. Simulation of the spectra is possible using an atomic multiplet code, which potentially allows determination of, e.g., crystal-field parameters in a quantitative manner. A protocol is discussed for determination of the Fe oxidation state in compounds by linear combination of spectra of ferric and ferrous end members. The presented results demonstrate the capabilities of Fe M2/3-edge spectroscopy by X-ray Raman scattering to extract information on the ratio of trivalent to total iron Fe3+/∑Fe and local coordination. As X-ray Raman scattering is performed with hard X-rays, this approach is suitable for in situ experiments at high pressure and temperature. It thus may provide indispensable information on oxidation state, electronic structure and local structure of materials that are important for physical and chemical processes of the deep Earth. © 2014 Springer-Verlag Berlin Heidelberg.
    view abstract10.1007/s00410-014-1012-8
  • PH controlled condensation of polysiloxane networks at the water-air interface
    Wieland, D.C.F. and Degen, P. and Paulus, M. and Schroer, M.A. and Rehage, H. and Tolan, M.
    Colloids and Surfaces A: Physicochemical and Engineering Aspects 455 (2014)
    Structural and mechanical properties of molecularly thick polysiloxane membranes were studied on different liquid subphases to investigate the impact of the subphase's pH value on the cross-linking process. The lateral structure of these films was studied in-situ by grazing incidence diffraction while torsions pendulum experiments reveal the response of the system to mechanical stress. The results show a hindered cross-linking on acidic subphases. At alkaline and neutral pH conditions the cross-linking process was not effected. The data revealed that the degree of polymerization can be tuned by regulating the subphase's pH value, which opens the opportunity to build complex polysiloxane membranes in a controlled manner. © 2014 Elsevier B.V.
    view abstract10.1016/j.colsurfa.2014.03.099
  • Pressure induced spin transition revealed by iron M2,3-edge spectroscopy
    Nyrow, A. and Tse, J.S. and Hiraoka, N. and Desgreniers, S. and Büning, T. and Mende, K. and Tolan, M. and Wilke, M. and Sternemann, C.
    Applied Physics Letters 104 (2014)
    We present a method to characterize pressure induced magnetic high to low spin transition in iron sulphide using x-ray Raman scattering spectroscopy at the iron M2,3-edge. The advantage of this method is that the observed spectral changes between pressures of 1.7 GPa and 10.1 GPa can be used with the help of atomic multiplet calculations to determine the crystal field splitting parameters associated with the spin transition. We discuss the potential of this M2,3-edge spectroscopy to investigate the irons electronic spin state in-situ at the conditions of the inner Earth, i.e., at high temperature and high pressure, providing exciting opportunities for geophysical and materials science applications. © 2014 AIP Publishing LLC.
    view abstract10.1063/1.4886971
  • Reentrant liquid-liquid phase separation in protein solutions at elevated hydrostatic pressures
    Möller, J. and Grobelny, S. and Schulze, J. and Bieder, S. and Steffen, A. and Erlkamp, M. and Paulus, M. and Tolan, M. and Winter, R.
    Physical Review Letters 112 (2014)
    We present results from small-angle x-ray scattering data on the effect of high pressure on the phase behavior of dense lysozyme solutions in the liquid-liquid phase separation region, and characterize the underlying intermolecular protein-protein interactions as a function of temperature and pressure in this region of phase space. A reentrant liquid-liquid phase separation region has been discovered at elevated pressures, which originates in the pressure dependence of the solvent-mediated protein-protein interactions. © 2014 American Physical Society.
    view abstract10.1103/PhysRevLett.112.028101
  • Specific anion effects on the pressure dependence of the protein-protein interaction potential
    Möller, J. and Grobelny, S. and Schulze, J. and Steffen, A. and Bieder, S. and Paulus, M. and Tolan, M. and Winter, R.
    Physical Chemistry Chemical Physics 16 (2014)
    We present a study on ion specific effects on the intermolecular interaction potential V(r) of dense protein solutions under high hydrostatic pressure conditions. Small-angle X-ray scattering in combination with a liquid-state theoretical approach was used to determine the effect of structure breaking/making salt anions (Cl-, SO4 2-, PO4 3-) on the intermolecular interaction of lysozyme molecules. It was found that besides the Debye-Hückel charge screening effect, reducing the repulsiveness of the interaction potential V(r) at low salt concentrations, a specific ion effect is observed at high salt concentrations for the multivalent kosmotropic anions, which modulates also the pressure dependence of the protein-protein interaction potential. Whereas sulfate and phosphate strongly influence the pressure dependence of V(r), chloride anions do not. The strong structure-making effect of the multivalent anions, dominating for the triply charged PO4 3-, renders the solution structure less bulk-water-like at high salt concentrations, which leads to an altered behavior of the pressure dependence of V(r). Hence, the particular structural properties of the salt solutions are able to influence the spatial organization and the intermolecular interactions of the proteins, in particular upon compression. These results are of interest for exploring the combined effects of ionic strength, temperature and pressure on the phase behavior of protein solutions, but may also be of relevance for understanding pressure effects on the hydration behavior of biological matter under extreme environmental conditions. This journal is © the Partner Organisations 2014.
    view abstract10.1039/c3cp55278k
  • Supramolecular x-ray signature of susceptibility amplification in hydrogen-bonded liquids
    Bierwirth, S.P. and Büning, T. and Gainaru, C. and Sternemann, C. and Tolan, M. and Böhmer, R.
    Physical Review E - Statistical, Nonlinear, and Soft Matter Physics 90 (2014)
    Mixing two nonconducting hydrogen-bonded liquids, each exhibiting a low dielectric relaxation strength, can result in a highly electrically absorbing fluid. This susceptibility amplification effect is demonstrated for mixtures of monohydroxy alcohols. Whereas in the pure liquids a tendency to form ringlike low-dipole moment clusters prevails, in the mixtures such supramolecular structures are disfavored leading to an up to tenfold enhancement of the dielectric loss. The compositional evolution of density and mean cluster-cluster separation is traced using x-ray scattering and indicates deviations from ideal mixing with decreased C-C but simultaneously increased O-O correlation lengths. Thus, the variation in the supramolecular absorption strength could be tracked using a static scattering technique. These observations are in harmony with volume exclusion and ring open effects that predict an optimized susceptibility amplification for mixtures in which the two components occupy equal volume fractions as experimentally observed. © 2014 American Physical Society.
    view abstract10.1103/PhysRevE.90.052807
  • Temperature-driven adsorption and desorption of proteins at solid-liquid interfaces
    Kiesel, I. and Paulus, M. and Nase, J. and Tiemeyer, S. and Sternemann, C. and Rüster, K. and Wirkert, F.J. and Mende, K. and Büning, T. and Tolan, M.
    Langmuir 30 (2014)
    The heat-induced desorption and adsorption of the proteins lysozyme, ribonuclease A, bovine serum albumin, and fibronectin at protein layers was investigated in two different environments: pure buffer and protein solution. Using two different environments allows us to distinguish between thermodynamic and kinetic mechanisms in the adsorption process. We observed a desorption in buffer and an adsorption in protein solution, depending upon protein properties, such as size, stability, and charge. We conclude that the desorption in buffer is mainly influenced by the mobility of the proteins at the interface, while the adsorption in protein solution is driven by conformational changes and, thereby, a gain in entropy. These results are relevant for controlling biofilm formation at solid-liquid interfaces. © 2014 American Chemical Society.
    view abstract10.1021/la404884a
  • The adsorption behavior of octafluoropropane at the water/gas interface
    Giebel, F. and Paulus, M. and Nase, J. and Bieder, S. and Kiesel, I. and Tolan, M.
