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  • Polymer and Materials Science  (67)
  • METEOROLOGY AND CLIMATOLOGY  (60)
  • Models, Molecular  (31)
  • 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
    Grafting of 2-(dimethylamino)ethyl methacrylate on linear low density polyethylene in the melt (1990)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 181 (1990), S. 1-22 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Das Pfropfen von 2-(Dimethylamino)ethyl methacrylat (DMAEMA) auf lineares Polyethylen niedriger Dichte (LLDPE) in der Schmelze wurde mittels Messungen des Monomerumsatzes, des Pfropfgrades und der Pfropfeffizienz untersucht. Die Ergebnisse zeigen, daß das Pfropfen von DMAEMA auf LLDPE bereits bei niedrigen Temperaturen von etwa 90°C in der Schmelze durchgeführt werden kann, obwohl der Schmelzpunkt von LLDPE bei etwa 120°C liegt. Wenn die Pfropfreaktion bei zu hohen oder zu niedrigen Temperaturen durchgeführt wird, kann nur ein sehr niedriger Pfropfgrad beobachtet werden. Hohe Reaktionstemperaturen begünstigen die Polymervernetzung, was sich im Absinken des Schmelzindex bemerkbar macht. Die meisten Pfropfvorgänge werden während der Anfangsphase der Reaktion (unter den vorliegenden Bedingungen während der ersten 3 min) beobachtet. Eine Verlängerung der Reaktionsdauer über diesen Zeitraum hinaus führt zu verstärkter Vernetzung und erhöhter Produktion des Homopolymeren, was die Effizienz des Prozesses verringert. Organische Peroxide sind über einen weiten Halbwertszeitenbereich effektive Initiatoren der Pfropfreaktion, während Azoinitiatoren keine Pfropfung bewirken.
    Notes: Grafting of 2-(dimethylamino)ethyl methacrylate (DMAEMA) on linear low density polyethylene (LLDPE) in the melt has been studied through measurements of monomer conversion, the degree of grafting and the grafting efficiency. Results show that the grafting of DMAEMA on LLDPE can be carried out in the melt at temperatures as low as 90°C even though the melting point of the LLDPE is as high as 120°C. When the grafting reaction is carried out at too low or too high temperature, a low degree of grafting is observed. High reaction temperature favoured crosslinking of the polymer as indicated by decreasing melt flow index. Most of the grafts were obtained during the early period of the reaction (before 3 min under the reaction conditions used). Further increase in reaction time increased crosslinking and also produced more homopolymer, thus decreasing the grafting efficiency. Organic peroxides are effective initiators for the grafting reaction over a broad range of half-lives while azo initiators do not produce grafting.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1990.051810101
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  • 3
    Electronic Resource
    Electronic Resource
    Hysteresis in the glucose permeability versus pH characteristic for a responsive hydrogel membrane (1996)
    Weinheim : Wiley-Blackwell
    Macromolecular Rapid Communications 17 (1996), S. 409-415 
    Details
    ISSN: 1022-1336
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A side-by-side diffusion cell was used to study the permeability of glucose through a temperature- and pH-sensitive poly(N-isopropylacrylamide-co-methacrylic acid) hydrogel membrane. At fixed temperature (37°C), lowering pH in one side of the cell induced hydrogel volume collapse and strongly attenuated glucose permeation across the membrane. Hysteresis was observed in the glucose permeability versus pH characteristic.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/marc.1996.030170607
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  • 4
    Electronic Resource
    Electronic Resource
    Determination of Molecular Weight of High Polymers by Measurement of Osmotic Pressures at Low Concentrations (1951)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Polymer Science 6 (1951), S. 585-600 
    Details
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: An equilibrium osmometer for the measurement of very low osmotic pressures has been designed. It is constructed of metal and employs a large horizontal membrane. A rapid approach to equilibrium is obtained by the use of a fine capillary and a bacterial cellulose membrane (Masson and Melville) in conjunction with complete thermostatting. To avoid displacement, the membrane is stretched in a frame and held over a grooved domed support of the Carter-Record type. Details of procedure, including concentration estimation and the preparation of membranes, are given.Measurements of the osmotic pressure of a fractionated sample of polystyrene, of molecular weight approximately one million, have served to determine the precision of the osmometer. At a pressure of 0.026 cm. of chloroform, the standard deviation was found to be 0.002 cm. The importance of correcting for the density of the solution, when measuring high molecular weights, is discussed.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1951.120060508
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  • 5
    Electronic Resource
    Electronic Resource
