Ephrin-A5 Suppresses Neurotrophin Evoked Neuronal Motility, ERK Activation and Gene Expression

During brain development, growth cones respond to attractive and repulsive axon guidance cues. How growth cones integrate guidance instructions is poorly understood. Here, we demonstrate a link between BDNF (brain derived neurotrophic factor), promoting axonal branching and ephrin-A5, mediating axonal repulsion via Eph receptor tyrosine kinase activation. BDNF enhanced growth cone filopodial dynamics and neurite branching of primary neurons. We show that ephrin-A5 antagonized this BDNF-evoked neuronal motility. BDNF increased ERK phosphorylation (P-ERK) and nuclear ERK entry. Ephrin-A5 suppressed BDNF-induced ERK activity and might sequester P-ERK in the cytoplasm. Neurotrophins are well established stimulators of a neuronal immediate early gene (IEG) response. This is confirmed in this study by e.g. c-fos, Egr1 and Arc upregulation upon BDNF application. This BDNF-evoked IEG response required the transcription factor SRF (serum response factor). Notably, ephrin-A5 suppressed a BDNF-evoked neuronal IEG response, suggesting a role of Eph receptors in modulating gene expression. In opposite to IEGs, long-term ephrin-A5 application induced cytoskeletal gene expression of tropomyosin and actinin. To uncover specific Eph receptors mediating ephrin-As impact on neurotrophin signaling, EphA7 deficient mice were analyzed. In EphA7 deficient neurons alterations in growth cone morphology were observed. However, ephrin-A5 still counteracted neurotrophin signaling suggesting that EphA7 is not required for ephrin and BDNF crosstalk. In sum, our data suggest an interaction of ephrin-As and neurotrophin signaling pathways converging at ERK signaling and nuclear gene activity. As ephrins are involved in development and function of many organs, such modulation of receptor tyrosine kinase signaling and gene expression by Ephs might not be limited to the nervous system

Synthesis, structure, thermodynamic properties, and stability relations of K-cymrite, K[AlSi3O8]⋅H2O\mathrm{K[AlSi_3O_8]·H_2O}

Single-phase K-cymrite, K[AlSi3O8]·H2O, has been synthesized in the P-T range 3≤P(GPa)≤4 and 350≤T(°C)≤650, and characterized by a variety of techniques like SEM, FTIR, and 29Si MAS-NMR. Its thermal expansivity and compressibility have been measured up to 375 °C and 6.0 GPa, respectively. Within the uncertainty of the microchemical determination of H2O by Karl-Fischer titration, it invariably contains 1 mol of H2O per mol of KAlSi3O8. Under the SEM, it appears a small idiomorphic prisms. It is optically negative, with no=1.553(1) and ne=1.521(1). FTIR spectrum identifies the water in its structure as molecular H2O. Its lattice constants are a=5.3348(1) Å, c=7.7057(1) Å, V= 189.924 Å3, the space group being P6/mmm. The 29Si MAS-NMR suggests a weak short-range order of Al and Si in the symmetrically equivalent tetrahedral sites. A Rietveld structure refinement demonstrates that it is isostructural with cymrite (BaAl2Si2O8·H2O), the structure comprising double tetrahedral sheets with H2O molecules residing in their cavities, K serving as an interlayer cation. Whereas cymrite, with its ordered tetrahedral Al/Si distribution, shows a Pm symmetry, the weak short-range Al/Si order in K-cymrite (abbreviated below as KCym) makes it crystallize in the space group P6/mmm. Three reversal experiments on the reaction K[AlSi3O8]·H2O (KCym)=K[AlSi3O8] (Kfs)+H2O, executed in this study, confirm the earlier results of Thompson (1994) and supplement her data. A simultaneous treatment of those reversals, together with the thermodynamic data for Kfs and H2O available in the literature, helps derive the standard enthalpy of formation (−4233±9.4 kJ/mol) and standard entropy (276.3±10.2 J/K·mol) for K-cymrite. The computed phase relations of KCym in the KAlSi3O8-H2O binary are shown in Figure 4 for three different values of aH2O. Given a 5 °C/km isotherm in a subducting slab of metasediments in a ultra-high-pressure metamorphic environment, KCym will be expected to grow by hydration of Kfs, unless the aH2O had been substantially less than 0.5. Nevertheless, how far it can survive exhumation of the subducted terrain will depend critically on the rate of uplifting and on the aH2O prevailing during that process

The structure of RUB-1, (C8H16N)6[B6Si48O108], a boron containing levyne-type zeolite, occluding N-methyl-quinuclidinium in the cage-like pores

C48H96B6N6O108Si48, trigonal, R3‾m$R\overline{3}m$ (no. 166), a = 12.8892(1) Å, c = 22.3058(2) Å, V = 3209.23(4) Å3, Z = 1, density = 2.02(2) g·cm−3, R(F) = 0.038, Chi2 = 2.86, T = 293 K

