Effectiveness of antioxidants: Suppression of evolution of gaseous degradation products from low-density polyethylene during thermo-oxidation

The present investigation is part of a project concerning improvements of the working environment for polymer manufacturing processes at high temperatures; for example, welding and extrusion coating.The evolution of gaseous degradation products from unstabilized and antioxidant stabilized low-density polyethylene during thermo-oxidation in air at 210°C has been studied by a simple technique using a modified gas chromatograph. Of the thirteen antioxidants investigated (phenols, phosphites, phosphonites, sulphides and metal dithiocarbamates), only phenols (radical scavengers) effectively suppress the formation of gaseous degradation products from the polymer during an induction period.The gaseous degradation products were analysed with combined gas chromatography-mass spectrometry (GC-MS), using direct trapping on the GC column (Porapak® QS). Apart from water and carbon dioxide, the major products are formaldehyde, acetaldehyde, formic and acetic acids. The addition of effective antioxidants strongly reduces the absolute amounts of the degradation products during the induction period, but does not change their relative quantities.     

On non-analytic thermodynamic behaviour of the classical linear chain

The free energy ? per particle and the two-particle distribution function g have been expressed as functionals of the nearest-neighbour interaction Φ(x) for a variety of boundary conditions. For some boundary conditions and potentials Φ(x), ? and g behave singularly at a critical density

$\text{ρ}{}_{\mathrm{<mtext>c</mtext>}}\text{=}\text{lim}\text{s→0}{}^{\mathrm{+}}\text{∫}\text{0}\text{∞}\text{e}{}^{\mathrm{?sx?\beta \Phi (x)}}\text{d}\text{x?}\text{∫}\text{0}\text{∞}\text{x}\text{e}{}^{\mathrm{?sx?\beta \Phi (x)}}\text{d}\text{x.}$

     

Melanin offers protection against induction of cyclobutane pyrimidine dimers and 6-4 photoproducts by UVB in cultured human melanocytes

The goal of this investigation was to correlate the melanin content in human pigmentary cells with the generation of UVB-induced photoproducts and to examine the relationship between the melanin content and the removal of the photoproducts. Cultured melanocytes from light-skinned individuals synthesized less melanin and produced more cyclobutane pyrimidine dimers and 6-4 photoproducts upon UVB exposure than did melanocytes from black skin. Tyrosine-stimulated melanogenesis provided protection against DNA damage in both cell types. In another set of pigmented cell lines a ratio between eumelanin and pheomelanin was determined. The assessment of association between DNA damage induction and the quantity and quality of melanin revealed that eumelanin concentration correlated better with DNA protection than pheomelanin. Skin type-I and skin type-VI melanocytes, congenital nevus (CN)-derived cells and skin type-II melanocytes from a multiple-melanoma patient were grown in media with low or high L-tyrosine concentration. The cells were irradiated with 200 J/m2 UVB, and the levels of the photoproducts were determined immediately and after 6 and 24 h. Once again the induction of the photoproducts was mitigated by increased melanogenesis, and it was inversely correlated with the skin type. No significant differences were found for the removal of photoproducts in the cultures of skin types I and VI and CN cells. No indications of a delay in the removal of photoproducts in the melanocytes from the multiple-melanoma patient were found either.     

Controlling cell attachment selectively onto biological polymer-colloid templates using polymer-on-polymer stamping

A new patterning approach using polymer-on-polymer stamping (POPS) has been developed to fabricate polymer-colloid templates for controlling selective cell attachment. In this paper, a polyamine surface patterned onto a poly(acrylic acid)/poly(allylamine hydrochloride) (PAA/PAH) cell resistant multilayer platform serves as a template for the deposition of close- or loose-packed colloidal particles. Peptides containing the RGD adhesion sequence were used to modify the PAH/colloid surface for specific cell attachment. Cell behavior was studied by varying colloidal packing array density, pattern geometry, and surface chemistry. It was found that loose-packed RGD-modified colloidal arrays enhance cell adhesion, as observed through the development of focal adhesion contacts and orientation of actin stress fibers, but close-packed colloidal arrays induce a rounded and nonadhesive cell morphology and yield a smaller number of attached cells. On loose-packed arrays, cells adjust their shapes to the pattern geometry when the stripe width is smaller than 50 microm and increase their extent of attachment when the concentration of surface RGD peptides is increased. This new biomaterials system allows the examination of cell behavior as a function of RGD surface distribution on the molecular to micrometer scale and reveals cellular response to different surface roughnesses.     

