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  • 1
    ISSN: 1572-8978
    Keywords: Plasma polymers ; oxidation ; XPS ; photoelectron binding energy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract The incorporation of oxygen into nitrogen-containing plasma deposited polymers was studied by X-ray Photoelectron Spectroscopy (XPS). As the oxygen content of the plasma polymer increased, the binding energy of the N 1s photoelectrons increased. Conversely, the binding energy of the O 1s photoelectrons was inversely proportional to the nitrogen content of the plasma polymer. The data from a large number of samples all obeyed the same “universal” correlations of photoelectron binding energy versus chemical composition. The data were described by the same curve regardless of whether the oxygen was incorporated rapidly into the thin film during plasma deposition or whether the oxygen was added slowly during spontaneous oxidation of the film in air. This implies that the same thermodynamic principles of radical reactions governed the addition of oxygen to the plasma polymer. The shift in the O 1s and N 1s photoelectron binding energies as a function of chemical composition was used to monitor the proximity of nitrogen and oxygen. By contrasting the experimental data with a simple binomial model which described the random addition of oxygen to a lattice containing carbon and nitrogen, we were able to show that oxygen was preferentially added near nitrogen-containing groups in plasma polymers.
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 164 (1995), S. 85-92 
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The growth-regulated vimentin gene contains a functional double AP-1 binding site formed by two nearly perfect inverted repeats. We present evidence for down-regulation of vimentin expression by the retinoic acid receptor (RAR) in two mesodermally derived cell types. By mutation analysis we prove that the double consensus element is responsible for this negative regulation. From in vitro protein-DNA interaction studies we conclude that AP-1 binding is inhibited at RAR amounts required for occupation of the cognate RAR binding site in nuclear extracts from 3T3 cells and differentiated embryonal carcinoma cells. Furthermore, we show that, unlike in other cases, trans-activation of the vimentin AP-1 enhancer element can occur in undifferentiated embryonal carcinoma cells, despite the low amount of Jun and Fos proteins present in these cells. Here, however, down-regulation by retinoic acid cannot be detected. © 1995 Wiley-Liss, Inc.
    Additional Material: 5 Ill.
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  • 3
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    Surface and Interface Analysis 26 (1998), S. 498-511 
    ISSN: 0142-2421
    Keywords: plasma polymers ; fluorocarbons ; oxidation ; ageing ; surface restructuring ; XPS ; FTIR ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: Plasma polymer coatings were deposited from perfluoro-1,3-dimethylcyclohexane (PFDMCH) and their composition and surface properties studied by XPS, grazing-angle Fourier transform infrared spectroscopy and contact angle measurements as a function of time after fabrication as they were stored under ambient conditions for more than 2 years. The spontaneous ambient oxidation of PFDMCH plasma polymers was found to be a multi-step process. The rapid initial oxygen uptake, assigned to reaction between carbon-centred radicals incorporated into the coating during deposition and in-diffusing atmospheric O2, was similar to that of plasma polymers deposited from hydrocarbon-based monomers (alkanes, alkylamines, alcohols), suggesting that the density of radicals incorporated during deposition was similar. Subsequently, however, the extent of oxidation was much lower for PFDMCH coatings. This can be attributed to the lack of availability of hydrogen abstraction reactions, which are important for radical propagation in hydrocarbon-based plasma polymers. While XPS recorded a continuous incorporation of oxygen for more than 2 years, the air/water contact angles decreased only during the first 2 months and on further storage remained stable. There appeared to be only a small extent of surface restructuring as assessed from the small depth variations of compositions. The surface was enriched in CF3 groups at all times. © 1998 John Wiley & Sons, Ltd.
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  • 4
    ISSN: 0142-2421
    Keywords: XPS ; coating thickness ; global analysis ; multilayers ; curvature ; roughness ; atomic force microscopy ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: Approaches are described for the analysis of XPS signals from samples comprising thin conformal coatings on substrates with non-ideal surface topography. In particular, attention is focused on arbitrarily shaped rough or curved substrates. Relations are derived for the relative x-ray photoelectron intensities emitted from various elements in such non-ideal samples. The surface topography of arbitrarily rough samples is analysed by atomic force microscopy to provide a frequency histogram of the local slopes, which is incorporated into a global, multi-element analysis method for interpretation of the observed XPS elemental intensities. An analogous approach is used for the analysis of curved samples. Our algorithms also enable simultaneous analysis of successively coated multilayer structures. When the elemental composition of the individual layers is known, the fit procedure enables determination of the thickness values of single-layer and multilayer coatings. The range of validity of the theory is discussed. © 1997 by John Wiley & Sons, Ltd.