    Journal of Applied Physics 116 (2014)
    We studied the adsorption behavior of the gas octafluoropropane at the water/gas interface as a function of different pressures. In a custom-made measurement cell, the gas pressure was varied in a range between 1 bar and close to the condensation pressure of octafluoropropane. The electron density profiles of the adsorption layers show that the layer thickness increases with pressure. The evolution of the layer electron density indicates that the bulk electron density is reached if a layer consisting of more than one monolayer of octafluoropropane is adsorbed on the water surface. © 2014 AIP Publishing LLC.
    view abstract10.1063/1.4902961
  • The Ba 4d-4f giant dipole resonance in complex Ba/Si compounds
    Sahle, C.H.J. and Sternemann, C. and Sternemann, H. and Tse, J.S. and Gordon, R.A. and Desgreniers, S. and Maekawa, S. and Yamanaka, S. and Lehmkühler, F. and Wieland, D.C.F. and Mende, K. and Huotari, S. and Tolan, M.
    Journal of Physics B: Atomic, Molecular and Optical Physics 47 (2014)
    The shape of the Ba 4d-4f giant dipole resonance is studied for Ba atoms embedded inside complex Si networks covering structures consisting of Si nanocages and nanotubes, i.e. the clathrate Ba8Si46, the complex compound BaSi6, and the semiconducting BaSi2. Here, non-resonant x-ray Raman scattering is used to investigate confinement effects on the shape of the giant resonance in the vicinity of the Ba N IV, V-edge. The distinct momentum transfer dependence of the spectra is analyzed and discussed. The measurements are compared to calculations of the giant resonance within time-dependent local density approximation in the dipole limit. No modulation of the giant resonance's shape for Ba atoms confined in different local environments was observed, in contrast to the calculations. The absence of such shape modulation for complex Ba/Si compounds is discussed providing important implications for further studies of giant resonance phenomena utilizing both theory and experiment. © 2014 IOP Publishing Ltd.
    view abstract10.1088/0953-4075/47/4/045102
  • The teaching of others
    Tolan, M.
    Nachrichten aus der Chemie 62 (2014)
    view abstract10.1515/nachrchem.2014.62.4.399
  • X-ray reflectivity measurements of liquid/solid interfaces under high hydrostatic pressure conditions
    Wirkert, F.J. and Paulus, M. and Nase, J. and Möller, J. and Kujawski, S. and Sternemann, C. and Tolan, M.
    Journal of Synchrotron Radiation 21 (2014)
    A high-pressure cell for in situ X-ray reflectivity measurements of liquid/solid interfaces at hydrostatic pressures up to 500 MPa (5 kbar), a pressure regime that is particularly important for the study of protein unfolding, is presented. The original set-up of this hydrostatic high-pressure cell is discussed and its unique properties are demonstrated by the investigation of pressure-induced adsorption of the protein lysozyme onto hydrophobic silicon wafers. The presented results emphasize the enormous potential of X-ray reflectivity studies under high hydrostatic pressure conditions for the in situ investigation of adsorption phenomena in biological systems.© 2014 International Union of Crystallography.
    view abstract10.1107/S1600577513021516
  • Carbon reactivity of binder metals in diamond-metal composites - Characterization by scanning electron microscopy and X-ray diffraction
    Tillmann, W. and Ferreira, M. and Steffen, A. and Rüster, K. and Möller, J. and Bieder, S. and Paulus, M. and Tolan, M.
    Diamond and Related Materials 38 (2013)
    Diamond tooling is a successfully used technique in machining of very hard materials such as minerals and concrete. The type and strength of bonding between the diamond grains, that are mainly responsible for the machining process (e.g. cutting or grinding), and the metallic binder phase is directly linked to the tools quality. Therefore it is of interest to investigate the carbon reactivity of commonly used binder materials. This paper reports about the investigation of the interfacial area between diamonds and one-component metallic binder matrices. As matrix material pure chromium, cobalt, copper, iron, and nickel was used. After the sintering process the diamonds were extracted from the metallic matrix and analyzed by scanning electron microscopy and X-ray diffraction. The morphology of the diamond surface was investigated and a phase analysis was done. These experimental studies support the hypothesis that the carbon reactivity of transition metals is linked to their d-orbital electron configuration. © 2013 Elsevier B.V.
    view abstract10.1016/j.diamond.2013.07.002
  • Formation of iron containing aggregates at the liquid-air interface
    Wieland, D.C.F. and Degen, P. and Paulus, M. and Schroer, M.A. and Bieder, S. and Sahle, C.J. and Möller, J. and Leick, S. and Chen, Z. and Struth, B. and Rehage, H. and Tolan, M.
    Colloids and Surfaces B: Biointerfaces 109 (2013)
    The early stages of the formation of inorganic aggregates, composed of iron compounds at the solution-air interface, were investigated in situ. The properties of the solution-air interface were changed by using different Langmuir layers. In order to get insight into the evolution of the sample system in situ, the processes were studied by X-ray scattering and spectroscopy techniques. The formation of aggregates was detected under cationic as well as under anionic Langmuir layers. The observed compounds lack long range order which indicates the formation of amorphous structures. This is supported by extended X-ray absorption fine structure measurements showing only minor order in the formed aggregates. © 2013 Elsevier B.V.
    view abstract10.1016/j.colsurfb.2013.03.006
  • Iron oxide film growth under ultrathin polysiloxane networks
    Degen, P. and Wieland, D.C.F. and Paulus, M. and Schroer, M.A. and Tolan, M. and Rehage, H.
    Colloid and Polymer Science 291 (2013)
    This study focuses on the preparation and characterization of magnetic switchable thin iron oxide-polymer films. In a series of experiments, the formation and growth of iron oxide under ultrathin polysiloxane layers was controlled by changing the concentration of iron ions in the aqueous subphase or by varying the residence time of ammonia in the gas phase above the liquid sample. The growth of the combined film structures is studied in situ by interfacial rheology, optical microscopy, and x-ray scattering experiments and ex situ by scanning electron microscopy. Different stages of iron oxide aggregation, from a very thin layer of amorphous iron oxide with thickness of a few nanometers up to micrometer thick coatings of crystalline maghemite (γ-Fe2O3) were investigated. The specific interactions between the inorganic iron oxide and the polymer membranes cause the creation of new composite materials which are sensitive to magnetic forces. © 2012 Springer-Verlag.
    view abstract10.1007/s00396-012-2767-y
  • Microscopic structure of water at elevated pressures and temperatures
    Sahle, C.J. and Sternemann, C. and Schmidt, C. and Lehtola, S. and Jahn, S. and Simonelli, L. and Huotari, S. and Hakala, M. and Pylkkänen, T. and Nyrow, A. and Mende, K. and Tolan, M. and Hämäläinen, K. and Wilke, M.
