On spacelike submanifolds with parallel mean curvature in an indefinite space form

In this work we use a Simon??s type inequality for a suitable tensor and apply it to obtain sharp estimates for the supremum of the scalar curvature for complete spacelike submanifold M ⁿ with parallel mean curvature vector in an indefinite space form ${N^{n+p}_p(c)}$ .     

Cu(II)-promoted methanolysis of N,N-dipicolylacetamide. multistep activation by decoupling of > ̈̈N-C═O resonance via Cu(II)-N binding, delivery of the Cu(II):((-)OCH3) nucleophile, and metal ion assistance of the departure of the leaving group

The methanolysis of the Cu(II) complex of N-acetyl-N,N-bis(2-picolyl)amine (2) was investigated by a kinetic study as a function of pH in methanol at 25 °C and computationally by DFT calculations. The active species is the basic form of the complex (3(-)), or (1:Cu(II))((-)OCH(3))(HOCH(3))), and the rate constant for its solvolysis is k(max) = 1.5 × 10(-4) s(-1). The mechanism involves Cu(II) binding to the amide N lone pair, decoupling it from >N-C═O resonance, concomitant with Cu(II):((-)OCH(3)) delivery to the adjacent >N-C═O unit, followed by Cu(II)-assisted departure of the N,N-bis(2-picolyl)amide from a tetrahedral intermediate.     

Structure analysis of naturally occurring alkyl porphyrins by hydrogen chemical ionisation mass spectrometry

Chemical ionisation (CI) mass spectrometry with H₂ as reagent gas has been used to obtain spectra of a number of demetallated alkyl porphyrins from an oil shale and a bitumen. The spectra give more structural informa- tion than the electron impact spectra, by way of odd electron dipyrrolic fragment ions. Thus, the structural possibilities for a novel /c30 aetio porphyrin have been narrowed to two, although¹HNMR only reduced the possibilities to six. The spectra of four types of components containing a five, six, seven or methyl-substituted six membered exocyclic ring show, for example, that three out of four C₃₂ isomers can be distinguished. The technique offers promise as a tool in structural elucidation of other novel naturally occurring porphyrins.     

Hydrogen catalysis and scavenging action of Pd-POSS nanoparticles

Prompted by the need for a self-supported, chemically stable, and functionally flexible catalytic nanoparticle system, we explore a system involving Pd clusters coated with a monolayer of polyhedral oligomeric silsesquioxane (POSS) cages. With an initial theoretical focus on hydrogen catalysis and sequestration in the Pd-POSS system, we report density functional theory (DFT) results on POSS binding energies to the Pd(1 1 0) surface, hydrogen storing ability of POSS, and possible pathways of hydrogen radicals from the catalyst surface to unsaturated bonds away from the surface.     

Syntheses and oxygenation of iron(II) “strapped” porphyrin complexes

A general route to ‘strapped’ porphyrins which are bridged between diagonally opposite meso-positions is described. Studies on the oxygenation and carbonylation of their iron(II) complexes have shown that they are inferior to ‘capped’ porphyrins as models for the oxygen-carrying haemoproteins. The results reported herein suggest that strapping structures which do not enforce well-defined and rigid cavities for oxygen binding afford little protection against irreversible oxidation of (dioxygen) (porphyrin) iron(II) complexes.     

Qualification of automated low-field NMR relaxometry for quality control of polymers in a production setting

Implementation of a low-field time-domain nuclear magnetic resonance (NMR) scanner as a diagnostic tool in the production of new polymer components is described in the context of qualification of a new QA/QC device. A study to determine the optimal experimental parameters was performed and a robotic autosampler was built to enable scanning of multiple pads. Relationships between T₂ values and physical properties of DC745 slabs were investigated, and the appropriate sampling parameters for the production setting were determined. Two versions of a robotic autosampler were built and, for the component described here, a fourth radial axis was required in addition to traditional X, Y, and Z movement to eliminate the large variability in T₂ due to inconsistent sample coverage caused by the complex rib geometry of the component. Data show that with appropriate choice of experimental conditions of the NMR detector and the detection geometry of the robotic autosampler, sufficient resolution of variations in cross-link density on the millimeter scale could be determined. All data to date demonstrate that low-field NMR devices are a feasible tool for use in production settings for non-destructive quality control of polymer components.