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- Heinzel, T., et al.
(författare)
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A complex containing N-CoR, mSin3 and histone deacetylase mediates transcriptional repression
- 1997
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Ingår i: Nature. - : Nature Publishing Group. - 0028-0836 .- 1476-4687. ; 387:6628, s. 43-48
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Tidskriftsartikel (refereegranskat)abstract
- Transcriptional repression by nuclear receptors has been correlated to binding of the putative co-repressor, N-CoR. A complex has been identified that contains N-CoR, the Mad presumptive co-repressor mSin3, and the histone deacetylase mRPD3, and which is required for both nuclear receptor- and Mad-dependent repression, but not for repression by transcription factors of the ets-domain family. These data predict that the ligand-induced switch of heterodimeric nuclear receptors from repressor to activator functions involves the exchange of complexes containing histone deacetylases with those that have histone acetylase activity.
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- Guo, J.-H., et al.
(författare)
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How the phenyle rings (benzene) act as building blocks in pi conjugated polymers
- 1998
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Ingår i: Advanced Light Source. - Berkeley : Ernest Orlando Lawrence Berkeley National Laboratory, University of California Berkeley, California, USA. ; , s. 129-132
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Organic conjugated polymers have the electronic structure of semiconductors and can be doped to become good conductors (1). Conjugated polymers are now used as active materials in a wide variety of prototype applications such as light emitting diodes [2] and organic transistors [3,4]. Most of the interesting chemistry and physics of conjugated polymers is associated with the details of the electronic structure at the valence and conduction band edges and, in this connection, various electron spectroscopies can be used as tools for diagnosis of the relevant electronic and geometric properties....
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- Guo, J.-H., et al.
(författare)
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Resonant and nonresonant x-ray scattering spectra of some poly(phenylenevinylene)s
- 1998
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 108:14, s. 5990-5996
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Tidskriftsartikel (refereegranskat)abstract
- The electronic structure of some poly(phenylenevinylene)s have been investigated by resonant and nonresonant x-ray inelastic scattering spectroscopies. The nonresonant as well as all resonant spectra for each polymer demonstrate benzene-like features, indicating a local character of the x-ray emission in which the phenyl ring acts as a building block. Theoretical simulations of x-ray energies and intensities taking the repeat unit as a model molecule of the polymer agree with the experimental spectra fairly well. The edges of the occupied bands have been identified in the nonresonant spectra of each polymer. By subtracting the emission energy of the highest occupied molecular orbital in the nonresonant spectrum from the core excitation energy in the resonant spectrum an alternative way to determine the optical band gap is obtained. As for free benzene the outer π band in the polymer spectra show a depletion of the emission going from the nonresonant to the resonant x-ray emission spectra. It is demonstrated that this transition, which is strictly symmetry forbidden for free benzene, becomes effectively forbidden in the polymer case as a result of strong interference effects, and it is argued that this is the general case for resonant x-ray emission of conjugated polymers as far as the frozen orbital approximation holds.
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- Liedberg, Bo, et al.
(författare)
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Self-assembly of alpha-functionalized terthiophenes on gold
- 1997
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Ingår i: JOURNAL OF PHYSICAL CHEMISTRY B. - : AMER CHEMICAL SOC. - 1089-5647 .- 1520-6106 .- 1520-5207. ; 101:31, s. 5951-5962
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Tidskriftsartikel (refereegranskat)abstract
- alpha-Functionalized terthiophenes containing disulfide (-S-T-3-H)(2) and alkanethiol (HS-(CH2)(11)-T-3-H) anchoring groups have been synthesized for direct immobilization onto gold. Monolayer structures of these compounds are prepared by spontaneous assembly from ethanol solutions on evaporated gold substrates and thoroughly characterized by ellipsometry, contact angle goniometry, infrared and X-ray photoelectron spectroscopy, and cyclic voltammetry. The two molecules coordinate to the gold substrate exclusively via the anchoring groups upon formation of gold-thiolate bonds. The kinetics of monolayer formation vary dramatically for the two compounds. The alkanethiol analogue assembles rapidly, within a few minutes, and forms a densely packed and highly organized monolayer, with the alkyl chains in an almost perfect all-trans conformation and the C-alpha-C-alpha axis of the alpha-T-3 units tilted about 14 degrees away from the surface normal. The assembly process is much slower for the disulfide, but an organized monolayer with an average alpha-T-3 chain tilt of about 33 degrees will eventually form when the assembly is allowed to equilibrate with a solution containing the disulfide for at least 1 day. Moreover, the two monolayer assemblies also display a remarkably different electrochemical, behavior. The heterogeneous electron-transfer rate at the disulfide-covered gold substrate is almost indistinguishable from that at bare gold, suggesting that the assembly contains a large number of easily accessible defects. An alternative mechanism for explaining the large electron-transfer rate involving electronic coupling via the conjugated pi-system of the alpha-T-3 units is also proposed. The electrochemical response is significantly reduced for the HS-(CH2)(11)-T-3-H assembly, but another type of defects, the so-called shallow defects originating from sparsely populated areas on the electrode surface, can be identified.
