THE KINETICS OF ELECTRON-TRANSFER REACTIONS OF THE [FECP(CPCH(2)N(CH3)(3)](+ 2+) COUPLE IN THE PRESENCE OF CYCLODEXTRINS IN AQUEOUS-MEDIA/

The stability constants for the inclusions of the [FeCp(CpCH(2)N(CH3)( 3)](+) cation in alpha- (150+/-10 M(-1)), beta- (4810+/-600 M(-1)), dm beta- (5010+/-800 M(-1)) and gamma-cyclodextrins (500+/-50 M(-1)) hav e been determined at 25 degrees C by means of H-1 NMR chemical shift t itrations. The effects of cyclodextrin inclusion of the substituted fe rrocene couple on the kinetics of its electron-transfer reactions have been investigated in aqueous solution at 25.0 degrees C. The inclusio ns of [FeCp(CpCH(2)N(CH3)(3)](+) by cyclodextrins decrease the rate co nstant for its oxidation by bis(pyridine-2,6-dicarboxylato)cobaltate(I II) (from 930 to 20 M(-1) s(-1) upon beta-CD inclusion). The rate cons tants for the oxidations of ascorbic acid by [FeCp(CpCH(2)N(CH3)(3)](2 +) increase (from 640 to 2600 M(-1) s(-1) far beta-CD) upon inclusion of the oxidant by alpha- (K-CD=10+/-5 M(-1)), beta- (150+/-15 M(-1)) a nd dm beta-cyclodextrin (140+/-30 M(-1)) inclusions of the oxidant. Th e gamma-cyclodextrin has a negligible effect on the electron-transfer rate constant. The effects of cyclodextrin inclusion on the kinetics o f these electron-transfer reactions are discussed in terms of changes in the thermodynamic driving force of the reaction and shielding of th e reactants.