The kinetics of electron-transfer reactions of the [FeCp(CpCH2N(CH3)3]+/2+ couple in the presence of cyclodextrins in aqueous media
1994; Elsevier BV; Volume: 225; Issue: 1-2 Linguagem: Inglês
10.1016/0020-1693(94)04028-1
ISSN1873-3255
AutoresJerome A. Imonigie, Donal H. Macartney,
Tópico(s)Analytical Chemistry and Sensors
ResumoThe stability constants for the inclusions of the [FeCp(CpCH2N(CH3)3]+ cation in α- (150±10 M−1), β- (4810±600 M−1), dmβ- (5010±800 M−1) and γ-cyclodextrins (500±50 M−1) have been determined at 25 °C by means of 1H NMR chemical shift titrations. The effects of cyclodextrin inclusion of the substituted ferrocene couple on the kinetics of its electron-transfer reactions have been investigated in aqueous solution at 25.0 °C. The inclusions of [FeCp(CpCH2N(CH3)3]+ by cyclodextrins decrease the rate constant for its oxidation by bis(pyridine-2,6-dicarboxylato)cobaltate(III) (from 930 to 20 M−1 s−1 upon β-CD inclusion). The rate constants for the oxidations of ascorbic acid by [FeCp(CpCH2N(CH3)3]2+ increase (from 640 to 2600 M−1 s−1 for β-CD) upon inclusion of the oxidant by α- (KCD=10±5 M−1), β- (150±15 M−1) and dmβ-cyclodextrin (140±30 M−1) inclusions of the oxidant. The γ-cyclodextrin has a negligible effect on the electron-transfer rate constant. The effects of cyclodextrin inclusion on the kinetics of these electron-transfer reactions are discussed in terms of changes in the thermodynamic driving force of the reaction and shielding of the reactants.
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