    Proceedings of the National Academy of Sciences of the United States of America 110 (2013)
    We report on the microscopic structure of water at sub- and supercritical conditions studied using X-ray Raman spectroscopy, ab initio molecular dynamics simulations, and density functional theory. Systematic changes in the X-ray Raman spectra with increasing pressure and temperature are observed. Throughout the studied thermodynamic range, the experimental spectra can be interpreted with a structural model obtained from the molecular dynamics simulations. A spatial statistical analysis using Ripley's K-function shows that this model is homogeneous on the nanometer length scale. According to the simulations, distortions of the hydrogen-bond network increase dramatically when temperature and pressure increase to the supercritical regime. In particular, the average number of hydrogen bonds per molecule decreases to ≈0.6at600 °C and p = 134 MPa.
    view abstract10.1073/pnas.1220301110
  • Stress-induced stabilization of crystals in shape memory natural rubber
    Heuwers, B. and Quitmann, D. and Hoeher, R. and Reinders, F.M. and Tiemeyer, S. and Sternemann, C. and Tolan, M. and Katzenberg, F. and Tiller, J.C.
    Macromolecular Rapid Communications 34 (2013)
    In contrast to all known shape memory polymers, the melting temperature of crystals in shape memory natural rubber (SMNR) can be greatly manipulated by the application of external mechanical stress. As shown previously, stress perpendicular to the prior programming direction decreases the melting temperature by up to 40 K. In this study, we investigated the influence of mechanical stress parallel to prior stretching direction during programming on the stability of the elongation-stabilizing crystals. It was found that parallel stress stabilizes the crystals, which is indicated by linear increase of the trigger temperature by up to 17 K. The crystal melting temperature can be increased up to 126.5 °C under constrained conditions as shown by X-ray diffraction measurements. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstract10.1002/marc.201200594
  • Structural changes in amorphous GexSiOy on the way to nanocrystal formation
    Nyrow, A. and Sternemann, C. and Sahle, Ch.J. and Hohl, A. and Zschintzsch-Dias, M. and Schwamberger, A. and Mende, K. and Brinkmann, I. and Moretti Sala, M. and Wagner, R. and Meier, A. and Völklein, F. and Tolan, M.
    Nanotechnology 24 (2013)
    Temperature induced changes of the local chemical structure of bulk amorphous GexSiOy are studied by Ge K-edge x-ray absorption near-edge spectroscopy and Si L2/3-edge x-ray Raman scattering spectroscopy. Different processes are revealed which lead to formation of Ge regions embedded in a Si oxide matrix due to different initial structures of as-prepared samples, depending on their Ge/Si/O ratio and temperature treatment, eventually resulting in the occurrence of nanocrystals. Here, disproportionation of GeOx and SiOx regions and/or reduction of Ge oxides by pure Si or by a surrounding Si sub-oxide matrix can be employed to tune the size of Ge nanocrystals along with the chemical composition of the embedding matrix. This is important for the optimization of the electronic and luminescent properties of the material. © 2013 IOP Publishing Ltd.
    view abstract10.1088/0957-4484/24/16/165701
  • Study of time and pressure dependent phenomena at the hard X-ray beamline BL9 of DELTA
    Wirkert, F.J. and Paulus, M. and Sternemann, C. and Nase, J. and Schroer, M.A. and Wieland, D.C.F. and Bieder, S. and Degen, P. and Rehage, H. and Tolan, M.
    Journal of Physics: Conference Series 425 (2013)
    The beamline BL9 of DELTA (Dortmund ELecTron Accelerator) is a multi-purpose beamline operating in an energy range between 4 and 27 keV. A short overview of the beamline and the experimental endstation is given. Exemplarily three typical applications, namely X-ray diffraction from interfaces, small angle X-ray scattering under high hydrostatic pressure and fast X-ray reflectivity measurements, are discussed in some detail in order to demonstrate the capabilities of the beamline.
    view abstract10.1088/1742-6596/425/20/202006
  • X-ray Raman scattering: An exciting tool for the study of matter at conditions of the Earth's interior
    Sternemann, C. and Sahle, C.J. and Mende, K. and Schmidt, C. and Nyrow, A. and Simonelli, L. and Sala, M.M. and Tolan, M. and Wilke, M.
    Journal of Physics: Conference Series 425 (2013)
    The study of minerals and melts at in situ conditions is highly relevant to understand the physical and chemical properties of the Earth's crust and mantle. Here, X-ray Raman scattering provides a valuable tool to investigate the local atomic and electronic structure of Earth materials consisting predominantly of low Z elements at high pressures and temperatures. The capabilities of X-ray Raman scattering to investigate silicate minerals, glasses, and melts are discussed and the application of the method to in situ studies of silicate melts using a hydrothermal diamond anvil cell is demonstrated.
    view abstract10.1088/1742-6596/425/20/202011
  • Adsorption of nanoparticles at the solid-liquid interface
    Brenner, T. and Paulus, M. and Schroer, M.A. and Tiemeyer, S. and Sternemann, C. and Möller, J. and Tolan, M. and Degen, P. and Rehage, H.
    Journal of Colloid and Interface Science 374 (2012)
    The adsorption of differently charged nanoparticles at liquid-solid interfaces was investigated by in situ X-ray reflectivity measurements. The layer formation of positively charged maghemite (γ-Fe 2O 3) nanoparticles at the aqueous solution-SiO 2 interface was observed while negatively charged gold nanoparticles show no adsorption at this interface. Thus, the electrostatic interaction between the particles and the charged surface was determined as the driving force for the adsorption process. The data analysis shows that a logarithmic particle size distribution describes the density profile of the thin adsorbed maghemite layer. The size distribution in the nanoparticle solution determined by small angle X-ray scattering shows an average particle size which is similar to that found for the adsorbed film. The formed magehemite film exhibits a rather high stability. © 2012 Elsevier Inc.
    view abstract10.1016/j.jcis.2012.02.010
  • Cross-amyloid interaction of Aβ and IAPP at lipid membranes
    Seeliger, J. and Evers, F. and Jeworrek, C. and Kapoor, S. and Weise, K. and Andreetto, E. and Tolan, M. and Kapurniotu, A. and Winter, R.
    Angewandte Chemie - International Edition 51 (2012)
    Membrane controlled protein assembly: A study of the amyloid interaction of the islet amyloid polypeptide (IAPP), β-amyloid (Aβ), and a mixture of both with an anionic model raft membrane showed the dominant effect of IAPP on the aggregation process and on the hydrogen-bonding pattern of the assemblies present in the mixture (see picture). The analysis of the interaction of Aβ with IAPP-GI-a non-amyloidogenic IAPP mimic-confirmed these findings. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstract10.1002/anie.201105877
  • Detection of lipid raft domains in neutral and anionic Langmuir monolayers and bilayers of complex lipid composition
    Evers, F. and Jeworrek, C. and Weise, K. and Tolan, M. and Winter, R.
    Soft Matter 8 (2012)
    In reference to the complexity and heterogeneity of cellular membranes, the structure and lateral ordering of lipid monolayers and bilayers composed of multi-component lipid mixtures have been investigated and compared in the present study. These complex model biomembrane systems represent valuable model systems, e.g. for studies of lipid-peptide interactions, where an integrated in situ multi-technique approach using both monolayer and bilayer techniques is required. A zwitterionic (3 components) and an anionic (5 components) heterogeneous model membrane system have been characterized that consist of saturated and unsaturated phospholipids as well as cholesterol. Lipid monolayers were analyzed by surface X-ray scattering techniques, and both the vertical structure (electron density profile) and the degree of in-plane ordering were determined as a function of surface pressure and temperature. The corresponding structure and lateral organisation of the bilayer membranes were characterized by atomic force microscopy. Both monolayers and bilayers reveal ordered domain formation, the monolayer ones being of much smaller size and different temperature stability, however. Furthermore, the charge density of the lipid monolayer has a drastic influence on the size of ordered domains as well as the intermolecular distances of the lipid molecules. © 2011 The Royal Society of Chemistry.
    view abstract10.1039/c2sm06835d
  • Exploring the thermodynamic derivatives of the structure factor of dense protein solutions
    Schroer, M.A. and Tolan, M. and Winter, R.
