Methane Decomposition and Carbon Growth on Y₂O₃, Yttria-Stabilized Zirconia, and ZrO₂

Carbon deposition following thermal methane decomposition under dry and steam reforming conditions has been studied on yttria-stabilized zirconia (YSZ), Y2O3 and ZrO2 by a range of different chemical, structural and spectroscopic characterization techniques, including aberration-corrected electron microscopy, Raman spectroscopy, electric impedance spectroscopy and volumetric adsorption techniques. Concordantly, all experimental techniques reveal the formation of a conducting layer of disordered nanocrystalline graphite covering the individual grains of the respective pure oxides after treatment in dry methane at temperatures T ≥ 1000 K. In addition, treatment under moist methane conditions causes additional formation of carbon-nanotube-like architectures by partial detachment of the graphite layers. All experiments show that during carbon growth, no substantial reduction of any of the oxides takes place. Our results therefore indicate that these pure oxides can act as efficient nonmetallic substrates for methane-induced growth of different carbon species with potentially important implications regarding their use in solid oxide fuel cells. By comparison of the three oxides we could moreover elucidate differences in the methane reactivities of the respective SOFC-relevant purely oxidic surfaces under typical SOFC operation conditions without the presence of metallic constituents

Loss of RAF kinase inhibitor protein is involved in myelomonocytic differentiation and aggravates RAS-driven myeloid leukemogenesis

RAS-signaling mutations induce the myelomonocytic differentiation and proliferation of hematopoietic stem and progenitor cells. Moreover, they are important players in the development of myeloid neoplasias. RAF kinase inhibitor protein (RKIP) is a negative regulator of RAS-signaling. As RKIP loss has recently been described in RAS-mutated myelomonocytic acute myeloid leukemia, we now aimed to analyze its role in myelomonocytic differentiation and RAS-driven leukemogenesis. Therefore, we initially analyzed RKIP expression during human and murine hematopoietic differentiation and observed that it is high in hematopoietic stem and progenitor cells and lymphoid cells but decreases in cells belonging to the myeloid lineage. By employing short hairpin RNA knockdown experiments in CD34+ umbilical cord blood cells and the undifferentiated acute myeloid leukemia cell line HL-60, we show that RKIP loss is indeed functionally involved in myelomonocytic lineage commitment and drives the myelomonocytic differentiation of hematopoietic stem and progenitor cells. These results could be confirmed in vivo, where Rkip deletion induced a myelomonocytic differentiation bias in mice by amplifying the effects of granulocyte macrophage-colony-stimulating factor. We further show that RKIP is of relevance for RAS-driven myelomonocytic leukemogenesis by demonstrating that Rkip deletion aggravates the development of a myeloproliferative disease in NrasG12D-mutated mice. Mechanistically, we demonstrate that RKIP loss increases the activity of the RAS-MAPK/ERK signaling module. Finally, we prove the clinical relevance of these findings by showing that RKIP loss is a frequent event in chronic myelomonocytic leukemia, and that it co-occurs with RAS-signaling mutations. Taken together, these data establish RKIP as novel player in RAS-driven myeloid leukemogenesis

RNPomics: Defining the ncRNA transcriptome by cDNA library generation from ribonucleo-protein particles

Up to 450 000 non-coding RNAs (ncRNAs) have been predicted to be transcribed from the human genome. However, it still has to be elucidated which of these transcripts represent functional ncRNAs. Since all functional ncRNAs in Eukarya form ribonucleo-protein particles (RNPs), we generated specialized cDNA libraries from size-fractionated RNPs and validated the presence of selected ncRNAs within RNPs by glycerol gradient centrifugation. As a proof of concept, we applied the RNP method to human Hela cells or total mouse brain, and subjected cDNA libraries, generated from the two model systems, to deep-sequencing. Bioinformatical analysis of cDNA sequences revealed several hundred ncRNP candidates. Thereby, ncRNAs candidates were mainly located in intergenic as well as intronic regions of the genome, with a significant overrepresentation of intron-derived ncRNA sequences. Additionally, a number of ncRNAs mapped to repetitive sequences. Thus, our RNP approach provides an efficient way to identify new functional small ncRNA candidates, involved in RNP formation

Structural, spectroscopic and computational studies on the monoclinic polymorph form I of potassium hydrogen disilicate KHSi2O5

