956 research outputs found
Toward a Flexible Breathing Organization: R&D Outsourcing at Bayer
No full textThe paper explores a model used in Bayer for identifying R&D tasks to be outsourced
Phase diagrams of the LiBH4-NaBH4-KBH4 system
No full textA combination of experimental and computational techniques has been used to fully describe the thermodynamic properties and phase diagrams of the LiBH4-NaBH4-KBH4 system. The Calphad method was used to assess the thermodynamic properties of LiBH4-NaBH4, LiBH4-KBH4, and NaBH4-KBH4 binary systems and to extend the investigation to the LiBH4-NaBH4-KBH4 ternary system. Samples with various compositions in the ternary system were synthesised, both by ball milling and manual mixing of the parent borohydrides, and their thermal stability has been studied using in situ synchrotron radiation X-ray diffraction as a function of temperature and using differential scanning calorimetry. From collected experimental and literature data, a thermodynamic assessment of the ternary system led to the determination of the phase diagrams. In all cases, the solid solutions can be described in the frame of the regular solution model, with interaction parameters positive or equal to zero (i.e. ideal solution). In contrast, the liquid phase was described using negative interaction parameters. A new ternary eutectic composition was estimated and it was confirmed experimentally to be equal to a molar fraction of 0.66LiBH(4)-0.11NaBH(4)-0.23KBH(4) with a melting temperature of 102 degrees C
Regulation of heterochromatic RNA decay via heterochromatin protein 1 (HP1)
No full textThe central dogma of molecular biology describes the directional flow of biological information from DNA via RNA to protein. Information stored in DNA is copied to an mRNA molecule during the process of transcription. The mRNA is used as a template for translation, in which polypeptides are synthesized. The regulation of this process, which is conserved through all trees of life, has been a central field of study over the last decades.
The discovery that RNA not only serves a simple role as a mere copy, but is much more versatile has created a lot of excitement. For example, RNA molecules themselves can act as enzymes. In the ribosome, rRNAs comprise the catalytic core for peptide bond formation. snRNAs form the core of the splicing machinery. tRNAs are the adaptors and thereby the actual readers of the genetic code. Last but not least, in the RNAi pathway, small RNAs serve as guides to target silencing complexes to complementary RNAs. Altogether, these findings placed RNA at the center of eukaryotic genome regulation.
On the other hand, DNA in eukaryotic cells does not exist as a mere fibre, but is wrapped around the core histone octamer to form a nucleosome. Nucleosomes are the basic building blocks to form higher order chromatin structures. Besides its architectural role in chromosome segregation, genome stability and recombination, chromatin has also been linked to gene expression. In contrast to the rather gene-rich euchromatin, heterochromatin is a highly condensed and repressive structure, serves as a safe storage place for transposable elements and makes up a large fraction of the genome of higher eukaryotes. Repression or activation in different chromatin contexts involves covalent modifications on the histone proteins. The nature and combination of these modifications create different docking sites for various effector proteins that have either activating or repressing function.
Surprisingly, recent studies have suggested that a substantial fraction of the genome, although heterochromatic, is transcribed at least to a certain extent and many of those transcripts do not encode proteins. Moreover, fascinating mechanisms have been discovered, in which the silencing of heterochromatic sequences involves RNA-dependent mechanisms. Altogether this suggests that the regulation of the genomic output in eukaryotes not only occurs at the level of transcription but to a substantial extent via co- or posttranscriptional gene silencing mechanisms (CTGS or PTGS, respectively). The cellular RNA decay machineries therefore have to be equipped with tools to specifically distinguish and degrade certain RNAs.
Generally, RNA decay mechanisms recognize aberrant features that are contained in the RNA molecule itself, for example the presence and length of a poly(A) tail at the 3’end. The RNAi pathway is triggered by the presence of short ssRNA molecules that are complementary to a target RNA and thereby lead to degradation. In some cases degradation induces feedback mechanisms back to chromatin resulting in histone modification and/or transcriptional modulation.
My work has identified a novel mechanism to regulate RNA decay, which is dependent on the chromatin context from which the RNA has been transcribed. This mechanism is independent of the actual RNA sequence/molecule but involves binding to the heterochromatin protein HP1(Swi6). I found that HP1(Swi6) binding to a heterochromatic transcript fulfils a checkpoint function, which mediates repression on at least two levels. First, HP1(Swi6) prevents translation of heterochromatic RNA by inhibiting association with ribosomes. This ensures repression even in the absence of RNA decay. Second HP1(Swi6) mediates elimination by capturing RNA at the site of transcription and escorting it to the degradation machinery. On a molecular level, this is achieved by RNA binding to the HP1(Swi6) hinge region. This renders the chromodomain structurally incompatible with stable H3K9me association leading to heterochromatin eviction and degradation of the RNA.