    Physical Chemistry Chemical Physics 14 (2012)
    Using small-angle X-ray scattering data of concentrated solutions of the protein lysozyme taken at different pressures and temperatures, the isothermal pressure derivative and the isobaric temperature derivative of the structure factor S(q) were determined. The pressure derivative of S(q) allows us to test various models for the triplet correlation function g 3. Significant differences were found in comparison to simple liquids reflecting the more complex interaction potential in dense protein solutions. © 2012 the Owner Societies.
    view abstract10.1039/c2cp41041a
  • On the spontaneous formation of clathrate hydrates at water-guest interfaces
    Boewer, L. and Nase, J. and Paulus, M. and Lehmkühler, F. and Tiemeyer, S. and Holz, S. and Pontoni, D. and Tolan, M.
    Journal of Physical Chemistry C 116 (2012)
    The formation of hydrates, cage-like water-gas structures, is of tremendous importance both in industries and research. Although of major significance, the formation process is not completely understood so far. We present a comprehensive study of hydrate formation at liquid-liquid interfaces between water and isobutane, propane, carbon dioxide, and at the liquid-gas interface between water and xenon. We investigated the structure of these interfaces under quiescent conditions in situ by means of X-ray reflectivity measurements both inside and outside the zone of hydrate stability. At the interfaces between water and liquid alkanes, no evidence for a structural change was found. In contrast, the accumulation of guest molecules inside nanothick interfacial layers was observed at the water-xenon and liquid-liquid water-CO 2 interfaces. We show that only those systems initially exhibiting such guest-enriched interfacial layers developed into macroscopic gas hydrates within our observation times (∼12 h). Therefore, these layers act as triggers for the spontaneous formation of macroscopic hydrates. © 2012 American Chemical Society.
    view abstract10.1021/jp211784w
  • Subsurface influence on the structure of protein adsorbates as revealed by in situ X-ray reflectivity
    Hähl, H. and Evers, F. and Grandthyll, S. and Paulus, M. and Sternemann, C. and Loskill, P. and Lessel, M. and Hüsecken, A.K. and Brenner, T. and Tolan, M. and Jacobs, K.
    Langmuir 28 (2012)
    The adsorption process of proteins to surfaces is governed by the mutual interactions among proteins, the solution, and the substrate. Interactions arising from the substrate are usually attributed to the uppermost atomic layer. This actual surface defines the surface chemistry and hence steric and electrostatic interactions. For a comprehensive understanding, however, the interactions arising from the bulk material also have to be considered. Our protein adsorption experiments with globular proteins (α-amylase, bovine serum albumin, and lysozyme) clearly reveal the influence of the subsurface material via van der Waals forces. Here, a set of functionalized silicon wafers enables a distinction between the effects of surface chemistry and the subsurface composition of the substrate. Whereas the surface chemistry controls whether the individual proteins are denatured, the strength of the van der Waals forces affects the final layer density and hence the adsorbed amount of proteins. The results imply that van der Waals forces mainly influence surface processes, which govern the structure formation of the protein adsorbates, such as surface diffusion and spreading. © 2012 American Chemical Society.
    view abstract10.1021/la300850g
  • The effect of ionic strength, temperature, and pressure on the interaction potential of dense protein solutions: From nonlinear pressure response to protein crystallization
    Möller, J. and Schroer, M.A. and Erlkamp, M. and Grobelny, S. and Paulus, M. and Tiemeyer, S. and Wirkert, F.J. and Tolan, M. and Winter, R.
    Biophysical Journal 102 (2012)
    Understanding the intermolecular interaction potential, V(r), of proteins under the influence of temperature, pressure, and salt concentration is essential for understanding protein aggregation, crystallization, and protein phase behavior in general. Here, we report small-angle x-ray scattering studies on dense lysozyme solutions of high ionic strength as a function of temperature and pressure. We show that the interaction potential changes in a nonlinear fashion over a wide range of temperatures, salt, and protein concentrations. Neither temperature nor protein and salt concentration lead to marked changes in the pressure dependence of V(r), indicating that changes of the water structure dominate the pressure dependence of the intermolecular forces. Furthermore, by analysis of the temperature, pressure, and ionic strength dependence of the normalized second virial coefficient, b2, we show that the interaction can be fine-tuned by pressure, which can be used to optimize b 2 values for controlled protein crystallization. © 2012 Biophysical Society.
    view abstract10.1016/j.bpj.2012.04.043
  • Concentration-induced wetting transition in water-tetrahydrofuran-isobutane systems
    Boewer, L. and Paulus, M. and Lehmkühler, F. and Tolan, M.
    Journal of Physical Chemistry C 115 (2011)
    The pressure-dependent wetting of isobutane at the aqueous tetrahydrofuran (THF) solution-isobutane interface was studied by means of X-ray reflectivity measurements. Using pure water and mixtures at low THF concentrations, a completely wetting isobutane layer is adsorbed onto the substrate. The pressure-dependent layer thickness can be described by a simple adsorption isotherm. In contrast, the formation of thick layers with low electron density is observed at high THF concentrations. The film growth shows an unpredictable behavior. This finding can be explained by the formation of partially wetting isobutane droplets on the water/THF substrate caused by a decrease of the liquids surface tension with increasing THF concentration. © 2011 American Chemical Society.
    view abstract10.1021/jp204663w
  • Dissolution of iron oxide nanoparticles inside polymer nanocapsules
    Möller, J. and Cebi, M. and Schroer, M.A. and Paulus, M. and Degen, P. and Sahle, C.J. and Wieland, D.C.F. and Leick, S. and Nyrow, A. and Rehage, H. and Tolan, M.
    Physical Chemistry Chemical Physics 13 (2011)
    The structure of poly(organosiloxane) nanocapsules partially filled with iron oxide cores of different sizes was revealed by small angle X-ray scattering and X-ray diffraction. The nanocapsules are synthesized by the formation of a poly(organosiloxane) shell around iron oxide nanoparticles and the simultaneous partial dissolution of these cores. Due to the high scattering contrast of the iron oxide cores compared to the polymer shell, the particle size distribution of the cores inside the capsules can be measured by small angle X-ray scattering. Additional information can be revealed by X-ray diffraction, which gives insights into the formation of the polymer network and the structure of the iron oxide cores. The study shows how the crystallinity and size of the nanoparticles as well as the shape and width of the size distribution can be altered by the synthesis parameters. © 2011 the Owner Societies.
    view abstract10.1039/c1cp22161b
  • Effect of magnetic nanoparticles on the surface rheology of surfactant films at the water surface
    Degen, P. and Wieland, D.C.F. and Leick, S. and Paulus, M. and Rehage, H. and Tolan, M.
