Poly[μ4‐sulfido‐tris(thiocyanato‐κN)tris(μ3‐1,2,4‐triazolato‐κ3N1:N2:N4)tetrazinc(II)]: a three‐dimensional zinc sulfide coordination polymer

The title compound, [Zn₄(C₂H₂N₃)₃(NCS)₃S]_n, is a three‐dimensional coordination polymer consisting of tetrahedral SZn₄ clusters bridged by triazole ligands. In the tetrahedral unit, three Zn atoms are connected to six bridging triazolate ligands, whereas the fourth Zn atom (site symmetry 3m) is bonded to three terminal thiocyanate anions that protrude into the void space created by the Zn–triazolate network. The network prototype is simple cubic, but a strong distortion along a body diagonal and the imposition of a polar direction by the arrangement of the molecular constituents lead to the trigonal space group R3m. This study demonstrates the use of the 3‐mercapto‐1,2,4‐triazole ligand as an effective source for sulfide ions in the synthesis of sulfide‐based coordination polymers.     

Near-surface and bulk deep trap states in AlxGa1-xAs/GaAs

We have measured the field-effect deep-level transient spectra of Al_xGa_1-xAs/GaAs (where x=0.385) at different reverse-bias fields to probe the near-surface deep trap and bulk deep trap states. In the temperature range 77 to 380 K and for a reverse-bias field -1 to -5 V/cm, four major deep traps were identified. The results of our investigation indicate a distinct effect on the deep-level spectra. Three of the deep trap states E1, E2 and E3 showed definite peak enhancement with the applied reverse-bias field and were identified as bulk deep trap states. The fourth deep trap state E4 was a very weak deep trap state and it showed a decrease of the peak height with the applied reverse-bias field. It was labeled as a near-surface deep trap state. PACS 73.60.Fw     

Spatial distribution of uranium and chemo-radiological assessment in Hamirpur district,Himachal Pradesh,India

Monitoring of radioactivity in an environment is an important step towards establishing the baseline for environment protection. This work highlights the spatial distribution of uranium (U); assessment of physico-chemical parameters and radiological assessment in groundwater of Hamirpur district, HP, India. The concentration of U ranges from 0.15 to 18.92 μg l^?1. High correlation of U is observed with TDS, Chloride and Nitrate. Major concentration of U is present along the NW–SE trend-line following the Siwalik in the areas where mineralisation is prevalent and is of geogenic source derived from granitic and volcanic rock fragments present in conglomerates. The water-quality-index indicates that the water is suitable for drinking purpose.

     

Analysis of stacking overlap in nucleic acid structures: algorithm and application

RNA contains different secondary structural motifs like pseudo-helices, hairpin loops, internal loops, etc. in addition to anti-parallel double helices and random coils. The secondary structures are mainly stabilized by base-pairing and stacking interactions between the planar aromatic bases. The hydrogen bonding strength and geometries of base pairs are characterized by six intra-base pair parameters. Similarly, stacking can be represented by six local doublet parameters. These dinucleotide step parameters can describe the quality of stacking between Watson–Crick base pairs very effectively. However, it is quite difficult to understand the stacking pattern for dinucleotides consisting of non canonical base pairs from these parameters. Stacking interaction is a manifestation of the interaction between two aromatic bases or base pairs and thus can be estimated best by the overlap area between the planar aromatic moieties. We have calculated base pair overlap between two consecutive base pairs as the buried van der Waals surface between them. In general, overlap values show normal distribution for the Watson–Crick base pairs in most double helices within a range from 45 to 50 Å² irrespective of base sequence. The dinucleotide steps with non-canonical base pairs also are seen to have high overlap value, although their twist and few other parameters are rather unusual. We have analyzed hairpin loops of different length, bulges within double helical structures and pseudo-continuous helices using our algorithm. The overlap area analyses indicate good stacking between few looped out bases especially in GNRA tetraloop, which was difficult to quantitatively characterise from analysis of the base pair or dinucleotide step parameters. This parameter is also seen to be capable to distinguish pseudo-continuous helices from kinked helix junctions.     

A Robust Electrochemical Sensor Based on Butterfly-shaped Silver Nanostructure for Concurrent Quantification of Heavy Metals in Water Samples

Heavy metals in drinking water have become a severe threat to human health. Detection of heavy metals has been achieved by electrochemical sensors that are modified with complex nanocomposites; however, reproducibility of these sensors is still a big challenge when applied in commercial settings. Here, a simple, very robust, and sensitive electrochemical sensor based on a screen-printed carbon electrode modified with butterfly-shaped silver nanostructure (AgNS/SPCE) has been developed for the concurrent determination of cadmium (II), lead (II), copper (II), and mercury (II) in water samples. The electrochemical behavior of the modified electrodes was investigated using cyclic voltammetry and differential pulse anodic stripping voltammetry. The AgNS/SPCE showed distinct peak potentials and a significant increase in the peak currents for all heavy metals, attributed to the high electrical conductivity and electrocatalytic activity of the synthesized butterfly-shaped AgNS. Moreover, the excellent stability and sensitivity towards simultaneous quantification of heavy metals have been obtained with detection limits of 0.4 ppb, 2.5 ppb, 7.3 ppb, and 0.7 ppb for Cd (II), Pb (II), Cu (II), and Hg (II), respectively. Besides, the constructed sensor was successfully applied to simultaneously quantify target heavy metals in spiked water samples. Owing to excellent sensitivity, high robustness, affordability, and fast response, the presented electrochemical sensor could be incorporated into a portable and miniaturized potentiostat device, making it a promising method for on-site water analysis.     

Investigation of gas transport and other physical properties in relation to the bromination degree of polymers of intrinsic microporosity

In this work, the synthesis of novel polymers of intrinsic microporosity (PIMs) with different degrees of bromine substitution by a free-radical substitution reaction was performed. The synthesized polymers were thoroughly characterized and their bromination degree was verified via nuclear magnetic resonance. The brominated PIMs were investigated by infrared spectroscopy, X-ray diffraction, and density measurements and correlated with their gas transport properties. It was found that with an increase in the bromination degree, the synthesized PIMs exhibited a significant increase in polymer chain packing density which led to reduced fractional free volume and consequent decrease in gas diffusion and permeability coefficients. The change in permeability coefficients caused an improvement in the CO₂/N₂, CO₂/CH₄, and O₂/N₂ ideal permeability selectivities. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 2752–2761     

Dimension der Bahnen lokal kompakter Gruppen

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