The Flip-Flop Diffusion Mechanism across Lipids in a Hybrid Bilayer Membrane.
In this study, we examine the mechanism of flip-flop diffusion of proton carriers across the lipid layer of a hybrid bilayer membrane (HBM). The HBM consists of a lipid monolayer appended on top of a self-assembled monolayer containing a Cu-based O2 reduction catalyst on a Au electrode. The flip-flop diffusion rates of the proton carriers dictate the kinetics of O2 reduction by the electrocatalyst. By varying both the tail lengths of the proton carriers and the lipids, we find the combinations of lengths that maximize the flip-flop diffusion rate. These experimental results combined with biophysical modeling studies allow us to propose a detailed mechanism for transmembrane flip-flop diffusion in HBM systems, which involves the bending of the alkyl tail of the proton carrier as the rate-determining step. Additional studies with an unbendable proton carrier further validate these mechanistic findings.
Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois.
Christopher J
CJ
Barile
Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois.
Edmund C M
ECM
Tse
Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois.
Ying
Y
Li
Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois.
John P
JP
Gewargis
Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois.
Nicholas A
NA
Kirchschlager
Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois.
Steven C
SC
Zimmerman
Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois; International Institute for Carbon Neutral Energy Research (WPI-I2CNER), Kyushu University, Fukuoka, Japan. Electronic address: agewirth@illinois.edu.
Andrew A
AA
Gewirth
D003300:Copper / Q000737:chemistry; D004058:Diffusion; D004566:Electrodes; D006046:Gold / Q000737:chemistry; D057927:Hydrophobic and Hydrophilic Interactions; D007700:Kinetics; D008051:Lipid Bilayers / Q000737:chemistry*; D008563:Membrane Lipids / Q000737:chemistry*; D008958:Models, Molecular; D010100:Oxygen / Q000737:chemistry; D017494:Proton Pumps / Q000378:metabolism; D011522:Protons; D012399:Rotation; D013499:Surface Properties; D014867:Water / Q000737:chemistry
D008051:Lipid Bilayers; D008563:Membrane Lipids; D017494:Proton Pumps; D011522:Protons; D014867:Water; D006046:Gold; D003300:Copper; D010100:Oxygen