Cation and anion ordering in synthetic lepidolites and lithian muscovites

A large number of lepidolites $K(Li_{x}Al_{3−x})$$[Si_{2x}Al_{4−2x}O_{10}]$$(OH)_{y}F_{2−y}$ and Li-muscovites $K(Li_{x}Al_{2-x/3}◻_{1-2x/3})$$[Si_{3}AlO_{10}]$$(OH)_{y}$$F_{2-y}$ were synthesised by a gelling method in combination with hydrothermal syntheses at a pressure of 2 kbar and a temperature of 873 K. The nominal composition ranged between 0.0 $\leq$ $\it x$ $\leq$ 2.0 and 0.0 $\leq$ $\it y$ $\leq$ 2.0, i.e. from polylithionite $K[Li_{2.0}Al][Si_{4.0}O_{10}]$$(OH)_{y}F_{2-y}$ over trilithionite $K[Li_{1.5}Al_{1.5}][AlSi_{3.0}O_{10}](OH)_{y}F_{2-y}$ to muscovite $K[AL_{2.0}□][AlSi_{3.0}O_{10}](OH)_{y}F_{2-y}$. $^{1}$H, $^{19}$F, $^{29}$Si and $^{27}$Al magic-angle spinning nuclear magnetic resonance (MAS NMR) and $^{27}$Al multiple-quantum magic-angle spinning (MQMAS) NMR spectroscopy has been performed to investigate the order and/or disorder state of Si and Al in the tetrahedral layers and of Li, Al, OH and F in the octahedral layer. The synthetic mica crystals are very small, ranging from 0.1 to 5 $\mu$m. With increasing Al content, the crystal sizes decrease. Rietveld structure analyses on 12 samples showed that nearly all samples consist of two mica polytypes (1M and $2M_{1}$) of varying proportions. In the case of lepidolites, the 1M  $2M_{1}$ ratio depends on the ratio of the reaction mixture. The refinement of the occupancy factors of octahedral sites shows that lepidolites (1.5 $\leq$ $\it x$ $\leq$ 2.0) represent a solid solution series with polylithionite and trilithionite as the endmembers. In the case of the Li-muscovites (0.0 $\leq$ $\it x$ $\leq$ 1.5), the 1M  $2M_{1}$ ratio depends on the number of impurity phases like eucryptite or sanidine depleting the reaction mixture of Li or Al. There is no solid solution between trilithionite and muscovite; instead, the Li-muscovite crystals consist of domains differing in the relative proportions of muscovite and trilithionite. The overall composition of the synthesised micas which consist of two polytypes can be characterised by $^{29}$Si, $^{1}$H and $^{19}$F MAS NMR spectroscopy. The ratio in the tetrahedral layers and thus the content of [4]Al were calculated by analysing the signal intensities of the $^{29}$Si MAS NMR experiments. The Li content $x_{est}$ was calculated from the measured tetrahedral ratio of the $^{29}$Si MAS NMR signals. The calculated Li contents $x_{est}$ of samples between polylithionite and trilithionite agree with the expected values. The F-rich samples show slightly increased values and the OH samples lower values. Lepidolites with only F ($\it x$ = 1.5 to 2.0, $\it y$ = 0.0), but not lepidolites with only OH ($\it x$ = 1.5 to 2.0 and $\it y$ = 2.0), were observed after synthesis. With decreasing Li content, $\it x$ $\leq$ 1.2, Li-muscovites containing mostly hydroxyl ($\it y$>1.0) are formed. It was possible to synthesise fluorine containing micas with a Li content as low as 0.3 and $\it y$ = 0.2 to 1.8. The $^{19}$F and $^{1}$H MAS NMR experiments reveal that F and OH are not distributed statistically but local structural preferences exist. F is attracted by Li-rich and OH by Al-rich environments. The quadrupolar coupling constant which represents the anisotropy of the Al coordination is low for polylithionite with $C_{Q}$=1.5 MHz and increases to $C_{Q}$=3.8 MHz for trilithionite. For tetrahedral Al a smaller increase of $C_{Q}$ from 1.7 to 2.8 MHz is observed. Advancing from trilithionite to muscovite both quadrupolar coupling constants decrease to 2.5 MHz for octahedral and 1.5 MHz for tetrahedral Al. In polylithionite there is the most isotropic environment for octahedral Al; there are only $Li_{2}Al$ sites coordinated by F in the octahedral sheets and O from the tetrahedral sheets which are regular, containing only Si. The distortion and anisotropy for Al in tetrahedral as well as octahedral sheets increases with rising Al content. The most anisotropic environment can be found in trilithionite, especially for octahedral Al

P-V-T behavior of FeO(OH) and MnO(OH)

