Delamination of layered double hydroxides in polar monomers: new LDH-acrylate nanocomposites

The layered double hydroxide Mg2Al(OH)6(C12H25SO4) was delaminated to give high levels of inclusion in acrylate monomers; subsequent polymerisation of the monomers containing the LDH dispersion gave polyacrylates with the inorganic component still in the delaminated form.     

Ring-closing metathesis of olefinic peptides: design, synthesis, and structural characterization of macrocyclic helical peptides

Heptapeptides containing residues with terminal olefin-derivatized side chains (3 and 4) have been treated with ruthenium alkylidene 1 and undergone facile ring-closing olefin metathesis (RCM) to give 21- and 23-membered macrocyclic peptides (5 and 6). The primary structures of peptides 3 and 4 were based upon a previously studied heptapeptide (2), which was shown to adopt a predominantly 3(10)-helical conformation in CDCl(3) solution and an alpha-helical conformation in the solid state. Circular dichroism, IR, and solution-phase (1)H NMR studies strongly suggested that acyclic precursors 3 and 4 and the fully saturated macrocyclic products 7 and 8 also adopted helical conformations in apolar organic solvents. Single-crystal X-ray diffraction of cyclic peptide 8 showed it to exist as a right-handed 3(10)-helix up to the fifth residue. Solution-phase NMR structures of both acyclic peptide 4 and cyclic peptide 8 in CD(2)Cl(2) indicated that the acyclic diene assumes a loosely 3(10)-helical conformation, which is considerably rigidified upon macrocyclization. The relative ease of introducing carbon-carbon bonds into peptide secondary structures by RCM and the predicted metabolic stability of these bonds renders olefin metathesis an exceptional methodology for the synthesis of rigidified peptide architectures.     

A theoretical analysis of a piezoelectric ultrasound device with an active matching layer

This paper investigates the use of magnetically active materials in the matching layer of a piezoelectric transducer. This then allows the performance of the device to be dynamically altered by applying an external field. The effect that this new matching layer has on the performance of a typical device is theoretically investigated here. It transpires that the additional flexibility of an active matching layer can be used to maintain the efficiency of the device as the external load is varied.     

LocalC α convergence of elliptic regularizations of parabolic equations

The solutions of elliptic regularizations of the heat equation converge to the solutions of the corresponding evolution equation in weak energy norms. The technique is of relevance in control theory as well as variational inequalities. We show that the convergence actually takes place in some Hölder space. The result holds for a class of parabolic equations in divergence form and sufficiently integrable forcing terms.

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Sommario Le soluzioni delle regolarizzanti ellittiche dell'equazione del calore, convergono alle soluzioni della corrispondente equazione di evoluzione in norme deboli dell'energia. Questa tecnica trova applicazione nelle teoric dei controlli e disuguaglianze variazionali. Si dimostra che la convergenza é forte ed ha luogo in norme Hölderiane. Il risultato si estende ad una classe di equazioni paraboliche in forma di divergenza con termini forzanti sufficientemente integrabili.

     

Triacylglycerol profiling of microalgae strains for biofuel feedstock by liquid chromatography-high-resolution mass spectrometry

Biofuels from photosynthetic microalgae are quickly gaining interest as a viable carbon-neutral energy source. Typically, characterization of algal feedstock involves breaking down triacylglycerols (TAG) and other intact lipids, followed by derivatization of the fatty acids to fatty acid methyl esters prior to analysis by gas chromatography (GC). However, knowledge of the intact lipid profile could offer significant advantages for discovery stage biofuel research such as the selection of an algal strain or the optimization of growth and extraction conditions. Herein, lipid extracts from microalgae were directly analyzed by ultra-high pressure liquid chromatography–mass spectrometry (UHPLC-MS) using a benchtop Orbitrap mass spectrometer. Phospholipids, glycolipids, and TAGs were analyzed in the same chromatographic run, using a combination of accurate mass and diagnostic fragment ions for identification. Using this approach, greater than 100 unique TAGs were identified over the six algal strains studied and TAG profiles were obtained to assess their potential for biofuel applications. Under the growth conditions employed, Botryococcus braunii and Scenedesmus obliquus yielded the most comprehensive TAG profile with a high abundance of TAGs containing oleic acid.     

C.A. Coulson's work on a contour-integral approach to the London theory of magnetic susceptibility of conjugated molecules

Mizoguchi has very recently cast London's theory of magnetic susceptibilities of conjugated molecules in terms of the Coulson contour-integral formulation of Hückel molecular-orbital theory. Since interest in this approach has been thus revived, we present here a previously unpublished document, dated May 16th, 1953, by the late Professor C.A. Coulson, FRS, in which he formulates the London theory in terms of his own contour-integral method. Coulson's treatment is based on bond-bond polarisabilities and it therefore provides an interesting parallel to certain aspects of the now-classic McWeeny polarisability method, advanced five years later. The Coulson polarisability formalism does not, however, provide for explicit computation of individual ring-current intensities, nor — since it preceded the experimental observations — for the direct calculation of ring-current secondary fields (and, hence,¹H-NMR chemical shifts).