[en] The equilibrium oxygen partial pressure over nonstoichiometric V₂O_5-x and the related two-phase mixture has been measured by coulometric titration using yttria-stabilized zirconia (YSZ) as the solid electrolyte at temperatures between 880 and 936 K. The nonstoichiometry (x) is observed up to 0.055 at 920 K and is related to the oxygen partial pressure (P_O2) as x∝P_O2^-1/4 in the region of x<0.017. This fact suggests the formation of the defect associate between an oxygen vacancy and a tetravalent vanadium ion. The equilibrium oxygen partial pressure over the coexisting mixture of V₂O₅ and V₄O₉ and the standard free energy change of the reaction, 4V₂O₅→2V₄O₉+O₂ at temperatures between 880 and 936 K are determined. 24 refs.; 8 figs.; 1 table

No abstract available

[en] Highlights: • Drosophila TRP 783–862 is a novel calmodulin binding site. • The shortest Ca²⁺-CaM interaction region and core CaM binding sequences in TRP 783–862 were dissected. • Ca²⁺-CaM binding induces helical structure formation of Drosophila TRP 783–862. Transient receptor potential (TRP) channels are a group of essential cation channels involved in many important sensory signal transduction processes, such as light, temperature, tastes and pressure sensing. Drosophila TRP channel is the first discovered family member and plays important roles in photo-transduction in Drosophila. Calmodulin (CaM), an important downstream effector of Ca²⁺ signal, was considered as a vital regulator of TRP activities. In this study, we discovered a novel Ca²⁺ dependent CaM binding site (TRP 783–862) in between the previously reported two calmodulin binding sites (CBSs). The isothermal titration calorimetry (ITC) and the size exclusion chromatography coupled with multi-angle static light scattering (SEC-MALS) results showed that the dissociation constant (Kd) between TRP 783–862 and Ca²⁺-CaM is 0.10 ± 0.04 μM and their binding stoichiometry is 1:1. In addition, the shortest Ca²⁺-CaM interaction region and core CaM binding sequences in TRP 783–862 were dissected by the boundary mapping and mutagenesis experiments. More interestingly, by comparing the circular dichroism (CD) spectra before and after Ca²⁺-CaM binding, the TRP 783–862 fragment showed Ca²⁺-CaM binding dependent secondary structure changes, indicating that the interaction between CaM and Drosophila TRP channel may have a conformational impact on TRP structure. In summary, by identifying and characterizing a novel CaM binding site in TRP C-terminus, our findings provided a biochemical and structural basis for further in vivo functional studies of Ca²⁺-mediated TRP channel regulation through CaM/TRP interaction.

[en] Highlights: • A full-scale experiment system was established to investigate the manhole explosion. • The effects of methane concentration, ignition location and cover weight on the peak overpressure were studied. • The results showed that there were two peaks in overpressure histories caused by manhole explosion. • When the methane concentration was 10%, the peak overpressure generated by explosion was the largest. • The peak overpressure increased with the depth of ignition position and the weight of manhole cover. -- Abstract: Gas explosion in manhole often occurs in cities. Many previous researches on gas explosion are not suitable for manhole explosion because of the particularity of manhole structure. To investigate the gas explosion in manhole, a full-scale manhole model was established, in which the explosion overpressure of methane/air mixtures were studied experimentally. The variation of blast wave overpressure with time at different distances was analyzed. In addition, the effects of methane concentration, ignition location and manhole cover weight on the external overpressure after manhole explosion were obtained. The results showed that at the experimental conditions in this paper, under the influence of vent mode and flame propagation, the maximum peak overpressure caused by manhole explosion was mostly at the third measuring point. And there were two peaks in the overpressure histories. It was also found that when the methane concentration was close to stoichiometric ratio, the ignition location was further away from the manhole head, and the weight of manhole cover increased, the peak overpressure of blast wave caused by explosion increased. Besides, some suggestions were put forward for the risk control of manhole explosion accident based on the experimental results.