    Formation and properties of polymer carbon (1955)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Polymer Science 16 (1955), S. 101-120 
    Details
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Divinylbenzene (48%)/ethylvinylbenzene copolymer was converted to a series of pyrolytic derivatives. Enough of the carbon bond network remained intact throughout thermal rearrangement and condensation to retain the original gross shape of the copolymer in the final polymer carbon. Although a carbon residue (6% by weight) was obtained by direct heating of the copolymer, yields were increased eightfold by preoxidation or prechlorination. Such an alteration of thermal degradation is obviously a complex process involving both “inhibition,” in the ordinary sense, and a considerable contribution toward an increased valence network density. As a consequence, the average molecular weight of volatile fragments evolved during carbonization is inversely proportional to the oxygen content of the original hydrocarbon polymer. Pyrolysis of divinylbenzene copolymer, containing 18% oxygen, resulted in a 50% volume shrinkage, 50% weight loss, and a 100% density gain. Unless these data are attributable to extensive microporosity, it is difficult to account for the sorption of up to 3 cc. of helium gas per gram of polymer carbon at 30°C. and 600 mm. pressure; and calculated surface areas as large as 1400 sq.m./g. Abrupt changes in the progress of polymer carbon formation occurred between 600 and 700°C. The residue became rigid; vigorous evolution of volatile products, principally hydrogen, suddenly diminished; and paramagnetic resonance absorption (unpaired electron concentration) dropped about tenfold while d.c. resistivity decreased 106 ohm cm. In this region, also, x-ray patterns were most diffuse, exhibiting no maxima characteristic of carbon scattering in either hydrocarbons or condensed rings. Finally, the x-ray patterns of polymer carbon intermediates became less diffuse in samples prepared at 700°C. or above. Yet, scattering indicated the presence of crosslinked graphitic layers of such stability that reordering or true graphitization did not occur at 2400°C.
    Additional Material: 18 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1955.120168202
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  • 6
    Electronic Resource
    Electronic Resource
    Etching of polyethylene terephthalate (1962)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Polymer Science 57 (1962), S. 993-1007 
    Details
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A degradative etching technique has been employed with polyethylene terephthalate films to demonstrate the existence of several different structures, the size of which vary from hundreds of microns to hundreds of Angstroms. The micron-sized structures are a function of the processing and orientation of the film and occur in regular geometric patterns. Thus, parallel stretch-direction lines are etched into one-way stretched film, the number of lines being dependent upon film history. Etched, two-way stretched films reveal a lamellate composition, each layer possessing a brick wall-like structure. This general structural pattern has been found in other types of film by similar methods. Examination of the etched areas by electron microscopy demonstrates that the micron-sized blocks are composed of spheres, 700 A. in diameter, which are aligned over moderate distances.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1962.1205716577
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  • 7
    Electronic Resource
    Electronic Resource
    Mechanical properties of discrete polymer moleculesPresented at the International Congress of Pure and Applied Chemistry, September, 1951. (1952)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Polymer Science 8 (1952), S. 129-155 
    Details
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A frequency-dependent stiffness μB was found from the action of high frequency shear waves on dilute solutions of polyisobutylene, polypropylene, polyethylene, polystyrene, hevea rubber, and polybutadiene microgel. A dynamic viscosity associated with streaming of solvent through the molecular coil, ηB, dropped far more rapidly with rising temperature than solvent viscosity, denoting that it, too, reflected configurational changes. (The μB for polyisobutylene in solution declined moderately with rising temperature, corresponding to an exponential coefficient of 2.3 kcal.) This behavior suggested three chief mechanisms for deformation of isolated chains: (1) viscoelastic configuration changes (W. Kuhn's “macroconstellation changes”) with contribution to rigidity per average molecule per cubic centimeter of solution of 〈 μ2 〉 or force constant 〈 f2 〉; (2) temporary entanglements of interpenetrating segments in the chain coil (like the interchain entanglements in concentrated solutions of J. D. Ferry), with contribution to rigidity 〈 μ3 〉; and (3) restrictions to rotational flexibility around chain linkages, with rigidity contribution 〈 μ4 〉. Arrangement of these processes in parallel with solvent viscosity yielded frequency-independent constants in agreement with the limited data so far obtained in the 103 to 108 cycle range.Such a model gave molecular mechanical constants correlating roughly with chemical structures. For polyisobutylene, force constants per average molecule were 〈 f2 〉 = 17.1 × 10-13 dyne cm., 〈 f3 〉 = 6.3 × 10-12 and 〈 f4 〉 = 1.6 × 10-10. Lower molecular weight (1.2 × 106 vs. 3.9 × 106) gave slightly lower values. 