Total synthesis of Eudistomins Y1-Y6

The first total synthesis of Eudistomins Y₁-Y₆, brominated phenolic β-carboline marine metabolites with a unique benzoyl moiety at C1, have been prepared in three steps, utilizing MAOS, in overall yields ranging from 6% to 25%.     

Understanding barium sulfate precipitation onto stainless steel

This paper investigates the influence of barium sulfate scaling and scaling inhibitors on the electrochemical behaviour of stainless steel. The results of a synchrotron radiation grazing incidence X-ray diffraction (SR-GIXRD) and electrochemical impedance spectroscopy (EIS) study on stainless steel shows that different scaling inhibitors interact uniquely with the substrate when barium sulfate is precipitated on the electrode surface. The main effect of the substrate in the presence of inhibitor is a tendency to form smaller barium sulfate particles. The SR-GIXRD patterns obtained in the presence of the two inhibitors were different to each other and to the control, with the carboxylate showing greater amounts of barite solids precipitated together with iron(III) and (II) sulfate, while the phosphonate showed low amounts of barite solid were precipitated. The presence of iron sulfates on the electrode surface as detected by SR-GIXRD, in the case of NTA, suggests that scaling inhibitors are not always benign, and can promote the dissolution of iron species from the substrate.     

Synthesis of the Bicyclic Lactone Core of Leonuketal,Enabled by a Telescoped Diels–Alder Reaction Sequence

The Diels–Alder cycloaddition reaction has become established as a fundamental approach for the preparation of complex natural products; however, successful application of the intermolecular Diels–Alder cycloaddition reaction to the synthesis of particularly congested scaffolds remains surprisingly problematic. Inspired by the terpenoid spiroketal natural product leonuketal, a challenging telescoped reaction sequence has been realized to access the core [2.2.2]‐bicyclic lactone ring system and its [3.2.1] isomer. Our four‐step, protecting‐group‐free process required detailed investigation to circumvent the problems of adduct fragmentation and intermediate instability. Successful solution of these practical issues, along with unambiguous structural determination of the target structures, provide useful insights that will facilitate future applications of the Diels–Alder cycloaddition reaction to challenging, highly congested molecular scaffolds and ongoing synthetic efforts towards this natural product.     

PbTe colloidal nanocrystals: synthesis, characterization, and multiple exciton generation

We report an alternative synthesis and the first optical characterization of colloidal PbTe nanocrystals (NCs). We have synthesized spherical PbTe NCs having a size distribution as low as 7%, ranging in diameter from 2.6 to 8.3 nm, with first exciton transitions tuned from 1009 to 2054 nm. The syntheses of colloidal cubic-like PbSe and PbTe NCs using a PbO "one-pot" approach are also reported. The photoluminescence quantum yield of PbTe spherical NCs was measured to be as high as 52 +/- 2%. We also report the first known observation of efficient multiple exciton generation (MEG) from single photons absorbed in PbTe NCs. Finally, we report calculated longitudinal and transverse Bohr radii for PbS, PbSe, and PbTe NCs to account for electronic band anisotropy. This is followed by a comparison of the differences in the electronic band structure and optical properties of these lead salts.     

Evolution of the interfacial phases in Al2O3–Kovar® joints brazed using a Ag–Cu–Ti-based alloy

Abstract

A systematic investigation of the brazing of Al₂O₃ to Kovar^® (Fe–29Ni–17Co wt.%) using the active braze alloy (ABA) Ag–35.25Cu–1.75Ti wt.% has been undertaken to study the chemical reactions at the interfaces of the joints. The extent to which silica-based secondary phases in the Al₂O₃ participate in the reactions at the ABA/Al₂O₃ interface has been clarified. Another aspect of this work has been to determine the influence of various brazing parameters, such as the peak temperature, T_p, and time at T_p, τ, on the resultant microstructure. As a consequence, the microstructural evolution of the joints as a function of T_p and τ is discussed in some detail. The formation of a Fe₂Ti layer on the Kovar^® and its growth, along with adjacent Ni₃Ti particles in the ABA, dominate the microstructural developments at the ABA/Kovar^® interface. The presence of Kovar^® next to the ABA does not change the intrinsic chemical reactions occurring at the ABA/Al₂O₃ interface. However, the extent of these reactions is limited if the purity of the Al₂O₃ is high, and so it is necessary to have some silica-rich secondary phase in the Al₂O₃ to facilitate the formation of a Ti₃Cu₃O layer on the Al₂O₃. Breakdown of the Ti₃Cu₃O layer, together with fracture of the Fe₂Ti layer and separation of this layer from the Kovar^®, has been avoided by brazing at temperatures close to the liquidus temperature of the ABA for short periods of time, e.g., for T_p between 820 and 830 °C and τ between 2 and 8 min.     

Anisotropy of constrained magnetostrictive materials

The magnetic anisotropy of a ferromagnetic material that is free to deform is defined as the effective anisotropy, which is the sum of intrinsic anisotropy and magnetostriction-induced anisotropy. Prior works [1] and [2] (Baltzer, 1957; Kittel, 1949) indicate that if the material is undeformed then the measured anisotropy is same as its intrinsic anisotropy. When magnetostrictive materials are used as actuators or sensors they are often mechanically loaded, resulting in a restriction on the deformation. To capture their behavior in such scenarios, a modelling approach is required. Therefore, in this work, the thermodynamic accuracy of the common expressions for magnetostriction-induced and stress-induced anisotropies is first investigated. A 3D magnetoelastic model is then developed using Armstrong's implementation of an energy model. This 3D magnetoelastic model is capable of predicting the stresses induced when the magnetostriction of these materials is constrained. Using this model, it is shown that when the bulk magnetostriction of the material is clamped, the measured anisotropy will not in general be the same as the intrinsic anisotropy. It is also shown that when the magnetostriction is clamped at the microscopic level, i.e. if the material is locally constrained at the exchange length scales, then the measured anisotropy is the intrinsic anisotropy.