28 research outputs found

    Surface-Attached Poly(glycidyl methacrylate) as a Versatile Platform for Creating Dual-Functional Polymer Brushes

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    Novel types of dual-functional surface-attached polymer brushes were developed by post-polymerization modification of poly­(glycidyl methacrylate) brushes on glassy carbon substrates. Azide and alcohol groups were initially introduced by epoxide ring-openings of the side chains. These polymer brushes represent an attractive chemical platform to deliberately introduce other molecular units at specific sites. In this work, ferrocene and nitrobenzene redox units were immobilized through the two groups to create redox polymers. In-depth analysis by infrared reflection–absorption spectroscopy and X-ray photoelectron spectroscopy revealed an almost quantitative conversion of the modification reactions. The electrochemical activity of the ferrocenyl part of this diode-like system was fully expressed with an electron transfer rate constant = 1.2 s<sup>–1</sup> and surface density = 0.19 nmol cm<sup>–2</sup> per nm section of the film, independent of its thickness. In contrast, for the nitrobenzene moieties diffusion of counterions (i.e., tetraalkylammonium) easily becomes the rate-controlling step, thereby leaving a substantial fraction of them electrochemically inactive

    Patterned Carboxylation of Graphene Using Scanning Electrochemical Microscopy

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    A simple, direct, and versatile scanning electrochemical microscopy (SECM) approach for local carboxylation of multilayered graphene on nickel is demonstrated, in which carbon dioxide serves as the carboxylation agent under reductive conditions in <i>N</i>,<i>N</i>-dimethylformamide. The use of SECM gives control over both the spatial dimensions and the degree of carboxylation. While the pattern size, in general, is governed by the dimension of the SECM tip, the degree of modification, expressed as the surface coverage of carboxylate groups introduced at the graphene substrate, is found to be controlled by the electrolysis time. This is supported by electrochemical measurements, two-dimensional X-ray photoelectron spectroscopy, Raman spectroscopy mapping, and He ion microscopy. Surprisingly, intercalation of the supporting electrolyte in the multilayered graphene on nickel occurs to a relatively small extent when compared to corresponding results obtained in previously described carboxylations of this kind of multilayered graphene

    Effects of DEX on the mRNA expression of <i>NeuroD1</i>, <i>Pan1</i> (<i>E47</i>), and <i>Rb</i> in AtT20 cells.

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    <p>(A) Dose-dependent effect of DEX on <i>NeuroD1</i> mRNA expression. AtT20 cells were treated with DEX (1 nM, 10 nM, or 100 nM) or 0.1% ethanol (vehicle control) for 24 hrs. Results are expressed as percentages of control (100%). Each point represents mean ± SEM (n = 4). ***<i>P</i><0.001 vs control. This experiment was also repeated three times with separate batches of cell preparation with consistent results. (B) Time-dependent effect of DEX on <i>NeuroD1</i> mRNA expression. AtT20 cells were treated with DEX (100 nM) for 1 hr, 3 hrs, 6 hrs, 9 hrs, or 24 hrs. Vehicle control: 0.1% ethanol. Results are expressed as percentages of control (100%). Each point represents mean ± SEM (n = 4). ***<i>P</i><0.001 vs control. (C) Dose-dependent effect of DEX on <i>Pan1</i> (<i>E47</i>) mRNA expression. AtT20 cells were treated with DEX (1 nM, 10 nM, or 100 nM) or 0.1% ethanol (vehicle control) for 24 hrs. Results are expressed as percentages of control (100%). NS denotes “Not Significant.” This experiment was also repeated three times with separate batches of cell preparation with consistent results. (D) Time-dependent effect of DEX on <i>Pan1</i> (<i>E47</i>) mRNA expression. AtT20 cells were treated with DEX (100 nM) for 1 hr, 3 hrs, 6 hrs, 9 hrs, or 24 hrs. Vehicle control: 0.1% ethanol. Results are expressed as percentages of each control (100%). NS denotes “Not Significant.” (E) Dose-dependent effect of DEX on <i>Rb</i> mRNA expression. AtT20 cells were treated with DEX (1 nM, 10 nM, or 100 nM) or 0.1% ethanol (vehicle control) for 24 hrs. Results are expressed as percentages of control (100%). NS denotes “Not Significant.” (F) Time-dependent effect of DEX on <i>Rb</i> mRNA expression. AtT20 cells were treated with DEX (100 nM) for 1 hr, 3 hrs, 6 hrs, 9 hrs, or 24 hrs. Vehicle control: 0.1% ethanol. Results are expressed as percentages of control (100%). NS denotes “Not Significant.”</p