    Soft Matter 7 (2011)
    The stability of fluid interfaces is important in many technical fields, e.g. suspensions, emulsions and foams. In this publication we investigated the influence of maghemite nanoparticles (γ-Fe<inf>2</inf>O<inf>3</inf>) on the surface stability of different surfactant films (SDS, CTAB, Brij 35). We investigated the interactions between nanoparticles and surfactant films by means of surface dilatation and surface shear rheological experiments. For further characterizations we used X-ray reflectivity (XRR) measurements, dynamic light scattering (DLS) and zeta (ζ)-potential measurements. For CTAB and more obvious for SDS it was found that at low to moderate surfactant concentrations, the viscoelasticity of the interface was increased drastically in the presence of the iron oxide nanoparticles. For films of Brij 35, however, the nanoparticles did not have any influence on the surface rheology. © The Royal Society of Chemistry 2011.
    view abstract10.1039/c1sm05248a
  • Effects of specific versus nonspecific ionic interactions on the structure and lateral organization of lipopolysaccharides
    Jeworrek, C. and Evers, F. and Howe, J. and Brandenburg, K. and Tolan, M. and Winter, R.
    Biophysical Journal 100 (2011)
    We report x-ray reflectivity and grazing incidence x-ray diffraction measurements of lipopolysaccharide (LPS) monolayers at the water-air interface. Our investigations reveal that the structure and lateral ordering of the LPS molecules is very different from phospholipid systems and can be modulated by the ionic strength of the aqueous subphase in an ion-dependent manner. Our findings also indicate differential effects of monovalent and divalent ions on the two-dimensional ordering of lipid domains. Na+ ions interact unspecifically with LPS molecules based on their ability to efficiently screen the negative charges of the LPS molecules, whereas Ca2+ ions interact specifically by cross-linking adjacent molecules in the monolayer. At low lateral pressures, Na+ ions present in the subphase lead to a LPS monolayer structure ordered over large areas with high compressibility, nearly hexagonal packing of the hydrocarbon chains, and high density in the LPS headgroup region. At higher film pressures, the LPS monolayer becomes more rigid and results in a less perfect, oblique packing of the LPS hydrocarbon chains as well as a smaller lateral size of highly ordered domains on the monolayer. Furthermore, associated with the increased surface pressure, a conformational change of the sugar headgroups occurs, leading to a thickening of the entire LPS monolayer structure. The effect of Ca2+ ions in the subphase is to increase the rigidity of the LPS monolayer, leading to an oblique packing of the hydrocarbon chains already at low film pressures, an upright orientation of the sugar moieties, and much smaller sizes of ordered domains in the plane of the monolayer. In the presence of both Na+-and Ca2+ ions in the subphase, the screening effect of Na+ is predominant at low film pressures, whereas, at higher film pressures, the structure and lateral organization of LPS molecules is governed by the influence of Ca2+ ions. The unspecific charge-screening effect of the Na+ ions on the conformation of the sugar moiety becomes less dominant at biologically relevant lateral pressures. © 2011 by the Biophysical Society.
    view abstract10.1016/j.bpj.2011.03.019
  • Exploring the piezophilic behavior of natural cosolvent mixtures
    Schroer, M.A. and Zhai, Y. and Wieland, D.C.F. and Sahle, C.J. and Nase, J. and Paulus, M. and Tolan, M. and Winter, R.
    Angewandte Chemie - International Edition 50 (2011)
    Marine organisms have evolved a surprising mechanism to counteract the deleterious effects of urea by trimethylammonium N-oxide (TMAO). The effect of pressure on the structure and intermolecular interactions of lysozyme in urea and TMAO solutions was studied (see picture). These findings help to understand the compensatory effect of urea-TMAO mixtures in deep-sea organisms. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstract10.1002/anie.201104380
  • Ge-Si-O phase separation and Ge nanocrystal growth in Ge:SiO x/SiO2 multilayers - A new dc magnetron approach
    Zschintzsch, M. and Sahle, C.J. and Borany, J.V. and Sternemann, C. and Mücklich, A. and Nyrow, A. and Schwamberger, A. and Tolan, M.
    Nanotechnology 22 (2011)
    Ge:SiOx/SiO2 multilayers are fabricated using a new reactive dc magnetron sputtering approach. The influence of the multilayer stoichiometry on the ternary Ge-Si-O phase separation and the subsequent size-controlled Ge nanocrystal formation is explored by means of x-ray absorption spectroscopy, x-ray diffraction, electron microscopy and Raman spectroscopy. The ternary system Ge-Si-O reveals complete Ge-O phase separation at 400 °C which does not differ significantly to the binary Ge-O system. Ge nanocrystals of < 5nm size are generated after subsequent annealing below 700°C. It is shown that Ge oxides contained in the as-deposited multilayers are reduced by a surrounding unsaturated silica matrix. A stoichiometric regime was found where almost no GeO2 is present after annealing. Thus, the Ge nanocrystals become completely embedded in a stoichiometric silica matrix favouring the use for photovoltaic applications. © IOP Publishing Ltd.
    view abstract10.1088/0957-4484/22/48/485303
  • Influence of hydrogen on thermally induced phase separation in GeO/SiO 2 multilayers
    Sahle, C.J. and Zschintzsch, M. and Sternemann, C. and Von Borany, J. and Mücklich, A. and Nyrow, A. and Jeutter, N.M. and Wagner, R. and Frahm, R. and Tolan, M.
    Nanotechnology 22 (2011)
    The influence of the annealing atmosphere on the temperature induced phase separation of Ge oxide in GeOx/SiO2 multilayers (x ≈ 1), leading to size controlled growth of Ge nanocrystals, is explored by means of x-ray absorption spectroscopy at the Ge K-edge. Ge sub-oxides contained in the as-deposited multilayers diminish with increasing annealing temperature, showing complete phase separation at approximately 450 °C using inert N 2 ambient. The use of reducing H2 in the annealing atmosphere influences the phase separation even at an early stage of the disproportionation. In particular, the temperature regime where the phase separation occurs is lowered by at least 50 °C. At temperatures above 400 °C the sublayer composition, and thus the density of the Ge nanocrystals, can be altered by making use of the reduction of GeO2 by H 2. © 2011 IOP Publishing Ltd.
    view abstract10.1088/0957-4484/22/12/125709
  • Intercalation in layered metal-organic frameworks: Reversible inclusion of an extended π-system
    Arslan, H.K. and Shekhah, O. and Wieland, D.C.F. and Paulus, M. and Sternemann, C. and Schroer, M.A. and Tiemeyer, S. and Tolan, M. and Fischer, R.A. and Wöll, C.
    Journal of the American Chemical Society 133 (2011)
    We report the synthesis of layered [Zn 2(bdc) 2(H 2O) 2] and [Cu 2(bdc) 2(H 2O) 2] (bdc = benzdicarboxylate) metal-organic frameworks (MOF) carried out using the liquid-phase epitaxy approach employing self-assembled monolayer (SAM) modified Au-substrates. We obtain Cu and Zn MOF-2 structures, which have not yet been obtained using conventional, solvothermal synthesis methods. The 2D Cu 2+ dimer paddle wheel planes characteristic for the MOF are found to be strictly planar, with the planes oriented perpendicular to the substrate. Intercalation of an organic dye, DXP, leads to a reversible tilting of the planes, demonstrating the huge potential of these surface-anchored MOFs for the intercalation of large, planar molecules. © 2011 American Chemical Society.
    view abstract10.1021/ja2037996
  • Manipulating thin polymer films by changing the pH value
    Wieland, D.C.F. and Degen, P. and Paulus, M. and Schroer, M.A. and Rehage, H. and Tolan, M.