[en] Fast chemical communication in the nervous system is mediated by neurotransmitter-gated ion channels. The prototypical member of this class of cell surface receptors is the cation-selective nicotinic acetylcholine receptor. As with most ligand-gated ion channels, nicotinic receptors assemble as oligomers of subunits, usually as hetero-oligomers and often with variable stoichiometries. This intrinsic heterogeneity in protein composition provides fine tunability in channel properties, which is essential to brain function, but frustrates structural and biophysical characterization. The α4β2 subtype of the nicotinic acetylcholine receptor is the most abundant isoform in the human brain and is the principal target in nicotine addiction. This pentameric ligand-gated ion channel assembles in two stoichiometries of α- and β-subunits (2α:3β and 3α:2β). Both assemblies are functional and have distinct biophysical properties, and an imbalance in the ratio of assemblies is linked to both nicotine addiction and congenital epilepsy. Here we leverage cryo-electron microscopy to obtain structures of both receptor assemblies from a single sample. Antibody fragments specific to β2 were used to ‘break’ symmetry during particle alignment and to obtain high-resolution reconstructions of receptors of both stoichiometries in complex with nicotine. Furthermore, the results reveal principles of subunit assembly and the structural basis of the distinctive biophysical and pharmacological properties of the two different stoichiometries of this receptor.

[en] Positron annihilation has been applied to study a series of non-stoichiometric pollucite samples with the composition Cs_(1−x)Al_(1−x)Si_(2+x)O₆ for x = 0.0–0.25. Lifetime results showed a monotonic increase in the o-Ps lifetime and intensity as the Cs concentration was reduced. This is consistent with literature suppositions that vacancies are created as the Cs content is reduced.

[en] We report a combined photoemission spectroscopy (PES) and inverse photoemission spectroscopy (IPES) study of distilled, phase pure films of C₆₀ and the monomeric fullerides Cs₆C₆₀, Cs₄C₆₀ and fcc RbC₆₀. The separation between the highest energy PES and lowest energy IPES features, which is a measure of the barrier to hopping, is 1.45 eV in Cs₄C₆₀ and 0.7 eV in RbC₆₀. This difference is large enough to explain, in a correlated electron picture, the reported differences in electronic mobility between the two stoichoimetries. From the PES-IPES energy separation, the value of the Hubbard U is estimated to be 1.5 eV in closed-shell C₆₀ and Cs₆C₆₀, while in Cs₄C₆₀ and RbC₆₀ such value is reduced to ∼1 and 0.7 eV, respectively. This trend can be only partially understood taking into account the different molecular polarizability and crystal structure of the various stoichiometries. The relatively low values found for open-shell compounds indicate that the bulk Hubbard U is smaller in open-shell fullerides than usually believed, which might help explain superconductivity and the observation of spin-singlets in odd-stoichiometry fullerides.

[en] Ternary half-Heusler compounds with widely tunable electronic structures, present a new platform to discover topological insulators (TIs). Due to time-consuming computations and synthesis procedures, the identification of new TIs is however a rough task. Here, we adopt a compressed-sensing approach to rapidly screen potential TIs in half-Heusler family, which is realized via a two-dimensional descriptor that only depends on the fundamental properties of the constituent atoms. Beyond the finite training data, the proposed descriptor is employed to screen many new half-Heusler compounds, including those with integer and fractional stoichiometry, and a larger number of possible TIs are predicted. (paper)

[en] Butacaine sulfate is an ester of p-aminobenzoic acid which has been widely used as a local anaesthetic and it is a long standing agent particularly for spinal anaesthesia. For this reason, a kinetic study of oxidation of butacaine sulfate by sodium N-chlorobenzenesulfonamide (chloramine-B or CAB) has been carried out in HClO₄ medium at 303 K in order to explore this redox system mechanistic chemistry. The rate shows a first-order dependence on both [CAB]_o, and [substrate]_o, and a fractional-order dependence on acid concentration. Decrease of dielectric constant of the medium, by adding methanol, increases the rate of the reaction. Variation of ionic strength and addition of benzenesulfonamide or NaCl have no significant effect on the rate. The reaction was studied at different temperatures and the activation parameters have been evaluated. The stoichiometry of the reaction has been found to be 1:2 and the oxidation products have been identified by spectral analysis. The observed results have been explained by plausible mechanism and the related rate law has been deduced

[en] Short note