New ylide anions. A vinyl anion equivalent for substituted fumarate esters

A new type of ylide anion is reported which upon alkylation and elimination of triphenylphosphine serves as a vinyl anion equivalent.     

Compact High-Order Finite Differences for Interface Problems in One Dimension

This paper is concerned with the construction and analysis ofcompact finite difference approximations to the model linearsource problem –(pu')' + qu = f where the functions p,q, and f can have jump discontinuities at a finite number ofpoints. Explicit formulae that give O(h²) O(h³) and O(h⁴) accuracyare derived, and a procedure for computing three-point schemesof any prescribed order of accuracy is presented. A rigoroustruncation and discretization error analysis is offered. Numericalresults are also given.     

Using the Exterior Matrix Method to find eigenfrequencies when the governing equations are systems of first-order equations

In this paper, we will apply the Exterior Matrix Method to the case where the governing equations for one piece of the structure is a system of 4 first-order equations. This generalizes a result when the governing equation was a single fourth-order equation. Ironically, the governing equations do not have to be solved in order to find the corresponding exterior matrix, and the exterior matrices can be used to find the eigenfrequencies of the system, even if there are dissipative joints added to the system. We will first look at the well-understood example of Euler–Bernoulli beams to illustrate the concept, and then move on to the more difficult inclined cable problem.     

Recent Developments in Solid-Propellant Binders

Abstract

The complex and important role of the propellant binder in solid-propellant rockets is described. The severe weight problems of space exploratrion cause high propellant performance to be of major concern in a highly competitive field. Binders contribute to performance, not only in terms of fuel value, but by being compatible with energetic components and by providing good mechanical properties. Both sterilization required for planetary landings and compatibility problems of new energetic oxidizers generate new requirements too stringent for existing binders; only binders composed essentially of saturated aliphatic hydrocarbon are predicted to be suitable. Several saturated-binder developments are in progress. The achievements of one of these programs, based on free-radical synthesis, are evaluated against the goals of the new binder.     

ET743: Chemical analysis of the sea squirt Ecteinascidia turbinata ecosystem

The sea squirt Ecteinascidia turbinata produces the powerful drug ET743. In this study Inductively Coupled Plasma-Atomic Emission Spectroscopy (ICP-AES) and Matrix Assisted Laser Desorption Ionization-Mass Spectrometry (MALDI-MS) are systematically used to measure elemental and molecular species in a Florida Keys mangrove ecosystem that contains the sea squirt. ICP-AES is used to measure the concentration of 27 elements down to the parts per billion level in 16 organisms and 3 sediment samples that reside in the mangrove ecosystem including turtle grass, blue crabs, fire sponge, and lettuce slugs. MALDI-MS is used to search for ET743 in these same organisms and sediment samples. A mass spectral feature corresponding to ET743 is identified in the extract of the sea squirt, red mangrove root (Rhizophera mangle), the schoolmaster snapper (Lutjanus griseus), and a sediment sample taken from the ecosystem. We use MALDI-MS to study the impact that various environmental conditions, such as UV light, I(2), cation binding (Fe(+3), Zn(+2), Pb(+2), Cu(+2)), metal oxide nanoparticles (FeO, CuO, TiO(2), ZnO, Al(2)O(3)), a common mineral (CaCO(3)), and extremes in acidity (0.1 M HCl, 0.1 M NaOH) have on the ET743 structure. The data provide potential structures (degradation products, metal-ligand complexes, etc.) that might be present in organism or sedimentary extracts that are similar to ET743. We are studying the marine geochemistry of this ecosystem so a broth can be developed and tested for producing this marine natural product.     

C−H Functionalization of Commodity Polymers

Synthetic manipulation of polymer substrates is one of the oldest and most reliable methods to increase the functional diversity of soft materials. Modifying the chemical structure of polymers that are already produced on a commodity scale leverages the current high‐volume and low‐cost production of commodity plastics for the discovery of modern materials. A myriad of polymer C?H functionalization methods have been developed which enable the modification of material properties on both a laboratory and industrial scale. More recently, driven by advances in C?H activation, photoredox catalysis, and radical chemistry, chemoselective approaches have emerged as a means to impart precise functionality onto commodity polymer substrates. This Review discusses the historical significance of and contemporary advances in the C?H functionalization of commodity polymers. The conceptual approach outlined herein presents exciting new directions for the field, including increasing the value of otherwise pervasive materials, uncovering entirely new material properties, and a viable path to upcycle post‐consumer plastic waste.     

Effect of heat treatment on the morphology and structure of crystals,powders, and fibers of polyacrylonitrile and saran

As part of a study of chemical and physical changes accompanying the formation of carbons by the pyrolysis of polymers, conventional electron microscopy, electron diffraction, and scanning electron microscopy techniques have been used to examine structural and morphological features of polyacrylonitrile (PAN) crystals, powder, and fibers, and of Saran and poly(vinylidene chloride) (PVDC) powder. Changes accompanying the heating of these polymers in air and in nitrogen have been investigated. PAN crystals grown from propylene carbonate were similar to those obtained by Klement and Geil. When heated in air at 220°C they retained their morphology, and electron diffraction gave the same reflections as PAN. On further heating to 400°C in nitrogen the morphology was retained, but the diffraction was lost. Crystals treated in nitrogen alone at 200°C showed morphology similar to that of the polymer. PAN powders and fibers retained discernable external features of their morphology on heating to 800°C. These results are discussed with reference to changes which take place when poly(vinylidene chloride) and Saran are heated in the range 150–180°C, which results in the loss of one hydrogen chloride per monomer unit, and are subsequently carbonized at 800°C. The development of pore structure and the adsorptive properties of Saran carbons are also discussed.