    Journal of Applied Physics 110 (2011)
    The structural change of Langmuir layers composed of alkyltrichlorosilanes under the influence of ammonia (NH3) was investigated. X-ray reflectivity and grazing incidence diffraction measurements along with surface pressure and surface potential measurements were performed in order to characterize the network structure. The data show an increase of the scattered intensity after addition of ammonia while the domain and unit cell size of the film did not change. These results show a higher surface coverage, which is not caused by a simple compression of the lipid tails. The effect can be attributed to a closing of voids in the polymer film caused by temporary breaking and annealing of the chemical bonds in the network by an increase of pH. © 2011 American Institute of Physics.
    view abstract10.1063/1.3661992
  • Nonlinear pressure dependence of the interaction potential of dense protein solutions
    Schroer, M.A. and Markgraf, J. and Wieland, D.C.F. and Sahle, C.J. and Möller, J. and Paulus, M. and Tolan, M. and Winter, R.
    Physical Review Letters 106 (2011)
    The influence of pressure on the structure and protein-protein interaction potential of dense protein solutions was studied and analyzed using small-angle x-ray scattering in combination with a liquid state theoretical approach. The structural as well as the interaction parameters of dense lysozyme solutions are affected by pressure in a nonlinear way. The structural properties of water lead to a modification of the protein-protein interactions below 4 kbar, which might have significant consequences for the stability of proteins in extreme natural environments. © 2011 American Physical Society.
    view abstract10.1103/PhysRevLett.106.178102
  • Reduced protein adsorption by osmolytes
    Evers, F. and Steitz, R. and Tolan, M. and Czeslik, C.
    Langmuir 27 (2011)
    Osmolytes are substances that affect osmosis and are used by cells to adapt to environmental stress. Here, we report a neutron reflectivity study on the influence of some osmolytes on protein adsorption at solid-liquid interfaces. Bovine ribonuclease A (RNase) and bovine insulin were used as model proteins adsorbing at a hydrophilic silica and at a hydrophobic polystyrene surface. From the neutron reflectivity data, the adsorbed protein layers were characterized in terms of layer thickness, protein packing density, and adsorbed protein mass in the absence and presence of urea, trehalose, sucrose, and glycerol. All data point to the clear effect of these nonionic cosolvents on the degree of protein adsorption. For example, 1 M sucrose leads to a reduction of the adsorbed amount of RNase by 39% on a silica surface and by 71% on a polystyrene surface. Trehalose was found to exhibit activity similar to that of sucrose. The changes in adsorbed protein mass can be attributed to a decreased packing density of the proteins in the adsorbed layers. Moreover, we investigated insulin adsorption at a hydrophobic surface in the absence and presence of glycerol. The degree of insulin adsorption is decreased by even 80% in the presence of 4 M of glycerol. The results of this study demonstrate that nonionic cosolvents can be used to tune and control nonspecific protein adsorption at aqueous-solid interfaces, which might be relevant for biomedical applications. © 2011 American Chemical Society.
    view abstract10.1021/la2010908
  • Structural plasticity of staphylococcal nuclease probed by perturbation with pressure and pH
    Kitahara, R. and Hata, K. and Maeno, A. and Akasaka, K. and Chimenti, M.S. and Garcia-Moreno, E.B. and Schroer, M.A. and Jeworrek, C. and Tolan, M. and Winter, R. and Roche, J. and Roumestand, C. and Montet de Guillen, K. and Royer, C.A.
    Proteins: Structure, Function and Bioinformatics 79 (2011)
    The ionization of internal groups in proteins can trigger conformational change. Despite this being the structural basis of most biological energy transduction, these processes are poorly understood. Small angle X-ray scattering (SAXS) and nuclear magnetic resonance (NMR) spectroscopy experiments at ambient and high hydrostatic pressure were used to examine how the presence and ionization of Lys-66, buried in the hydrophobic core of a stabilized variant of staphylococcal nuclease, affect conformation and dynamics. NMR spectroscopy at atmospheric pressure showed previously that the neutral Lys-66 affects slow conformational fluctuations globally, whereas the effects of the charged form are localized to the region immediately surrounding position 66. Ab initio models from SAXS data suggest that when Lys-66 is charged the protein expands, which is consistent with results from NMR spectroscopy. The application of moderate pressure (<2 kbar) at pH values where Lys-66 is normally neutral at ambient pressure left most of the structure unperturbed but produced significant nonlinear changes in chemical shifts in the helix where Lys-66 is located. Above 2 kbar pressure at these pH values the protein with Lys-66 unfolded cooperatively adopting a relatively compact, albeit random structure according to Kratky analysis of the SAXS data. In contrast, at low pH and high pressure the unfolded state of the variant with Lys-66 is more expanded than that of the reference protein. The combined global and local view of the structural reorganization triggered by ionization of the internal Lys-66 reveals more detectable changes than were previously suggested by NMR spectroscopy at ambient pressure. Proteins 2011. © 2011 Wiley-Liss, Inc.
    view abstract10.1002/prot.22966
  • Structure and phase behavior of archaeal lipid monolayers
    Jeworrek, C. and Evers, F. and Erlkamp, M. and Grobelny, S. and Tolan, M. and Chong, P.L.-G. and Winter, R.
    Langmuir 27 (2011)
    We report X-ray reflectivity (XRR) and grazing incidence X-ray diffraction (GIXD) measurements of archaeal bipolar tetraether lipid monolayers at the air-water interface. Specifically, Langmuir films made of the polar lipid fraction E (PLFE) isolated from the thermoacidophilic archaeon Sulfolobus acidocaldarius grown at three different temperatures, i.e., 68, 76, and 81 °C, were examined. The dependence of the structure and packing properties of PLFE monolayers on surface pressure were analyzed in a temperature range between 10 and 50 °C at different pH values. Additionally, the interaction of PLFE monolayers (using lipids derived from cells grown at 76 °C) with the ion channel peptide gramicidin was investigated as a function of surface pressure. A total monolayer thickness of approximately 30 Å was found for all monolayers, hinting at a U-shaped conformation of the molecules with both head groups in contact with the interface. The monolayer thickness increased with rising film pressure and decreased with increasing temperature. At 10 and 20 °C, large, highly crystalline domains were observed by GIXD, whereas at higher temperatures no distinct crystallinity could be observed. For lipids derived from cells grown at higher temperatures, a slightly more rigid structure in the lipid dibiphytanyl chains was observed. A change in the pH of the subphase had an influence only on the structure of the lipid head groups. The addition of gramicidin to an PLFE monolayer led to a more disordered state as observed by XRR. In GIXD measurements, no major changes in lateral organization could be observed, except for a decrease of the size of crystalline domains, indicating that gramicidin resides mainly in the disordered areas of the monolayer and causes local membrane perturbation, only. © 2011 American Chemical Society.
    view abstract10.1021/la202027s
  • Temperature-induced structural changes of tetrahydrofuran clathrate and of the liquid water/tetrahydrofuran mixture
    Lehmkühler, F. and Sakko, A. and Steinke, I. and Sternemann, C. and Hakala, M. and Sahle, C.J. and Buslaps, T. and Simonelli, L. and Galambosi, S. and Paulus, M. and Pylkkänen, T. and Tolan, M. and Hämäläinen, K.
