PRIMITIVE MOLECULAR RECOGNITION EFFECTS IN ELECTRON-TRANSFER PROCESSES - MODULATION OF ((TRIMETHYLAMMONIO)METHYL)FERROCENIUM FERROCENE SELF-EXCHANGE KINETICS VIA HYDROPHOBIC ENCAPSULATION/

H-1 NMR line broadening measurements show that the electron self-excha nge rate constant for ((trimethylamino)-methyl)ferrocenium/ferrocene ( TMAFc(2+/+)) in D2O as solvent is decreased by ca. 20-50 fold in the p resence of excess beta-cyclodextrin. The rate effect is associated wit h the selective hydrophobic encapsulation of the ferrocene form of the redox couple (i.e., the ferrocenium form is not significantly encapsu lated). Selective encapsulation leads to a coupling of electron transf er to host (cyclodextrin) transfer. Optical intervalence absorption me asurements 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 activa tion parameter measurements. The barrier increase ultimately can be un derstood in terms of a redox asymmetry effect upon the isolated electr on transfer event, where the overall exchange mechanism likely entails sequential electron and host transfer.