Solvents host-guest binding

Estimating Solvent Contributions to Host-guest Binding... 

A linear correlation has been found between the solvent-dependent AG° values and the empirical parameter of solvent polarity, t(30) (see Section 7.4). Thus, the host/guest binding strength increases steadily on going from nonpolar solvents to water, thus shifting the complexation equilibrium more and more to the right-hand side with increasing solvent polarity. 

When the guest and host interact with the solvent, the guest binding is expected to become weaker. In the above case, both imidazole and the host (Fig. 4) can more strongly interact with ether solvents, in comparison to... 

Figure 1.12 Host-guest binding equilibrium showing the desolvation of both species required prior to the binding occurring. The final complex is still solvated but overall there are more free solvent molecules present, hence increasing the entropy of the system.

In the case of nonstructured solvents, the interaction of solvent molecules in the bulk solution is rather weak and plays only a limited role in host/guest binding. However, the extent of solvation, that is, the amount of solvating molecules, the thickness of solvation shell, and the strength of the host-solvent and guest-solvent interactions, critically varies depending on the nature of the solvent employed, as exemplified below for CDCI3 versus CeDe. 

The origin for the less-than-optimal repeatability of ITC titrations can be traced to systematic errors in sample treatment as well as to difficulties in data evaluation. First in line of the factors that interfere with the reproducibility of calorimetric results is the purity of the compounds used. Owing to the ubiquity of heat effects, even small deviations from a nontinal composition of a compound may result in dramatic differences in the calorimetric output. A frequent problem of this kind in abiotic host-guest binding is the presence of the solvent of crystallization. Ordinarily, this is not considered an impurity, as it is often present in a fixed stoichiometric ratio and can be accounted for in elemental analyses and in the spectroscopic evaluation. In calorimetry, however, solvent of crystallization adds a heat contribution of unknown size, which does not emerge from the interaction under study and thus tends to falsify the results. The problem is amplified by the polarity... 

ASAHSAh+g (A ), the change of solvent-accessible hydrophobic surface area occurring during the host-guest binding process. 

Table 3. Studies of guest binding to host 20 from a two-component solvent mixture 26>...

Table 2. Preference of guest binding of host 1 from a two-component solvent system...

The results obtained have suggested a sandwich conformation of the host-guest complex in which DABCO was protected from the solvent and other molecules. The cross-peaks between coordinated DABCO and complex protons in the 2D ROESY spectra have indicated the accommodation of the DABCO molecule in the host cavity and confirmed the sandwich binding mode. 

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