    Superhydrophilic Polyelectrolyte Brush Layers with Imparted Anti-Icing Properties: Effect of Counter ions

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    This work demonstrates the feasibility of superhydrophilic polyelectrolyte brush coatings for anti-icing applications. Five different types of ionic and nonionic polymer brush coatings of 25–100 nm thickness were formed on glass substrates using silane chemistry for surface premodification followed by polymerization via the SI-ATRP route. The cationic [2-(methacryloyloxy)­ethyl]­trimethylammonium chloride] and the anionic [poly­(3-sulfopropyl methacrylate), poly­(sodium methacrylate)] polyelectrolyte brushes were further exchanged with H<sup>+</sup>, Li<sup>+</sup>, Na<sup>+</sup>, K<sup>+</sup>, Ag<sup>+</sup>, Ca<sup>2+</sup>, La<sup>3+</sup>, C<sub>16</sub>N<sup>+</sup>, F<sup>–</sup>, Cl<sup>–</sup>, BF<sub>4</sub><sup>–</sup>, SO<sub>4</sub><sup>2–</sup>, and C<sub>12</sub>SO<sub>3</sub><sup>–</sup> ions. By consecutive measurements of the strength of ice adhesion toward ion-incorporated polymer brushes on glass it was found that Li<sup>+</sup> ions reduce ice adhesion by 40% at −18 °C and 70% at −10 °C. Ag<sup>+</sup> ions reduce ice adhesion by 80% at −10 °C relative to unmodified glass. In general, superhydrophilic polyelectrolyte brushes exhibit better anti-icing property at −10 °C compared to partially hydrophobic brushes such as poly­(methyl methacrylate) and surfactant exchanged polyelectrolyte brushes. The data are interpreted using the concept of a quasi liquid layer (QLL) that is enhanced in the presence of highly hydrated ions at the interface. It is suggested that the ability of ions to coordinate water is directly related to the efficiency of a given anti-icing coating based on the polyelectrolyte brush concept

    Effects of DEX on the mRNA expression of <i>Tpit</i>, <i>Pitx1</i>, <i>Nur77</i> and <i>Nurr1</i> in AtT20 cells.

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    <p>(A) Time-dependent effect of DEX on <i>Tpit</i> mRNA expression. AtT20 cells were treated with DEX (100 nM) for 1 hr, 3 hrs, 6 hrs, 9 hrs, or 24 hrs. Vehicle control: 0.1% ethanol. Results are expressed as percentages of control (100%). Each point represents mean ± SEM (n = 4). NS denotes “Not Significant.” Two independent experiments were performed with consistent results. (B) Time-dependent effect of DEX on <i>Pitx1</i> mRNA expression. AtT20 cells were treated with DEX (100 nM) for 1 hr, 3 hrs, 6 hrs, 9 hrs, or 24 hrs. Vehicle control: 0.1% ethanol. Results are expressed as percentages of each control (100%). NS denotes “Not Significant.” Two independent experiments were performed with consistent results. (C) Time-dependent effect of DEX on <i>Nur77</i> mRNA expression. AtT20 cells were treated with DEX (100 nM) for 1 hr, 3 hrs, 6 hrs, 9 hrs, or 24 hrs. Vehicle control: 0.1% ethanol. Results are expressed as percentages of control (100%). NS denotes “Not Significant.” Two independent experiments were performed with consistent results. (D) Time-dependent effect of DEX on <i>Nurr1</i> mRNA expression. AtT20 cells were treated with DEX (100 nM) for 1 hr, 3 hrs, 6 hrs, 9 hrs, or 24 hrs. Vehicle control: 0.1% ethanol. Results are expressed as percentages of control (100%). Each point represents mean ± SEM (n = 4). NS denotes “Not Significant.” ***<i>P</i><0.001 vs control. Two independent experiments were performed with consistent results.</p

    Effects of DEX on <i>Pomc</i> mRNA expression in AtT20 cells.

