Threading Driven by Enthalpy

Threading driven by enthalpy is different from the statistical method in that an in-termolecular attractive force exists between the linear species and the cyclic to 

It is well known that crown ethers can complex with metal ions through ion-dipole interaction and form hydrogen bonds with acidic protons such as NH, OH, and ammonium ions [9, 25, 26]. However, it was not until very recently that scientists started to utilize this interaction in the preparation of rotaxanes. 

Cyclodextrins (CD) can form inclusion complexes with small molecules by hydrophilic-hydrophobic interactions [33-37], Three CDs are readily available - 20, 21, and 22, denoted a, / , and y-CD, respectively. As the number of saccharides in the cyclic increases from 20 to 22, the cavity becomes larger. The hydroxy groups occupy the outside surface, resulting in hydrophilicity and high solubility in polar solvents. Their interiors consist of hydrocarbon units, making the cavity hydro-phobic. Thus when CD and a hydrophobic chain dissolve in a common polar solvent, the chain tends to occupy the cavity of the CD to achieve a lower energy level relative to its state in the polar medium this is hydrophobic-hydrophilic interaction. 

In the 1980s Ogino first applied this interaction in rotaxane synthesis, i.e., threading CD on to an a,co-diamine [38—40]. Almost at the same time, Yamanari et al. reported the preparation of very similar rotaxanes by the same approach [41,42]. Lawrence and coworkers prepared a stable rotaxane by threading / -CD 

Self-Assembly n-n Stacking and Charge-Transfer Accompanied by Hydrogen-Bonding and Dipole-Dipole Interaction 

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