Self-inhibition or the lack of it in the pyrolyses of neopentane and n-hexane

Published data show that in its early stages (up to 3% decomposition), the pyrolysis of n-hexane in the ranges 723–823 K and 10–100 Torr is not inhibited by the olefin products, in contrast with neopentane pyrolysis which is very strongly inhibited in similar conditions. Detailed consideration of the chain mechanisms for the two pyrolyses shows that the reactivity of the chain terminating radical towards hydrogen abstraction from an allylic C? H bond in product olefin is the factor which determines whether or not observable self-inhibition occurs. Thus, n-hexane pyrolysis, whose chain decomposition is terminated by recombination and disproportionation of ethyl, is not significantly self-inhibited, whereas that of neopentane which is terminated by recombination of methyl is very strongly inhibited because methyl is 14× more reactive than ethyl. The implications for other alkanes are briefly discussed.     

Determination of nitric acid in ambient air using diffusion denuder tubes

A method has been developed for the determination of gaseous nitric acid in air based on its separation from particulate nitrate aerosol using diffusion denuder tubes. An integrated value of nitric acid concentration in air is obtained. The experimentally derived absorption efficiencies of the diffusion denuder tubes ranged from 87.6 to 96.9%. The standard deviation of the method was calculated as 0.10 mug/m(3) for nitric acid concentrations in the range 0.54-1.72 mug/m(3). A correction procedure, using two diffusion denuders in series, should be applied if measurements are made in the presence of high levels of nitrogen oxides.     

Observation and analysis ofE mesons in\bar p p annihilation at rest in H2 gas

Antiproton-proton annihilation at rest in a gaseous H₂ target at NTP into the final state π⁺ π^? K ^± π^? (K ⁰) with an undetectedK ⁰ or \(\bar K^0 \) has been investigated. We observe theE(1420) resonance in the invariant mass spectrum (K ⁰)_miss K ^± π^? with massM _E =1413±8 MeV/c² and widthГ ^E =62 ± 16MeV/c² and find evidence for the production of thef ₁(1285). The absolute branching ratio of \(\bar p\) p → π⁺ π^? E ⁰,E ⁰ →K ₀ ^L K ^± π ^? at (61±6)%P wave annihilation is (3.0±0.9)·10^?4 of all annihilations. The observed suppression of theE production fromP wave with respect to theS wave together with some simple selection rules suggest that the quantum numbers of theE(1420) areJ ^pc=0^?+ and not I⁺⁺.     

Crystallinity of ethylene oxide oligomers

Nonaethylene glycol and pentadecaethylene glycol and their dimethyl ethers have been prepared and characterized, with respect to crystallinity by wide- and small-angle X-ray scattering, Raman scattering, i.r. spectroscopy and differential scanning calorimetry. Wide-angle X-ray scattering is similar to that from high molecular weight poly(ethylene oxide). The crystal habit is lamella. The lamellae are highly crystalline and the surface layers are ordered. Comparison with crystalline poly(ethylene oxide) prepared conventionally, and having a distribution of chain lengths, shows that such samples crystallize into lamellae with disordered surface layers.     

Pectin in controlled drug delivery – a review

Controlled drug delivery remains a research focus for public health to enhance patient compliance, drug efficiency and reduce the side effects of drugs. Pectin, an edible plant polysaccharide, has been shown to be useful for the construction of drug delivery systems for specific drug delivery. Several pectin derived formulations have been developed in our laboratory and tested in vitro, ex vivo, and in vivo for the ability to deliver bioactive substances for therapeutic purposes in the context of interactions with living tissues. Pectin derivatives carrying primary amine groups were more mucoadhesive and have shown potential in nasal drug delivery and other mucosal drug delivery. Pectin derivatives with highly esterified galacturonic acid residues are more hydrophobic and able to sustain the release of incorporated fragrances for a prolonged duration. Less esterified pectin derivatives are able to penetrate deeper into the skin and may be useful in aromatherapy formulations. Pectin, in combination with zein, a corn protein, forms hydrogel beads. The bound zein restricts bead swelling and retains the porosity of the beads; the pectin networks shield the zein from protease attack. The complex beads are ideal vehicles for colon-specific drug delivery. Studies presented in this paper indicate the flexibility and possibility to tailor pectin macromolecules into a variety of drug delivery systems to meet different clinical requirements. Mention of trade names or commercial products in this article is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the US Department of Agriculture.     

Cyclophanes—13: Crystal and molecular structure of [2.2][2,5]furano(1,4)naphthalenophane

The crystal and molecular structure of [2.2](2,5)furano(1,4)naphthalenophane (1) was determined by X-ray crystallography. The molecule exists in the anti-conformation and the study represents the first instance in which the structural features of a naphthalenoid ring within a cyclophane were determined. Crystals of cyclophane 1 are orthorhombic, space group Pbca, with a = 7.859(2). b = 11.482(3) and c = 28.818(8) Å. While the nonbridged portion of the naphthalenoid ring is planar, the portion which is bridged to the furanoid ring through its 1 and 4 C atoms is puckered and boat-shaped. These C atoms are positioned 14° out of the plane of the other four C atoms of this ring. The furanoid ring is essentially planar but is not parallel to the naphthalenoid ring. It is inclined 22° to the least squares plane of the bridged portion of the naphthalenoid ring. This angle of inclination staggers the atoms of the furanoid and bridged naphthalenoid ring and positions the 3 and 4 C atoms, the 2 and 5 C atoms and the 0 atom of the furanoid ring 3.4. 2.9 and 2.6 Å. respectively, from the least squares plane of the bridged portion of the naphthalenoid ring. While the internal angles around the bridging C atoms α- to the naphthalenoid ring are 109°, those α- to the furanoid ring are 113°. In addition unusually large bond angles ($\text{\$}\text{?}$137°) at the 2 and 5 C atoms of the furanoid ring, external to the ring, are also observed. The distortions are considered with respect to the strain within the cyclophane macrocycle and are compared with other similar systems.     

Electron impact mass spectrometry of the acetates of zinc,magnesium, cobalt and manganese

The electron impact mass spectra of the acetates of zinc, magnesium, cobalt and manganese have been investigated using a direct inlet probe. Volatile tetrahedral complexes are produced on heating, and ions of the form [M₄(OCOCH₃)₆O]^+˙ (M = Co and Mn) and [N₄(OCOCH₃)₅O]⁺ (N = Zn or Mg) are observed. A mixture of magnesium and cobalt acetates produces ions of the form [Mg_nCo_4–n(OCOCH₃)₆O]^+˙.