Noncovalent interactions in supramolecular complexes

This dissertation presents investigations of representatives belonging to three major classes of hosts used in supramolecular chemistry: cyclophanes, cyclodextrins, and calixarenes. Computational and experimental studies on a series of substituted phenyl and biphenyl guests with the cyclophane host cyclobis(paraquat-p-phenylene) clearly delineated the various and previously unknown components of molecular association and showed that polarizability, not charge-transfer, as was previously thought, was the main differential factor in determining the strength of association. The incorporation of solvation gave a computational model giving good correlation between the experimental and computed binding energies. Further studies on the same host\u27s complexation with guests extended with chains of varied structure established the role played by chain length and functionality number, type, and placement in the association process. Heteroatoms along the chain were found to be essential for complexation and their placement was also crucial, exhibiting a strong chelate effect. The chain heteroatoms dominated the overall complexation but the aromatic ring was necessary for guest placement within the host\u27s cavity, suggesting a cooperative relationship.Cyclodextrin complexation is mainly driven by hydrophobic and Van der Waals interactions. Water insoluble polyamine dendrimers containing 4, 8, and 16 ferrocene units on their periphery were solubilized in water using $\beta$-cyclodextrin, giving the first examples of complexed dendrimers. Inclusion complexation of the ferrocenes\u27 unsubstituted cyclopentadienyl rings by the cyclodextrin formed large supramolecular assemblies exhibiting interesting electrochemical properties suggesting steric crowding at the surface of the dendrimer. Dimeric bipyridinium (viologen) guests having a long aliphatic chain were also shown to form inclusion complexes with $\alpha$-cyclodextrin and the complexation was switchable by protonating the guest and making it more hydrophilic. The viologen guests\u27 interactions with the cyclodextrin was contrasted with their association with a water soluble calix (6) arene hexasulfonate driven by electrostatic interactions with the positively charged viologen units. The calixarene was also used in a separate investigation involving its complexation with the metal cage compound cobalt sepulchrate. The strong association was shown to be of ion paring in nature and the 1:1 solution complex contrasted sharply with the neutral 2:1 sepulchrate/calixarene complex in the solid state for which the crystal structure was obtained