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Contributors
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- By Mark S. Aloia, Ellemarije Altena, Peter Anderer, Christopher L. Asplund, Nitin Bangera, Jeroen S. Benjamins, Daniela Berg, Bohdan Bybel, Vincenza Castronovo, Suk-tak Chan, Michael W. L. Chee, Pietro Cortelli, Michael Czisch, Joseph T. Daley, Thien Thanh Dang-Vu, Yazmín de la Garza-Neme, Lourdes DelRosso, Derk-Jan Dijk, Maria Engström, Thorleif Etgen, Bruce J. Fisch, Ariane Foret, Patrice Fort, Steffen Gais, Anne Germain, Jana Godau, Andrew L. Goertzen, William A. Gomes, Ronald M. Harper, Seung Bong Hong, Romy Hoque, Scott A. Huettel, Yuichi Inoue, Alex Iranzo, Mathieu Jaspar, Zayd Jedidi, Alejandro Jiménez-Genchi, Eun Yeon Joo, Gerhard Klösch, Karsten Krakow, Rajesh Kumar, Caroline Kussé, Hans-Peter Landolt, Helmut Laufs, Jeffrey David Lewine, Camilo Libedinsky, Michael L. Lipton, Mordechai Lorberboym, Cheng Luo, Pierre-Hervé Luppi, Paul M. Macey, Pierre Maquet, Laura Mascetti, Christelle Meyer, Sarah Moens, Vincenzo Muto, Shadreck Mzengeza, Eric Nofzinger, Takashi Nomura, Daniela Perani, Jennifer R. Ramautar, Bernd Saletu, Michael T. Saletu, Gerda Saletu-Zyhlarz, Christina Schmidt, Monika Schönauer, Richard J. Schwab, Sophie Schwartz, Keivan Shifteh, Sanjib Sinha, Victor I. Spoormaker, Ryan P. J. Stocker, A. Jon Stoessl, Diederick Stoffers, A. B. Taly, Robert Joseph Thomas, Michael J. Thorpy, Emily Urry, Jason Valerio, Ysbrand D. Van Der Werf, Gilles Vandewalle, Hans P. A. Van Dongen, Eus J. W. Van Someren, Vinod Venkatraman, Frederic von Wegner, Thomas C. Wetter, Dezhong Yao
- Edited by Eric Nofzinger, University of Pittsburgh, Pierre Maquet, Université de Liège, Belgium, Michael J. Thorpy
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- Book:
- Neuroimaging of Sleep and Sleep Disorders
- Published online:
- 05 March 2013
- Print publication:
- 07 March 2013, pp viii-xii
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Age Determination of Carboniferous Basic Rocks of Shropshire and Colonsay
- W. D. Urry, Arthur Holmes
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- Journal:
- Geological Magazine / Volume 78 / Issue 1 / February 1941
- Published online by Cambridge University Press:
- 01 May 2009, pp. 45-61
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The helium method of determining the ages of fine-grained basic igneous rocks has now been so far developed as to be applicable to various geological and petrological problems, particularly where geological periods are involved, as in the problem here discussed. For details of the history of this development up to the beginning of 1937 reference may be made to Holmes, 1931; Urry, 1933; Lane and Urry, 1935; Urry, 1936 (b); Holmes and Paneth, 1936; and Holmes, 1937. During 1937 it was found that many of the helium-ratios on which the ‘helium’ time-scale had been based were too high, because of a previously unsuspected error in radium determination due to reliance having being placed on a radium standard which was seriously at fault. To clear up this embarrassing situation an immediate effort was made by several investigators in collaboration, and the first fruits of their work have recently become available (Evans, Goodman, Keevil, Lane, and Urry, 1939).
