Submitted to: Journal Electroanalytical Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 10, 2001
Publication Date: N/A
Interpretive Summary: Ionic liquids are a new, nonvolatile, environmentally friendly class of solvents than can be substituted for volatile organic solvents. One of our goals is to invent methods of transforming agricultural products to higher value products that use ionic liquids instead of more common organic solvents. This study examines the use of electrodes in ionic liquids to activate molecules containing iron atoms. These results provide preliminary evidence that iron-containing enzymes can be activated by electricity in ionic liquids to carry out a variety of reactions to make agriculturally based cosmetics, skin care products, and nutrition supplements. The fact that the iron-containing enzymes can be used several times in the environmentally friendly ionic liquids results in less waste and a "greener" method of producing the desired products.
Technical Abstract: The direct electrochemical reduction of hemin was investigated in the ionic liquids (IL), 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]) and 1-octyl-3-methylimidazolium hexafluorophosphate ([omim][PF6]), using cyclic voltammetry and chronocoulometry. The reduction of hemin in 14% (v:v) N-methylimidazole:IL solutions using a gold electrode produced midpoint potentials of 208 mV to 216 mV more negative than values obtained in 14% (v:v) pyridine:IL, depending on the IL. [Bmim][PF6] solutions consistently yielded midpoint potentials 30 mV more negative than [omim][PF6] solutions. The diffusion coefficients of hemin in the molecular solvent: IL media ranged between 1.50 and 2.80 e-7 cm2/s, while the heterogeneous electron-transfer rate constants ranged between 3.7 and 14.3 e-3 cm/s. In neat IL media, cyclic voltammetry of hemin adsorbed to the gold electrode through 2,2-bispyridyl disulfide linkages resulted in a postwave, indicating that the hemin is desorbed upon reduction. The surface concentration of the adsorbed hemin was determined to be 1.21 e-10 mol/cm2, indicating the presence of one or more complete monolayer of hemin.