Direct observation of highly effective hydrogen isotope separation at active metal sites by in situ DRIFT spectroscopy.

In situ diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy was developed for the first time to observe the hydrogen isotope separation behavior at active CuI sites within CuI-MFU-4l, and clear evidence of the preferential adsorption of D2 over H2 was directly captured. More importantly, our results show direct spectral proof to clarify the chemical affinity quantum sieving mechanism of hydrogen isotope separation within porous adsorbents.

Loss of exosomal miR-34c-5p in cancer-associated fibroblast for the maintenance of stem-like phenotypes of laryngeal cancer cells.

BACKGROUND: Cancer-associated fibroblasts (CAFs) reconstitute cancer stemness. This study aims to investigate whether the loss of CAF-derived exosomal miR-34c-5p contributes to the maintenance of stem-like properties of laryngeal squamous cell carcinoma (LSCC). METHODS: Exosomes from primarily cultured CAFs and paired normal fibroblasts (NFs) were collected and identified. The differential expression of exosomal miR-34c-5p between CAFs and NFs was detected by next-generation sequencing. In vitro and in vivo assays were performed to examine the effects of miR-34c-5p on the maintenance of stem-like properties. RESULTS: MiR-34c-5p expression is significantly reduced in CAF-derived exosomes. In vitro and in vivo assays revealed that exosomal miR-34c-5p can regulate the stem-like properties of LSCC cells, such as proliferation, invasion, sphere and plate colony formation, chemoresistance, tumorigenicity in nude mice, as well as the expression of cancer stem cell genes. CONCLUSIONS: Loss of miR-34c-5p in CAF-derived exosomes contributes to the maintenance of stem-like phenotypes of LSCC.

Effect of doping Ti on the vacancy trapping mechanism for helium in ZrCo from first principles.

The interactions of dopants with point defects such as that between vacancies and helium can affect helium evolution and ultimately the macroscopic properties of materials. Herein, the microscopic vacancy trapping mechanism for He defects and the formation of small HemVacn (consisting of m He atoms and n vacancies) clusters in pure and Ti-doped ZrCo systems are investigated by carrying out an extensive set of first-principles calculations based on density functional theory. Our results uncover the following: the helium atom can segregate from the adjacent interstitial (tetrahedral and octahedral) sites towards the vacancy center spontaneously, and therefore, a single He atom is energetically favorable to occupy a vacancy whether in the pure or in the doped system. The dopant Ti can act as a trapping center for He impurities similar to a vacancy. Moreover, it can improve the trapping ability and increase the trapping radius of the vacancies for helium. As for the effect of the Ti atom on the trapping of multiple helium atoms by the vacancy, the higher barrier in the doped systems than in the pure one implies that doping inhibits the formation of large HemVac clusters. Furthermore, in order to evaluate the effect of dopant Ti on the stability of He atoms in multiple vacancies, the binding energies of a helium atom, a vacancy (Vac), and a self-interstitial atom (SIA) to a helium-vacancy cluster (HemVacn) were obtained and compared with that of the pure system. The results suggest that the cluster growth can be inhibited by the dopant Ti, and therefore, the formation of large helium bubbles is also hindered. All the binding energies do not depend much on the cluster size but primarily on the helium-to-vacancy ratio (m/n) of the clusters. The stability of the clusters is decided by the competitive processes among the emission of He atoms, vacancies, and SIAs, and also depends on the helium-to-vacancy ratio. The present results provide an in-depth explanation for the effect of the dopant on helium behavior and could aid future tritium storage material design.

The performance of adsorption, dissociation and diffusion mechanism of hydrogen on the Ti-doped ZrCo(110) surface.

Compared with pristine ZrCo(110), the adsorption, dissociation, and successive diffusion of hydrogen on the Ti-decorated ZrCo(110) have been investigated based on first-principles calculation. For the purpose of having fast absorption kinetics, both activation processes need to overcome small energy barriers. The adsorption energies of molecular as well as atomic hydrogen on the Ti-decorated ZrCo(110) surface were calculated using first-principles calculations with the periodic density functional theory (DFT). The H2 molecule on ZrCo(110) and Ti-doped ZrCo(110) surfaces could be spontaneously partially dissociated due to the interaction with the substrate surfaces, producing H atoms strongly chemisorbed to the hollow sites. The H2 dissociation energy barrier and the H diffusion barrier were also determined. Our results show that the activation energy for H2 dissociation on the decorated surface (0.052 eV) is much smaller than that of the pure surface (0.524 eV), elucidating that the activation condition of H2 on the pure ZrCo(110) is more severe than that on the Ti-doped surface. Particularly, Ti-decoration facilitates the H2 dissociation. Moreover, the re-desorption performance of the two dissociated H atoms is improved by lowering the energetic barrier from 1.798 eV (on the pure surface) to 1.315 eV (on the decorated surface). The calculations also reveal that decorating the surface with Ti eliminates the barrier for the into-bulk penetration of a hydrogen atom. Based on the local density of states, the Bader charge and differential charge density, as well as the influence of the Ti atom on topological properties were analyzed. Theoretical results presented in this study are generally in well accordance with the available theoretical and experimental data.

