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Structure Modification (structure + modification)
Selected AbstractsStructure modification of isotactic polypropylene through chemical crosslinking: Toughening mechanismJOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2007S. Bouhelal Abstract Reversibly crosslinked isotactic polypropylene (iPP) was prepared in the presence of dicumyl peroxide. The effects of the peroxide oxy-radicals in the melt were investigated in relation to the modification of the polymer. The dynamic rheology analysis of the crosslinking process was carried out by using a plastograph. The crosslinking reaction was evaluated by the Monsanto method. The resulting structure of the modified samples was studied by means of differential scanning calorimetry (DSC), wide-angle X-ray scattering (WAXS), microhardness, and mechanical properties. The degree of crystallinity of the modified iPP, derived from DSC and WAXS, remains almost unchanged, i.e., the crystalline structure is unaffected, though the lamellar thickness slightly decreases. The impact strength of the crosslinked iPP is greatly improved with reference to that of the unmodified material. A transition from brittle to ductile behavior appears in the modified iPP for all the crosslinking agents studied. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2968,2976, 2007 [source] A Dramatic Substituent Effect in Silver(I)-Catalyzed Regioselective Cyclization of ortho -Alkynylaryl Aldehyde Oxime DerivativesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 1-2 2009Hongyin Gao Abstract A dramatic substituent effect was found in the silver(I)-catalyzed cyclization reaction of ortho -alkynylaryl aldehyde oxime derivatives. When R is an alkyl group, the Ag(I)-catalyzed reaction in dimethylacetamide at 110,°C (conditions A) affords isoquinolines in good to excellent yields, in contrast, isoquinolin-1(2,H)-ones were produced in moderate to high yields under conditions B (dimethylformamide, room temperature) when R is an acetyl group. A plausible mechanism was proposed for this product selectivity control reaction (PSCR) by subtle structure modification. [source] Thermal analysis of merino wool fibres without internal lipidsJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2007M. Martí Abstract Merino wool is made up of cuticle and cortical cells held together by the cell membrane complex (CMC), which contains a small amount of internal lipids (IWL) (1.5% by mass). IWL have been extracted from wool on account of their considerable dermatological interest owing to their proportion of ceramides. IWL have been extracted by different methods and solvents, methanol and acetone at laboratory and pilot plant levels. Thermal analysis of these extracted wool fibers is presented using thermogravimetry (TG) and differential scanning calorimetry (DSC). TG provides a measurement of the weight loss of the sample as a function of time and temperature. DSC gives information about possible structure modification of extracted wool fibers. Thermoporometry was applied to evaluate the pore size distribution of extracted wool fibers. The results showed that the extraction process increased the pore size distribution and the cumulated pore volume, which is consistent with some changes in the extracted wool CMC. Extracted fiber becomes more hydrophilic and absorbs a large amount of water. We can conclude that the lipid extraction of wool produced no relevant changes in the crystalline fraction when extracted with acetone. However, part of the amorphous keratin material was extracted with methanol, the rest of the crystalline material becoming more stable. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 545,551, 2007 [source] Haptoglobin from psoriatic patients exhibits decreased activity in binding haemoglobin and inhibiting lecithin-cholesterol acyltransferase activityJOURNAL OF THE EUROPEAN ACADEMY OF DERMATOLOGY & VENEREOLOGY, Issue 4 2008L Cigliano Abstract Objective, The aim of this work was to assess whether psoriasis is associated with phenotype prevalence and altered activity of haptoglobin (Hpt). Background, Hpt is a plasma acute-phase glycoprotein, displaying in humans three phenotypes. Phenotype prevalence or structure modification of Hpt was associated with several diseases. The Hpt main function is to bind and carry to the liver free haemoglobin for degradation and iron recycling. Hpt was recently found able to bind the apolipoprotein A-I (ApoA-I), thus impairing its stimulation on the activity of the enzyme lecithin-cholesterol acyl-transferase (LCAT). Study design, Hpt was isolated from patients with psoriasis vulgaris, and its activity in haemoglobin or ApoA-I binding and LCAT inhibition was compared with that of normal protein. Methods, Two affinity chromatography steps, the first using resin-coupled haemoglobin and the second anti-Hpt antibodies, were used to purify Hpt. The protein phenotype was assessed by electrophoresis. Binding experiments were performed by Enzyme-linked immunosorbent assay with stationary haemoglobin or ApoA-I, Hpt in solution and anti-Hpt antibodies for detection of bound Hpt. Standard LCAT assays were carried out in the presence of Hpt purified from patients or healthy subjects. Results, Phenotype prevalence of Hpt in psoriasis was not found. After affinity chromatography by haemoglobin, albumin and ApoA-I were routinely found heavily contaminating only Hpt from normal subjects. Isolated Hpt from patients had lower activity than normal protein in both haemoglobin binding and LCAT inhibition. Conclusions, In psoriasis, Hpt displays some structure modification(s), which might be associated with the protein function in the disease. [source] Recent progress in the development of coumarin derivatives as potent anti-HIV agents,MEDICINAL RESEARCH REVIEWS, Issue 3 2003Donglei Yu Abstract Numerous plant-derived compounds have been evaluated for inhibitory effects against HIV replication, and some coumarins have been found to inhibit different stages in the HIV replication cycle. This review article describes recent progress in the discovery, structure modification, and structure,activity relationship studies of potent anti-HIV coumarin derivatives. A dicamphanoyl-khellactone (DCK) analog, which was discovered and developed in our laboratory, and calanolide A are currently in preclinical studies and clinical trials, respectively. © 2003 Wiley Periodicals, Inc. Med Res Rev, 23, No. 3, 322-345, 2003 [source] | ||||||||||