    Additional Material: 7 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    BioEssays 18 (1996), S. 379-389 
    ISSN: 0265-9247
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Lysosomes are the site of degradation of obsolete intracellular material during autophagy and of extracellular macromolecules following endocytosis and phagocytosis. The membrane of lysosomes and late endosomes is enriched in highly glycosylated transmembrane proteins of largely unknown function. Significant progress has been made in recent years towards elucidating the pathways by which these lysosomal membrane proteins are delivered to late endosomes and lysosomes. While some lysosomal membrane proteins follow the constitutive secretory pathway and reach lysosomes indirectly via the cell surface and endocytosis, others exit the trans-Golgi network in clathrin-coated vesicles for direct delivery to endosomes and lysosomes. Sorting from the Golgi or the plasma membrane into the endosomal system is mediated by signals encoded by the short cytosolic domain of these proteins. This review will discuss the role of lysosomal membrane proteins in the biogenesis of the late endosomal and lysosomal membranes, with particular emphasis on the structural features and molecular mechanisms underlying the intracellular trafficking of these proteins.
    Additional Material: 4 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 1399-1414 
    ISSN: 0887-624X
    Keywords: plasma polymers ; oxidation ; XPS ; FTIR ; SEM ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Long-term compositional changes were observed when n-hexane plasma polymers were stored in air at ambient temperature. These post-deposition changes were monitored over periods exceeding one year using XPS, grazing angle FTIR, and SEM. A rapid initial increase in the oxygen content was followed by a slower oxygen uptake, which continued for many months. In contrast to the reported autocatalytic acceleration of the oxidation of polyolefins, the rate of oxidation of n-hexane plasma polymers was found to decrease continuously, and it did not proceed to the same extent toward higher oxidation states. The plasma polymer coatings did not show physical manifestations of oxidative degradation such as cracking, reduction in thickness, or loss of physical integrity. Comparison of the XPS and FTIR data suggested that the top few nanometers of the plasma polymer coatings oxidized at a faster rate than the “bulk.” The experimental data were interpreted using a model comprising reactions known from the oxidative degradation of polyolefins: carbon-centered radicals, trapped in the course of the plasma deposition, combine with atmospheric oxygen to form metastable peroxy radicals and hydroperoxides, which decompose to generate a variety of stable product groups such as hydroxyl, carbonyl, and carboxylic groups. There was broad agreement between the XPS data and the time dependence of particular species in model calculations. © 1994 John Wiley & Sons, Inc.
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  • 7
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 985-1000 
    ISSN: 0887-624X
    Keywords: plasma polymers ; methyl methacrylate ; oxidation ; long-term stability ; XPS ; FTIR ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Plasma polymer films were deposited from methyl methacrylate (MMA) vapor under various plasma conditions and XPS and FTIR used to study the changes to the compositions of the films as they were stored in air for longer than 1 year. The plasma power input per monomer mass unit (W/FM) markedly affected the composition of the freshly deposited MMA plasma polymers. A low value of W/FM led to a high degree of retention of the original monomer structure, whereas a high value of W/FM resulted in substantial monomer fragmentation and the formation of a partially unsaturated material considerably different to conventional PMMA. As the MMA plasma coatings were stored in ambient air after fabrication, all showed spontaneous oxidative changes to their composition, but the extents and reaction products differed substantially. Deposition at low W/FM led to moderate oxidative changes, whereas high power led to a pronounced increase in the oxygen content over time and resulted in a wide range of carbon-oxygen functionalities in the aged material. As the initial compositions/plasma deposition conditions thus influenced the oxidative postdeposition reactions, MMA plasma polymers deposited under different conditions not only varied in their initial composition but then became even more diverse as they aged. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 985-1000, 1998
    Additional Material: 11 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    New York, N.Y. : Wiley-Blackwell
    Journal of Cellular Biochemistry 59 (1995), S. 117-125 
    ISSN: 0730-2312
    Keywords: AIDS ; anticarcinogen ; antiviral ; chemoprevention ; dithiolethiones ; glutathione ; reverse transcriptase ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Glutathione (GSH) levels are markedly depleted in patients infected with human immunodeficiency virus type 1 (HIV-1) and supplementation of media with high concentrations (5-20 mM) of low-molecular weight thiols prevents HIV-1 replication in cultured cells. We were intrigued whether chemo-preventive enzyme inducers might represent a more pharmacologically feasible method to inhibit HIV-1 replication since these compounds elevate intracellular concentrations of GSH at nontoxic doses in vivo. After establishing that all inducers surveyed were able to elevate GSH levels in human T-cell and monocytoid cell lines, we were surprised to find that olitpraz (5-pyrazinyl-4-methyl-1,2-dithiole-3-thione) was uniquely able to inhibit HIV-1 replication (IC50 = 5-15 μM). Oltipraz and other antiviral 1,2-dithiole-3-thiones (DTTs) appear to inhibit acute HIV-1 replication by inactivating reverse transcriptase (RT). However, among DTTs that inhibit HIV-1 replication in acutely infected cells, only oltipraz was able to inhibit HIV-1 replication in a chronic infection model. Thus, in addition to inactivating RT, oltipraz appears to have an additional antiviral mechanism distal to viral integration. Our laboratories are attempting to determine the mechanism by which oltipraz inhibits HIV-1 replication in chronically infected cells; we are also attempting to determine the bioorganic mechanism for the inactivation of RT. Since the covalent modification of schistosomal protein and transcription factor(s) are thought to be responsible for the antiparasitic and chemopreventive activities of DTTs, respectively, our studies should be relevant to understanding the diverse medicinal properties of DTTs. Oltipraz, an antischistosomal drug undergoing clinical evaluation as an anticarcinogen, inhibits HIV-1 replication at concentrations achievable in human serum. It is intriguing to consider oltipraz as a therapeutic agent not only for its antiretroviral activity, but also for the prevention of HIV-1 associated neoplasms.
