Thermal degradation of polyethylene

Thermal degradation of low-density polyethylene (LDPE) in the temperature range from 450 to 525°C has been studied using a sieve-bottom reactor with inert gas as heat-transferring agent bubbled through the PE melt. Temperature dependence of the degradation rate was determined. Full degradation of LDPE into gaseous and wax-like hydrocarbons (alkanes and 1-alkenes) was achieved. Temperature rise and prolonging of the contact time increased the yield of the gaseous hydrocarbons and decreased the molecular weight of the wax-like product.     

Polysaccharide gels for colon targeting

Polysaccharides appear to have a potential as drug carriers for site-specific drug delivery to the colon due to the well-known fermentation of polysaccharides by the anaerobic microflora in the colon. This paper gives a short presentation of the rationale of colon-specific drug delivery and briefly describes various in vitro and in vivo methods for testing of polysaccharide gels for colonic drug delivery. The application of dextran hydrogels is used as an illustrative example of a polysaccharide based colonic drug delivery system.     

Group IVB organometallic compounds of furan: 13C, 29Si and 119Sn n.m.r. Spectra

The ¹³C, ²⁹Si and ¹¹⁹Sn chemical shifts of 2- and 2,5-substituted organometallic (M=C, Si, Ge, Sn, Pb) derivatives of furan were measured. The most important factors, determining the specific features of the studied spectra, are d-orbital availability and atomic radius of the central atom M, as well as the relatively higher (as compared with benzene) energies of the π-electron energy levels of the furan ring.     

Carbon-13 chemical shifts of bicyclo[3.2.1]octane and bicyclo[2.2.1]heptane derivatives

¹³C chemical shifts of more than fifty bicyclo[3.2.1]octane and bicyclo[2.2.1]heptane derivatives (hydrocarbons, alcohols, ketones and esters) have been determined. The usefulness of ethyl derivatives for the assignment of close ¹³C chemical shifts in bicyclic methyl derivatives is shown both for the bicyclo[3.2.1]octane and bicyclo[2.2.1]heptane series. Comparison of substituent effects on α-, β-, γ- and δ-carbons in both series of compounds shows remarkable differences in steric interactions. In contrast to the rigid bicyclo[2.2.1]heptane system, both chair and boat conformations can be predominant in the bicyclo[3.2.1]octane series with the conformationally flexible 6-membered ring.     

High resolution broad line 13C NMR and relaxation in solid norbornadiene

High resolution NMR of rare spins in solids has been used for selective measurement through transverse relaxation of the shapes of lines corresponding to nonequivalent ¹³C nuclei in solid norbornadiende between 195 and 225 K. The broad lines have different shapes and widths, whose temperature dependence indicates slow translational diffusion of molecules.     

Structure investigations of solid organosilicon polymers by high resolution solid state 29Si NMR

The high resolution ²⁹Si NMR spectra of five solid silicon polymers of different structure have been studied and the ²⁹Si chemical shifts of characteristic structure units determined. ²⁹Si¹H cross-polarization in combination with high speed magic angle sample spinning and high power proton decoupling was used to achieve high resolution in the solid state spectra. Comparison of the latter with the results obtained in the liquid state clearly indicates that no special solid state effects on ²⁹Si chemical shifts arise and the relations between δ(Si) and the molecular structure, well known from investigations of liquids, can be used for interpretation of the solid state spectra. It is shown that high resolution solid state ²⁹Si NMR spectroscopy offers detailed information about the structural units of the siloxane resin framework, and this opens up new possibilities for structural determinations of solid organosilicon polymers.     

Variety identification of wheat using mass spectrometry with neural networks and the influence of mass spectra processing prior to neural network analysis

The performance of matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry with neural networks in wheat variety classification is further evaluated.1 Two principal issues were studied: (a) the number of varieties that could be classified correctly; and (b) various means of pre-processing mass spectrometric data. The number of wheat varieties tested was increased from 10 to 30. The main pre-processing method investigated was based on Gaussian smoothing of the spectra, but other methods based on normalisation procedures and multiplicative scatter correction of data were also used. With the final method, it was possible to classify 30 wheat varieties with 87% correctly classified mass spectra and a correlation coefficient of 0.90.     

Arsenic accumulation and speciation analysis in wool from sheep exposed to arsenosugars

Wool or hair fibre is a metabolically dead material after it has left the epidermis. During growth the fibre in the root is a metabolically very active organ, which is highly influenced by the health status of the living being. Arsenic is one of the elements that is easily taken up by the cells of the root and stored in the fibre afterwards. Here we show that arsenic can quantitatively be extracted by boiling the wool fibre or hair in water. The high intake of arsenic species by the sheep of North Ronaldsay (the seaweed-eating sheep) leads to a high arsenic concentration in wool (mean 5.2+/-2.3 mug g(-1)). The wool of lambs of these sheep, which are not exposed to seaweed, contains about 10 times less arsenic, which is still elevated compared to uncontaminated wool. The arsenic species identified in wool extract are arsenite (As(III)), arsenate (As(V)), monomethylarsonic acid (MMA(V)) and monomethylarsonious acid (MMA(III)) as minor species. The major species is dimethylated arsenic DMA in its tri- and pentavalent form (dimethylarsinous acid (DMA(III)) and dimethylarsinic acid (DMA(V))) accounting for 85% of the specified arsenic in the wool which reflects the amount of dimethylated species (i.e. the arsenoribofuranosides) taken up by seaweed being the main food source of the sheep. However, there are unknown arsenic species in the extract, which are not eluting from a strong anion exchange column. In vitro incubation experiments with this kind of wool showed that it has reducing properties but no demethylation was recorded. The absorption ability of the wool for methylated arsenic species is negligible, while inorganic arsenic is easier to be absorbed in the fibre (11-17%). This means that the species integrity is only guaranteed in terms of the degree of methylation but not in terms of their redox status.     

Mass spectrometry and partial least-squares regression: a tool for identification of wheat variety and end-use quality

Rapid methods for the identification of wheat varieties and their end-use quality have been developed. The methods combine the analysis of wheat protein extracts by mass spectrometry with partial least-squares regression in order to predict the variety or end-use quality of unknown wheat samples. The whole process takes approximately 30 min. Extracts of alcohol-soluble storage proteins (gliadins) from wheat were analysed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Partial least-squares regression was subsequently applied using these mass spectra for making models that could predict the wheat variety or end-use quality. Previously, an artificial neural network was used to identify wheat varieties based on their protein mass spectra profiles. The present study showed that partial least-squares regression is at least as useful as neural networks for this identification. Furthermore, it was demonstrated that partial least-squares regression could be used to predict wheat end-use quality, which has not been possible using neural networks.