# A Spectroelectrochemical Study of the Effect of Asymmetry on the Electrochemical Response of Lipid Bilayers

## TL;DR

This study uses spectroscopy to investigate how asymmetry in lipid bilayers affects their electrochemical behavior.

## Contribution

The study introduces a method to separately analyze each leaflet of asymmetric lipid bilayers using PM-IRRAS.

## Key findings

- DMPC is more ordered than DMPE in asymmetric bilayers compared to symmetric ones.
- Asymmetric bilayers decouple under potential changes, with each leaflet responding independently.
- The electrolyte-facing leaflet has a stronger influence on symmetric bilayer behavior.

## Abstract

The effect of asymmetry in supported lipid bilayers on
their electrochemical
phase behavior has been studied using in situ Polarization Modulation
Infrared Reflection Absorption Spectroscopy (PM-IRRAS). Dimyristoylphosphatidylcholine
(DMPC) and dimyristoylphosphatidylethanolamine (DMPE), which have
the same tails and different headgroups, have been used to construct
asymmetric bilayers on Au(111) electrodes. The organization and orientation
of the hydrocarbon tails in each leaflet of the asymmetric bilayers
have been characterized separately by deuterating the tails in the
opposing leaflet. The vibrational frequencies of the chain methylene
stretching modes show that DMPC is relatively ordered in asymmetric
bilayers, and DMPE is relatively disordered, compared with their respective
symmetric bilayers. The tail orientations in the as-deposited asymmetric
bilayers are similar, showing the two monolayers influence each other,
but the changes induced in each bilayer by the application of a potential
difference across the bilayer are different and indicate that the
bilayers decouple, with each monolayer responding separately to the
imposed field. The results suggest that the behavior of previously
reported symmetric systems may be more strongly influenced by the
properties of the electrolyte-facing leaflet and highlight the value
of using electrochemical perturbation of lipid bilayers in structural
studies to provide additional insights into lipid–lipid interactions.