|Compton, David - Dave|
Submitted to: Meeting Abstract
Publication Type: Abstract only
Publication Acceptance Date: 5/14/2002
Publication Date: 5/12/2001
Citation: COMPTON, D.L., LASZLO, J.A. BIOELECTROCATALYTIC REACTIONS IN ROOM TEMPERATURE IONIC. MEETING ABSTRACT. 2001. Interpretive Summary:
Technical Abstract: The goal of our research is to develop new technology platforms utilizing novel enzymatic methods and processes for the modification of lipids to produce value-added products. Our approach to developing these new processes and products follows the established principles of green chemistry by using non-toxic catalysts, inherently benign solvents, and high-atom-economy synthetic routes, accordingly. More recently, we have demonstrated the first example of a bioelectrocatalytic reaction, involving hemin, to be carried out in room temperature ionic liquids. The direct electrochemical reduction of hemin, ligated with strong or weak heterocyclic bases, was investigated in the ionic liquids (IL), 1-butyl- and 1-octyl-3-methylimidazolium hexafluorophosphate ([bmin][PF6] and [omim][PF6]), using cyclic voltammetry and chronocoulometry. Hemin complexed with N-methylimidazole (NMI) or with pyridine had E1/2 values slightly (4 to 59 mV) more positive in IL (without electrolyte) than in methanol (1.0 M electrolyte) using a gold electrode. NMI-ligated hemin had a lower E1/2 than pyridine-ligated hemin in either IL, consistent with the stronger electron donor characteristic of NMI. [Bmim][PF6] solutions consistently yielded E1/2 values 30 mV more negative than [omin] [PF6] solutions. The diffusion coefficients of hemin in the IL ranged between 1.50 and 2.80 x 10-7 cm2 s-1, while the heterogeneous electron-transfer rate constants ranged between 3.7 and 14.3 x 10-3 cm s-1. Cyclic voltammetry of hemin adsorbed to a gold surface through 4,4'bispyridyl disulfide linkages showed a large positive shift in the oxidation wave, indicating that adsorption stabilizes the reduced hemin state.