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

Abstract

We report herein the electrochemical dehalogenation of vicinal dibromides in microemulsions using cross-linked films of the redox protein myoglobin (Mb) and poly-l-lysine (PLL) covalently bonded to carbon electrodes. Catalytic reduction of the dibromides to olefins was more efficient in an SDS microemulsion than in a CTAB microemulsion. SDS shifts the Mb redox potential more negative, but a comparison to Mb-SDS films suggests that the activation free energy of the reduction is controlled by an inner-sphere mechanism. SDS also enters the positively charged Mb-PLL films and preconcentrates the dibromide reactants, enhancing catalytic efficiency in SDS microemulsions. Shifts in formal potential and Soret absorbance bands for Mb-PLL films suggested binding of trans-1,2-dibromocyclohexane in the iron heme distal pocket with little catalysis. Results are consistent with active catalytic reduction sites for reactant bound on the protein surface and less-reactive sites in the distal heme pocket. Preconcentration into catalytic PLL films using SDS incorporated from microemulsions may be a general way to improve catalytic efficiency for nonpolar reactants in microemulsions.

Thermostable Peroxidase−Polylysine Films for Biocatalysis at 90 °C

“…We used our previously reported method to construct cross-linked protein-PLL films (see Supporting Information for full details). , This involved initial covalent linkage of a layer of PLL (MW 150−300) onto electrochemically oxidized pyrolytic graphite electrodes, aminosilyl fused silica slides with poly(acrylic acid) attached, or carboxylated 0.5 μm diameter silica beads. A layer of PLL was first attached to the carboxylated surfaces by amide linkages promoted by using freshly prepared 24 mM 1-[3-(dimethylamino)propyl]-3-ethylcarbodiimide (EDC).…”

“…Quartz crystal microbalance measurements suggested that these 2 bilayer films of enzyme-PLL are 400−600 nm thick . Standard, previously reported procedures were used for voltammetry and spectroscopy. − …”

“…When we later wanted to use biocatalyst films in microemuslions, we found that enhancing enzyme stability in these media required covalent cross-linking between proteins, polyions, and solid surfaces. Excellent stability and catalytic efficiency in buffers and microemuslions at room temperature was obtained for films made by linking Mb to poly( l -lysine) (PLL) covalently bound to graphite electrodes. , …”

Biochemical applications of ultrathin films of enzymes, polyions and DNA

“…They are useful for biocatalysis because they can dissolve organic reactants in their oil nanophases while keeping the enzymes in LbL films in a largely aqueous environment. [43][44][45] Additional stabilization was required for LbL films to be usable in microemulsions. Excellent stability and catalytic efficiency in buffers and microemulsions at room temperature was obtained for LbL films on electrodes by linking Mb to poly(L-lysine) (PLL) covalently bound to graphite electrodes.…”

Unveiling the Behavior of Curcumin in Biocompatible Microemulsion and Its Differential Interaction with Gold and Silver Nanoparticles

“…Ionic liquid-in-oil (IL/O) microemulsion allows chemical reactions that require nonaqueous medium to successfully take place in its core . Some microemulsions also function as bioreactors, where biocatalytic and enzymatic reactions occur selectively in the polar core. , A major limitation of using microemulsion as a drug delivery system is the toxicity resulting from a large amount of surfactants used to stabilize it. This disadvantage can be overcome by using biocompatible surfactants.…”