Infrared and Raman spectroscopic investigations of the Nb(V) fluoro and oxofluoro complexes in the LiF-NaF-KF eutectic melt with development of a diamond IR cell

A vacuum-tight cell for infrared spectroscopic investigations of extremely corrosive melts, e.g., molten fluorides, has been constructed and tested up to 750 degrees C. The cell has a gold-lined sample chamber and a diamond window transparent for the infrared light. It can be furnished with a gold piston that enables the recording of short-path-length FTIR spectra of liquid samples. Solutions of Nb(V) in LiF-NaF-KF eutectic (FLINAK) with and without oxide additions have been investigated by FTIR and Raman spectroscopy. The presence of NbF7(2-), NbOF5(2-), and NbO2F4(3-) complexes was established in the molten state at 600 degrees C. After solidification NbF7(2-) was still the only Nb(V) all-fluoro complex present. Three oxofluoro complexes, NbOF6(3-), NbOF5(2-), and NbO2F4(3-), have been identified in the solid state. Typical frequency regions for the different complexes are established. Finally, it was shown that K2NbF7 can be used as an indicator to determine the oxide content of the sample melts.     

Lambda scale for the improved latticeO(N) non-linear sigma model

Using the background field technique I computeι _L ^I /ι _L ^S =e ^{(0.5928(N?)/2+0.2044)/(N?2)} in agreement with a calculation by Symanzik. Implications for Monte Carlo simulations are also discussed.     

Rearrangement of spiro[2H‐1‐benzopyran‐2,2′‐[2H]indoles] to pyrrolo[1,2‐a]indole derivatives

Heating of 1′‐(N‐substituted carbamoyl)methylspiro[2H‐1‐benzopyran‐2,2′‐[2H]indoles] with potassium hydroxide in ethanol yields diastereomeric 5a,13‐methano‐6H‐1,3‐benzoxazepino[3,2‐a]indole‐12‐carbox‐amides. Reduction of the latter with sodium borohydride affords 1,2,3,9a‐tetrahydro‐2‐hydroxyaryl‐9H‐pyrrolo[ 1,2‐a] indole‐3 ‐carboxamides.     

SEDIMENTATION ANALYSIS OF DNA PHOTOOXIDIZED IN THE PRESENCE OF THIOPYRONINE

Abstract. Illumination of single-stranded φ×174 phage DNA with visible lightλ > 500 nm) in the presence of the sensitizer thiopyronine results in both chain scissions detectable by velocity sedimentation in neutral medium and in alkali-labile bonds which yield secondary strand breaks after alkaline treatment. Compared with the generation of primary strand breaks, the formation of alkali-labile sites seems to be the predominant reaction.
Photodynamic treatment of homogeneous double-stranded Ta, phage DNA leads to changes in the overall conformation of DNA as revealed by an initial increase of the sedimentation coefficient. The simultaneous occurrence of different effects (decrease of molecular weight, increase of effective DNA flexibility) is particularly evident from changes in the sedimentation coefficient distribution. The fact that both processes influence the sedimentation behaviour questions the common procedure of calculating double-strand break numbers from sedimentation coefficient distributions on the basis of s#-M relations which are valid for intact DNA only.
Photooxidized double-stranded DNA exhibits an increased sensitivity against shear forces.     

Low-temperature vibrational spectra of cis-dichloro-(meso-2,3-diaminobutane)palladium(II) and platinum(II)

IR and Raman spectra of MCl₂(meso-2,3-diaminobutane), (M = Pd, Pt), have been recorded down to liquid nitrogen temperature or lower. It is shown that correlation coupling occurs between closely spaced hydrogen-bonded pairs of molecules, which form a “super molecule,” but not between all eight molecules in the unit cell. The lattice mode region is also understood in outline on the basis of motions of the “super molecules” Methyl torsional modes appear to be near 140 cm^?1.     

Fast, generic gradient high performance liquid chromatography coupled to fourier transform ion cyclotron resonance mass spectrometry for the accurate mass analysis of mixtures

Fast gradient high performance liquid chromatography (HPLC) has been combined with a commercially available Fourier transform ion cyclotron resonance (FTICR) mass spectrometer for the routine and high performance analysis of mixtures. With this combination we were able to separate and detect, under high mass accuracy conditions, a six-component drug mixture in less than 5 minutes. The fast gradients described are now possible due to the development of mechanically robust, ultra pure silica packing materials, which allow relatively high flow rates (ca. 1 mL/min for a 2 mm diameter column). For the six compounds present in the model mixture, relative mass errors of less than 1 ppm were obtained (based on an external calibration) providing sufficient mass accuracy to make unequivocal assignments of empirical formulae. Preliminary results of fast gradient HPLC/FTICR-MS/MS are also shown for the same six-component mixture. Copyright 2000 John Wiley & Sons, Ltd.