Influence of Ti on the dissolution and migration of He in ZrCo based on first principles investigation.

We have performed state-of-the-art ab initio calculations based on density functional theory to study the effect of Ti on helium dissolution and migration in a dilute Ti-doped ZrCo system. The formation energy of He-related defects predicts that it is preferable to occupy the VZr (Zr vacancy) at first. As for the Heint (interstitial site He), the results corroborate that Hetet (tetrahedral site He) is more stable than Heoct (octahedral site He) by 0.25 eV. The Heoct in the vicinity of Ti atoms becomes unstable, being relaxed into a nearby tetrahedral site, unlike in the pure ZrCo. We also reveal that ZrCo is susceptible to dopant Ti in terms of helium diffusion. The energy barrier for a Hetet to diffuse into a neighboring tetrahedral site is found to be about three times as large as the migration barrier between two adjacent octahedral interstitial sites (0.35 vs. 0.12 eV). In addition, the He atom can migrate from one octahedral site to another without going through a tetrahedral one in pure ZrCo. Furthermore, Hetet needs to overcome higher energy barriers of 0.27 eV and 0.58 eV in Ti-doped ZrCo than in the pure one (0.22 eV and 0.35 eV) along the 1nn (the first nearest neighbor) → 1nn → 2nn (the second nearest neighbor) pathway with the He atom escaping away from the Ti region. In addition, the dissociative energy barrier of the HeZr (Zr position substituted by the He atom) or HeCo (Co position substituted by the He atom) is somewhat higher in the presence of Ti than the pure one. All these conclusions elucidate that Ti acts as a trapping center for He impurities and blocks interstitial He mobility in ZrCo alloys.

Complete mitochondrial genome of Procapra picticaudata, with phylogenetic implication.

The Tibetan gazelle Procapra picticaudata is endemic to the Tibetan plateau. The species is listed as a Near Threatened (NT) species by the IUCN Red List of Threatened Animals and the Red List of China's Vertebrates. In this study, we sequenced the complete mitochondrial genome of P. picticaudata and examined its phylogenetic position with other nine species in Artiodactyla. The complete mitochondrial genome is 16,620 bp in length and contained 22 transfer RNA genes, 2 ribosomal RNA genes, 13 protein-coding genes, and 1 control region. Our data would provide reference information for further study of this species and be useful for evolutionary and phylogenetics studies for this NT species.

Effect of external static electric fields on the dynamic heterogeneity of ionic liquids.

Ionic liquids (ILs) exhibit behavior analogous to supercooled liquids at room or even higher temperatures. ILs usually work under an externally applied static electric field (E). In this work, molecular dynamics simulations were performed with 1-ethyl-3-methyl-imidazolium tetrafluorborate ([EMI+][BF4-]) under E, with the aim of discovering the influence of E on the dynamic heterogeneity of ILs. ILs show more homogeneous dynamics with increasing E, as indicated by non-Gaussian parameters and dynamic susceptibility. The dynamic heterogeneity is greater in the E direction than that in the perpendicular directions under the same E. Despite the dynamic heterogeneity, only a small decoupling between diffusion and relaxation is observed under E.

Structural and Kinetic Hydrogen Sorption Properties of Zr0.8Ti0.2Co Alloy Prepared by Ball Milling.

The effects of ball milling on the hydrogen sorption kinetics and microstructure of Zr0.8Ti0.2Co have been systematically studied. Kinetic measurements show that the hydrogenation rate and amount of Zr0.8Ti0.2Co decrease with increasing the ball milling time. However, the dehydrogenation rate accelerates as the ball milling time increases. Meanwhile, the disproportionation of Zr0.8Ti0.2Co speeds up after ball milling and the disproportionation kinetics is clearly inclined to be linear with time at 500°C. It is found from X-ray powder diffraction (XRD) results that the lattice parameter of Zr0.8Ti0.2Co gradually decreases from 3.164 Å to 3.153 Å when the ball milling time extends from 0 h to 8 h, which is mainly responsible for the hydrogen absorption/desorption behaviors. In addition, scanning electron microscope (SEM) images demonstrate that the morphology of Zr0.8Ti0.2Co has obviously changed after ball milling, which is closely related to the hydrogen absorption kinetics. Besides, high-resolution transmission electron microscopy (HRTEM) images show that a large number of disordered microstructures including amorphous regions and defects exist after ball milling, which also play an important role in hydrogen sorption performances. This work will provide some insights into the principles of how to further improve the hydrogen sorption kinetics and disproportionation property of Zr0.8Ti0.2Co.

