PM-IRRAS Studies of DMPC Bilayers Supported on Au(111) Electrodes Modified with Hydrophilic Monolayers of Thioglucose

Abstract

A phospholipid bilayer composed of 1,2-dimyristoyl-d54-sn-glycero-3-phosphocholine (d54-DMPC) was deposited onto the Au(111) electrode modified with a self-assembled monolayer of 1-thio-β-d-glucose (β-Tg) via the Langmuir-Blodgett and Langmuir-Schaefer (LB-LS) techniques. Polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS) measurements were used to characterize structural and orientational changes in this model biological membrane on a hydrophilic surface modified gold electrode. The results of the spectroscopic measurements showed that the tilt angle of acyl chains obtained for deuterated DMPC bilayers supported on the β-Tg-modified gold is significantly lower than that reported previously for DMPC bilayers deposited directly on Au(111) electrodes. Moreover, tilt angles of ∼18° were obtained for d54-DMPC bilayers on β-Tg self-assembled monolayers (SAMs) at positive potentials, which are similar to the values calculated for h-DMPC deposited on bare gold in the desorbed state and to those observed for a stack of hydrated DMPC bilayers. This data confirms that the β-thioglucose SAM promotes the formation of a water cushion that separates the phospholipid bilayer from the metal surface. As a result, the DMPC polar heads are not in direct contact with the electrode and can adopt a zigzag configuration, which strengthens the chain-chain interactions and allows for an overall decrease in the tilt of the acyl chains. These novel supported model membranes may be especially useful in studies pertaining to the incorporation of peptides and proteins into phospholipid bilayers.

Physicochemical Characterization of Sparsely Tethered Bilayer Lipid Membranes: Structure of Submembrane Water and Nanomechanical Properties

“…Therefore, we can conclude that the amount as well as the orientation of lipid molecules does not change within this potential window. Similar behavior was reported by Matyszewska and coworkers for fBLMs where the DMPC bilayer was separated from the electrode surface by water cushion [35] . These authors have shown that polarization of the electrode causes rather limited changes in orientation of the acyl chains.…”

“…Similar behavior was reported by Matyszewska and coworkers for fBLMs where the DMPC bilayer was separated from the electrode surface by water cushion. [35] These authors have shown that polarization of the electrode causes rather limited changes in orientation of the acyl chains. The tilt angle with respect to the surface normal varied from~18°for positive potentials to~14°for negative potentials and the observed differences were within experimental uncertainties.…”

Electrochemical Properties of Lipid Membranes Self-Assembled from Bicelles

“…The immobilization of the membrane at the supporting substrate offers a unique opportunity to probe the properties of such an assembly with numerous surface-sensitive techniques. These include scanning probe microscopy, infrared reflective absorption spectroscopy, quartz crystal microbalance, and for conductive supports, electrochemical methods can be used as well [8][9][10][11]. Most popular approaches for supported lipid membrane formation involve vesicles spreading or Langmuir-Blodgett and Langmuir-Schafer techniques [12][13][14][15].…”

In Situ and Operando Techniques for Investigating Electron Transfer in Biological Systems

“…The technique provides information regarding the conformation, orientation, and hydration of biomembranes. For instance, PM‐IRRAS allows the investigation of how water cushion formation separates a phospholipid bilayer from the electrode surface influencing the membrane orientation and ET processes [110,111] . Capacitance and chronocoulometric measurements coupled with PM‐IRRAS are effective for probing the stability of the lipid monolayer on electrodes and determining the conformation and orientation of acyl chains as a function of applied potentials [112–114] as well as for studying ion channel properties, lipid‐peptide interactions, and transmembrane ion transport mechanisms [115–117] .…”