The P-V-T behavior of FeO(OH) and MnO(OH) has been determined under high pressure and high temperature up to 7.5 GPa and 500 °C using a MAX 80 cubic anvil high-pressure apparatus. The samples, synthetic goethite, α-FeO(OH), respectively, a natural groutite/manganite, α-MnO(OH)/γ-MnO(OH), specimen were mixed with Vaseline to ensure hydrostatic pressure-transmitting conditions, and NaCl served as an internal standard for pressure calibration. Energy-dispersive diffraction patterns were collected at a fixed 2θ angle (θ ≈ 4.52°). At pressures >7.1 GPa and temperatures >310 °C, respectively, P > 6.3 GPa and T > 350 °C, the transformation goethite ↔ ε-FeO(OH) was observed. Between 400 and 450 °C, the sample dehydrated to magnetite due to the reducing conditions caused by the graphite-tube furnace. By fitting a Birch–Murnaghan equation of state to the data, the bulk modulus of goethite was determined as (112.26 ± 2.26) GPa, (K′ = 4), V$_{T,0}$ = (138.79 ± 0.10) Å$^3$·exp [∫(0.497 ± 0.103) × 10$^{−4}$ dT], (∂KT/∂T)P = (–0.033 ± 0.020) GPa K$^{−1}$. For ε-FeO(OH), the values K = (142.8 ± 15.1) GPa, V0 = (66.18 ± 0.16) Å$^3$, (K′ = 4), were obtained. Groutite and manganite are more compressible than their Fe analogues. K(groutite) = (84.0 ± 2.9) GPa, V$_0$ = (139.92 ± 0.13) Å$^3$, (K′ = 4). K(manganite) = (82.2 ± 3.0) GPa, V$_0$ = (135.37 ± 0.15) Å$^3$, (K′ = 4). Groutite disappeared at P ≈ 5.5 GPa and T = 300 °C, only manganite remained. At T > 400 °C, the sample dehydrated first to Mn$_3$O$_4$ [II] and then to manganosite (MnO) again pointing to reducing conditions

Co-templating ionothermal synthesis and structure characterization of two new 2D layered aluminophosphates

For the first time, the co-templating ionothermal methodology was used in the preparation of layered aluminophosphate materials. With the addition of either 1,2-ethylenediamine or 1,6-hexanediamine to the ionic liquid 1-ethyl-3-methyl imidazolium chloride, two new 2D layered aluminophosphates RUB-A1 [Al3P4O16][NH3CH2CH2NH3](0.5)[C6N2H11](2) and RUB-A2 [Al3P4O16][NH3(CH2)(6)NH3]-[NH3(CH2)(6)NH2](0.5)[C6N2H11](0.5)[H2O] have been synthesized ionothermally by co-templating. The structure of RUB-A1 has been determined from single-crystal X-ray diffraction data using direct methods, while the structure of RUB-A2 has been solved ab initio from powder X-ray diffraction data with limited resolution using direct-space methods. Both of these two compounds have a 2D layered structure consisting of macroanionic sheets of composition [Al3P4O16](3-) stacked in an AAAA sequence. The inorganic layers are built up from alternatively vertex-sharing [AlO4](-) and [PO3(=O)]-tetrahedral units forming a 4.6.8 and a 4.6.12 network for RUB-A1 and RUB-A2, respectively. The layer topology of RUB-A1 is closely related to the previously known 4.6.8-layer topology but with a different sequence of phosphoryl group orientation. Combining the results of structure analysis with the NMR, chemical analysis and TG-DTA experiments, we show that both the ionic liquid cation and the protonated diamines are located in the interlayer space and together direct the formation of these two structures

Die lokale Oberflächenstruktur und -zusammensetzung bestimmt die Wasserstoffentwicklung an Eisen-Nickelsulfiden

Um leistungsfähigere Elektrokatalysatoren zu entwickeln, ist es notwendig, den Einfluss der Oberflächenstruktur und -zusammensetzung von Materialien mit hoher lokaler Auflösung besser zu verstehen. Dies trifft insbesondere auf die Entwicklung geeigneter Alternativen für Platin bei der elektrokatalytischen Wasserstofferzeugung zu. Elektrochemische Rasterzellmikroskopie (scanning electrochemical cell microscopy, SECCM) wurde benutzt, um die lokale elektrochemische Aktivität der Wasserstoffbildung an einkristallinen (111)-Oberflächen von Fe4.5Ni4.5S8, einem hochaktiven Elektrokatalysator für die Wasserstofferzeugung, zu untersuchen. In Kombination mit strukturaufklärenden Methoden zeigen wir, dass kleinste Veränderungen der chemischen Zusammensetzung die Aktivitat signifikant verändern können. Somit stellen die auf der Nanoskala durchgeführten elektrochemischen Messungen, ergänzt mit lokalen strukturellen Messungen sowie Kenntnis der lokalen Zusammensetzung ein wichtiges Hilfsmittel für das rationale Design neuer Katalysatoren dar