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    <p>(A) Dose-dependent effect of DEX on <i>Pomc</i> mRNA expression. AtT20 cells were treated with DEX (1 nM, 10 nM, or 100 nM) or 0.1% ethanol (vehicle control) for 24 hrs. Results are expressed as percentages of control (100%). Data represents mean ± SEM (n = 4). ***<i>P</i><0.001 vs control. This experiment was repeated three times with separate batches of cell preparation with consistent results. (B) Time-dependent effect of DEX on <i>Pomc</i> mRNA expression. AtT20 cells were treated with 100 nM DEX for 1 hr, 3 hrs, 6 hrs, 9 hrs, or 24 hrs. Vehicle control: 0.1% ethanol. Results are expressed as percentages of control (100%). Each point represents mean ± SEM (n = 4). NS denotes “Not Significant.” ***<i>P</i><0.001 vs control. This experiment was also repeated three times with separate batches of cell preparation with consistent results.</p

    Effects of DEX on <i>Pomc</i> mRNA expression in primary culture cells of rat anterior pituitary.

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    <p>(A) Time-dependent effect of DEX on rat <i>Pomc</i> mRNA expression. Untreated rat anterior pituitary primary culture cells were expressed as percentages of control (100%). The cells were treated with 100 nM DEX or 0.1% ethanol (Vehicle control) for 1 hr, 3 hrs, 6 hrs, or 24 hrs. Each point represents mean ± SEM (n = 4). *<i>P</i><0.05 vs control. NS denotes “Not Significant.” This experiment was repeated two times with separate batches of cell preparation with consistent results. (B) Time-dependent effect of DEX on rat <i>Pomc</i> mRNA expression. Untreated rat anterior pituitary primary culture cells were expressed as percentages of control (100%). The cells were treated with 1 μM DEX or 0.1% ethanol (Vehicle control) for 1 hr, 3 hrs, 6 hrs, or 24 hrs. Each point represents mean ± SEM (n = 4). NS denotes “Not Significant.”</p

    Effects of DEX on interaction between NeuroD1 and E-box on <i>Pomc</i> promoter in AtT20 cells.

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    <p>(A) Effect of of DEX on interaction between NeuroD1 and E-box on <i>Pomc</i> promoter examined by ChIP assay using E-box primer. ChIP assay was performed using digested chromatin extracted from the cells cultured in the presence (100 nM) or absence (control) of DEX for 30 min (B), 60 min (C), or 24 hrs (D). Chromatin fragments were immunoprecipitated either by normal rabbit IgG (negative control) or NeuroD1 antibody. Purified DNA was analyzed by qPCR using primers specific for E-box containing sequence on <i>Pomc</i> promoter. The expected size of E-box is 196 bp. Few qPCR products observed in the input samples were detected in the immunoprecipitation using normal IgG. Immunoprecipitated DNA was quantified by qPCR and normalized to the values obtained after amplification of unprecipitated 1% input DNA. Each point represents mean ± SEM (n = 3). **P<0.01, significantly different from the level of control group. These experiments were repeated three times with separate batches of cell preparation with consistent results.</p

    Effects of NeuroD1 overexpression on <i>Pomc</i> mRNA expression and <i>Pomc</i> promoter activity in AtT20 cells.

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    <p>(A) Effect of NeuroD1 overexpression on the DEX-mediated <i>Pomc</i> mRNA decrease. AtT20 cells were transiently transfected with pcDNA3 and NeuroD1 plasmid (volume adjusted to 300 ng each with pcDNA3 empty vector) and incubated either in the presence (100 nM) or absence (control) of DEX for 24 hrs. Results are expressed as percentages of each control (100%). Each point represents mean ± SEM (n = 4). ***<i>P</i><0.001 vs control. NS denotes “Not Significant.” Two independent experiments were performed with consistent results. (B) Effect of Pan1 overexpression on the DEX-mediated <i>Pomc</i> mRNA decrease. AtT20 cells were transiently transfected with pcDNA3 and Pan1 plasmid (volume adjusted to 300 ng each with pcDNA3, empty vector) and incubated either in the presence (100 nM) or absence (control) of DEX for 24 hrs. Results are expressed as percentages of each control (100%). Each point represents mean ± SEM (n = 4). ***<i>P</i><0.001 vs control. Two independent experiments were performed with consistent results. (C) Effect of overexpression of NeuroD1 on the DEX-mediated suppression of <i>Pomc</i> promoter activity. AtT20 cells were transiently transfected with pcDNA3 and NeuroD1 plasmid (volume adjusted to 300 ng each with pcDNA3 empty vector), 135 ng r<i>Pomc</i>-Luc, and 65 ng pRSV-β-gal were incubated either in the presence (100 nM) or absence (control) of DEX for 24 hrs before the luciferase assay. Results are expressed as percentages of each control (100%). Each point represents mean ± SEM (n = 4). ***<i>P</i><0.001 vs control. NS denotes “Not Significant.” Two independent experiments were performed with consistent results.</p
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