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  • 9
    ISSN: 0730-2312
    Keywords: aflatoxin B1 ; aflatoxin albumin adducts ; biomarkers ; enzyme induction ; glutathione S-transferases ; hepatocellular carcinoma ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Oltipraz has been used clinically in many regions of the world as an antischistosomal agent and is an effective inhibitor of aflatoxin hepatocarcinogenesis in rats. This chemopreventive action of oltipraz results primarily from an altered balance in aflatoxin metabolic activation and detoxication. In 1995, a randomized, placebo-controlled, double-blind intervention was conducted in residents of Qidong, People's Republic of China, who are at high risk for exposure to aflatoxin and development of hepatocellular carcinoma. The major study objectives were to define a dose and schedule for oltipraz that would reduce levels of aflatoxin biomarkers in biofluids of the participants, and to further characterize dose-limiting side effects. Two hundred thirty-four healthy eligible individuals, including those infected with HBV, were randomized to receive either 125 mg oltipraz daily, 500 mg oltipraz weekly, or placebo. Blood and urine specimens were collected to monitor potential toxicities and evaluate biomarkers over the 8-week intervention and subsequent 8-week follow-up periods. Overall, compliance in the intervention was excellent; approximately 85% of the participants completed the study. Objective evaluation of adverse events was greatly facilitated by inclusion of a placebo arm in the study design. A syndrome involving numbness, tingling, and pain in the fingertips was the only event that occurred more frequently among the active groups (18 and 14% of the daily 125 mg and weekly 500 mg arms, respectively) compared to placebo (3%). These symptoms were reversible and could be relieved with non-steroidal antiinflammatory agents. A more complete understanding of the chemopreventive utility of oltipraz awaits completion of an assessment of the efficacy of oltipraz in modulating levels of aflatoxin biomarkers. J. Cell. Biochem. Suppls. 28/29:166-173. © 1998 Wiley-Liss, Inc.
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  • 10
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 98 (1979), S. 31-39 
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Total cellular calcium levels do not change when 3T3-4a cells stop proliferating due to serum depletion, or when serum-arrested quiescent cells are incubated for up to 44 hours in calcium-deficient medium (∼10 μM Ca++). Upon stimulation with dialyzed serum cells enter S and progress through at least one cycle even at extremely low calcium levels in the culture medium (≥10 μM). Cells divide until a final cell density is attained which is proportional to the calcium concentration in the medium and cells reversibly arrest in G1. Cells which arrested in G1 in medium containing ≤26 μM Ca++ in the presence of excess serum can be stimulated to enter S in response to added calcium after a prereplicative phase of 14 to 16 hours. Serum does not affect 45Ca-uptake in these cells. Benzo[a]pyrene transformed 3T3 (BP3T3) cells have a 100-200 times lower Ca++-requirement than 3T3 cells but arrest in G1 at low Ca++ levels. In contrast, SV40-virus transformed 3T3 (SV3T3) cells that grow without restriction in monolayer cultures have even lower Ca++-requirements for growth than BP3T3 cells and have no Ca++-sensitive restriction point. Therefore, 3T3 and BP3T3 cells have retained the capacity to sense intracellular Ca++-pool sizes and to arrest in G1 at subthreshold cellular Ca++-levels.
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