Synthesis of pyrido[1,2-a]indole malonates and amines through aryne annulation

Pyrido[1,2-a]indoles are known as medicinally and pharmaceutically important compounds, but there is a lack of efficient methods for their synthesis. We report a convenient and efficient route to these privileged structures starting from easily accessible 2-substituted pyridines and aryne precursors. A small library of compounds has been synthesized utilizing the developed method, affording variously substituted pyrido[1,2-a]indoles in moderate to good yields.     

The importance of surface morphology in controlling the selectivity of polycrystalline copper for CO2 electroreduction

This communication examines the effect of the surface morphology of polycrystalline copper on electroreduction of CO(2). We find that a copper nanoparticle covered electrode shows better selectivity towards hydrocarbons compared with the two other studied surfaces, an electropolished copper electrode and an argon sputtered copper electrode. Density functional theory calculations provide insight into the surface morphology effect.     

Education: a microfluidic platform for university-level analytical chemistry laboratories

We demonstrate continuous flow acid-base titration reactions as an educational microfluidic platform for undergraduate and graduate analytical chemistry courses. A series of equations were developed for controlling and predicting the results of acid-base neutralisation reactions conducted in a microfluidic format, including the combinations of (i) a strong base and a strong acid, (ii) a strong base and a weak acid, and (iii) a strong base and a multiprotic acid. Microfluidic titrations yielded excellent repeatability. The small experimental footprint is advantageous in crowded teaching laboratories, and it offers limited waste and exposure to potentially hazardous acids and bases. This platform will help promote the utilisation of microfluidics at an earlier stage of students' careers.     

1D CdS/PbS heterostructured nanowire synthesis using cation exchange

Heterostructured CdS nanowires with PbS deposits forming p-n junctions have been synthesized by successive cation exchange. The method developed herein opens up the possibility of preparing a spatially distributed heterojunction-based multifunctional electrode. The (photo)electrochemical activity of the material may be chemically tuned by changing the size and density of the p type PbS nanoparticles.     

Variation in structure and Li<Superscript>+</Superscript>-ion migration in argyrodite-type Li<Subscript>6</Subscript>PS<Subscript>5</Subscript>X (X = Cl,Br, I) solid electrolytes

All-solid-state rechargeable lithium-ion batteries (AS-LIBs) are attractive power sources for electrochemical applications due to their potentiality in improving safety and stability over conventional batteries with liquid electrolytes. Finding a solid electrolyte with high ionic conductivity and compatibility with other battery components is a key factor in raising the performance of AS-LIBs. In this work, we prepare argyrodite-type Li₆PS₅X (X = Cl, Br, I) using mechanical milling followed by annealing. X-ray diffraction characterization reveals the formation and growth of crystalline Li₆PS₅X in all cases. Ionic conductivity of the order of 7?×?10^?4 S cm^?1 in Li₆PS₅Cl and Li₆PS₅Br renders these phases suitable for AS-LIBs. Joint structure refinements using high-resolution neutron and laboratory X-ray diffraction provide insight into the influence of disorder on the fast ionic conductivity. Besides the disorder in the lithium distribution, it is the disorder in the S^2?/Cl^? or S^2?/Br^? distribution that we find to promote ion mobility, whereas the large I^? cannot be exchanged for S^2? and the resulting more ordered Li₆PS₅I exhibits only a moderate conductivity. Li⁺ ion migration pathways in the crystalline compounds are modelled using the bond valence approach to interpret the differences between argyrodites containing different halide ions.     

