Title

Electrochemical generation and reactions of ferrylmyoglobin in microemulsions, aqueous media and surfactant films

Date of Completion

January 1996

Keywords

Chemistry, Analytical

Degree

Ph.D.

Abstract

This thesis shows that films cast from didodecyldimethyl-ammonium bromide (DDAB) microemulsions containing the protein myoglobin (Mb) onto pyrolytic graphite electrodes gave good electron-transfer properties when used in these same microemulsions. The films became thinner during the first 10 min after initial insertion into the microemulsion. A film $<$1 $\mu$m thick remained on the surface of the electrode in DDAB microemulsions and exhibited direct electron transfer between the electrode and the Fe(III)/Fe(II) redox couple of myoglobin. Mb-DDAB films could be used for nearly a week in an unstirred DDAB/water/dodecane (13/28/59) microemulsion. The position of the Soret electronic absorbance band suggests that Mb in these films may be partly denatured. Mb-DDAB films were used to facilitate redox reactions of polar and non polar solutes in DDAB microemulsions, as illustrated by the reductions of polar trichloroacetic acid and the non polar oxygen.^ A major question addressed by this thesis was whether electrochemical methods could be used to form the well-known ferrylmyoglobin (MbFe(IV) = O) species. Such ferrylmyoglobin were characterized spectroscopically. Results reported in this thesis shows that MbFe(IV) = O was generated via electrochemical reduction of metmyoglobin (MbFe(III)) in the presence of oxygen in pH 7.3 buffer and in the DDAB microemulsion. Reduction of metmyoglobin at $-$0.4 V vs. SCE catalyzed the reduction of oxygen to hydrogen peroxide at the electrode. The electrogenerated hydrogen peroxide in turn oxidized MbFe(III) in solution to give MbFe(IV) = O. This complex reduction-oxidation process converted nearly all of the 30 $\mu$M MbFe(III) in a spectroelectrochemical cell to MbFe(IV) = O in about 15 min. in pH 7.3 buffer, and in 18 min. in the microemulsion. Characteristic iron heme absorbance bands near 421, 548, and 584 nm were used to identify the product as MbFe(IV) = O. Confirmation was provided by reducing this species to metmyoglobin with ascorbate. The electrochemical method produced ferrylmyoglobin analogous to that formed by the chemical reaction of metmyoglobin with hydrogen peroxide, but with a controllable rate of hydrogen peroxide production. ^