Electric and dielectric properties of solution-gas interface-grown PbS films

Dielectric properties andI–V characteristics of solution-gas interface-formed PbS thin-film capacitors (Al/PbS/Al) of various thicknesses have been studied in the frequency range 10-10⁶ Hz at various temperatures (300–443 K). Current-voltage (I–V) characteristics show space-charge-limited conduction. Dielectric constant (ε) increases with increasing film thickness and temperature and decreases with increase of frequency. The loss factor (tanδ) peaks observed in tanδ vs frequency and tanδ vs temperature reveal relaxation effect from dipolar orientation. These maxima shift to higher-temperature region with increasing frequency. The large increase in capacitance (C) and dielectric constant (ε) towards low-frequency (f) region indicates the possibility of an interfacial polarization mechanism in this region.     

Synthesis and Characterization of Segmented Block Copolymers Based on Hydroxyl‐Terminated Liquid Natural Rubber and α,ω‐Diisocyanato Telechelics

Summary: Segmented block copolymers, consisting of non‐polar soft segments from hydroxyl‐terminated liquid natural rubber (HTNR) and polar hard segments from α,ω‐diisocyanato telechelics obtained by “criss‐cross”‐cycloaddition, have been synthesized. The block copolymer formation took place under relatively mild reaction conditions at 80 °C in dichloroethane in the presence of dibutyltin dilaurate as a catalyst. The resulting block copolymers were characterized by spectroscopic techniques (¹H NMR, FTIR, UV‐vis spectroscopy) as well as GPC for molar mass determination. The block copolymers were compression molded in a hot stage press, and the resulting samples were characterized by DSC and stress‐strain measurement. The solubility and phase morphology of the materials have also been studied.

Segmented block copolymer from HTNR and α,ω‐diisocyanato telechelics     

多孔材料在催化CO2与环氧化物环加成反应中的研究进展

以CO2为原料与环氧化物合成环状碳酸酯是实现CO2资源利用最为有效的途径之一，也是缓解温室效应的有效方式之一。在该反应中催化剂的选择至关重要，多孔材料由于具有相对密度低、强度高、比表面积大、稳定性好、合成方法多样等优点而被广泛应用于催化CO2环加成。重点综述了近年来无机多孔材料、多孔有机聚合物材料、金属有机骨架材料在催化CO2与环氧化物合成环状碳酸酯中的研究进展，介绍了各催化剂的优缺点并对未来多孔材料的发展进行了展望。     

Highly Exposed ?NH2 Edge on Fragmented g-C3N4 Framework with Integrated Molybdenum Atoms for Catalytic CO2 Cycloaddition: DFT and Techno-Economic Assessment

This study focuses on the applicability of single-atom Mo-doped graphitic carbon nitride (GCN) nanosheets which are specifically engineered with high surface area (exfoliated GCN),  NH₂ rich edges, and maximum utilization of isolated atomic Mo for propylene carbonate (PC) production through CO₂ cycloaddition of propylene oxide (PO). Various operational parameters are optimized, for example, temperature (130 °C), pressure (20 bar), catalyst (Mo₂GCN), and catalyst mass (0.1 g). Under optimal conditions, 2% Mo-doped GCN (Mo₂GCN) has the highest catalytic performance, especially the turnover frequency (TOF) obtained, 36.4 h⁻¹ is higher than most reported studies. DFT simulations prove the catalytic performance of Mo₂GCN significantly decreases the activation energy barrier for PO ring-opening from 50–60 to 4.903 kcal mol⁻¹. Coexistence of Lewis acid/base group improves the CO₂ cycloaddition performance by the formation of coordination bond between electron-deficient Mo atom with O atom of PO, while  NH₂ surface group disrupts the stability of CO₂ bond by donating electrons into its low-level empty orbital. Steady-state process simulation of the industrial-scale consumes 4.4 ton h⁻¹ of CO₂ with PC production of 10.2 ton h⁻¹. Techno-economic assessment profit from Mo₂GCN is estimated to be 60.39 million USD year⁻¹ at a catalyst loss rate of 0.01 wt% h⁻¹.     

