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Stabilization Effect (stabilization + effect)
Selected AbstractsTuning the Thermal Relaxation of a Photochromic Dye in Functionalized Mesoporous SilicaADVANCED FUNCTIONAL MATERIALS, Issue 13 2009Lea A. Mühlstein Abstract In this study, it is shown that the kinetics of the back-switching reaction of a photochromic spirooxazine dye encapsulated in mesoporous silica materials can be significantly influenced both by the space available to the dye molecules and by the functionalization of the silica wall. Steric hindrance of the ring-closing process due to high dye content or small pore size leads to a slow fading speed of the irradiated dye species. Further, the density of surface silanol-groups present at the silica walls has an effect on the switching behavior of the dye because of their ability to stabilize the zwitterionic merocyanine isomers, thereby slowing the fading process from the open to the closed form. This stabilization effect is further enhanced in the presence of acidic functional groups, while, in contrast, basic functional groups reduce the stabilization of the open-from dye isomers, and thus a faster decay of the irradiated species is observed. Control over the fading speed of photochromic dyes is interesting for applications requiring a particularly fast or slow fading speed. [source] IL-1, induces stabilization of IL-8 mRNA in malignant breast cancer cells via the 3, untranslated region: Involvement of divergent RNA-binding factors HuR, KSRP and TIAR,INTERNATIONAL JOURNAL OF CANCER, Issue 6 2005Esther A. Suswam Abstract IL-8 plays an integral role in promoting the malignant phenotype in breast cancer, and its production is directly influenced by inflammatory cytokines in the tumor microenvironment. Here, we show that activation of IL-1, receptors on malignant HS578t and MDA-MB-231 breast cancer cells strongly induces IL-8 expression and that RNA stabilization is persistently activated at least 12,24 hr after stimulation. SB 203580 and rapamycin reversed the RNA stabilization effect of IL-1, in a dose-dependent manner, suggesting involvement of the p38/MAP kinase and mTOR pathways. A luciferase reporter assay indicated that the stabilization effect was dependent on cis elements in the 3,-untranslated region (UTR) of the IL-8 transcript. By UV cross-linking, we identified multiple cellular factors that interact with the IL-8 3,UTR, ranging 34,76 kDa. Immunoprecipitation analysis indicated that HuR, KSRP and TIAR bound to one or more loci in the 3,UTR. While the cross-linking patterns were similar, quantitative immunoprecipitation of native IL-8 RNA from IL-1,-stimulated cytoplasmic extract revealed a 20-fold greater association of transcript with the stabilizing factor HuR vs. the destabilizing factor KSRP. In conclusion, IL-1, is a potent cytokine stimulus for IL-8 RNA stabilization in breast cancer cells, possibly by enhanced binding of cytoplasmic HuR to the 3,UTR. Published 2004 Wiley-Liss, Inc. [source] DFT study and NBO analysis of the mutual interconversion of cumulene compoundsJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 5 2007Davood Nori-Shargh Abstract The B3LYP/6-31G* method was used to investigate the configurational properties of allene (1,2-propadiene) (1), 1,2,3-butatriene (2), 1,2,3,4-pentateriene (3), 1,2,3,4,5-hexapentaene (4), 1,2,3,4,5,6-heptahexaene (5), 1,2,3,4,5,6,7-octaheptaene (6), 1,2,3,4,5,6,7,8-nonaoctaene (7), and 1,2,3,4,5,6,7,8,9-decanonaene (9). The calculations at the B3LYP/6-31G* level of theory showed that the mutual interconversion energy barrier in compounds 1,8 are: 209.73, 131.77, 120.34, 85.00, 80.91, 62.19, 55.56, and 46.83,kJ,mol,1, respectively. The results showed that the difference between the average CC double bond lengths () values in cumulene compounds 1 and 2, is larger than those between 7 and 8, which suggest that with large n (number of carbon atoms in cumulene chain), the values approach a limiting value. Accordingly, based on the plotted data, the extrapolation to n,=,,, gives nearly the same limiting (i. e., ). Also, NBO results revealed that the sum of , -bond occupancies, , decrease from 1 to 8, and inversely, the sum of , -antibonding orbital occupancies, , increase from compound 1 to compound 8. The decrease of values for compounds 1,8, is found to follow the same trend as the barrier heights of mutual interconversion in compounds 1,8, while the decrease of the barrier height of mutual interconversion in compounds 1,8 is found to follow the opposite trend as the increase in the number of carbon atom. Accordingly, besides the previously reported allylic resonant stabilization effect in the transition state structures, the results reveal that the values, , ,(EHOMO,,,ELUMO), and the C atom number could be considered as significant criteria for the mutual interconversion in cumulene compounds 1,8. This work reports also useful predictive linear relationships between mutual interconversion energy barriers () in cumulene compounds and the following four parameters: , , ,(EHOMO,,,ELUMO), and CNumber. Copyright © 2007 John Wiley & Sons, Ltd. [source] Comparative study of the effects of chlorinated polyethylene and acrylic impact modifier on the thermal degradation of poly(vinyl chloride) compounds and poly(vinyl chloride)/(oil palm empty fruit bunch) compositesJOURNAL OF VINYL & ADDITIVE TECHNOLOGY, Issue 2 2010Aznizam Abu Bakar The