title: Characterization of interacting ferrocene-cyclodextrin systems and their role in mediated biosensors.
abstract: Inclusion complexes of 1,1'-dimethylferrocene (DMFe) with alpha-, 2-hydroxypropyl-beta- or gamma-cyclodextrins were formed in aqueous systems. For the first time, the interacting DMFe-cyclodextrin systems have been characterized using cyclic voltammetry which enabled the estimation of the complexation order, the formation constant and the diffusivity. Cyclic voltammetry was performed at a stationary electrode, yielding complexation ratios of 1:2 for DMFe with alpha-cyclodextrin and 1:1 with the other two cyclodextrins, as expected from the known cavity dimensions for the cyclodextrins. Formation constants of 4.4 x 10(4) M-2, 1.2 x 10(3) M-1 and 2.9 x 10(2) M-1 were then determined for the complexes between DMFe and the alpha-, beta- and gamma-cyclodextrins, respectively, in relative agreement with the literature. The maximum complexation efficiency, diffusivity and solubility were observed for the DMFe:2-hydroxypropyl-beta-cyclodextrin inclusion complex, which, combined with cost factors, resulted in the selection of this form for bioelectrocatalysis studies. The efficiency of the complex as a mediator for the glucose:glucose oxidase system was determined by measuring the rate constant (ks) for reaction of the oxidized DMFe with the reduced enzyme. The ks value decreased from 3.4 x 10(4) M-1 s-1 to 1.9 x 10(4) M-1 s-1 with an increase in 2-hydroxypropyl-beta-cyclodextrin concentration from 4 mM to 10 mM. In this range, the ks value is similar to that of free ferrocene, implying a high efficiency of the DMFe:2-hydroxypropyl-beta-cyclodextrin inclusion complex.
authors.affiliation: Biotechnology Research Institute, National Research Council Canada, Montreal.
authors.forename: J H
authors.initials: JH
authors.lastname: Luong
authors.forename: R S
authors.initials: RS
authors.lastname: Brown
authors.forename: P M
authors.initials: PM
authors.lastname: Schmidt
mesh_terms: D015374:Biosensing Techniques; D002384:Catalysis; D003505:Cyclodextrins; D004058:Diffusion; D004563:Electrochemistry / Q000379:methods; D005296:Ferrous Compounds; D005947:Glucose / Q000032:analysis*; D005949:Glucose Oxidase / Q000032:analysis / Q000378:metabolism*; D007202:Indicators and Reagents; D007700:Kinetics; D008962:Models, Theoretical; D009942:Organometallic Compounds; D011048:Polarography / Q000379:methods
chemical_list: D003505:Cyclodextrins; D005296:Ferrous Compounds; D007202:Indicators and Reagents; D009942:Organometallic Compounds; C050099:1,1'-dimethylferrocene; D005949:Glucose Oxidase; D005947:Glucose