The ortho-to-para ratio of interstellar NH2_2: Quasi-classical trajectory calculations and new simulations

Based on recent $Herschel$ results, the ortho-to-para ratio (OPR) of NH$_2$ has been measured towards the following high-mass star-forming regions: W31C (G10.6-0.4), W49N (G43.2-0.1), W51 (G49.5-0.4), and G34.3+0.1. The OPR at thermal equilibrium ranges from the statistical limit of three at high temperatures to infinity as the temperature tends toward zero, unlike the case of H$_{2}$. Depending on the position observed along the lines-of-sight, the OPR was found to lie either slightly below the high temperature limit of three (in the range $2.2-2.9$) or above this limit ($\sim3.5$, $\gtrsim 4.2$, and $\gtrsim 5.0$). In low temperature interstellar gas, where the H$_{2}$ is para-enriched, our nearly pure gas-phase astrochemical models with nuclear-spin chemistry can account for anomalously low observed NH$_2$-OPR values. We have tentatively explained OPR values larger than three by assuming that spin thermalization of NH$_2$ can proceed at least partially by H-atom exchange collisions with atomic hydrogen, thus increasing the OPR with decreasing temperature. In this paper, we present quasi-classical trajectory calculations of the H-exchange reaction NH$_2$ + H, which show the reaction to proceed without a barrier, confirming that the H-exchange will be efficient in the temperature range of interest. With the inclusion of this process, our models suggest both that OPR values below three arise in regions with temperatures $\gtrsim20-25$~K, depending on time, and values above three but lower than the thermal limit arise at still lower temperatures.Comment: 12 pages, 12 figures. Accepted for publication in A&

Rotational control of reactivity: Reaction of SiO+^+ ions in extreme rotational states

Optical pumping of molecules provides unique opportunities for the control of chemical reactions at a wide range of rotational energies. Chemical reactivity for the hydrogen abstraction reaction SiO$^+$ + H$_2$ $\rightarrow$ SiOH$^+$ + H is investigated in an ion trap. The SiO$^+$ cation is prepared with a narrow rotational state distribution, including super-rotor states with rotational quantum number $\it{(j)}$ as high as 170 using a broad-band optical pumping method. The super-rotor states of SiO$^+$ are shown to substantially enhance the reaction rate, a trend reproduced by complementary theoretical studies. The mechanism for the rotational enhancement of the reactivity is revealed to be a strong coupling of the SiO$^+$ rotational mode with the reaction coordinate at the transition state on the dominant dynamical pathway. This work reports for the first time a chemical reaction with extreme rotational excitation of a reactant and its kinetic characterization

Well-defined PE-b-PTFE diblock copolymers via combination of coordination chain transfer polymerization and condensation reaction: Facile preparation and surface modification of polyethylene film

In this paper, a series of well-defined polyethylene-b-polytetrafluoroethylene diblock copolymers (PE–b– PTFEs) were prepared by a coupling reaction of hydroxyl-terminated polyethylene (PE–OH) and isocyanateterminated 1H,1H-perfluoro-1-tetradecanol (PFDO–NCO). PE–OH was prepared by the coordination chain transfer polymerization using 2,6-bis[1-(2,6-diisopropylphenyl)imino ethyl] pyridine iron (II) dichloride /dry ethylaluminoxane/ZnEt2 as catalyst and subsequent in situ oxidation with oxygen. PFDO–NCO was synthesized through the condensation reaction of 1H,1H- perfluoro-1-tetradecanol (PFDO) with isophoronediisocyanate (IPDI). Subsequently, the thermal characterization and the application of these diblock copolymers were investigated. The relationship between the molecular structure and the properties was disclosed. The results indicated that the diblock copolymers were effective surface modification agents for linear low density polyethylene (LLDPE). After that the PE–b–PTFE being spin-coated onto the surface of LLDPE film, the film was dramatically turned into a superhydrophobic film with a water contact angle as high as 151.4º. This kind of film is potential to be used as selfcleaning, anti-icing and anticorrosion material

Towards Understanding the Roaming Mechanism in H + MgH → Mg + HH Reaction

The roaming mechanism in the reaction H + MgH →Mg + HH is investigated by classical and quantum dynamics employing an accurate ab initio three-dimensional ground electronic state potential energy surface. The reaction dynamics are explored by running trajectories initialized on a four-dimensional dividing surface anchored on three-dimensional normally hyperbolic invariant manifold associated with a family of unstable orbiting periodic orbits in the entrance channel of the reaction (H + MgH). By locating periodic orbits localized in the HMgH well or involving H orbiting around the MgH diatom, and following their continuation with the total energy, regions in phase space where reactive or nonreactive trajectories may be trapped are found. In this way roaming reaction pathways are deduced in phase space. Patterns similar to periodic orbits projected into configuration space are found for the quantum bound and resonance eigenstates. Roaming is attributed to the capture of the trajectories in the neighborhood of certain periodic orbits. The complex forming trajectories in the HMgH well can either return to the radical channel or “roam” to the MgHH minimum from where the molecule may react

A novel lytic phage potentially effective for phage therapy against Burkholderia pseudomallei in the tropics.

