MW Fraction (mw + fraction)

Distribution by Scientific Domains

Selected Abstracts

Studies on the association between immunoglobulin E autoreactivity and immunoglobulin E-dependent histamine-releasing factors

IMMUNOLOGY, Issue 2 2002
Ilona Kleine Budde
Summary It has been reported that serum immunoglobulin E (IgE) from certain atopic patients can sensitize basophils to release histamine in response to IgE-dependent histamine-releasing factors (HRFs). It has also been shown that patients suffering from severe forms of atopy may contain IgE autoantibodies. It was investigated whether HRF-responsive sera contained IgE autoantibodies and if there was an association between IgE autoreactivity and IgE-dependent responsiveness to HRF. The presence of HRF-responsive IgE (IgE+) in serum of patients with respiratory atopy was determined by stimulating stripped human basophils sensitized by serum with peripheral blood mononuclear cell (PBMC)-derived HRF, and measuring the release of histamine. In parallel, these sera were screened for the presence of IgE autoantibodies to nitrocellulose-blotted human cellular extracts. The capacity of IgE autoantigen-containing preparations to induce histamine release was tested in the stripped basophil assay. Eleven out of 52 sera contained IgE autoantibodies to blotted cellular extracts of human PBMCs or of the human epithelial cell line A431. No significant association was found between IgE autoreactivity and IgE-dependent responsiveness to HRF: 7/26 IgE+ sera contained IgE to human cellular extracts, and 4/26 of the sera without IgE+ did also. IgE autoantigen-containing extracts did not induce histamine release of appropriately sensitized basophils. By size-exclusion chromatography it was shown that a 32,000 MW autoantigen eluted in the >55,000 MW fraction, which indicates that this protein forms polymers or complexes with other macromolecules. This might explain the discrepancy between binding and histamine-releasing activity. A 20,000 MW IgE-defined autoantigen cross-reacted with a shrimp allergen. Our results indicate that IgE-reactivity to immunoblotted human protein and IgE-dependent HRF activity are distinct entities that may co-occur in atopic patients. [source]

Effect of aluminoxane on molecular weight and molecular weight distribution of polyethylene prepared by an iron-based catalyst

Dr Qi Wang
Abstract A series of aluminoxanes, tetraethylaluminoxane (TEAO), tetraalkylaluminoxane (TAAO), Et2AlOB(4 , F , C6H4)OAlEt2 (BTEAO) and ethyl-iso-butylaluminoxane modified with p -fluorophenylboric acid (BEBAO), were prepared and their effects on molecular weight (MW) and molecular weight distribution (MWD) of polyethylene prepared by the iron-based catalyst [(ArNC(Me))2C5H3N]FeCl2 (Ar2,6-dimethylphenyl) (1) were investigated. It was found that TEAO and BTEAO were highly efficient activators for iron-based catalysts and introducing the branched bulky group (eg iso-Bu) into the aluminoxane activator could improve the MW of the resulting polyethylene. The MW of polyethylene produced by activators modified by p -fluorophenylboric acid was higher than for other aluminoxane activators. The TEAO- and TAAO-based polyethylene exhibited attractive bimodal MWD, and the lower MW fraction of bimodal MWD was shown to be produced in the early stage of polymerization due to chain transfer to the aluminium activator. Copyright 2004 Society of Chemical Industry [source]

Temperature-Resolved Local and Macroscopic Charge Carrier Transport in Thin P3HT Layers,

Patrick Pingel
Abstract Previous investigations of the field-effect mobility in poly(3-hexylthiophene) (P3HT) layers revealed a strong dependence on molecular weight (MW), which was shown to be closely related to layer morphology. Here, charge carrier mobilities of two P3HT MW fractions (medium-MW: Mn,=,7,200 g mol,1; high-MW: Mn,=,27,000 g mol,1) are probed as a function of temperature at a local and a macroscopic length scale, using pulse-radiolysis time-resolved microwave conductivity (PR-TRMC) and organic field-effect transistor measurements, respectively. In contrast to the macroscopic transport properties, the local intra-grain mobility depends only weakly on MW (being in the order of 10,2 cm2 V,1 s,1) and being thermally activated below the melting temperature for both fractions. The striking differences of charge transport at both length scales are related to the heterogeneity of the layer morphology. The quantitative analysis of temperature-dependent UV/Vis absorption spectra according to a model of F. C. Spano reveals that a substantial amount of disordered material is present in these P3HT layers. Moreover, the analysis predicts that aggregates in medium-MW P3HT undergo a "pre-melting" significantly below the actual melting temperature. The results suggest that macroscopic charge transport in samples of short-chain P3HT is strongly inhibited by the presence of disordered domains, while in high-MW P3HT the low-mobility disordered zones are bridged via inter-crystalline molecular connections. [source]

Speciation of essential and toxic elements in edible mushrooms: size-exclusion chromatography separation with on-line UV,inductively coupled plasma mass spectrometry detection

Rodolfo G. Wuilloud
Abstract Size-exclusion liquid chromatography was coupled to UV and inductively coupled plasma mass spectrometry (ICP-MS) for detection to perform elemental speciation studies on different edible mushrooms. Molecular weight (MW) distribution patterns of several elements among different fractions present in various edible mushrooms are presented. The association of the elements with the high and low MW fractions was observed using sequential detection by UV and ICP-MS. Separation was performed using a Superdex 75 column. Variability of the fractionation patterns with three different extraction media (0.05 mol l,1 NaOH; 0.05 mol l,1 HCl; hot water at 60C) was evaluated for mushroom species. A comparative elemental speciation study was performed in order to determine the differences in the fractionation patterns of silver, arsenic, cadmium, mercury, lead, and tin in Boletus edulis, Agaricus bisporus, and Lentinus edodes. Differences in the fractionation patterns of the elements were found to depend on the mushroom species and the extraction medium. Most of the elements were associated with high mw fractions. It was not possible to assess the trace metal contributions from the mushroom growth media. Copyright 2004 John Wiley & Sons, Ltd. [source]