effects of chlorinated polyethylene (CPE) and acrylic impact modifier (AIM) on the thermal degradation of poly(vinyl chloride) (PVC) compounds and composites were investigated. The amounts of AIM and CPE used were fixed at 9 parts per hundred parts of resin (phr), while oil palm empty fruit bunch (OPEFB) fiber content was increased from 0 to 40 phr. To produce composites, the PVC formulations were dry-blended by using a laboratory blender before being milled into sheets on a two-roll mill at 165°C. The milled sheets were then hot-pressed at 180°C. The thermal degradation of the specimens was evaluated by using thermogravimetry in a nitrogen environment. Thermal stability of the PVC/CPE compounds and PVC/CPE/OPEFB composites was improved by the addition of CPE. The CPE retarded the dehydrochlorination of PVC. However, the stabilization effect was reduced by the incorporation of OPEFB at levels of 30 and 40 phr. The presence of AIM accelerated the dehydrochlorination of PVC/AIM compounds and PVC/AIM/OPEFB composites. J. VINYL ADDIT. TECHNOL., 2010. © 2010 Society of Plastics Engineers [source] Exploitation of the complex chemistry of hindered amine stabilizers in effective plastics stabilization,JOURNAL OF VINYL & ADDITIVE TECHNOLOGY, Issue 3 2007J. Pospķ Hindered amine stabilizers (HAS) remain a prominent class of stabilizers having a fortunate development with continuous interest in shaping the future properties of plastics: increase in polymer durability, application extension, reaching new effects. Commercial tests provided much information. Insufficient mechanistic interpretations of the complex effects of environmental factors (harshness of testing, penetration of radiation and oxygen, superposition of temperature, atmospheric impurities) and those of the microenvironment (morphology of the polymer matrix, physical relations of HAS,polymer, interference between HAS and other additives) are a drawback. Model experiments complement commercial studies and explain some phenomena. A careful transfer of information from model experiments must be done to avoid misinterpretation of mechanisms, particularly of the HAS regenerative cycle. A critical analysis of primary steps of the HAS activity mechanism in the polymer matrix based on HAS-related primary nitroxides, formation of their stationary concentration and concentration gradients influenced by polymer morphology, spatial competition between autoreactions, and oxidation of polymer-developed alkyl radicals and their scavenging by nitroxides (the key process of HAS efficiency) is outlined. Cyclic regeneration of nitroxides affected by the structure of the amino moiety in the HAS molecule, influence of acid environment, atmospheric ozone or singlet oxygen, cooperative mixtures of HAS with UV absorbers, combinations with additives increasing the thermal stabilization effect and improving color retention, assessment of the heat stabilization performance of HAS by proper testing, and influence of the molecular weight of HAS are mentioned together with examples of the chemical consumption of HAS in the final phases of their lifetime. lifetime. J. VINYL ADDIT. TECHNOL., 13:119,132, 2007. © 2007 Society of Plastics Engineers [source] Chemoprotective effect of plant phenolics against anthracycline-induced toxicity on rat cardiomyocytes.PHYTOTHERAPY RESEARCH, Issue 2 2004Part I. Silymarin, its flavonolignans Abstract Silymarin, an extract of ,avonolignans from the dried fruits of milk thistle (Silybum marianum L. Gaertneri) and its constituents silibinin, dehydrosilibinin, silychristin and silydianin were tested for protective effects on rat cardiomyocytes exposed to doxorubicin. Silymarin and individual ,avonolignans did not exert cytotoxicity in the range 25,100 µm (incubation 9 h). Dehydrosilibinin was tested only at 25 µm concentration due to its low solubility. All substances increased the cell ATP level. Silymarin and ,avonolignans displayed a dose-dependent cytoprotection against doxorubicin (100 µm, incubation 8 h). The protective effects of silymarin, silibinin, dehydrosilibinin and silychristin were comparable to that of dexrasoxane, while silydianin exerted the best protective effect. The ability of silymarin complex and its components to protect cardiomyocytes against doxorubicin-induced oxidative stress is due mainly to their cell membrane stabilization effect, radical scavenging and iron chelating potency. Copyright © 2004 John Wiley & Sons, Ltd. [source] Short communication: An alternative and effective catalyst for the silastannation of arylacetylenes with Me3SiSnBu3 at room temperatureAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 2 2004Taichi Nakano Abstract The palladium-catalyzed silastannation of acetylenes with tributyl(trimethylsilyl)stannane in the presence of triethylphosphite is reported for the first time. The reaction occurs at room temperature to give (Z)-silyl(stannyl)ethenes in high yields. The protodemetallation of the resulting adducts with HCl,tetraethylammonium chloride is described first, which demonstrates that the reaction is governed only by the stability of a carbonium ion arising from the protonation to (Z)-silyl(stannyl)ethenes rather than the hard and soft acid and base principle, i.e. the ,-cation stabilization effect (,,, stabilization one) of a stannyl group in the carbonium ion is rather significant. Copyright © 2004 John Wiley & Sons, Ltd. [source] | ||||||||||||||||