The statistical evolution of multiple generations of oxidation products in the photochemical aging of chemically reduced organic aerosol

The heterogeneous reactions of hydroxyl radicals (OH) with squalane and bis(2-ethylhexyl) sebacate (BES) particles are used as model systems to examine how distributions of reaction products evolve during the oxidation of chemically reduced organic aerosol. A kinetic model of multigenerational chemistry, which is compared to previously measured (squalane) and new (BES) experimental data, reveals that it is the statistical mixtures of different generations of oxidation products that control the average particle mass and elemental composition during the reaction. The model suggests that more highly oxidized reaction products, although initially formed with low probability, play a large role in the production of gas phase reaction products. In general, these results highlight the importance of considering atmospheric oxidation as a statistical process, further suggesting that the underlying distribution of molecules could play important roles in aerosol formation as well as in the evolution of key physicochemical properties such as volatility and hygroscopicity.     

Substrate clamping effects on irreversible domain wall dynamics in lead zirconate titanate thin films

The role of long-range strain interactions on domain wall dynamics is explored through macroscopic and local measurements of nonlinear behavior in mechanically clamped and released polycrystalline lead zirconate-titanate (PZT) films. Released films show a dramatic change in the global dielectric nonlinearity and its frequency dependence as a function of mechanical clamping. Furthermore, we observe a transition from strong clustering of the nonlinear response for the clamped case to almost uniform nonlinearity for the released film. This behavior is ascribed to increased mobility of domain walls. These results suggest the dominant role of collective strain interactions mediated by the local and global mechanical boundary conditions on the domain wall dynamics. The work presented in this Letter demonstrates that measurements on clamped films may considerably underestimate the piezoelectric coefficients and coupling constants of released structures used in microelectromechanical systems, energy harvesting systems, and microrobots.     

Adventures in ozoneland: down the rabbit-hole

In this perspective we describe a 15 year pursuit of the Stabilized Criegee Intermediate (SCI). We have conducted several complementary experiments to measure the pressure dependence of product yields-including OH radical and ozonides-on sequences of alkene + ozone systems. In so doing we have been able to bring into gradual focus a succession of weakly bound intermediates, starting with the primary ozonide, then the SCI, and finally a vinyl hydroperoxide (VHP) product of SCI rearrangement. We have narrowed the phase space in our hunt for direct SCI observations to a range of alkene carbon numbers and system pressures, but the system continues to deliver surprises. One surprise is strong evidence that the VHP is a significant bottleneck along the reaction coordinate. These findings support the search for the SCI, build our fundamental understanding of collisional energy transfer in highly excited, multiple-well, chemically activated systems, and finally directly inform atmospheric chemistry on topics including HO(x) radical formation and reactions associated with secondary organic aerosol formation.     

Belohorec‐type oscillation theorem for second order sublinear dynamic equations on time scales

Consider the Emden‐Fowler sublinear dynamic equation (0.1) where $p\in C(\mathbb{T},R)$, where $\mathbb{T}$ is a time scale, 0 < α < 1. When p(t) is allowed to take on negative values, we obtain a Belohorec‐type oscillation theorem for (0.1). As an application, we get that the sublinear difference equation (0.2) is oscillatory, if and the sublinear q‐difference equation (0.3) where $t\in q^{\mathbb{N}_0}, q>1$, is oscillatory, if      

Weyl connections and the local sphere theorem for quaternionic contact structures

We apply the theory of Weyl structures for parabolic geometries developed by Čap and Slovák (Math Scand 93(1):53–90, 2003) to compute, for a quaternionic contact (qc) structure, the Weyl connection associated to a choice of scale, i.e. to a choice of Carnot–Carathéodory metric in the conformal class. The result of this computation has applications to the study of the conformal Fefferman space of a qc manifold, cf. (Geom Appl 28(4):376–394, 2010). In addition to this application, we are also able to easily compute a tensorial formula for the qc analog of the Weyl curvature tensor in conformal geometry and the Chern–Moser tensor in CR geometry. This tensor was first discovered via different methods by Ivanov and Vasillev (J Math Pures Appl 93:277–307, 2010), and we also get an independent proof of their Local Sphere Theorem. However, as a result of our derivation of this tensor, its fundamental properties—conformal covariance, and that its vanishing is a sharp obstruction to local flatness of the qc structure—follow as easy corollaries from the general parabolic theory.