Hybrid bilayer membrane: a platform to study the role of proton flux on the efficiency of oxygen reduction by a molecular electrocatalyst.

In this report, we present a novel platform to study proton-coupled electron transfer (PCET) by controlling the proton flux using an electrode-supported hybrid bilayer membrane (HBM). Oxygen reduction by an iron porphyrin was used as a model PCET reaction. The proton flux was controlled by incorporating an aliphatic proton carrier, decanoic acid, into the lipid layer of the HBM. Using this system, we observed a different catalytic behavior than obtained by simply changing the pH of the solution in the absence of an HBM.

Electrocatalytic O2 reduction by covalently immobilized mononuclear copper(I) complexes: evidence for a binuclear Cu2O2 intermediate.

A Cu(I) complex of 3-ethynyl-phenanthroline covalently immobilized onto an azide-modified glassy carbon surface is an active electrocatalyst for the four-electron (4-e) reduction of O(2) to H(2)O. The rate of O(2) reduction is second-order in Cu coverage at moderate overpotential, suggesting that two Cu(I) species are necessary for efficient 4-e reduction of O(2). Mechanisms for O(2) reduction are proposed that are consistent with the observations for this covalently immobilized system and previously reported results for a similar physisorbed Cu(I) system.

Ferrocene embedded in an electrode-supported hybrid lipid bilayer membrane: a model system for electrocatalysis in a biomimetic environment.

An electrode-supported system in which ferrocene molecules are embedded in a hybrid bilayer membrane (HBM) has been prepared and characterized. The redox properties of the ferrocene molecules were studied by varying the lipid and alkanethiol building blocks of the HBM. The midpoint potential and electron transfer rate of the embedded ferrocene were found to be dependent on the hydrophobic nature of the electrolyte and the distance at which the ferrocene was positioned in the HBM relative to the electrode and the solution. Additionally, the ability of the lipid-embedded ferrocenium ions to oxidize solution phase ascorbic acid was evaluated and found to be dependent on the nature of the counterion.

Enzyme modification of platinum microelectrodes for detection of cholesterol in vesicle lipid bilayer membranes.

Platinum microelectrodes are modified with a lipid bilayer membrane incorporating cholesterol oxidase. Details for electrode surface modification are presented along with characterization studies of electrode response to cholesterol solution and to cholesterol contained in the lipid bilayer membrane of vesicles. Ferrocyanide voltammetric experiments are used to track deposition of a submonolayer of a thiol-functionalized lipid on the platinum electrode surface, vesicle fusion for bilayer formation on the thiolipid-modified surface, and incorporation of cholesterol oxidase in the electrode-supported thiolipid/lipid bilayer membrane. The data are consistent with formation of a lipid bilayer structure on the electrode surface that contains defects. Experiments for detection of cholesterol solubilized in cyclodextrin solution show steady-state current responses that correlate with cholesterol concentration. Direct contact between the electrode and a vesicle lipid bilayer membrane shows a response that correlates with vesicle membrane cholesterol content.

Steady-state detection of cholesterol contained in the plasma membrane of a single cell using lipid bilayer-modified microelectrodes incorporating cholesterol oxidase.

Platinum microelectrodes modified with a lipid bilayer membrane incorporating cholesterol oxidase are used for detection of cholesterol contained in the plasma membrane of a single cell. Amperometric responses are consistent with enzymatic catalysis being rate limiting and cholesterol diffusing laterally in the plasma membrane to the electrode contact site. Importantly, electrode response appears to correlate with the cholesterol content of the cell plasma membrane. The electrodes should be useful for characterizing cellular cholesterol tracking pathways involved in pathogenesis of disease.