CyDs thermodynamic parameters

TABLE 40.4 Effect of Temperature on Stability Constants (Kj.) of Inclusion Complexes of Ethyl 4-Biphenylylacetate with Various (3-CyDs, and Their Thermodynamic Parameters in Water... 

Table 38.4 Effect of temperature on stability constants (KJ of inclusion complexes of ethyl 4-biphenylylacetate with various -CyDs, and their thermodynamic parameters in water...

Determination of the Stoichiometry and Stability of the Complexes 115 Tab. 5.2. Thermodynamic parameters of complexation of selected compounds by CyDs. 

In spite of very diverse successful practical applications, the mechanism of com-plexation and the relationship between structure and selectivity are still at best only partly solved and remain open for discussion. Thermodynamic studies could supply some valuable information facilitating an understanding of the physicochemical basis of the complexation processes. The GC modified with CyDs is one of a variety of experimental methods employed in the determination of thermodynamic quantities for the formation of CyD inclusion complexes (see Chapters 8-10). The thermodynamic parameters for separation of the enantiomers were determined for various derivatives of CyDs dissolved in various stationary phases [63-65] or as a Uquid derivatized form [66]. Interesting observations were made by Armstrong et al. [66]. The authors postulated two different retention mechanisms. The first involved classical formation of the inclusion complex with high thermodynamic values of AH, AAH, and AAS and a relatively low column capacity and the second loose, probably external, multiple association with the CyD characterized by lower AH, AAH, and AAS values. The thermodynamic parameters of complexation processes obtained from liquid and gas chromatography measurements are collected in Table 5.2. It is clear from those data that for all the compounds presented the complexation processes are enthalpy-driven since in all cases AH is more negative than TAS. 

The thermodynamic parameters for estriol, estradiol, ethinyloestradiol, and estrone with and y-CyD measured by Sadlej-Sosnowska [49] in methanol-water and acetonitrile-water mixtures indicate that the values of enthalpy changes due to complex formation with and y-CyD are more negative in methanol than in... 

It is interesting to compare the thermodynamic parameters obtained for the 1 1 complexation of Cbz-Gly with y-CyD with those for the 1 1 complexation of Cbz-Gly with j8-CyD. This comparison may also be taken as an independent assessment of the reliability of the above-mentioned four-parametric fit. The equilibrium constant for the 1 1 complex formation of Cbz-Gly with y-CyD is about one-tenth as large as that for Cbz-Gly complexation with fi-CyD [82], and the heat effect obtained for the y-CyD complex is about one third as large as that for the fi-CyD complex. It is reasonable to expect less-pronounced van der Waals interactions and therefore a smaller exothermic heat effect, when the cavity is too large to comfort-... 

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