4 - Ideal Protein Elasticity: The Elastin Models
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- By D. W. Urry, T. Hugel, M. Seitz, H. Gaub, L. Sheiba, J. Dea, J. Xu, L. Hayes, F. Prochazka, T. Parker
- Edited by Peter R. Shewry, University of Bristol, Arthur S. Tatham, University of Bristol, Allen J. Bailey, University of Bristol
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- Book:
- Elastomeric Proteins
- Published online:
- 13 August 2009
- Print publication:
- 30 October 2003, pp 54-93
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Summary
INTRODUCTION
Definition of Ideal or Perfect Elasticity
Ideal elasticity is the property whereby the energy expended in deformation of the elastomer is completely recovered on removal of the deforming force. Because the energy expended in deformation is given by the area under the force, f, versus increase in length, ΔL, curve, a perfectly reversible force-extension curve means complete recovery on relaxation of the energy expended on deformation. Therefore, ideal elastomers exhibit perfectly reversible force-extension curves.
Perhaps our earliest perspective of the mechanism underlying ideal elasticity comes from a fundamental observation concerning rubber elasticity. In the mid-nineteenth century, Joule and Thomson noted a quantitative correlation between the increase in temperature of the elastomer due to stretching and the increase in force due to increasing the temperature (Flory, 1968). Thermodynamics provides for the analysis underlying this correlation, and the Boltzmann relation provides the bridge between experimental thermodynamic quantities and statistical mechanical description of molecular structures.
Continuing qualitatively with the Joule and Thomson correlation, heat produces motion, and the energy represented by heat distributes into the various available degrees of freedom in the chain molecules comprising the elastomer. Accordingly, the release of heat on stretching correlates with a loss of motion. By means of statistical mechanics, the loss of motion is seen as a decrease in entropy on extension. In addition, should solvent be essential for elasticity, this requires explicit consideration.
Biophysics of Energy Converting Model Proteins
- D. W. Urry
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- Journal:
- MRS Online Proceedings Library Archive / Volume 330 / 1993
- Published online by Cambridge University Press:
- 15 February 2011, 321
- Print publication:
- 1993
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The biophysics of energy converting model proteins is presented as a general set of three postulates with fifteen corollaries for fifteen subtypes of molecular machines. All of the molecular machines utilize a common structural transition, an inverse temperature transition characterized by increased hydrophobic folding and/or assembly as the temperature is increased through a transition temperature range identified by Tt. These molecular machines, which can be polymers (e.g., proteins or protein-based polymers), are capable of interconverting the free energies involving the six intensive variables of mechanical force, temperature, pressure, chemical potential, electrochemical potential, and electromagnetic radiation.
First-order molecular machines of the Tt-type are molecular engines which, with the appropriate energy input, can result in the production of useful mechanical motion. Postulate I is for the thermally-driven molecular engine. Postulate II with four corollaries is for the four cases where the energy inputs drive hydrophobic folding by lowering the temperature, Tt, at which the inverse temperature transition occurs. This is called the ΔTt-mechanism. The four energy inputs that have been shown to change the value of Tt are due to changes (1) in concentrations of chemicals, (2) in oxidative state of attached prosthetic groups, (3) in pressure, and (4) resulting from the absorption of light by attached chromophores. Postulate III with ten corollaries are for the ten pairwise energy conversions involving the intensive variables listed above exclusive of mechanical force. These energy conversions utilize the hydrophobic association transition but do not result in the motion implicit in the folding or assembly process. These are second-order molecular machines of the Tt-type.
The physical basis for the ΔTt-mechanism of energy conversion of Postulates II and III is proposed to arise due to competition for hydration between apolar (hydrophobic) and polar moieties. This competition is capable of effecting large changes in pKa values of Glu, Asp, Lys and His residues. This mechanism is proposed to be a dominant process in protein folding, assembly, and function.
Properties And Prevention of Adhesions Applications of Bioelastic Materials
- D. W. Urry, D. Channe Gowda, Betty A. Cox, Lynne D. Hoban, Adam Mckee, Taffy Williams
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- Journal:
- MRS Online Proceedings Library Archive / Volume 292 / 1992
- Published online by Cambridge University Press:
- 15 February 2011, 253
- Print publication:
- 1992
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The origins, syntheses, variable composition and physical properties of bioelastic materials are discussed. The latter includes their capacity to undergo inverse temperature transitions to increased order on raising the temperature and to be designable to interconvert free energies involving the intensive variables of mechanical force, temperature, pressure, chemical potential, electrochemical potential and light.
