Cyclodextrin (CD) dimers bind amino acid side chains, and such binding can dissociate aggregated proteins, including citrate synthase (dimer) and lactic dehydrogenase (tetramer). A CD dimer can bind a hydrophobic photosensitizer that, upon irradiation, generates singlet oxygen. This cleaves the dimer and releases the photosensitizer. CD dimers in a cytochrome P-450 mimic steer catalyzed hydroxylation to a bound steroid with geometric control. Chelate binding has also led to a group of cytodifferentiating agents whose mechanism has been recently established. They have promising anticancer properties, and are currently entering human trials as therapeutic agents.