Hydrothermal treatment of quartz with 2 M K2CO3 solutions at 623 K and 1 kbar resulted in the formation of single crystals of the monoclinic polymorph of potassium hydrogen disilicate KHSi2O5 or KSi2O4 OH . Basic crystallographic data of this so called phase I at room conditions are as follows space group C2 m, a 14.5895 10 , b 8.2992 3 , c 9.6866 7 , b 122.756 10 , V 986.36 10 3, Z 8. The structure was determined by direct methods and refined to a residual of R F 0.0224 for 892 independent observed reflections with I gt; 2s I . The compound belongs to the group of chain silicates. It is based on crankshaft like vierer double chains running parallel to [010]. The H atoms are associated with silanol groups. Hydrogen bonding between neighbouring double chains results in the formation of 5 A amp; 730; wide slabs. The three crystallographically independent K cations with six to eight O ligands provide linkage 1 between the chains of a single slab or 2 between adjacent slabs. Structural investigations have been supplemented by micro Raman spectroscopy. The interpretation of the spectroscopic data including the allocation of the bands to certain vibrational species has been aided by DFT calculation

One pot occurrence of two polymorphs of Rb2Sc[Si4O10]F and their structural, spectroscopic and computational characterization

Single crystal growth experiments in the system RbF Sc2O3 SiO2 resulted in the simultaneous crystallization of two polymorphs of Rb2ScSi4O10F within the same run. Basic crystallographic data of the two forms at ambient conditions are as follows phase I space group I 4 m, a 11.2619 3 , c 8.3053 4 , V 1053.36 6 3, Z 4; phase II space group P 21 m, a 11.5085 6 , b 8.3805 3 , c 11.6750 6 , amp; 946; 111.147 6 , V 1050.19 9 3, Z 4. The structures were determined by direct methods and refined to residuals of R F 0.0231 phase I for 516 and 0.0249 phase II for 2050 independent observed reflections with I gt; 2 amp; 963; I . Phase I showed twinning by merohedry which was accounted for during the refinement process. Both compounds are based on multiple chains of [SiO4] tetrahedra forming closed columns or tubes. The multiplicity of the unbranched fundamental chains is two for phase I and four for phase II , respectively. The periodicity of the multiple chains has a value of four in both modifications which is also reflected in similar translation periods along the chain directions phase I t[001] 8.30 ; phase II t[010] 8.38 . Alternatively, both polymorphs can be described as mixed octahedral tetrahedral frameworks, which can be classified according to their polyhedral microensembles. A topological analysis of both networks is presented. Structural investigations have been supplemented by micro Raman spectroscopy. The interpretation of the spectroscopic data, including the allocation of the bands to certain vibrational species as well as considerations concerning the stabilities of both modifications, have been aided by DFT calculation

Rb2Ca2Si3O9 the first rubidium calcium silicate

The crystal structure of Rb2Ca2Si3O9 has been characterized by X ray diffraction techniques and Raman spectroscopy. Crystal growth was performed by the flux method in closed platinum capsules using a polycrystalline ceramic precursor as well as RbCl as a mineralizer. The crystal structure was solved from a single crystal diffraction data set acquired at 23 C and refined to a final residual of R F 0.022 for 1871 independent reflections. Basic crystallographic data are as follows monoclinic symmetry, space group type P1n1, a 6.5902 3 , b 7.3911 3 , c 10.5904 4 , amp; 946; 93.782 3 , V 514.72 3 3, Z 2. With respect to the silicate anions the compound can be classified as a sechser single chain silicate. The undulated chains run parallel to [ 101] and are connected by Rb and Ca cations, which are distributed among four crystallographically independent sites. In a first approximation the coordination polyhedra of the two different calcium ions in the asymmetric unit can be described by distorted trigonal prisms and tetragonal pyramids, respectively. The two rubidium sites exhibit more irregular coordination spheres with eight to nine next neighbors. Structural investigations on the new phase are completed by solid state micro Raman spectroscopy. DFT calculations were employed for the interpretation of the spectroscopic data including the allocation of the bands to certain vibrational specie

On the ambient pressure polymorph of K2Ca3Si3O10 An unusual mixed anion silicate and its structural and spectroscopic characterization