〈 f4 〉 represents restrictions to rotation per isobutylene residue in the chain of 2.3 × 10-15, or about 104 less than valence bond infrared vibrational or twisting force constants for hydrocarbons. The combined average chain rigidities expressed by the force constant 〈 fB 〉, at 20 kc. and 25°C. were, for polyisobutylene of M̄V ∼ 106, 1.8 × 10-12; hevea rubber of M̄V = 2.3 × 105, 1.5 × 10-15; polystyrene of M̄V = 2.3 × 105, 4.5 × 10-16. Hence, single polystyrene chains are quite flexible, but polybutadiene microgel has 〈 fB 〉 = 5.2 × 10-11, for M̄W ∼ 18 × 106, showing effect of internal cross-linking.“Poor” solvents (“solvent power” μ 〉 0) caused chain rigidity of polyisobutylene and polystyrene to decrease, compared to good solvents (“solvent power” μ ∼ 0), and viscosity decreased also. Apparent decrease in 〈 fB 〉 apparently means external (solvent) “compression” of chain, and agrees with technological efficiency of poorly compatible plasticizers.Complete theory of effects has been outlined by Kirkwood, for a rod model. Great range of rigidities shown even by hydrocarbon chains (intrinsic rigidity of polyethylene soln., [μ] = 906 dynes/cm.2, of polypropylene soln., [μ] = 92 dynes/cm.2) has not yet been treated, however.
    Additional Material: 20 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1952.120080201
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  • 8
    Electronic Resource
    Electronic Resource
    Mechanical properties of discrete polymer molecules (1952)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Polymer Science 9 (1952), S. 170-170 
    Details
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1952.120090205
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  • 9
    Electronic Resource
    Electronic Resource
    A Study of the Chemical Bonding and Microstructure of Ion Beam-deposited CNx Films Including an XPS C 1s Peak Simulation (1997)
    Chichester [u.a.] : Wiley-Blackwell
    Surface and Interface Analysis 25 (1997), S. 629-642 
    Details
    ISSN: 0142-2421
    Keywords: XPS ; FTIR ; carbon nitride ; thin film ; simulation ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: The chemical bonding and microstructure of dual ion beam-deposited CNx films with nitrogen contents in the range 20-33 at.% have been examined by Fourier transform infrared spectroscopy (FTIR) and x-ray photoelectron spectroscopy (XPS). The FTIR spectra together with other published data have been used to construct a model microstructure of the CNx films. The XPS N 1s peak is composed of two components corresponding to N-sp2 C and N-sp3 C bonds. Using the quantified N 1s data and making certain assumptions, the model microstructure has been used as the basis of a C 1s peak simulation in which nine C components have been combined. At an N content of 20 at.% the simulation agrees well with the experimentally recorded XPS C 1s peak. The FTIR spectra, XPS N 1s peak shape and C 1s peak simulations support a microstructure of N substitution into an amorphous sp2/sp3 hybridized carbon structure. Above an N content of ∽20%, a new (nitrile-like) chemical form also emerges in the material, its abundance increasing with N content. It is proposed that this new structure occurs due to the presence, in the surface region of the condensing film, of C≡N dimers, which are formed when a C atom is surrounded by many N atoms. This molecule becomes trapped in the material and bonds to atoms at neighbouring sites. © 1997 by John Wiley & Sons, Ltd.
    Additional Material: 12 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    Auger electron spectroscopy studies on TiNx (1994)
    Chichester [u.a.] : Wiley-Blackwell
    Surface and Interface Analysis 22 (1994), S. 167-170 
    Details
    ISSN: 0142-2421
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: A new method for the determination of N/Ti ratio for TiNx samples has been proposed. High energy resolution Auger spectra recorded of the Ti L3M23M45 peak have shown that on nitridation of Ti to TiNx a second peak, labelled the L3M23Hybrid peak, emerges at 3.9 eV below the L3M23M45 peak in the raw data, which grows with the grade of nitridation. After a simple Shirley background correction a linear dependence between the ratio of the L3M23Hybrid/L3M23M45 peak height of the raw data and the N/Ti ratio was found. This relation can be used directly to evaluate the nitrogen content of an unknown TiNx compound by recording only the Ti L3M23M45 region. The changes of the L3M23M45 peak structure have been interpreted and compared with earlier DOS calculations for Ti and TiN. Good agreement between experiment and theory was found, enabling a discussion of the valence electronic structure changes for Ti on nitridation.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/sia.740220137
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