Formation and thermal stability of BMI-based interpenetrating polymers for gas separation membranes

Semi-interpenetrating polymer networks (semi-IPNs) were prepared by sol–gel technique through in situ polymerization of bismaleimide (BMI) in thermoplastic polyetherimide (PEI) as well as in polysulfone (PSF). This synthesis route allows arresting thermoset/thermoplastic phase separation at an early stage by solidifying the semi-IPNs through membrane phase inversion. The phase separation could be observed visually in the casting solution or by optical microscope on the surface of the produced membranes. These semi-IPNs with a density lower than their thermoplastic base polymer allowed easier water penetration during membrane phase inversion. This led to improved membrane morphology that was confirmed by scanning electron microscopy. Membranes fabricated from these semi-IPN materials had thinner skin layers and longer straight fingers perpendicular to membrane surface. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) showed that these semi-IPNs membranes have improved glass transition temperatures but a lower thermal stability. However, at ambient conditions, these membranes with their improved structure and morphology showed superior gas separation characteristics compared to base polymers. For example, the permeance was increased by 12–15 times without a significant decrease in the selectivity of oxygen over nitrogen in air separation experiments.     

A mixed valence Cu(I)/Cu(II) chain compound: crystal structure of 1,4,8,11-tetraazacyclotetradecanecopper(II) tribromocuprate(I)

The essentially anaerobic reaction of CuBr₂ and 14ane-N₄ in water/acetone solvent (14ane-N₄ = 1,4,8,11-tetraazacyclotetradecane) yields a mixed valence Cu(I)/Cu(II) compound. The compound is orthorhombic, space group Pcnn, with a = 23.6310(1) Å, b = 23.6429(2) Å, c = 12.4537(1) Å and V = 6957.95(9) ų with Z = 16, for _calc = 2.349 g/cc. Refinement of a twinned crystal with 8,504 unique reflections yielded final values of R₁ = 0.0725 (|F| > 2) and w R₂ = 0.114 and a goodness of fit of 1.448. The compound contains chains of Cu(14ane-N₄)²⁺ cations and CuBr₃ ^2– anions, which are linked together by long semicoordinate Cu(II)···Br bonds. The chains run perpendicular to the c axis and are arranged in layers in which the chains alternately run parallel to the (1 1 0) and to the (1 –1 0) crystal directions. The Cu(II) ion is coordinated by the tetradentate macrocycle to yield an approximate square planar coordination. The CuBr₃ ^2– anions have a nearly trigonal planar with Cu–;Br(ave) = 2.38(1) Å.     

Effect of alpha-tocopherol on pulmonary antioxidant defence system and lipid peroxidation in cigarette smoke inhaling mice

Background  

Free radicals generated in biological systems by cigarette smoke (CS) inhalation can cause oxidative stress in tissues, resulting in lipid peroxidation (LPO). In view of the antioxidant properties of α-tocopherol (AT), in the present study, effects of AT on antioxidant defence system and LPO were investigated in mice inhaling CS for different time intervals.     

Self‐Assembly Behaviors of a Penta‐Phenylene Maltoside and Its Application for Membrane Protein Study

We prepared an amphiphile with a penta‐phenylene lipophilic group and a branched trimaltoside head group. This new agent, designated penta‐phenylene maltoside (PPM), showed a marked tendency to self‐assembly into micelles via strong aromatic–aromatic interactions in aqueous media, as evidenced by ¹H NMR spectroscopy and fluorescence studies. When utilized for membrane protein studies, this new agent was superior to DDM, a gold standard conventional detergent, in stabilizing multiple proteins long term. The ability of this agent to form aromatic–aromatic interactions is likely responsible for enhanced protein stabilization when associated with a target membrane protein.     

Phase-selective active sites on ordered/disordered titanium dioxide enable exceptional photocatalytic ammonia synthesis

Photocatalytic N₂ fixation to NH₃via defect creation on TiO₂ to activate ultra-stable N N has drawn enormous scientific attention, but poor selectivity and low yield rate are the major bottlenecks. Additionally, whether N₂ preferentially adsorbs on phase-selective defect sites on TiO₂ in correlation with appropriate band alignment has yet to be explored. Herein, theoretical predictions reveal that the defect sites on disordered anatase (A_d) preferentially exhibit higher N₂ adsorption ability with a reduced energy barrier for a potential-determining-step (*N₂ to NNH*) than the disordered rutile (R_d) phase of TiO₂. Motivated by theoretical simulations, we synthesize a phase-selective disordered-anatase/ordered-rutile TiO₂ photocatalyst (Na-A_d/R_o) by sodium-amine treatment of P25-TiO₂ under ambient conditions, which exhibits an efficient NH₃ formation rate of 432 μmol g⁻¹ h⁻¹, which is superior to that of any other defect-rich disordered TiO₂ under solar illumination with a high apparent quantum efficiency of 13.6% at 340 nm. The multi-synergistic effects including selective N₂ chemisorption on the defect sites of Na-A_d with enhanced visible-light absorption, suitable band alignment, and rapid interfacial charge separation with R_o enable substantially enhanced N₂ fixation.

This work highlights the importance of a rational design for more energetically suitable nitrogen reduction reaction routes and mechanisms by regulating the electronic band structures with phase-selective defect sites.     

Small-molecule-dependent split aptamer ligation

Here we describe the first use of small-molecule binding to direct a chemical reaction between two nucleic acid strands. The reported reaction is a ligation between two fragments of a DNA split aptamer using strain-promoted azide-alkyne cycloaddition. Utilizing the split aptamer for cocaine, we demonstrate small-molecule-dependent ligation that is dose-dependent over a wide range of cocaine concentrations and is compatible with complex biological fluids such as human blood serum. Moreover, studies of split aptamer ligation at varying salt concentrations and using structurally similar analogues of cocaine have revealed new insight into the assembly and small-molecule binding properties of the cocaine split aptamer. The ability to translate the presence of a small-molecule target into the output of DNA ligation is anticipated to enable the development of new, broadly applicable small-molecule detection assays.