My data points towards a model in which binding of HP1(Swi6) to a heterochromatic RNA creates a heterochromatin-specific ribonucleoprotein (hsRNP) that is prone to degradation. Importantly, HP1(Swi6) can induce degradation of any RNA of heterochromatic origin, which could be a crucial feature to repress the expression of deleterious sequences and transposons. Last but not least, my work is the first example that demonstrates that RNAs can act as “repellents” for chromatin proteins
A thermodynamic investigation of the LiBH4-NaBH4 system
No full textThe LiBH4–NaBH4 pseudo-binary system has been investigated by X-ray diffraction, temperature-programmed photographic analysis, and differential scanning calorimetry, in order to establish the phase diagram. The polymorphic orthorhombic-to-hexagonal phase transition of LiBH4 was observed at 94 °C in samples containing NaBH4, i.e. 15 °C lower than for pure LiBH4, which indicates the dissolution of sodium into LiBH4. The formation of solid solutions was confirmed by powder X-ray diffraction measurements performed as a function of temperature. A new eutectic composition between Li0.65Na0.35BH4 and Li0.70Na0.30BH4, with a melting temperature of 216 °C, is observed. Ab initio calculations have been performed to establish the relative stabilities of the pure compounds in orthorhombic, hexagonal and cubic structures. The obtained experimental and calculated data were compared with available literature values and they were used for a thermodynamic assessment of the LiBH4–NaBH4 system by the calphad method. The enthalpy of mixing for solid and liquid solutions has been estimated on the basis of experimental data
Mg–Ti nanoparticles with superior kinetics for hydrogen storage
No full textMg nanoparticles (NPs) with addition of Ti catalysts were synthesised by inert gas condensation and in situ hydrogenation at 150 °C. The NPs size and composition were systematically investigated by scanning electron microscopy, energy dispersive X-ray spectroscopy and powder X-ray diffraction (PXD), while time resolved in situ synchrotron radiation-PXD was used to monitor the mechanism for hydrogen uptake and release at 280 °C. The Mg–Ti NPs reveal activation energies of 68 kJ mol−1 for absorption and 78 kJ mol−1 for desorption by isothermal kinetics analysis, similar to the lowest values reported in the literature for MgH2 using Nb2O5 as a catalyst. Hence, hydrogen desorption (pdes = 8 mbar) and absorption (pabs = 260 mbar) is achieved at 200 °C in ∼2000 s, while keeping 5.3 wt% storage capacity. Thermodynamic data extracted from van ’t Hoff plots reveal unchanged values compared to bulk MgH2. Therefore, the improved hydrogen storage performances are assigned to the enhanced kinetics only
Nanoconfined 2LiBH4eMgH2eTiCl3 in carbon aerogel scaffold for reversible hydrogen storage
No full textNanoconfinement of 2LiBH4–MgH2–TiCl3 in resorcinol–formaldehyde carbon aerogel scaffold (RF–CAS) for reversible hydrogen storage applications is proposed. RF–CAS is encapsulated with approximately 1.6 wt. % TiCl3 by solution impregnation technique, and it is further nanoconfined with bulk 2LiBH4–MgH2 via melt infiltration. Faster dehydrogenation kinetics is obtained after TiCl3 impregnation, for example, nanoconfined 2LiBH4–MgH2–TiCl3 requires ∼1 and 4.5 h, respectively, to release 95% of the total hydrogen content during the 1st and 2nd cycles, while nanoconfined 2LiBH4–MgH2 (∼2.5 and 7 h, respectively) and bulk material (∼23 and 22 h, respectively) take considerably longer. Moreover, 95–98.6% of the theoretical H2 storage capacity (3.6–3.75 wt. % H2) is reproduced after four hydrogen release and uptake cycles of the nanoconfined 2LiBH4–MgH2–TiCl3. The reversibility of this hydrogen storage material is confirmed by the formation of LiBH4 and MgH2 after rehydrogenation using FTIR and SR-PXD techniques, respectively.Fil: Gosalawit Utke, Rapee. Helmholtz-Zentrum Geesthacht; Alemania. Suranaree University of Technology; TailandiaFil: Milanese, Chiara. Universita degli Studi di Pavia; ItaliaFil: Javadian, Payam. University Aarhus; DinamarcaFil: Jepsen, Julian. Helmholtz-Zentrum Geesthacht; AlemaniaFil: Laipple, Daniel. Helmholtz-Zentrum Geesthacht; AlemaniaFil: Karmi, Fahim. Helmholtz-Zentrum Geesthacht; AlemaniaFil: Puszkiel, Julián Atilio. Helmholtz-Zentrum Geesthacht; Alemania. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Jensen, Torben. University Aarhus; DinamarcaFil: Marini, Amedeo. Universita degli Studi di Pavia; ItaliaFil: Klassen, Thomas. Helmholtz-Zentrum Geesthacht; AlemaniaFil: Dornheim, Martin. Helmholtz-Zentrum Geesthacht; Alemani
Boron-nitrogen based hydrides and reactive composites for hydrogen storage
No full textHydrogen forms chemical compounds with most other elements and forms a variety of different chemical bonds. This fascinating chemistry of hydrogen has continuously provided new materials and composites with new prospects for rational design and the tailoring of properties. This review highlights a range of new boron and nitrogen based hydrides and illustrates how hydrogen release and uptake properties can be improved. © 2014 Elsevier Ltd