Bioelastic materials include analogues and other chemical variations of the viscoelastic polypeptide, poly(Val-Pro-Gly-Val-Gly), and cross-linked elastomeric matrices thereof. This parent material has been shown to be remarkably biocompatible; it can be minimally modified to vary the rate of hydrolytic breakdown; it can contain enzymatically reactive sites; and it can have cell attachment sites included which promote excellent cell adhesion, spreading and growth to confluence.
One specific application is in the prevention of postoperative adhesion. There are some 30,000,000 per year surgical procedures in this country and a large portion of these would benefit if a suitable material were available for preventing adhesions. Bioelastic materials have been tested in a contaminated peritoneal model, and promising preliminary studies have been carried out in the rabbit eye model for strabismus surgery. In the peritoneal model, 90% of the 29 control animals exhibited significant adhesions; whereas, only 20% of the 29 animals using gas sterilized matrices had significant adhesions. On the basis of this data, it appears that cross-linked poly(VPGVG) is an effective physical barrier to adhesion formation in a trauma model with resulting hemorrhage and contamination.
The potential use of bioelastic materials as a pericardial substitute following the more than 400,000 open heart surgeries per year in the U.S. is under development beginning with the use of bioelastic matrices to prevent adhesions to the total artificial heart being used as a bridge to heart transplantation such that the site will be less compromised when receiving the donor heart.
Hierarchical and Modulable Hydrophobic Folding and Self-assembly in Elastic Protein-based Polymers: Implications for Signal Transduction
- D. W. Urry, C.-H. Luan, S. O. Peng, T. M. Parker, D. C. Gowda
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- Journal:
- MRS Online Proceedings Library Archive / Volume 255 / 1991
- Published online by Cambridge University Press:
- 21 February 2011, 411
- Print publication:
- 1991
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When the hydrophobic (apolar) and polar moieties of elastomeric polypeptides are properly balanced, the polypeptides are soluble in water at lower temperatures but undergo folding and assembly transitions to increased order on raising the temperature. The temperatures, Tt, and heats, ΔHt, of these inverse temperature transitions are determined by differential scanning calorimetry for a series of elastomeric polypentapeptides: poly(VPAVG), poly(IPAVG), poly(VPGVG), poly(IPGVG), poly[0.5(VPGVG),0.5(IPGVG)] and poly[0.82(IPGVG),0.18(IPGEG)] where V = Val, P = Pro, A = Ala, G = Gly, I = lle and E = Glu.
On increasing the hydrophobicity as when replacing V(Val) by I(lle) which is the addition of one CH2 moiety per pentamer, the temperature of the transition is lowered by 15 to 20°C and the heat of the transition is increased by more than one kcal/mole, for the above examples, by more than a factor of two.
When differential scanning calorimetry thermograms are obtained on mixtures of poly(VPAVG) plus poly(IPAVG) or of poly(VPGVG) plus poly(IPGVG), it is found that the polypentapeptides self-separate, i.e., they de-mix, even though in the latter case the conformations have been shown to be essentially identical before and after their respective transitions.
When the polymer, poly[0.82(IPGVG),0.18(IPGEG)], is studied as a function of pH, increasing the degree of ionization is found to increase the temperature and to decrease the heat of the transition such that, with the correct balance of I with the variable E(GluCOO−), the values of Tt and ΔHt can be made to approach those of poly(VPGVG). Acid-base titration studies indicate that less than one Glu(COO−) in 200 residues can raise the value of Tt by 25°C and decrease ΔHt by 90%.
These and additional data are interpreted to mean that there exists an hierarchical hydrophobic folding, that the hierarchical hydrophobic folding can be modulated by changing the degree of ionization or by changes in a number of intensive variables, that changes in these intensive variables can be used to drive folding/unfolding-assembly/disassembly transitions under isothermal conditions, and that these unfolding/folding and disassembly/assembly transitions can be used to achieve signal transduction. This is called the ΔTt mechanism of free energy (signal) transduction.