Enthalpic Contributions

T Lazaridis, G Archontis, M Karplus. Enthalpic contribution to protein stability Atom-based calculations and statistical mechanics. Adv Protein Chem 47 231-306, 1995. 

In the first category of solutions ( regular solutions ), it is the enthalpic contribution (the heat of mixing) which dominates the non-ideality, i.e. In such solutions, the characteristic intermolecular potentials between unlike species differ significantly from the average of the interactions between Uke species, i.e. 

As is known, SEC separations require interaction-free conditions. Therefore, the enthalpic contribution to the free energy term vanishes when no enthalpic interaction is postulated between analyte and sorbent ... 

The value of EM for a cooperative self-assembled structure provides a measure of the monomer concentration at which trivial polymeric structures start to compete, and therefore EM represents the upper limit of the concentration range within which the cooperative structure is stable (Scheme 2). The lower limit of this range is called the critical self-assembly concentration (csac) and is determined by the stoichiometry of the assembly and the strength of the non-covalent binding interactions weaker interactions and larger numbers of components raise the csac and narrow the stability window of the assembly (8). Theoretical treatments of the thermodynamics of the self-assembly process have been reported by Hunter (8), Sanders (9), and Mandolini (10). The value of EM is lowered by enthalpic contributions associated with... 

The thermoelastic behavior of these materials has also been reported [188]. Such experiments resolve the nematic to isotropic transition into entropic and enthalpic contributions as already described, and provides values of the corresponding energetic and entropic parts of the force, fe and fs [175] (see Section 7). 

Flory-Huggins interaction parameter (-) enthalpic contribution to x ( ) entropic contribution to x ( ) efficiency factor for sorption (-)... 

As noted in table 11.1, the ability of THFTCA to separate LJO from trivalent lanthanide ions is mainly of enthalpic origin. Reaction 11.33 has a considerably more unfavorable enthalpic contribution than reaction 11.32. The complexation is, however, predominantly entropy driven because the T ArS° term dominates the ArH° contribution for all systems. The large positive entropy changes observed for reactions 11.32 and 11.33 result from the release of water molecules coordinated to the metal on complexation with the tridentate THFTCA2- ligand. Note that a negative entropy contribution would be expected if these reactions were truly 2 particle = 1 particle reactions [226]. 

In the absence of enthalpic contributions, the activities of the components in the mixture become... 

In addition to enthalpic contributions, the entropy effects accompanying protein-metal ion interactions are substantial. These effects manifest themselves in the desolvation of the metal ion and its binding site. However, as the metal ion binds to a protein, the entropy gain of solvent release may be offset to some degree by the reduction of the conformational entropy of the polypeptide chain as it becomes more firmly bound... 

The + 2/0 reduction potentials have enthalpic contributions from the terms in the equation ... 

Referring to the analysis of kinetic barriers that contribute to the differential rates, outlined above, it would appear that enantioselectivity may not reside in any single part of the kinetic scheme. In fact, analysis of the distribution of entropic and enthalpic contributions to the enantioselectivity of CaLB in mixtures of organic solvents showed that the gradual replacement of one organic solvent with the other may lead to a switch from one state to another [145]. More information on the response of individual steps in the kinetic scheme to a change of solvent is needed to arrive at a conclusive answer. 

Thus, determination of the hydrogen-hydrogen interaction from Equation 4 can give values which include both entropic and enthalpic contributions, whereas in Equation 7, there are only enthalpic contributions. Boureau et al. (40, 41) have determined values of f/fiH from calorimetric measurements. They found H ih = -125.5 kj (mol H)-1 (555°K), and from their P-C-T data, W/,H, -52.7 kj (mol H)-1 (555°K). Burch and Francis (36), on the other hand, found, from their P-C-T data (-600°K), tf/,H = -54.2 kJ(mol H)-1. 

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