Guest-host thermodynamic interactions

The relatively low thermodynamic stability of complexes of hemicarcerands or other container-type hosts is a direct consequence of structural aspects of the walls that make up the inner surface of such compounds. These walls are lined by aromatic subunits while free electron pairs of heteroatoms such as those of the ether oxygen atoms are preferentially oriented to the outside. Complexes are therefore enthalpically stabilized only by weak dispersive interactions. In the case of positively charged guests cation-re interactions can contribute to binding enthalpy as in a self-assembled calixarene-derived capsule [9], but directed interactions such as hydrogen-bonding interactions are usually absent. 

Koen de Vries, Coussens and Meier likewise found that a combined molecular mechanics and molecular dynamics approach is a valuable tool for rationalizing qualitative gas chromatographic trends [69]. Experimentally they evaluated the thermodynamic parameters (AG, AAG, AH, AAH, etc.) for guest-host complexation of six analytes on a variety of derivatized CD columns. Their interpretation of the computational results is that one enantiomer fits the CD cavity better than the other resulting in a larger Interaction energy and greater loss of mobility. 

The building blocks of supramolecular systems are held together by intramolecular interactions and these systems are reversible. This intrinsic property is not only a consequence of the more labile interactions within supermolecules, compared to covalent bonds in molecules, but reversibility is essential for the function expressed by supramolecular systems. Kinetics can never be inferred from thermodynamic studies. For example, the knowledge of a host-guest equilibrium constant does not... 

An attempt to treat globally the thermodynamic data is a classification by the major and minor factors contributing to the complex stability, using the signs of enthalpy and entropy changes (A//° and Thus, all host-guest interactions... 

Since the present theory has been shown to be useful in analyzing molecular recognition of relatively simple guests with most synthetic hosts, we now proceed to the supramolecular interactions in more sophisticated biological systems where relatively abundant thermodynamic data are available in the literature. 

Johnson, D.W. and Raymond, KN. (2001) The self-assembly of a [Ga4L6]12-tetrahedral cluster thermodynamically driven by host-guest interactions. Inorg. Chem., 40 (20), 5157-5161. 

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