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  • Articles  (103)
  • Polymer and Materials Science  (67)
  • Models, Molecular  (31)
  • Protein Conformation  (23)
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  • Articles  (103)
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  • 1
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    Gating machinery of InsP3R channels revealed by electron cryomicroscopy (2015)
    Nature Publishing Group (NPG)
    Details
    Publication Date: 2015-10-13
    Description: Inositol-1,4,5-trisphosphate receptors (InsP3Rs) are ubiquitous ion channels responsible for cytosolic Ca(2+) signalling and essential for a broad array of cellular processes ranging from contraction to secretion, and from proliferation to cell death. Despite decades of research on InsP3Rs, a mechanistic understanding of their structure-function relationship is lacking. Here we present the first, to our knowledge, near-atomic (4.7 A) resolution electron cryomicroscopy structure of the tetrameric mammalian type 1 InsP3R channel in its apo-state. At this resolution, we are able to trace unambiguously approximately 85% of the protein backbone, allowing us to identify the structural elements involved in gating and modulation of this 1.3-megadalton channel. Although the central Ca(2+)-conduction pathway is similar to other ion channels, including the closely related ryanodine receptor, the cytosolic carboxy termini are uniquely arranged in a left-handed alpha-helical bundle, directly interacting with the amino-terminal domains of adjacent subunits. This configuration suggests a molecular mechanism for allosteric regulation of channel gating by intracellular signals.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Fan, Guizhen -- Baker, Matthew L -- Wang, Zhao -- Baker, Mariah R -- Sinyagovskiy, Pavel A -- Chiu, Wah -- Ludtke, Steven J -- Serysheva, Irina I -- P41 GM103832/GM/NIGMS NIH HHS/ -- P41GM103832/GM/NIGMS NIH HHS/ -- R01 GM072804/GM/NIGMS NIH HHS/ -- R01 GM079429/GM/NIGMS NIH HHS/ -- R01 GM080139/GM/NIGMS NIH HHS/ -- R01GM072804/GM/NIGMS NIH HHS/ -- R01GM079429/GM/NIGMS NIH HHS/ -- R01GM080139/GM/NIGMS NIH HHS/ -- R21 AR063255/AR/NIAMS NIH HHS/ -- R21 GM100229/GM/NIGMS NIH HHS/ -- R21AR063255/AR/NIAMS NIH HHS/ -- R21GM100229/GM/NIGMS NIH HHS/ -- S10 OD016279/OD/NIH HHS/ -- S10OD016279/OD/NIH HHS/ -- England -- Nature. 2015 Nov 19;527(7578):336-41. doi: 10.1038/nature15249. Epub 2015 Oct 12.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Biochemistry and Molecular Biology, Structural Biology Imaging Center, The University of Texas Medical School at Houston, 6431 Fannin Street, Houston, Texas 77030, USA. ; National Center for Macromolecular Imaging, Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, One Baylor Plaza, Houston, Texas 77030, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/26458101" target="_blank"〉PubMed〈/a〉
    Keywords: Allosteric Regulation ; Animals ; Apoproteins/chemistry/metabolism/ultrastructure ; Calcium/metabolism ; Calcium Signaling ; *Cryoelectron Microscopy ; Cytosol/chemistry/metabolism ; Inositol 1,4,5-Trisphosphate Receptors/chemistry/*metabolism/*ultrastructure ; Ion Channel Gating ; Models, Molecular ; Protein Folding ; Protein Structure, Quaternary ; Protein Structure, Secondary ; Protein Structure, Tertiary ; Protein Subunits/chemistry/metabolism ; Rats ; Ryanodine Receptor Calcium Release Channel/chemistry/metabolism
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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  • 2
    Electronic Resource
    Electronic Resource
    Effect of reaction conditions on the grafting of 2-(dimethylamino)ethyl methacrylate onto hydrocarbon substrates (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 1691-1702 
    Details
    ISSN: 0887-624X
    Keywords: grafting ; basic functionalization ; free radical polymerization ; methacrylate ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The grafting of 2-(dimethylamino)ethyl methacrylate (DMAEMA) onto two model hydrocarbons, squalane and n-eicosane, and to linear low density polyethylene (LLDPE) has been investigated. The results of the study indicate that a high reaction temperature, 160°C, and a low concentration of monomer, less than 0.3 M, are optimum conditions for the grafting reaction. Reaction products, which consisted of grafted hydrocarbons and poly(DMAEMA), were separated by solvent extraction and vacuum distillation; samples were then analyzed by NMR and FTIR spectroscopy and size exclusion chromatography. 1H-NMR spectroscopy indicates that grafted squalane contained approximately 6 DMAEMA units per squalane residue. 1H- and 13C-NMR and molecular weight studies strongly suggest that the grafts onto the model hydrocarbons consist of single DMAEMA units. Results of the melt grafting of DMAEMA onto LLDPE show that the grafting efficiency and degree of grafting are substantially lower than were expected from the model system. © 1994 John Wiley & Sons, Inc.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1994.080320911
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  • 3
    Electronic Resource
    Electronic Resource
    Kinetics and mechanism of the grafting of 2-(dimethylamino)ethyl methacrylate onto hydrocarbon substrates (1995)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 33 (1995), S. 633-642 
    Details
    ISSN: 0887-624X