H-Solid State NMR Studies of Tunneling Phenomena and Isotope Effects in Transition Metal Dihydrides

In many transition metal dihydrides and dihydrogen complexes the hydrogens are relatively weakly bound and exhibit a fairly high mobility, in particular with respect to their mutual exchange. Part of this high mobility is due to the exchange symmetry of the two hydrogens, which causes an energy splitting into even and odd spatial energy eigenfunctions, resulting in the typical coherent tunneling of a two-level system. Owing to the quantum mechanical symmetry selection principles the eigenfunctions are connected to the possible nuclear spin states of the system. If the tunneling frequency is in the proper frequency window it is thus possible to observe these tunneling transitions by NMR at very low temperatures, where no thermally induced exchange reactions overshadow the tunneling. The first part of this review gives an introduction into the interplay of chemical kinetics and tunneling phenomena in general, rotational tunneling of dihydrogen in a two-fold potential in particular and the Bell tunnel model, followed by a summary of solid state NMR techniques for the observation of these tunnel processes. Then a discussion of the effects of these processes on the ²H NMR line shape is given. The second part of the review reports results of a ²H-solid state NMR spectroscopy and T₁ relaxatiometry study of trans-[Ru(D₂)Cl(PPh₂CH₂CH₂PPh₂)₂]PF₆, in the temperature regime from 5.4 to 320 K. In the Ru-D₂ sample coherent tunneling and incoherent exchange processes on the time scale of the quadrupolar interaction are observed. From the spectra and T₁-data the height of the tunneling barrier is determined. Next results of ²H-spin–lattice relaxation measurements for a selectively η² − D₂ labeled isotopomer of the complex W(PCy₃)₂(CO)₃)(η² − D₂) are presented and discussed. The relaxation measurements are analyzed in terms of a simple one dimensional Bell tunnel model and comparison to incoherent neutron scattering (INS) data from the H₂ complex. The comparison reveals a strong isotope effect of 2 × 10³ for the exchange rates of the deuterons versus hydrons.     

Synthetic Applications and Methodological Developments of Donor−Acceptor Cyclopropanes and Related Compounds

Donor−acceptor cyclopropanes are convenient precursors to reactive and versatile 1,3-dipoles, and have found application in the synthesis of a variety of carbo- and heterocyclic scaffolds. This perspective review details our laboratory's use of donor−acceptor cyclopropanes as intermediates toward the total synthesis of various natural products. We also discuss our work in the development of novel cycloadditions and rearrangements of donor−acceptor cyclopropanes and aziridines, as well as an example of an aryne insertion proceeding via fragmentation of a transient donor−acceptor cyclobutane.     

Synthesis of perylene dianhydride-incorporated main chain polyimides and sequential structural transformation through a dipolar cycloaddition

Perylene dianhydride (PDA)-incorporated polyimides were prepared. The perylene unit in the polyimide was thermally converted to the corresponding N-heterocyclic polyarene unit through a Diels–Alder reaction. The monomer, 2,2-bis(3-amino-4-hydroxyphenyl) hexafluoropropane (6FAP), was modified via O-alkylation to improve the solubility of the polymer. 2-Ethylhexyl-attached 6FAP yielded a soluble copolyimide that contained ca. 70 mol% PDA using pyromellitic dianhydride. The perylene unit of the copolyimide transformed to a polyarene unit through the dipolar cycloaddition of 4-aryl-1,2,4-triazole-3,5-dione (TAD) and maleic anhydride. The perylene transformation of the polyimide occurred with 50% conversion with maleic anhydride and quantitatively with TAD. The PDA-copolymer exhibited a spectral blue-shift and red-shift by maleic anhydride and TAD, respectively.     

Development of Simplified Heterocyclic Acetogenin Analogues as Potent and Selective Trypanosoma brucei Inhibitors

Neglected tropical diseases caused by parasitic infections are an ongoing and increasing concern. They are a burden to human and animal health, having the most devastating effect on the world′s poorest countries. Building upon our previously reported triazole analogues, in this study we describe the synthesis and biological testing of other novel heterocyclic acetogenin‐inspired derivatives, namely 3,5‐isoxazoles, furoxans, and furazans. Several of these compounds maintain low‐micromolar levels of inhibition against Trypanosoma brucei, whilst having no observable inhibitory effect on mammalian cells, leading to the possibility of novel lead compounds for selective treatment.     

POSS-based hybrid thermosets via photoinduced copper-catalyzed azide–alkyne cycloaddition click chemistry

An efficient approach for the preparation of inorganic/organic hybrid thermosets via photoinduced copper-catalyzed azide–alkyne cycloaddition click chemistry is established. Highly cross-linked thermoset polymers have been practically obtained by this technique using multifunctional compounds, tri-alkyne (1,1,1-tris[4-(2-propynyloxy) phenyl]-ethane) with octakis-azido-POSS or tri-azide (3,3′-((2-((3-azido-2-hydroxypropoxy)methyl)-2-ethylpropane-1,3-diyl)bis(oxy))bis(1-azidopropan-2-ol)) in the presence of Cu(II)Br₂/N,N,N′,N″,N?-pentamethyldiethylenetriamine/2-dimethoxy-2-phenyl acetophenone. The homogeneously distributed POSS nanoparticles are clearly detected in the TEM micrographs; whereas the TGA analysis shows that the obtained hybrid thermosets are thermally stable up to 360 °C and begin to lose weight at higher temperatures with a char yield of 23–50% at 800 °C.