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Thermodynamic Quantities (thermodynamic + quantity)
Selected AbstractsSelf-Assembly of Rod-Like Copolymers into Monolayers: A Simple Theoretical Estimate of Molecular Recognition QualityMACROMOLECULAR THEORY AND SIMULATIONS, Issue 7-8 2008Anatoly V. Berezkin Abstract A discrete model of a monolayer, consisting of identical rod-like copolymer molecules, is suggested. The influence of the copolymer's composition and sequence on its self-assembly was studied. Thermodynamic quantities of monolayers were calculated. It is shown that the system undergoes an "order-disorder" transition upon temperature increase. The most regular monolayers are formed by copolymers with quasi-random sequences. Nevertheless, the monomer composition of such "good" sequences can vary over a wide range. It is shown that homopolymers, copolymers with a predominance of one-type monomer units and copolymers consisting of a small number of large blocks have a reduced ability to self-assembly. [source] Use of affinity capillary electrophoresis for characterizing pharmaceutical colloidal vehicle systems thermodynamicallyBIOPHARMACEUTICS AND DRUG DISPOSITION, Issue 7-8 2001Neubert Reinhard Abstract This review offers a detailed discussion of the interaction between pharmaceutical compounds and vehicles using the affinity capillary electrophoresis and the microemulsion electrokinetic chromatography. Partition coefficients of drugs were calculated between a micelle and an aqueous phases from the measurement of the migration time, provided the critical micelle concentration and the phase ratio are known. Thermodynamic quantities such as enthalpy and entropy changes of micellar solubilization were calculated from the temperature dependence of the partition coefficients. Partial specific volumes were measured using dynamic light scattering. The logarithm of the partition coefficients and the capacity factor in the micellar system were correlated with the logarithm of the n-octanol/water partition coefficients. Copyright © 2001 John Wiley & Sons, Ltd. [source] Phase Diagrams and Glass Formation in Metallic Systems,ADVANCED ENGINEERING MATERIALS, Issue 6 2007M. Baricco Abstract The basic thermodynamic aspects of glass-formation in metallic systems are reviewed. In particular, the specific features of a phase diagram with respect to glass-formation are evidenced. On the basis of the regular solution model, the effect of various thermodynamic quantities on the free energy difference between undercooled liquid and crystal phases are outlined. In order to describe the amorphous phase, a specific heat difference between liquid and solid phases in the undercooling regime is introduced in the CALPHAD assessment of various binary systems. The glass-transition is described as a second order transition. Examples are given for different systems, including Fe-B and Cu-Mg. From the description of the free energy of various phases as a function of composition and temperature, the driving forces for nucleation of crystal phases and the T0 curves are estimated. [source] Simulated Annealing Study of Self-Assembly of Symmetric ABA Triblock Copolymers Confined in Cylindrical NanoporesMACROMOLECULAR THEORY AND SIMULATIONS, Issue 2-3 2008Zheng Wang Abstract We report a simulated annealing study of the self-assembly of symmetric lamella-forming ABA triblock copolymers confined in cylindrical nanopores. We systematically examine the dependence of the self-assembled morphologies and structural parameters on the degree of confinement and the strength of the surface preference. We find that the confined morphologies for the symmetric ABA triblocks with fA,=,1/2 are similar to those for the symmetric or nearly symmetric AB diblock copolymers under the same confinement. We also find that different structural parameters can reflect different information. The predicted bridging fraction value for the bulk phase is in good agreement with previously established values, whereas the predicted values for the confined morphologies change with both the degree of confinement and the strength of the surface preference. We further explore the self-assembling process by examining the morphology and various ensemble-averaged thermodynamic quantities and structure parameters as a function of the reduced temperature. [source] Quantum phase transition in a spin-½ XX chain with three-spin and uniform long-range interactionsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 15 2005Ping Lou Abstract A spin-½ XX chain with three-spin and uniform long-range interactions among the z components of the spins is constructed. Based upon the model, using the Jordan,Wigner transformation, the thermodynamic quantities and spin transports of the system are evaluated exactly. The phase diagram together with the key parameters characterizing quantum phase transitions is presented. It is noted that, similarly to classical first-order phase transitions, there are also the metastable states "supercooled" and "superheated" in the first-order quantum phase transitions. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Temperature and urea induced denaturation of the TRP-cage mini protein TC5b: A simulation study consistent with experimental observationsPROTEIN SCIENCE, Issue 10 2009Z. Gattin Abstract The effects of temperature and urea denaturation (6M urea) on the dominant structures of the 20-residue Trp-cage mini-protein TC5b are investigated by molecular dynamics simulations of the protein at different temperatures in aqueous and in 6M urea solution using explicit solvent degrees of freedom and the GROMOS force-field parameter set 45A3. In aqueous solution at 278 K, TC5b is stable throughout the 20 ns of MD simulation and the trajectory structures largely agree with the NMR-NOE atom,atom distance data available. Raising the temperature to 360 K and to 400 K, the protein denatures within 22 ns and 3 ns, showing that the denaturation temperature is well below 360 K using the GROMOS force field. This is 40,90 K lower than the denaturation temperatures observed in simulations using other much used protein force fields. As the experimental denaturation temperature is about 315 K, the GROMOS force field appears not to overstabilize TC5b, as other force fields and the use of continuum solvation models seem to do. This feature may directly stem from the GROMOS force-field parameter calibration protocol, which primarily involves reproduction of condensed phase thermodynamic quantities such as energies, densities, and solvation free energies of small compounds representative for protein fragments. By adding 6M urea to the solution, the onset of denaturation is observed in the simulation, but is too slow to observe a particular side-chain side-chain contact (Trp6-Ile4) that was experimentally observed to be characteristic for the denatured state. Interestingly, using temperature denaturation, the process is accelerated and the experimental data are reproduced. [source] Structural and thermodynamic encoding in the sequence of rat microsomal cytochrome b5,BIOPOLYMERS, Issue 5 2008Juliette T. J. Lecomte Abstract The water-soluble domain of rat microsomal cytochrome b5 is a convenient protein with which to inspect the connection between amino acid sequence and thermodynamic properties. In the absence of its single heme cofactor, cytochrome b5 contains a partially folded stretch of ,30 residues. This region is recognized as prone to disorder by programs that analyze primary structures for such intrinsic features. The cytochrome was subjected to amino acid replacements in the folded core (I12A), in the portion that refolds only when in contact with the heme group (N57P), and in both (F35H/H39A/L46Y). Despite the difficulties associated with measuring thermodynamic quantities for the heme-bound species, it was possible to rationalize the energetic consequences of both types of replacements and test a simple equation relating apoprotein and holoprotein stability. In addition, a phenomenological relationship between the change in Tm (the temperature at the midpoint of the thermal transition) and the change in thermodynamic stability determined by chemical denaturation was observed that could be used to extend the interpretation of incomplete holoprotein stability data. Structural information was obtained by nuclear magnetic resonance spectroscopy toward an atomic-level analysis of the effects. © 2007 Wiley Periodicals, Inc. Biopolymers 89: 428,442, 2008. This article was originally published online as an accepted preprint. The "Published Online" date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com [source] | |||||||||||||