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Concentration Leads (concentration + lead)
Selected AbstractsGrafting itaconic anhydride onto polyethylene using extrusionJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2010C. J. R. Verbeek Abstract Reactive extrusion was employed to graft itaconic anhydride (IA) onto polyethylene, using thermally induced peroxide decomposition. It was found that an increase in IA concentration lead to an increase in the degree of grafting (DOG), but only up to 6 wt % IA. Using di-cumyl peroxide (DCP) as the initiator resulted in a higher DOG compared to di- tert -butyl peroxide (DTBP) and required less reaction time to achieve the same DOG. However, raising the IA concentration also resulted in an increase in cross-linking. Increasing the initiator concentration from 0.2 to 2 wt % resulted in a higher DOG. However, 5 wt % initiator showed similar results compared to using 0.2 wt % due to termination by disproportionation, which has been shown to be more prevalent at high initiator concentrations. Degradation was clearly observed by the inability to form a continuous extrudate during extrusion as well as discolouration. A residence time of more than 50 seconds, using DCP and 120 s for DTBP didn't offer any further increase in the DOG and also resulted in more pronounced degradation. Optimizing grafting is therefore a trade-off between maximal DOG and minimizing side reactions. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Activity-dependent somatostatin gene expression is regulated by cAMP-dependent protein kinase and Ca2+ -calmodulin kinase pathwaysJOURNAL OF NEUROSCIENCE RESEARCH, Issue 4 2010Isabel Sánchez-Muńoz Abstract Ca2+ influx through L-type voltage-gated Ca2+ channels (L-VSCC) is required for K+ -induced somatostatin (SS) mRNA. Increase in intracellular Ca2+ concentration leads to the activation of cyclic AMP-responsive element binding protein (CREB), a key regulator of SS gene transcription. Several different protein kinases possess the capability of driving CREB upon membrane depolarization. We investigated which of the signalling pathways involved in CREB activation mediates SS gene induction in response to membrane depolarization in cerebrocortical cells exposed to 56 mM K+. Activity dependent phosphorylation of CREB in Ser133 was immunodetected. Activation of CREB was biphasic showing two peaks at 5 and 60 min. The selective inhibitors of extracellular signal related protein kinase/mitogen-activated protein kinase (ERK/MAPK) PD098059, cyclic-AMPdependent protein kinase (cAMP/PKA) H89 and RpcAMPS, and Ca2+/calmodulin-dependent protein kinases (CaMKs) pathways KN62 and KN93 were used to determine the signalling pathways involved in CREB activation. Here we show that the early activation of CREB was dependent on cAMP/PKA along with CaMKs pathways whereas the ERK/MAPK and CaMKs were implicated in the second peak. We observed that H89, RpcAMPS, KN62 and KN93 blocked K+ -induced SS mRNA whereas PD098059 did not. These findings indicate that K+ -induced SSmRNA is mediated by the activation of cAMP/PKA and CaMKs pathways, thus suggesting that the early activation of CREB is involved in the induction of SS by neuronal activity. We also demonstrated, using transient transfections of cerebrocortical cells, that K+ induces the transcriptional regulation of the SS gene through the cAMP-responsive element (CRE) sequence located in the SS promoter. © 2009 Wiley-Liss, Inc. [source] Retention of arsenic species on zwitterionic stationary phase in hydrophilic interaction chromatographyJOURNAL OF SEPARATION SCIENCE, JSS, Issue 6-7 2010Dan Xie Abstract Zwitterionic hydrophilic interaction chromatography (ZIC® -HILIC) was used to study the retention of selected organoarsenicals. The retention behavior of nine organic arsenic species on ZIC® -HILIC was investigated to elucidate which is the driving force for their separation, hydrophilic partitioning or adsorption driven by hydrogen bonds with surface H-donor/acceptor groups of the stationary phase. For this, the retention factor of the compounds k was correlated with log PO/W and with the calculated strength of hydrogen bonding of the analytes. By examining aliphatic and phenylic compounds separately, improved correlation was received. This indicates that both phenomena contribute to the separation of these arsenic species on ZIC® -HILIC. The results obtained evidence that considerable electrostatic interactions also occur on ZIC® -HILIC. Retention behavior of arsenic species was investigated by varying the separation conditions, which shows that the composition of the eluent has a strong influence on the retention behavior. It is highly dependent on water/acetonitrile ratio, pH value and salt additives. Dissociation degree and polarity of arsenic species, which are varying with pH, regulate the distribution of arsenic species between stationary and mobile phases in HILIC. Increase in the ammonium acetate concentration leads to shortened or to prolonged retention depending on the structure of the arsenic species. [source] Ion irradiation and reduction effect on the conductivity and optical absorption of heavily MgO-doped LiNbO3 single crystalsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2005V.F. Pichugin Abstract The confirmation of MgNb defects in heavily MgO doped LiNbO3 single crystals were investigated through optical absorption, electrical conductivity measurements, optical spectroscopy with nanosecond time resolution, and Raman spectroscopy technique. An increase in the MgO concentration up to 10 mole% provides an essential change of the luminescence of LiNbO3, the appearance of a supplementary optical absorption band at the 1.1 eV, an alteration of the Raman spectra caused by the formation of (MgNb) defects, a shift of the edge of the supplementary optical absorption due to ion irradiation toward the shorter wavelength region as the MgO concentration increases. The effect of Ar+ ions irradiation on the conduction of the MgO doped LiNbO3 samples was studied. The important role of reduction in modification of the conducting properties of the ion-irradiated crystals was established. The increase of the MgO concentration leads to a decrease of the reduction efficiency. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] 2-Hydroxyethylmethacrylate carrying uniform porous particles: preparation and electron microscopyPOLYMER INTERNATIONAL, Issue 1 2002A Tuncel Abstract Uniform macroporous particles carrying hydroxyl groups have been obtained in the size range 3,11.5,µm by seeded polymerization. For this purpose, uniform polystyrene particles in the size range 1.9,6.2,µm were used as seeds. The seed particles were successively swollen by dibutyl phthalate (DBP) and a monomer mixture comprising styrene, 2-hydroxyethylmethacrylate (HEMA) and a crosslinker. Two different crosslinkers, divinylbenzene (DVB) and ethylene glycol dimethacrylate (EGDMA), were tested. Size distribution properties together with bulk and surface structures of the particles have been characterized by both scanning and transmission electron microscopy. While EGDMA provides uniform particles with a non-porous surface, DVB produces uniform particles having a highly porous surface and interior. The comparison of FTIR and FTIR-DRS spectra shows that the HEMA concentration is higher on the particle surface than within the particle interior. Seed latex size and monomer/seed latex ratios are identified as the most important variables affecting the final particles. Different seed latexes have been tried; the result is that highly macroporous particles with a sponge-like pore structure both on the surface and in the particle interior have been obtained by use of the seed latex with the largest particles and the lowest molecular weight. An increase in the HEMA feed concentration leads to final particles with a non-porous surface and a crater-like porosity in the particle interior. The average pore size significantly decreases with increasing DBP/seed latex and monomer/seed latex ratios. © 2001 Society of Chemical Industry [source] Study of Cytochrome P4502E1 mRNA Level of Mononuclear Cells in Patients With Alcoholic Liver DiseaseALCOHOLISM, Issue 2001Hirokazu Yano Background: Cytochrome P-4502E1 (CYP2E1) is an important enzyme because of its unique ability to convert many substrates to cytotoxins. The increased production of reactive intermediates by elevated enzyme concentrations leads to various pathological conditions. Therefore, it is important to detect induced CYP2E1 levels in alcoholic individuals to avoid xenobiotic-promoted liver injury. In the present investigation, we detected CYP2E1 mRNA levels of mononuclear cells obtained from 10 ml of blood by using competitive polymerase chain reaction (PCR) method. Methods: Mononuclear cells were obtained from healthy individuals who did and did not drink habitually and patients with alcoholic liver disease (ALD). Complementary DNA synthesis was performed with RNA obtained from mononuclear cells by reverse transcription-PCR. Competitive PCR of CYP2E1 was performed with the sense (5,-CTGCAACGTCATA-GCCGACA-3,) and antisense (5,-TCCATTTCCACGAGCAGGCA-3,) primer and competitor DNA. Competitive PCR of ,-actin also was performed. Electrophoresis was scanned, and each band was digitized. The concentration of CYP2E1 and ,-actin mRNA was calculated from the ratio of competitor DNA. Results: In healthy individuals who did and did not drink habitually, CYP2E1 mRNA levels were 103.3 copies/,l RNA and 101.7 copies/,l RNA, respectively. In actively drinking patients with ALD, CYP2E1 mRNA levels were 103.5 copies/,l RNA, but those levels decreased to 101.7 copies/,l RNA after 4 days of abstinence. No significant difference was observed in CYP2E1 mRNA levels between alcoholic fibrosis and cirrhosis. As control, we measured ,-actin mRNA levels in mononuclear cells in all samples. The mean value of ,-actin mRNA was 104.3 copies/,l RNA in all cases, which included patients with ALD. Conclusions: The results demonstrated that it is possible to measure the CYP2E1 mRNA levels of mononuclear cells in a 10 ml blood sample. The CYP2E1 mRNA level in mononuclear cells increases during drinking and decreases in abstinence for a short period of 3 to 4 days. It is concluded that CYP2E1 mRNA level may be used as an effective marker for alcoholic intake. [source] | ||||||||||