    Journal of Physical Chemistry C 115 (2011)
    We present two complementary inelastic X-ray scattering studies on the structure of tetrahydrofuran (THF) clathrate hydrate and the supercooled stoichiometric liquid mixture of water and THF. Compton scattering experiments of the liquid mixture show that formation of hydrate precursors is unlikely. By comparing experimental spectra of THF hydrate and water/THF mixtures at temperatures above 250 K with density functional theory calculations, structural changes that manifest in OH bond length changes are observed. X-ray Raman scattering measurements of the oxygen K-edge in the same temperature range corroborate these results. The experimental results of THF hydrate at temperatures between 20 and 244 K can be modeled best by assuming thermal expansion only. Therefore, dependency on the system's temperature different structural behavior of THF hydrate is reported. © 2011 American Chemical Society.
    view abstract10.1021/jp207027p
  • Anomalous energetics in tetrahydrofuran clathrate hydrate revealed by X-ray compton scattering
    Lehmkühler, F. and Sakko, A. and Sternemann, C. and Hakala, M. and Nygård, K. and Sahle, C.J. and Galambosi, S. and Steinke, I. and Tiemeyer, S. and Nyrow, A. and Buslaps, T. and Pontoni, D. and Tolan, M. and Hämääinen, K.
    Journal of Physical Chemistry Letters 1 (2010)
    Changes in the ground-state electron momentum density of tetrahydrofuran clathrate hydrate are studied in a temperature range between 93 and 275 K by means of X-ray Compton scattering. At temperatures above 253 K, large rather unexpected differences from the Compton profiles of ice are observed. Configurational enthalpies are extracted and exhibit a rapid rise above 253 K, whereas a constant configurational heat capacity of 0.23 ± 0.07 J g -1 K-1 is found below 253 K. Density functional theory calculations suggest that this anomalous behavior originates from the structural change of the hydrate, however, no indication was found for the formation of hydrogen bonds between tetrahydrofuran and water molecules. © 2010 American Chemical Society.
    view abstract10.1021/jz1010362
  • Effect of surface charge distribution on the adsorption orientation of proteins to lipid monolayers
    Tiemeyer, S. and Paulus, M. and Tolan, M.
    Langmuir 26 (2010)
    The adsorption orientation of the proteins lysozyme and ribonuclease A (RNase A) to a neutral 1,2-dipalmitoyl-snglycero- 3-phosphocholine (DPPC) and a negatively charged stearic acid lipid film was investigated by means of X-ray reflectivity. Both proteins adsorbed to the negatively charged lipid monolayer, whereas at the neutral monolayer, no adsorption was observed. For acquiring comprehensive information on the proteins' adsorption, X-ray reflectivity data were combined with electron densities obtained from crystallographic data. With this method, it is possible to determine the orientation of adsorbed proteins in solution underneath lipid monolayers. While RNase A specifically coupled with its positively charged active site to the negatively charged lipid monolayer, lysozyme prefers an orientation with its long axis parallel to the Langmuir film. In comparison to the electrostatic maps of the proteins, our results can be explained by the discriminative surface charge distribution of lysozyme and RNase A. © 2010 American Chemical Society.
    view abstract10.1021/la102616h
  • Effect of urea and glycerol on the adsorption of ribonuclease a at the air-water interface
    Hüsecken, A.K. and Evers, F. and Czeslik, C. and Tolan, M.
    Langmuir 26 (2010)
    This study reports on the influence of nonionic cosolvents on the interfacial structure of ribonuclease A (RNase) adsorbed at the air-water interface. We applied X-ray reflectometry to obtain detailed volume fraction profiles of the adsorbed layers and to follow the effect of glycerol and urea on the adsorbate structure as a function of cosolvent concentration. Under all conditions studied, the adsorbed RNase layer maintains its compact shape, and the adsorbed RNase molecules adopt a flat-on orientation at the interface. Both kosmotropic glycerol and chaotropic urea exert profound effects on the adsorbate: The surface excess decreases linearly with glycerol content and is also reduced at low urea concentration. However, at high urea concentration, parts of the adsorbed layer are dehydrated and become exposed to air. The electron density and volume fraction profiles of the adsorbed protein provide clear evidence that these effects are ruled by different mechanisms. © 2010 American Chemical Society.
    view abstract10.1021/la102222z
  • High-pressure SAXS study of folded and unfolded ensembles of proteins
    Schroer, M.A. and Paulus, M. and Jeworrek, C. and Krywka, C. and Schmacke, S. and Zhai, Y. and Wieland, D.C.F. and Sahle, C.J. and Chimenti, M. and Royer, C.A. and Garcia-Moreno, B. and Tolan, M. and Winter, R.
    Biophysical Journal 99 (2010)
    A structural interpretation of the thermodynamic stability of proteins requires an understanding of the structural properties of the unfolded state. High-pressure small-angle x-ray scattering was used to measure the effects of temperature, pressure, denaturants, and stabilizing osmolytes on the radii of gyration of folded and unfolded state ensembles of staphylococcal nuclease. A set of variants with the internal Val-66 replaced with Ala, Tyr, or Arg was used to examine how changes in the volume and polarity of an internal microcavity affect the dimensions of the native state and the pressure sensitivity of the ensemble. The unfolded state ensembles achieved for these proteins with high pressure were more compact than those achieved at high temperature, and were all very sensitive to the presence of urea and glycerol. Substitutions at the hydrophobic core detectably altered the conformation of the protein, even in the folded state. The introduction of a charged residue, such as Arg, inside the hydrophobic interior of a protein could dramatically alter the structural properties, even those of the unfolded state. The data suggest that a charge at an internal position can interfere with the formation of transient hydrophobic clusters in the unfolded state, and ensure that the pressure-unfolded form of a protein occupies the maximum volume possible. Only at high temperatures does the radius of gyration of the unfolded state ensemble approach the value for a statistical random coil. © 2010 by the Biophysical Society.
    view abstract10.1016/j.bpj.2010.09.046
  • Phase separation and Si nanocrystal formation in bulk SiO studied by x-ray scattering
    Feroughi, O.M. and Sternemann, C. and Sahle, Ch.J. and Schroer, M.A. and Sternemann, H. and Conrad, H. and Hohl, A. and Seidler, G.T. and Bradley, J. and Fister, T.T. and Balasubramanian, M. and Sakko, A. and Pirkkalainen, K. and Hämäläinen, K. and Tolan, M.
    Applied Physics Letters 96 (2010)
    We present an x-ray scattering study of the temperature-induced phase separation and Si nanocrystal formation in bulk amorphous SiOx with x≈1. X-ray Raman scattering at the Si LII,III -edge reveals a significant contribution of suboxides present in native amorphous SiO. The suboxide contribution decreases with increasing annealing temperature between 800-1200 °C pointing toward a phase separation of SiO into Si and SiO2 domains. In combination with x-ray diffraction and small angle x-ray scattering the SiO microstructure is found to be dominated by internal suboxide interfaces in the native state. For higher annealing temperatures above 900 °C growth of Si nanocrystals with rough surfaces embedded in a silicon oxide matrix can be observed. © 2010 American Institute of Physics.
    view abstract10.1063/1.3323106
  • Probing adsorption and aggregation of insulin at a poly(acrylic acid) brush
    Evers, F. and Reichhart, C. and Steitz, R. and Tolan, M. and Czeslik, C.