Synthesis and crystal structure of deca-carbon-yl(µ3-3,7-di-thia-nonane-1,9-di-thiol-ato)bis-(µ2-propane-1,3-di-thiol-ato)nickel(II)tetra-iron(II) di-chloro-methane disolvate.

The title compound,, [Fe4Ni(C3H6S2)2(C7H14S4)(CO)10]·2CH2Cl2, is reported as a biomimic model for the active site of [FeFe]-hydrogenases. Bis(2-mercaptoeth-yl)-1,3-propane-dithio ether nickel(II) was firstly introduced into [Fe2(C3H6S2)(CO)5] as an S-containing ligand. It coordinates with two [Fe2(C3H6S2)(CO)5] groups, and a five-metal core complex is formed. The Fe2S2 core is in a butterfly conformation. The Fe-Fe distances in the [Fe2(C3H6S2)(CO)5] groups are 2.5126 (6) and 2.5086 (7) Å. The distances between the adjacent Fe and Ni atoms are 3.5322 (1) and 3.5143 (1) Å. There are intra-molecular C-H⋯O and C-H⋯S contacts present in the complex. In the crystal, the five metal cores are linked via C-H⋯O hydrogen bonds, forming columns lying parallel to (110). The di-chloro-methane solvent mol-ecules are each partially disordered over two positions and only one is linked to the five-metal core complex by a C-H⋯O hydrogen bond.

Three-way DNA junction based platform for ultra-sensitive fluorometric detection of multiple metal ions as exemplified for Cu(II), Mg(II) and Pb(II).

A DNA-based fluorometric method is described for simultaneous determination of multiple metal ions. It is based on recycling cleavage of hairpins by using a three-way DNA junction structure. Three DNA sequences containing a binding region and an enzyme-strand (E-DNA) region are hybridized to form a three-way DNA junction. The enzyme strand regions at the end of the DNA sequence binds to the substrate sequence (S-DNA) at the loop of the hairpin to form typical DNAzyme structures. In the presence of analyte metal ions, the DNAzyme structure thus formed cleaves the loop of hairpins. This is accompanied by a release of fluorescently labeled DNA fragments and by quenching of fluorescence. The detection limits are 35 pM for Cu(II), 2 nM for Mg(II), and 8 pM for Pb(II). This method was successfully applied to the simultaneous determination of these ions in spiked human serum. Graphical abstract Schematic presentation of the recycling cleavage of hairpins by using a three-way DNA junction structure. It causes a release of fluorescently labeled DNA fragments and quenching of fluorescence. It was successfully applied to the simultaneous determination of Cu(II), Mg(II) and Pb(II) in spiked human serum.

Influence of macroscopic defects on the corrosion behavior of U-0.79 wt%Ti alloy in sodium chloride solution.

Uranium alloys containing a low concentration of titanium have received wide attention due to their greatly enhanced corrosion resistance and outstanding mechanical performances. Herein, we investigated the effect of macroscopic defects on the corrosion behavior of U-0.79 wt%Ti (denoted as U-Ti) alloy in 0.01 M NaCl solution using traditional electrochemical testing technologies and a novel scanning electrochemical composite probe (SECP). The results demonstrate that pitting corrosion occurs rapidly on the alloy surface due to macroscopic defects. Moreover, macroscopic defects led to a decrease in corrosion potential and polarization resistance, and an increase in corrosion current density. Furthermore, the potential and pH value distributions were detected in the same region using the composite probe. The results show that the region around the macroscopic defects become corrosion-active positions and the potential difference (vs. the average potential of the alloy surface) in this area is significantly higher than that at positions without macroscopic defects, while the opposite was observed for the pH value distribution. In addition, the distribution of the vertical direction (Z) potential at the active point was clearly different from that at the inactive point. A possible reason for this could lie in the difference in the electric field distribution and electrode reaction type between the active point and inactive point on the alloy surface.

Crystal structure and electrochemical properties of [Ni(bztmpen)(CH3CN)](BF4)2 {bztmpen is N-benzyl-N,N',N'-tris-[(6-methyl-pyridin-2-yl)meth-yl]ethane-1,2-di-amine}.