An ambient pressure polymorph of K2Ca3Si3O10 has been synthesized via solid state reactions. Single crystal X ray diffraction experiments show, that this new modification crystallizes in the triclinic space group P 1. The structure was solved by direct methods and subsequently refined. A special feature of the crystal structure is the coexistence of two different types of silicate anions. Isolated [SiO4] tetrahedra as well as [Si4O12] vierer single rings occur in the ratio 2 1, resulting in the crystallochemical formula K4Ca6[SiO4]2[Si4O12]. To the best of our knowledge, this is the first example of an oxo silicate where insular and cyclic silicate anions appear concomitantly. Further characterization of this new compound was carried out by electron microprobe analysis and Raman spectroscopy. DFT calculations were employed i to assign Raman bands to certain vibrational modes and ii to determine the relative stabilities of the monoclinic high pressure and the triclinic ambient pressure polymorph of K2Ca3Si3O1

Surface Reactivity of YSZ, Y2O3, and ZrO2 toward CO, CO2, and CH4: A Comparative Discussion

The C1-surface chemistry of catalytically and technologically relevant oxides (YSZ, ZrO2, and Y2O3) toward CH4, CO, and CO2 was comparatively studied by electrochemical impedance (EIS) and spectroscopic (FT-IR) methods. Highly correlated in situ measurements yield a consistent picture with respect to qualitative and quantitative surface modifications as a function of temperature and gas phase composition. This includes not only a detailed study of carbon deposition in methane and adsorption of CO and CO2 but also proof of the strong influence of surface chemistry. On all studied oxides, carbon deposited during methane treatment grows dynamically forming interconnected islands and eventually a continuous conducting carbon layer at T 1073 K. Before methane dissociation via gas phase radical reactions/H-abstraction and carbon growth, a complex redox interplay of total oxidation as well as formate and carbonate formation leads to associated surface and grain conductivity changes. For CO adsorption, these measurements yield data on the time and temperature dependence of the adsorbate- and carburization-induced conductivity processes. In that respect, an equivalent circuit model in dry CO allows to disentangle the different contributions of grain interiors, grain boundaries, and electrode contributions. For YSZ, temperature regions with different charge carrier activation energies could be identified, perfectly corresponding to significant changes in surface chemistry. Hydroxyl groups, carbonates, or formates strongly influence the impedance properties, suggesting that the conductivity properties of YSZ, e.g., in a realistic reforming gas mixture, cannot be reduced to exclusive bulk ion conduction. Because of the different degree of hydroxylation and the different ability to chemisorb CO and CO2, the influence of the surface chemistry on the electrochemical properties is varying strongly: in contrast to ZrO2, the impact of the studied C1-gases on YSZ and Y2O3 is substantial. This also includes the reoxidation/reactivation behavior of the surfaces.(VLID)1020310Accepted versio

Mechanical Properties, Quantum Mechanical Calculations, and Crystallographic Spectroscopic Characterization of GaNbO4, Ga Ta,Nb O4, and GaTaO4

Single crystals as well as polycrystalline samples of GaNbO4, Ga Ta,Nb O4, and GaTaO4 were grown from the melt and by solid state reactions, respectively, at various temperatures between 1698 and 1983 K. The chemical composition of the crystals was confirmed by wavelength dispersive electron microprobe analysis, and the crystal structures were determined by single crystal X ray diffraction. In addition, a high P T synthesis of GaNbO4 was performed at a pressure of 2 GPa and a temperature of 1273 K. Raman spectroscopy of all compounds as well as Rietveld refinement analysis of the powder X ray diffraction pattern of GaNbO4 were carried out to complement the structural investigations. Density functional theory DFT calculations enabled the assignment of the Raman bands to specific vibrational modes within the structure of GaNbO4. To determine the hardness H and elastic moduli E of the compounds, nanoindentation experiments have been performed with a Berkovich diamond indenter tip. Analyses of the load displacement curves resulted in a high hardness of H 11.9 0.6 GPa and a reduced elastic modulus of Er 202 9 GPa for GaTaO4. GaNbO4 showed a lower hardness of H 9.6 0.5 GPa and a reduced elastic modulus of Er 168 5 GPa. Spectroscopic ellipsometry of the polished GaTa0.5Nb0.5O4 ceramic sample was employed for the determination of the optical constants n and k. GaTa0.5Nb0.5O4 exhibits a high average refractive index. Furthermore, in situ high temperature powder X ray diffraction experiments enabled the study of the thermal expansion tensors of GaTaO4 and GaNbO4, as well as the ability to relate them with structural feature