Thermodynamic Tuning of Calcium Hydride by Fluorine Substitution
No full textFluorine substitution in CaH2 has been studied by means of experimental and theoretical
methods. Samples with various compositions have been prepared by ball milling. In situ X-ray
diffraction analysis has been carried out as a function of temperature by synchrotron radiation
experiments. An increase of mixing has been observed during heating, suggesting that mixing is
thermodynamically favoured but it is kinetically hindered at low temperatures. Ab initio DFT
calculations have been performed to estimate the thermodynamic mixing properties of both
orthorhombic and cubic solid solutions. On the basis of ab initio results and literature
information, a thermodynamic assessment within the CALPHAD framework has been performed
and the pseudo binary CaH2-CaF2 phase diagram has been calculated. The formation of
orthorhombic and cubic terminal solid solutions in the CaH2-CaF2 system is predicted, in good
agreement with experimental findings
2LiBH4–MgH2–0.13TiCl4 confined in nanoporous structure of carbon aerogel scaffold for reversible hydrogen storage
No full textThe investigations based on kinetic improvement and reaction mechanisms during melt infiltration, dehydrogenation, and rehydrogenation of nanoconfined 2LiBH4-MgH2-0.13TiCl4 in carbon aerogel scaffold (CAS) are proposed. It is found that TiCl4 and LiBH4 are successfully nanoconfined in CAS, while MgH2 proceeds partially. In the same temperature (25-500ºC) and time (0?5 h at constant temperature) ranges nanoconfined 2LiBH4-MgH2-0.13TiCl4 dehydrogenates completely 99% of theoretical H2 storage capacity, while that of nanoconfined 2LiBH4?MgH2 is only 94%. Nanoconfined 2LiBH4-MgH2-0.13TiCl4 performs three-step dehydrogenation at 140, 240, and 380ºC. Onset (the first-step) dehydrogenation temperature (140ºC), significantly lower than those of nanoconfined sample of 2LiBH4-MgH2 and 2LiBH4-MgH2-TiCl3 (DT = 140 and 110ºC, respectively) is in agreement with the decomposition of eutectic LiBH4-Mg(BH4)2 and lithium?titanium borohydride. For the second and third steps (240 and 380ºC),decompositions of LiBH4 destabilized by LiCl solvation and MgH2 are accomplished, respectively. In conclusion, dehydrogenation products are B, Mg, LiH, and TiH. Reversibility of nanoconfined 2LiBH4-MgH2-0.13TiCl4 sample is confirmed by the recovery of LiBH4 after rehydrogenation together with the formation of [B12H12] derivatives. The superior kinetics during the 2nd, 3rd, and 4th cycles of nanoconfined2LiBH4-MgH2-0.13TiCl4 to the nanoconfined 2LiBH4-MgH2 can be due to the formations of Ti-MgH2 alloys (Mg0.25Ti0.75H2 and Mg6TiH2) during the 1st rehydrogenation.Fil: Gosalawit Utke, Rapee. Institute of Materials Research; Alemania. Suranaree University of Technology; TailandiaFil: Milanese, Chiara. University of Pavia; ItaliaFil: Javadian, Payam. University of Aarhus; DinamarcaFil: Girella, Alessandro. University of Pavia; ItaliaFil: Laipple, Daniel. Institute of Materials Research; AlemaniaFil: Puszkiel, Julián Atilio. Institute of Materials Research; Alemania. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Cattaneo, Alice S.. University of Aarhus; DinamarcaFil: Ferrara, Chiara. University of Aarhus; DinamarcaFil: Wittayakhun, Jatuporn. Suranaree University of Technology; TailandiaFil: Skibsted, Jørgen. University of Aarhus; DinamarcaFil: Jensen, Torben R.. University of Aarhus; DinamarcaFil: Marini, Amedeo. University of Pavia; ItaliaFil: Klassen, Thomas. Institute of Materials Research; AlemaniaFil: Dornheim, Martin. Institute of Materials Research; Alemani
Halide substitution in Ca(BH4)(2)
No full textHalide substitution in Ca(BH4)2 has been investigated in ball milled mixtures of Ca(BH4)2 and CaX2 (X 1⁄4 F, Cl, Br) with different molar ratios. In situ synchrotron radiation powder X-ray diffraction measurements of Ca(BH4)2 + CaCl2 with 1 : 0.5, 1 : 1 and 1 : 2 molar ratios reveal that no substitution of Cl for BH4 occurs from the ball milling process. However, substitution readily occurs after the transitions from a- to b-Ca(BH4)2 and from orthorhombic to tetragonal CaCl2 upon heating above 250 C, which is evident from both contraction of the unit cell and changes in the relative Bragg peak intensities, in agreement with theoretical calculations. Rietveld analyses of the obtained b-Ca((BH4)1xClx)2 solid solutions indicate compositions from x 1⁄4 0 to 0.6, depending on the amount of CaCl2 in the parent mixtures. b-Ca((BH4)0.5Cl0.5)2 was investigated by differential scanning calorimetry and has a slightly higher decomposition temperature compared to pure Ca(BH4)2. No substitution with CaF2 or CaBr2 is observed
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