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- Liedberg, B, et al.
(författare)
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Self-assembly of alpha-functionalized terthiophenes on gold
- 1997
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Ingår i: JOURNAL OF PHYSICAL CHEMISTRY B. - : AMER CHEMICAL SOC. - 1089-5647. ; 101:31, s. 5951-5962
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- alpha-Functionalized terthiophenes containing disulfide (-S-T-3-H)(2) and alkanethiol (HS-(CH2)(11)-T-3-H) anchoring groups have been synthesized for direct immobilization onto gold. Monolayer structures of these compounds are prepared by spontaneous asse
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- Söderström, Mats, et al.
(författare)
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Differential effects of nuclear receptor corepressor (N-CoR) expression levels on retinoic acid receptor-mediated repression support the existence of dynamically regulated corepressor complexes
- 1997
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Ingår i: Molecular Endocrinology. - : The Endocrine Society. - 0888-8809 .- 1944-9917. ; 11:6, s. 682-692
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Tidskriftsartikel (refereegranskat)abstract
- Thyroid hormone and retinoic acid receptors are members of the nuclear receptor superfamily of ligand-dependent transcription factors that stimulate the transcription of target genes in the presence of activating ligands and repress transcription in their absence. Transcriptional repression by the thyroid hormone and retinoic acid receptors has been proposed to be mediated by the nuclear receptor corepressor, N-CoR, or the related factor, SMRT (silencing mediator of retinoic acid and thyroid hormone receptors). Recent studies have suggested that transcriptional repression by N-CoR involves a corepressor complex that also contains mSin3A/B and the histone deacetylase, RPD3. In this manuscript, we demonstrate that transcriptional repression by the retinoic acid receptor can be either positively or negatively regulated by changes in the levels of N-CoR expression, suggesting a relatively strict stoichiometric relationship between N-CoR and other components of the corepressor complex. Consistent with this interpretation, overexpression of several functionally defined domains of N-CoR also relieve repression by nuclear receptors. N-CoR is distributed throughout the nucleus in a nonuniform pattern, and a subpopulation becomes concentrated into several discrete dot structures when highly expressed. RPD3 is also widely distributed throughout the nucleus in a nonuniform pattern. Simultaneous imaging of RPD3 and N-CoR suggest that a subset of each of these proteins colocalize, consistent with the existence of coactivator complexes containing both proteins. In addition, a substantial fraction of both N-CoR and mSin3 A/B appear to be independently distributed. These observations suggest that interactions between RPD3 and Sin3/N-CoR complexes may be dynamically regulated.
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- Yang, Y-W, et al.
(författare)
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Association and phase behaviour of statistical and block copolymers of ethylene oxide and butylene oxide in water
- 1997
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Ingår i: Polymer. - 0032-3861 .- 1873-2291. ; 38, s. 1659-1668
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Tidskriftsartikel (refereegranskat)abstract
- Three copolymers of ethylene oxide (EO) and 1,2-butylene oxide (BO) were prepared by anionic polymerization to have similiar molar masses (Mn ≈ 7000 g mol-1), molar mass distributions (Mw/Mn<1.1) and compositions (80mol% oxythylene) but different chain structures. A triblock copolymer was prepared by sequential copolymerization of EO followed by BO, and two statistical copolymers were prepared from mixed monomers, either to low (15%) or to high (93%) conversion. The disparity in reactivity ratios in the EO/BO copolymerization resulted in pronounced composition drift along the chains of the high conversion statistical copolymer, giving it the character of a block copolymer. This composition profile was checked by 13C n.m.r. spectroscopy. The association behaviour of the statistical copolymers in aqueous solution at 25°C was studied by dynamic and static light scattering. The low conversion statistical copolymer remained in its molecular state across the concentration range studied (up to 100 g dm-3), but the high conversion statistical copolymer associated into molecular clusters and micelles. Cloud point curves were determined for solutions of the three copolymers. The effect of associations on phase behaviour is discussed.
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