title: Primitive Molecular Recognition Effects in Electron Transfer Processes: Modulation of ((Trimethylammonio)methyl)ferrocenium/ferrocene Self-Exchange Kinetics via Hydrophobic Encapsulation.
abstract: 1H NMR line broadening measurements show that the electron self-exchange rate constant for ((trimethylamino)methyl)ferrocenium/ferrocene (TMAFc(2+/+)) in D(2)O as solvent is decreased by ca. 20-50 fold in the presence of excess beta-cyclodextrin. The rate effect is associated with the selective hydrophobic encapsulation of the ferrocene form of the redox couple (i.e., the ferrocenium form is not significantly encapsulated). Selective encapsulation leads to a coupling of electron transfer to host (cyclodextrin) transfer. Optical intervalence absorption measurements for a closely related mixed-valence system strongly suggest that the coupling decreases the self-exchange rate by increasing the thermal activation barrier-an inference that is corroborated by activation parameter measurements. The barrier increase ultimately can be understood in terms of a redox asymmetry effect upon the isolated electron transfer event, where the overall exchange mechanism likely entails sequential electron and host transfer.
authors.affiliation: Department of Chemistry, Northwestern University, Evanston, Illinois 60208.
authors.forename: Roger M.
authors.initials: RM
authors.lastname: Nielson
authors.forename: L. Andrew
authors.initials: LA
authors.lastname: Lyon
authors.forename: Joseph T.
authors.initials: JT
authors.lastname: Hupp