Interfacial and mass transport enhancement effects on rates of styrene epoxidation catalyzed by myoglobin films in microemulsions

Abstract

Biocatalytic surfaces hold promise for future clean methods of chemical synthesis. Biocatalyst films utilizing inexpensive redox proteins can operate in low-toxicity microemulsions with high capacities to dissolve nonpolar reactants. Crosslinked films of myoglobin (Mb) and poly(L-lysine) (PLL) attached to oxidized carbon cathodes gave up to 40-fold larger turnover rates in bicontinuous microemulsions compared to o/w microemulsions and micelles. Larger synthetic turnover rates are correlated with up to 10-fold faster diffusion of solutes in oil phases of the bicontinuous fluids, as measured by voltammetry. Visible and circular dichroism spectra suggest that myoglobin resides in the film in a largely aqueous environment. The reactant sites in films monitored by a fluorescent probe were more polar when films were in CTAB than in SDS microemulsions. These combined results suggest that larger mass transport rates in the bicontinuous fluids is a major factor for enhanced turnover rates. Electrostatic interactions between the charged films and oppositely charged surfactants may significantly influence turnover rates when reactant mass transport is not fast enough.

Microemulsion-Controlled Reaction Sites in Biocatalytic Films for Electrochemical Reduction of Vicinal Dibromides

“…6,8 Fluorescence probe studies with pyrene in Mb-PLL films exposed to microemulsions showed that the pyrene residence site in CTAB microemulsions is somewhat more polar than the residence site in films that are exposed to SDS microemulsions. 9 Pyrene sites in both systems were more polar than a hydrocarbon environment but much less polar than water. Because the vicinal dibromides in the present study are relatively nonpolar, we assume that they reside in the films in regions similar to the pyrene residence sites.…”

“…SDS entering into the cationic PLL films was revealed previously from quartz crystal microbalance (QCM) studies of PLL films containing cobalt corrin catalysts 23 and by preliminary studies of Mb-PLL films. 9 Here we provide more detailed QCM results for Mb-PLL films made on gold-coated quartz QCM resonators and then immersed in the CTAB and SDS microemulsions. In QCM, the change in frequency (-∆F) for dry films is proportional to mass per unit area (M/A) in the absence of viscoelasticity changes.…”

“…6 However, residence sites of nonpolar reactants within the Mb-PLL films as monitored by the fluorescent probe pyrene were more polar in CTAB than in SDS microemulsions, which was a secondary factor in determining reactivity. 9 We found that the reduction of tert-butylhydroperoxide by Mb-PLL films with simultaneous oxidative activation of the iron heme protein follows Michaelis-Menten kinetics. 8 A unique property of iron heme proteins such as Mb is that they can transfer electrons relatively efficiently from MbFe II to vicinal dibromides.…”

“…We have used Mb-PLL films for the electrochemical catalytic oxidation of styrene in the presence of oxygen and found 40-fold-larger turnover rates in bicontinuous microemulsions compared to those in oil-in-water (o/w) microemulsions correlated mainly with faster mass transport of reactants in the oil phases of the bicontinuous fluids . However, residence sites of nonpolar reactants within the Mb-PLL films as monitored by the fluorescent probe pyrene were more polar in CTAB than in SDS microemulsions, which was a secondary factor in determining reactivity . We found that the reduction of tert -butylhydroperoxide by Mb-PLL films with simultaneous oxidative activation of the iron heme protein follows Michaelis−Menten kinetics …”

Electrochemical catalysis by crosslinked films of cobalt reconstituted myoglobin and poly(l-lysine) in a bicontinuous microemulsion

“…We investigated control of catalytic activity with microemulsion composition for adsorbed FeMb films [14]. More recently we made crosslinked films of FeMb-PLL that were stable in microemulsions and studied the factors important for efficient catalysis [15,16]. Given this background, we sought to combine the catalytic activity of the cobalt corrin surrounded by protein envelope with the reactivity control of microemulsions.…”