    Physical Chemistry Chemical Physics 12 (2010)
    A planar poly(acrylic acid) (PAA) brush provides an unusual substrate for the unspecific immobilization of proteins on material surfaces. At neutral pH-values, proteins adsorb at a PAA brush when the ionic strength of the protein solution is low. In contrast, raising the ionic strength to a few 100 mM transforms a PAA brush into a rather protein-resistant surface coating. Moreover, a PAA brush represents a mild environment for adsorbed proteins which preserves their secondary structure and biological activity. In this study, we focus on the biocompatibility of a PAA brush with an insulin solution. Insulin can form amyloid fibrils, which may also be triggered by interfaces. Using neutron reflectometry and attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy, the effects of pD value, ionic strength, and glycerol concentration on the density profile and the secondary structure of adsorbed insulin molecules at a PAA brush have been studied. At pD 7, insulin adsorbs at a PAA brush despite its negative net charge. As has been found for other proteins in earlier studies, increasing the ionic strength of the insulin solution to 500 mM decreases the amount of adsorbed insulin drastically. In contrast, at pD 2, addition of salt to the insulin solution induces a thick insulin adsorbate at a PAA brush suggesting both protein-brush and protein-protein interactions, i.e., insulin adsorption and aggregation to be effective. However, in the presence of 2 M glycerol, insulin adsorption is largely suppressed. Furthermore, no major alterations of the secondary structure of adsorbed insulin can be detected by ATR-FTIR spectroscopy under all conditions studied. Hence, the performed experiments demonstrate that a PAA brush does not promote the formation of insulin amyloid structures, which represents a fundamentally new aspect of the biocompatibility of this material surface coating. © 2010 the Owner Societies.
    view abstract10.1039/b925134k
  • Sticking polydisperse hydrophobic magnetite nanoparticles to lipid membranes
    Paulus, M. and Degen, P. and Brenner, T. and Tiemeyer, S. and Struth, B. and Tolan, M. and Rehage, H.
    Langmuir 26 (2010)
    The formation of a layer of hydrophobic magnetite (Fe3O 4) nanoparticles stabilized by lauric acid is analyzed by in situ X-ray reflectivity measurements. The data analysis shows that the nanoparticles partially disperse their hydrophobic coating. Consequently, a Langmuir layer was formed by lauric acid molecules that can be compressed into an untilted condensed phase. A majority of the nanoparticles are attached to the Langmuir film integrating lauric acid residue on their surface into the Langmuir film. Hence, the particles at the liquid-gas interface can be identified as so-called Janus beads, which are amphiphilic solids having two sides with different functionality. © 2010 American Chemical Society.
    view abstract10.1021/la102882j
  • Suboxide interface in disproportionating a -SiO studied by x-ray Raman scattering
    Sakko, A. and Sternemann, C. and Sahle, C.J. and Sternemann, H. and Feroughi, O.M. and Conrad, H. and Djurabekova, F. and Hohl, A. and Seidler, G.T. and Tolan, M. and Hämäläinen, K.
    Physical Review B - Condensed Matter and Materials Physics 81 (2010)
    The microscopic structure of disproportionating amorphous silicon monoxide is studied by inelastic x-ray scattering at the silicon LII,III edge. This material arranges into nanocrystalline regions of Si embedded in amorphous SiO2 at proper annealing temperatures and in this work we demonstrate how the contribution of the suboxide interfaces between these regions can be extracted from the experimental data. The resulting near-edge spectra are analyzed in detail using a computational framework that combines molecular-dynamics simulations and density-functional theory calculations. The results indicate that the amount of silicon atoms with oxidation states between +1 and +3 is significant and depends strongly on the annealing temperature. Furthermore, the presented s, p, and d -type local densities of states (DOS) demonstrate that the most significant differences are found in the p -type DOS. © 2010 The American Physical Society.
    view abstract10.1103/PhysRevB.81.205317
  • The new x-ray lithography beamline BL1 at DELTA
    Lietz, D. and Paulus, M. and Sternemann, C. and Berges, U. and Hippert, B. and Tolan, M.
    AIP Conference Proceedings 1234 (2010)
    Lithography using synchrotron radiation in the x-ray regime provides a powerful method to produce mechanical components of sub-millimeter size with a very good quality for microtechnological applications. In recent years the demand for x-ray lithography beamtime for industrial production of microparts increased rapidly resulting in the development of new experimental endstations at synchrotron radiation sources dedicated for the production of micromechanical devices. We present in this work the layout of the new x-ray lithography beamline BL1 at the synchrotron radiation source DELTA in Dortmund and discuss first results of exposure tests. © 2010 American Institute of Physics.
    view abstract10.1063/1.3463213
  • Unique features of the folding landscape of a repeat protein revealed by pressure perturbation
    Rouget, J.-B. and Schroer, M.A. and Jeworrek, C. and Pühse, M. and Saldana, J.-L. and Bessin, Y. and Tolan, M. and Barrick, D. and Winter, R. and Royer, C.A.
    Biophysical Journal 98 (2010)
    The volumetric properties of proteins yield information about the changes in packing and hydration between various states along the folding reaction coordinate and are also intimately linked to the energetics and dynamics of these conformations. These volumetric characteristics can be accessed via pressure perturbation methods. In this work, we report high-pressure unfolding studies of the ankyrin domain of the Notch receptor (Nank1-7) using fluorescence, small-angle x-ray scattering, and Fourier transform infrared spectroscopy. Both equilibrium and pressure-jump kinetic fluorescence experiments were consistent with a simple two-state folding/unfolding transition under pressure, with a rather small volume change for unfolding compared to proteins of similar molecular weight. High-pressure fluorescence, Fourier transform infrared spectroscopy, and small-angle x-ray scattering measurements revealed that increasing urea over a very small range leads to a more expanded pressure unfolded state with a significant decrease in helical content. These observations underscore the conformational diversity of the unfolded-state basin. The temperature dependence of pressure-jump fluorescence relaxation measurements demonstrated that at low temperatures, the folding transition state ensemble (TSE) lies close in volume to the folded state, consistent with significant dehydration at the barrier. In contrast, the thermal expansivity of the TSE was found to be equivalent to that of the unfolded state, indicating that the interactions that constrain the folded-state thermal expansivity have not been established at the folding barrier. This behavior reveals a high degree of plasticity of the TSE of Nank1-7. © 2010 by the Biophysical Society.
    view abstract10.1016/j.bpj.2010.02.044
  • γ-Fe2O3 nanoparticle adsorption at an OTS Langmuir monolayer
    Degen, P. and Paulus, M. and Leick, S. and Tolan, M. and Rehage, H.
    Colloid and Polymer Science 288 (2010)
    The assembling of magnetic nanoparticles in ordered structures as well as the preparation of very thin magnetic switchable polymer membranes is an important aim in many technical fields. We studied the influence of γ-Fe2O3 nanoparticles on the polymerization process and on the properties of the poly(organosiloxane)/nanoparticle-composite layer by surface rheological measurements, surface pressure/area (π/A) isotherm measurements, and Brewster angle microscopy. The adsorption process dynamics were studied by X-ray reflectivity and surface potential measurements. The results confirm the presence of attractive electrostatic interactions between the partial negatively charged monolayer and the positively charged nanoparticles. For further investigations, we prepared Langmuir-Blodgett layers of these polymer-nanoparticle composite and investigated them by atomic force microscopy and UV-Vis spectroscopy. We found that the concentration of nanoparticles was very low and the particles were mainly arranged below the polymer layer. © 2010 Springer-Verlag.
    view abstract10.1007/s00396-010-2191-0
  • adsorption

  • nanoparticles

  • phase interfaces

  • physical vapor deposition

  • proteins

  • scattering

  • thermodynamics

  • x-ray diffraction

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