    Keywords: free radicals ; grafting ; kinetics ; methacrylate ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The kinetics of grafting a basic monomer, 2-(dimethylamino)-ethyl methacrylate (DMAEMA) to hydrocarbon substrates have been investigated. These systems were chosen as models for the grafting of a homopolymerizable monomer to polyolefins such as polyethylene. The reactions with squalane and n-eicosane were initiated by an organic peroxide, 2,5-dimethyl 2,5 dit-butylperoxy)-3-hexyne; grafting yields become significant at high reaction temperatures and low monomer concentrations. In squalane, the order of reaction with respect to monomer increased from about 1.1 for 0.22-0.44M DMAEMA to almost 2 at 0.69M DMAEMA; the order with respect to initiator was 0.56. The overall activation energy in the 130-160°C temperature range was, however, surprisingly low, 42±5 kJ mol-1. When analytical data were used to separate the overall rate into those for grafting and homopolymerization, different kinetic paths were observed for the competing reactions. These results are interpreted in terms of two different mechanisms; intramolecular chain transfer plays an important role in grafting, while depropagation becomes a major factor in homopolymerization at temperatures above 150°C. © 1995 John Wiley & Sons, Inc.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1995.080330405
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  • 4
    Electronic Resource
    Electronic Resource
    Peroxide-initiated vinylsilane grafting: Structural studies on a hydrocarbon substrate (1997)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 35 (1997), S. 3517-3525 
    Details
    ISSN: 0887-624X
    Keywords: peroxide ; vinylsilane ; grafting ; polymers ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The peroxide-initiated grafting of vinyltrimethoxysilane (VTMS) onto dodecane has been examined as a model for grafting onto polyethylene. At 160°C, 2% v/v VTMS and 0.08% v/v initiator, the monomer was grafted onto dodecane with a 59% conversion and an average of 2.37 VTMS grafts per dodecane. These values were obtained by separation of the grafted material through reduced pressure distillation then characterization with FTIR and NMR spectroscopy, mass spectrometry, and gel permeation chromatography. NMR studies strongly indicate that the multiple grafts consist predominantly of multiple single grafts rather than homopolymer grafts. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3517-3525, 1997
    Additional Material: 4 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    Aminolysis kinetics of model and polymer-bound anhydride moieties in low- and high-viscosity media (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 1573-1582 
    Details
    ISSN: 0887-624X
    Keywords: amic acid ; secondary amine ; maleic anhydride ; melt reaction kinetics ; model compounds ; polymer-bound functional groups ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This study examines the legitimacy of using the reaction kinetics of low molecular weight model compounds in solution to predict the chemical kinetics of polymer-bound species in a homogeneous melt. The reaction under study takes place between an aliphatic secondary amine, diisooctadecylamine (DiOA), and a 5-membered anhydride ring, saturated maleic anhydride (MA), forming an amic acid product. The MA species was present as a pendant graft on either a model compound, dodecane-g-(maleic anhydride) (dodecane-g-MA), or a polymer chain, linear low-density polyethylene-g-(maleic anhydride) (LLDPE-g-MA). Pseudo-second-order kinetics of the anhydride consumption are followed by infrared spectroscopy, either in situ in dodecane solution or by scanning frozen film samples taken from a linear low-density polyethylene melt. It was found that the LLDPE-g-MA/DiOA system reacted at a slightly slower rate than the dodecane-g-MA/DiOA system in the low-viscosity solution at 140°C. In the melt, the dodecane-g-MA/DiOA system experienced a small decrease in the overall reaction rate compared to the same reaction carried out in dodecane. However, the LLDPE-g-MA/DiOA system underwent a 65% decrease in the observed second-order rate constant on going from a solution to the melt. To explain these phenomena, the effects of diffusion, miscibility, and chain entanglements in the melt are examined here. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1573-1582, 1998
    Additional Material: 3 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    A systematic nomenclature for cascade polymers (1993)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 31 (1993), S. 641-651 
    Details
    ISSN: 0887-624X
    Keywords: cascade polymers ; dendritic polymers ; arborols ; dendrimers ; starburst polymers ; nomenclature ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Cascade (dendritic) polymers are discrete, highly branched, monodisperse polymers that possess branching patterns described by a mathematical progression. A systematic nomenclature that accurately represents these molecules is described. © 1993 John Wiley & Sons, Inc.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1993.080310307
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  • 7
    Electronic Resource
    Electronic Resource
    Chemical reactions and reactivity of primary, secondary, and tertiary diamines with acid functionalized polymers (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 1589-1600 
    Details
    ISSN: 0887-624X
