Conformational compression

Guimaraes CRW, MP Repasky, J Chandrasekhar, J Tirado-Rives, WL Jorgensen (2003) Contributions of conformational compression and preferential transition state stabilization to the rate enhancement by chorismate mutase. J. Am. Chem. Soc. 125 (23) 6892-6899... 

Advance the technology elements required to develop a semi-conformal, Compressed Hydrogen Gas Integrated Storage System (CH2-ISS) for light-duty fuel cell vehicles (FCVs)... 

Schwahn, D Frielinghaus, H. Mortensen, K. Almdal, K. (1996) Temperature and Pressure Dependence of the Order Parameter Fluctuations, Conformational Compressibility, and the Phase Diagram of the PEP-PDMS Diblock Copolymer, Phys. Rev. Lett. 77, 3153 - 3156. 

The exact mechanism of the action by chorismate mutase is stUl not clear, in spite of extensive experimental and theoretical investigations. Several suggestions have been proposed concerning the origin of the catalysis. They include (a) the stabilization of transition state by the enzyme, presumably through electrostatic interactions from the active site residues (b) the promotion of substrate conformational transition to generate the reactive CHAIR conformer at the active site (see Scheme 1.2) (c) the increase of populations of near attack conformers (NACs) and (d) strain effects and conformational compression. These proposals will be discussed below. 

Strains and conformational compression of the substrate at the enzyme active site were also proposed to explain the rate acceleration by chorismate mutase [66, 70,... 

For instance, Jorgensen and his coworkers [78] suggested, based on the results of their calculations and analysis, that the stabilization of the transition state in chorismate mutase plays only a secondary role and that the rate enhancement is primarily due to conformational compress of the substrate. However, the analysis of Jorgensen and coworkers has been called into question [80], and it was shown that the results might be interpreted differently [80]. 

Schwahn et al. 1995, ginzburg criterion for the mean-field to 3-dimensional ising crossover in polymer blends, Phys. Rev. E, Vol. 52, No. 2, PP. 1288-1291 19%, Temperature and pressure dependence of the order parameter fluctuations, conformational compressibility, and the phase diagram of the PEP-PDMS diblock copolymer. Physical Reuieiv Letters, Vol. 77, No. 15, PP. 3153-3156 2001, Abnormal pressure dependence of the phase boimdaiies in PEE-PDMS and PEP-PDMS binary homopolymer blends and diblock copwlymers. Macromolecules, Vol. 34, No. 6, PP. 1694-1706... 

PCTFE plastic is available in products that conform to ASTM 1430-89 Type 1 (Grades 1 and 2) and is suitable for processing into parts that meet MIL-P 46036 (Federal Specification LP-385C was canceled 1988). Standards for fabricated forms are available for compression molded heavy sections (AMS-3645 Class C), thin-walled tubing, rod, sheet, and molded shapes (AMS-3650). PCTFE plastics have been approved for use in contact with food by the FDA (55). 

The monolayer resulting when amphiphilic molecules are introduced to the water—air interface was traditionally called a two-dimensional gas owing to what were the expected large distances between the molecules. However, it has become quite clear that amphiphiles self-organize at the air—water interface even at relatively low surface pressures (7—10). For example, x-ray diffraction data from a monolayer of heneicosanoic acid spread on a 0.5-mM CaCl2 solution at zero pressure (11) showed that once the barrier starts moving and compresses the molecules, the surface pressure, 7T, increases and the area per molecule, M, decreases. The surface pressure, ie, the force per unit length of the barrier (in N/m) is the difference between CJq, the surface tension of pure water, and O, that of the water covered with a monolayer. Where the total number of molecules and the total area that the monolayer occupies is known, the area per molecules can be calculated and a 7T-M isotherm constmcted. This isotherm (Fig. 2), which describes surface pressure as a function of the area per molecule (3,4), is rich in information on stabiUty of the monolayer at the water—air interface, the reorientation of molecules in the two-dimensional system, phase transitions, and conformational transformations. 

Cork compositions 250 Low cost. Truly compressible materials which permit substantial deflections with negligible side flow. Conform well to irregular surfaces. High resistance to oils good resistance to water, many chemicals. Should not be used with inorganic acids, alkalies, oxidizing solutions, live steam. 

For sustained low oil consumption, narrow, deep-groove piston rings conform easily to liner walls. Top compression ring is chrome-plated to condition liners during break-in. 

Persons employed to use compressed air in carrying out a specific work task must be correctly equipped to prevent injury. The minimum requirement is to wear eye protectors, which conform to BS 2092. 

The crystallization of polymer melts at high pressure (several thousand of atmospheres), just as the crystallization in flowing melts and stirred solutions, leads to the formation of ECC in which the molecules assume almost completely extended conformations. This suprising feet (the crystallization was carried out at hydrostatic compression) was first extablished experimentally by Wunderlich30 and then confirmed by other authors31 33. However, diverse opinions exist about the mechanism of ECC formation. 

The thermodynamic analysis of conformational and structural transformations in the melt at high pressures34 showed that the free volume and free energy minimum required for hydrostatic compression is attained as a result of the transition of the molecules in the melt into a more extended conformation (gauche —> trans transitions) since the extended molecules ensure a more compact packing of the chains at compression. Chain uncoiling leads to a decrease in their flexibility parameter f with increasing pressure p ... 

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