Abstract
Here we propose a new parameter, the Expanding Coefficient (EC), that can be correlated with the thermodynamic stability of supramolecular complexes governed by weak secondary interactions and obeying the induced-fit model. The EC values show a good linear relationship with the log Kapp of the respective pseudorotaxane complexes investigated. According to Cram’s Principle of Preorganization, the EC can be considered an approximate mechanical measure of the host’s reorganization energy cost upon adopting the final bound geometry.
Highlights
We propose a new parameter, the Expanding Coefficient (EC), that can be correlated with the thermodynamic stability of supramolecular complexes governed by weak secondary interactions and obeying the induced-fit model
In the field of synthetic receptors, a single value parameter, the Packing Coefficient (PC), defined as the ratio between the van der Waals volume of the hosted guest and the volume of the host cavity,7 was introduced by Rebek and Mecozzi to simplify the assessment of the complex stability for rigid, lockand-key-like systems
It was found that the optimal PC value, the fraction of occupied volume, is 0.55 ± 0.09 (55%)7 in the liquid state when weak intermolecular interactions are present
Summary
Letter both free and complexed hosts (see Supporting Information (SI)). In some instances, competition experiments with known pseudo[2]rotaxanes were used (see SI). These data seem to be in accord with the “reorganization” point of view, and a good linear correlation (R2 = 0.79) was found by regression analysis between ΔEReorg vs log Kapp values (Figure S50). This analysis indicates that, under the above assumption of weak intermolecular interactions (dispersion forces, van der Waals interactions), the primary determinant to the stability of induced-fit complexes will be the degree of deformation with respect to the ground conformation. Experimental details, characterization data, NMR spectra, calculations details, and Cartesian coordinates (PDF)
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