Context-Dependent Significance of London Dispersion

Single-Molecule Exchange inside a Nanocage Provides Insights into the Origin of π–π Interactions

“…As a result, exchange of π-molecules could be observed at the single-molecule level, and their binding strength quantitatively compared. Nevertheless, it should be noted that the conclusion drawn from this work may not be extrapolated to other circumstances where solute–solvent interactions can compete with π–π interactions, as illustrated in recent reviews by Cockroft and Nau . Besides, it is important to acknowledge that the K D values derived from this study are not absolute dissociation constants.…”

Distinction and Quantification of Noncovalent Dispersive and Hydrophobic Effects

“…These barrel-shaped receptors have low polarizability inside the cavity and no hydrogen bond acceptors or donors inside; they contain only a few water molecules in their cavities, depending on the cavity size (Figure 8) [99]. These factors lead to extraordinarily high binding enthalpies of up to ∆H = 90 kJ/mol, larger than observed with any biological receptors [3], and to a small dependence on specific binding sites in comparison to many other supramolecular complexes. The binding strength of alkenes in CBs is, however, stronger relative to alkanes, and increases roughly with the size/polarizability of the hydrocarbons, which speaks to some dispersive contribution [108].…”

“…The release of high-energy water from cavities as a driving force for complexation was suggested early on for cyclodextrin complexes [104], water predicted by MD simulations for water in cyclophanes [105], and in the last few years put on a firm basis with extensive analyses of complexes with cucurbiturils (CBs) [3,106,107]. These barrel-shaped receptors have low polarizability inside the cavity and no hydrogen bond acceptors or donors inside; they contain only a few water molecules in their cavities, depending on the cavity size (Figure 8) [99].…”

“…Another solvophobic contribution has been proposed for cavitation energies which, e.g., for noble gases are smaller in the cucurbit [5]uril cavity than that necessary for cavity creation in bulk water [109]. Water with less than the optimal number of hydrogen bonds occurs in many supramolecular receptors, including CBs, cyclophanes, cryptophanes, pillarenes, fullerenes, and calixarenes [3]. As a measure of the high-energy water contribution, one can use a factor Z = N (3.62 − m), in which N is total number of water molecules in a cavity and m = 3.62 is the optimal number of interwater hydrogen bonds in bulk water.…”

“…The interactions are often indiscriminately described as hydrophobic, although the most important contributions, namely dispersive interactions and hydrophobic factors, describe opposite mechanisms: Compounds lending themselves to lipophilic associations will prefer a hydrophobic environment, but interact less by London-type dispersive forces. These forces, customarily regarded as weak, have long been underestimated, due their small energies when compared to single noncovalent interactions and in solution due to the competition with a bulk solvent of sizable polarizability [1][2][3][4]. The essential role of polarizability both of the reaction partners and of the medium, as well as the large difference of host compounds' propensity for dispersion interactions has been aptly reviewed [5].…”