The mononuclear nickel title complex (acetonitrile-κN){N-benzyl-N,N',N'-tris-[(6-methyl-pyridin-2-yl)meth-yl]ethane-1,2-di-amine}-nickel(II) bis-(tetra-fluor-ido-borate), [Ni(C30H35N5)(CH3CN)](BF4)2, was prepared from the reaction of Ni(BF4)2·6H2O with N-benzyl-N,N',N'-tris-[(6-methyl-pyridin-2-yl)meth-yl]ethane-1,2-di-amine (bztmpen) in aceto-nitrile at room temperature. With an open site occupied by the aceto-nitrile mol-ecule, the nickel(II) atom is chelated by five N-atom sites from the ligand and one N atom from the ligand, showing an overall octa-hedral coordination environment. Compared with analogues where the 6-methyl substituent is absent, the bond length around the Ni2+ cation are evidently longer. Upon reductive dissociation of the acetro-nitrile mol-ecule, the title complex has an open site for a catalytic reaction. The title complex has two redox couples at -1.50 and -1.80 V (versus Fc+/0) based on nickel. The F atoms of the two BF4- counter-anions are split into two groups and the occupancy ratios refined to 0.611 (18):0.389 (18) and 0.71 (2):0.29 (2).

Crystal structure of [Cu(tmpen)](BF4)2 {tmpen is N,N,N',N'-tetra-kis-[(6-methyl-pyridin-2-yl)meth-yl]ethane-1,2-di-amine}.

The mononuclear copper title complex {N,N,N',N'-tetra-kis-[(6-methyl-pyridin-2-yl)meth-yl]ethane-1,2-di-amine-κ6N}copper(II) bis-(tetra-fluorido-borate), [Cu(C30H36N6)](BF4)2, is conveniently prepared from the reaction of Cu(BF4)2·6H2O with N,N,N',N'-tetra-kis-[(6-methyl-pyridin-2-yl)meth-yl]ethane-1,2-di-amine (tmpen) in aceto-nitrile at room temperature in air. The complex shows a distorted octa-hedral environment around the CuII cation (site symmetry 2) and adopts the centrosymmetric space group C2/c. The presence of the 6-methyl substituent hinders the approach of the pyridine group to the CuII core. The bond lengths about the CuII atom are significantly longer than those of analogues without the 6-methyl substituents.

Enzyme-free and label-free ultra-sensitive colorimetric detection of Pb(2+) using molecular beacon and DNAzyme based amplification strategy.

An enzyme-free and label-free colorimetric Pb(2+) sensor based on DNAzyme and molecular beacon (MB) has been developed and demonstrated by recycle using enzyme strand for signal amplification. The substrate strand DNA (S-DNA) of DNAzyme could be converted into MB structure with base pairs of stem part at the both ends. The MB could hybridize with enzyme strand DNA (E-DNA) to form DNAzyme, and be activated and cleaved in the presence of Pb(2+). The cleaved MB is much less stable, releasing from the DNAzyme as two product pieces. The product pieces of MB are flexible and could bind to unmodified AuNPs to effectively stabilize them against salt-induced aggregation. Then, the E-DNA is liberated to catalyze the next reaction and amplify the response signal. By taking advantage of repeated using of E-DNA, our proposed method exhibited high sensitive for Pb(2+) detection in a linear range from 0.05 to 5 nM with detection limit of 20 pM by UV-vis spectrometer. Moreover, this method was also used for determination of Pb(2+) in river water samples with satisfying results. Importantly, this strategy could reach high sensitivity without any modification and complex enzymatic or hairpins based amplification procedures.

Ultrasensitive visual detection of DNA with tunable dynamic range by using unmodified gold nanoparticles and target catalyzed hairpin assembly amplification.

A simple and novel strategy for enzyme-free ultrasensitive DNA detection platform has been present here based on gold nanoparticles (AuNPs) colorimetry and target catalyzed hairpin assembly amplification. Three hairpin auxiliary probes (H1, H2, and H3) are designed with signal-stranded DNA (ssDNA) sticky ends which could effectively stabilize AuNPs against salt-induced aggregation. However, a cascade of assembly steps with H1, H2, and H3 are activated in the presence of the target DNA, followed by a disassembly step in which H3 displaces the target DNA from the complex, freeing the target DNA to catalyze the self-assembly of additional branched junctions. The formed branched junction consisted with dsDNA is stiffer, and cannot prevent salt-induced AuNPs aggregation, corresponding to a red-to-blue color change. The result can be read out by naked eyes or UV-vis spectrometer. The detection limit of this method is 0.1 pM by naked eyes, and this result is comparable or even better than enzyme or hybridization chain reaction (HCR) based amplification AuNPs colorimetric assays. Moreover, the dynamic range of sensor could be tuned by using different concentration of hairpins. Importantly, this strategy provides a versatile ultrasensitive detection platform for the DNA and related filed targets including metal ions, small molecules, proteins, cells et al. by combining with specific DNAzymes and aptamers.

Separation and characterization of the active species in Ti-doped NaAlH4.

The catalytic mechanism of doped complex hydrides for hydrogen storage remains unconfirmed. Here, we report a simple method to separate the active species of Ti-based catalysts in NaAlH(4) by filtration using tetrahydrofuran (THF) as solvent. The results show that the average particle size of the obtained Al-Ti active species is 30-50 nm.