    Keywords: reactivity ; amines ; functional polymers ; anhydride ; carbonxylic acid ; crosslink ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reactive melt processing of different types of diamines with polyethylene containing carboxylic acid groups and polystyrene containing anhydride groups was carried out. The reactivity of primary, secondary, and tertiary diamines with these acid polymers was determined using various techniques. Molecular weight increases due to crosslinking were observed through (1) changes in the torque during the reactive processing, (2) decrease in melt flow indices, and (3) decrease in solubility of the reaction products. The chemical compositions of the reaction products were examined by Fourier transform infrared (FTIR) spectroscopy. Thermal analysis using differential scanning calorimetry (DSC) was carried out to determine the crystallization behavior, glass transition temperatures, and thermal stabilities of the reaction products. Results show that the primary amine is the most reactive towards carboxylic acid or anhydride groups followed by the secondary and then the tertiary amine. Anhydride groups on polymers are of higher activity towards secondary or primary amino groups than carboxylic acid groups in the nucleophilic acyl substitution reactions. Reaction products crosslinked with the primary diamine are less stable than their parent acidic polymers. On the other hand, crosslinking with the secondary or tertiary diamine gives products with higher thermal stability than the parent acidic polymers. The formation of reversible and irreversible crosslinks with different types of diamines is also reported. © 1992 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1992.080300811
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  • 8
    Electronic Resource
    Electronic Resource
    Functionalization of polyethylenes and their use in reactive blending (1990)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 41 (1990), S. 2285-2300 
    Details
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The grafting of maleic anhydride (MAn) to low density polyethylenes (PEs) dissolved in 1,2-dichlorobenzene (DCB) has been studied. Grafting was successful at temperatures of about 160°C both in air without initiator and under nitrogen with the radical initiator 2,5-di(t-butylperoxy)-2,5-dimethyl-3-hexyne (LPO). The presence of succinic anhydride grafts was shown by FTIR spectroscopy of the product; 1H-NMR spectroscopy indicates that the grafts consist of single succinic anhydride units. The graft content was determined by nonaqueous titration, and the extent of crosslinking inferred from the melt flow rates (MFR) of the products. The effects of concentration of initiator, MAn, and PE on the graft content were determined; the influence of PE structure, reaction time, and temperature was also studied. Melt blending of the grafted PE with polystyrene containing oxazoline functional groups (OPS) was investigated using a Rheomix mixer. The interpolymer reaction which occurs during blending was studied by means of FTIR, and the morphology of the blends by scanning electron microscopy (SEM). Information was also gained from the change in torque viscosity during the blending process.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1990.070410931
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  • 9
    Electronic Resource
    Electronic Resource
    In situ compatibilization of polystyrene/polyethylene blends using amino-methacrylate-grafted polyethylene (1992)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 44 (1992), S. 2167-2177 
    Details
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Blends of a styrene-maleic anhydride copolymer (SMA) with polyethlene (PE) or polyethylene melt grafted with tertiary (PE-g-DMAEMA) or secondary (PE-g-tBAEMA) amino methacrylate were prepared by blending in a batch melt mixer. The morphology of these blends at various compositions was examined with a scanning electron microscope (SEM) and related to their tensile and impact properties. The SMA/PE blends are found to have the typical coarse morphology of incompatible blends and poor mechanical properties, while their reactive conterparts, SMA/PE-g-DMAEMA or SMA/PE-g-tBAEMA blends, show finer morphology and modestly improved tensile and impact strength. This was attributed to chemical interaction of the acidic anhydride and the basic amino groups. The greater improvement in morphology for SMA/PE-g-tBAEMA than for SMA/PE-g-DMAEMA suggests a stronger interaction between the secondary amino groups and the anhydride groups, possibly with the formation of SMA-g-tBAEMA-g-PE graft polymer through amide covalent bonds. The amide formation appears to occur at the interfacial region in the blends and is too little to be detected by Fourier transform infrared (FTIR) spectra. However, differential scanning calorimeters (DSC) and the viscosity measurements indicate crystallinity and molecular weight changes for the SMA/PE-g-tBAEMA blends, supporting an argument for the formation of SMA-g-tBAEMA-g-PE grafts at the phase interface.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1992.070441213
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  • 10
    Electronic Resource
    Electronic Resource
    Polymer encapsulation of arsenic-containing waste (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 58 (1995), S. 2039-2046 
    Details
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The potential for encapsulation of arsenic waste by combination with two commodity polymers was evaluated. Initial studies employed nontoxic substitutes, these being gypsum and calcium carbonate, with host polymers being predominately a recycled grade of polyethylene (PE) and a synthetic elastomer. The latter was used at low processing temperatures with rather volatile arsenic compounds. The gypsum caused processing difficulties due to evolved water, but the CaCO3 was able to be readily combined at high volumes. Arsenic trioxide was able to be incorporated at modest levels in PE and was less successfully combined with the rubber. However, the higher processing temperatures needed for PE caused the As2O3 to sublime. Less volatile calcium arsenite, readily prepared from As2O3, was able to be mixed at high volume ratios with the rubber, although processing with PE was less successful. These results may be used in conjunction with other methods for stabilization and would be applicable to other forms of medium- to high-level waste. © 1995 John Wiley & Sons, Inc.
    Additional Material: 18 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1995.070581115
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