Entropic and enthalpic contributions

An important part of the optimization process is the stabilization of the monomer-template assemblies by thermodynamic considerations (Fig. 6-11). The enthalpic and entropic contributions to the association will determine how the association will respond to changes in the polymerization temperature [18]. The change in free volume of interaction will determine how the association will respond to changes in polymerization pressure [82]. Finally, the solvent s interaction with the monomer-template assemblies relative to the free species indicates how well it will stabilize the monomer-template assemblies in solution [16]. Here each system must be optimized individually. Another option is simply to increase the concentration of the monomer or the template. In the former case, a problem is that the crosslinking as well as the potentially nonselective binding will increase simultaneously. In the... 

ENTHALPIC AND ENTROPIC CONTRIBUTIONS TO RUBBER ELASTICITY THE FORCE-TEMPERATURE RELATIONS... 

Moreover, the solvent-annealing process is rather complex and the underlying delicate balances of enthalpic and entropic contributions to the free energy are not yet understood in detail. Besides the solvent type, the sol-... 

Data for the 4-chlorophenyl derivative were obtained at three temperatures (Table A4.1). At the lower temperatures, the rate acceleration is greater because the transition state binding is strengthened more than the substrate binding. The data may be analysed to elicit the enthalpic and entropic contributions to the free energy of transition state stabilization, obtainable from the variation of AGrs(=AHyS TAS s) with temperature (Table 2). If desired, the data may be further dissected since, from (9),... 

Correlation of structures of diastereomeric complexes with estimated enthalpic and entropic contributions to free energy of complexation (0°C) ... 

Relationships having the same form as eq 14 can also be written for the enthalpic and entropic contributions to the intrinsic free energy barriers (10). Provided that the reactions are adiabatic and the conventional collision model applies, eq 14 can be written in the familiar form relating the rate constants of electrochemical exchange and homogeneous self-exchange reactions (13) ... 

Chowdhury, M.A.J., Boysen, R.I., Ihara, H., and Hearn, M.T.W., Binding behavior of crystalhne and noncrystalhne phases evaluation of the enthalpic and entropic contributions to the separation selectivity of nonpolar solutes with a novel chromatographic sorbent, J. Phys. Chem. B, 106, 11936, 2002. 

Theory. The most widely accepted mechanism of size separation is based on steric exclusion (1). In terms of thermodynamic properties, the distribution coefficient consists of enthalpic and entropic contributions ... 

The conclusion from these experiments is that the associated ions [RXY]-are stereochemically related to the SN2 transition state. Furthermore, little variation occurs in the stability of the associated ions for CH3C1, CH3Br and CH3I, and steric hindrance is apparently of small consequence in the enthalpic and entropic contributions of these equilibria. These data can be compared directly to the solution values for enthalpy and entropy of activation to show that solvation effects on both parameters are indeed responsible for the large variations in rates observed in solution. 

A2 from equation (5.16) or the cross second virial coefficient from equation (5.17). In turn, this knowledge of the second virial coefficients and their temperature dependence allows calculation of the values of the chemical potentials of all components of the biopolymer solution or colloidal system, as well as enthalpic and entropic contributions to those chemical potentials. On the basis of this information, a full description and prediction of the thermodynamic behaviour can be realised (see chapter 3 and the first paragraph of this chapter for the details). 

Another approach is to carry out free-energy simulations at several different temperatures, and then construct the equivalent of a van t Hoff plot to separate, say, the enthalpic and entropic contributions to the free energy. This approach is obviously extraordinarily demanding of resources, since every temperature point requires a new free-energy simulation, and unless there are many points, the error in the temperature dependence of the free energy determined by linear regression of the latter on the former may be rather large. 

Enthalpic and Entropic Contributions to the Excess Free Energy Molecular Picture of the Dissolution Process Model for Description of the Aqueous Activity Coefficient Box 5.1 Estimating Molar Volumes from Structure Illustrative Example 5.2 Evaluating the Factors that Govern the Aqueous Activity Coefficient of a Given Compound... 

Enthalpic and Entropic Contributions to the Excess Free Energy... 

These results imply that homopolymer PS is not always miscible with the PS blocks of the copolymer, i.e. confinement of PS to an interface in a block copolymer can lead to immiscibility with homopolymer PS (Hashimoto et al. 1990). This has been interpreted in terms of the enthalpic and entropic contributions to the free energy (Hasegawa and Hashimoto 1996). For a < 1 uniform solubilization increases the translational entropy of the homopolymer, but chain stretching in the homopolymer and in the PS chain of the diblock leads to a decrease in conformational entropy. At the same time, the lateral swelling of microdomains leads... 

Manzo, R. H. and A. A. Ahumada. 1990. Effects of solvent medium on solubility. V Enthalpic and entropic contributions to the free energy changes of di-substituted benzene derivatives in enthanol water and enthanofcyclohexane mixtur fc. Pharm. Sci79 1109—1116. 

The values of the CMC or CMT collected as a function of temperature or concentration can be used to extract the enthalpic and entropic contributions to the association process. For a closed association mechanism with relatively large aggregation number and a narrow distribution, the standard free energy and standard enthalpy of micelle formaMi nd AH°, per mole of the solute in the micelle) are related to the CMC and its temperature dependence in the form (Lindman and V fennerstrom, 1980 Zhou and Chu, 1994). 

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