BACKGROUND: Burkholderia pseudomallei is a tropical pathogen that causes melioidosis. Its intrinsic drug-resistance is a leading cause of treatment failure, and the few available antibiotics require prolonged use to be effective. This study aimed to assess the clinical potential of B. pseudomallei phages isolated from Hainan, China. METHODS: Burkholderia pseudomallei strain (HNBP001) was used as the isolation host, and phages were recovered from domestic environmental sources, which were submitted to the host range determination, lytic property assays, and stability tests. The best candidate was examined via the transmission electron microscope for classification. With its genome sequenced and analyzed, its protective efficacy against B. pseudomallei infection in A549 cells and Caenorhabditis elegans was evaluated, in which cell viability and survival rates were compared using the one-way ANOVA method and the log-rank test. RESULTS: A phage able to lyse 24/25 clinical isolates was recovered. It was classified in the Podoviridae family and was found to be amenable to propagation. Under the optimal multiplicity of infection (MOI) of 0.1, an eclipse period of around 20 min and a high titer (1012 PFU/ml) produced within 1 h were demonstrated. This phage was found stabile at a wide range of temperatures (24, 37, 40, 50, and 60 °C) and pH values (3-12). After being designated as vB_BpP_HN01, it was fully sequenced, and the 71,398 bp linear genome, containing 93 open reading frames and a tRNA-Asn, displayed a low sequence similarity with known viruses. Additionally, protective effects of applications of vB_BpP_HN01 (MOI = 0.1 and MOI = 1) alone or in combination with antibiotics were found to improve viability of infected cells (70.6 ± 6.8%, 85.8 ± 5.7%, 91.9 ± 1.8%, and 96.8 ± 1.8%, respectively). A significantly reduced mortality (10%) and a decreased pathogen load were demonstrated in infected C. elegans following the addition of this phage. CONCLUSIONS: As the first B. pseudomallei phage was isolated in Hainan, China, phage vB_BpP_HN01 was characterized by promising lytic property, stability, and efficiency of bacterial elimination during the in vitro/vivo experiments. Therefore, we can conclude that it is a potential alternative agent for combating melioidosis

Relative elemental concentrations of Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Ga, Ge, and As of a drill core sample of the Kuruman BIF with microbands measured by the synchrotron-radiation-based µ-XRF

Modern-day solar cycles due to the solar magnetic field oscillation are well recognized. Owing to the response of Earth's climate to solar activity fluctuation, solar cycles in the Phanerozoic eon have been recorded by laminites and fossil tree rings. However, the existence of magnetic cycles within the Sun younger than 3100 million-year-old is still unknown. The deposition of Precambrian banded iron formations (BIFs) reflects the primary productivity of the early ferruginous oceans and is coupled to climatic fluctuations. Here we apply synchrotron-radiation-based µ-XRF with 20 µm interval on a 60 mm long, 2470 million-year-old BIF from the Kuruman Formation, South Africa. The sample is from core GKF01 drilled at the location S 28° 56' 06.0” E 023° 15' 00.0”, as described in Schröder et al. (2006). µ-XRF measurements of the sample were performed at beamline BL15U1 of Shanghai synchrotron radiation facilities (SSRF) with a designed 3.5 GeV electron storage ring and 150-250 mA current. For these measurements, the beam size was controlled at 5 µm × 3 µm (horizontal × vertical). For the XRF measurement, the excitation energy was set at 14.0 KeV, and the dwelling time was set to 5 s. A line of 2972 points was scanned with an interval of 20 µm, perpendicular to the BIF sample's microbands. Relative elemental concentrations in counts per second (cps) were obtained by fitting the µ-XRF profiles using PyMca (raw). Segments with systematic measuring anomalies were removed (tail removed). Our spectral analyses of multiple elemental concentration series reveal prominent and consistent 80-year cyclicity, which is best explained as the Gleissberg solar cycle. The result is reported in the article 2470 million-year-old banded iron formation reveals a climatic oscillation consistent with the Gleissberg solar cycle published in Communications Earth & Environment