The Structure of Lipid Bilayers Adsorbed on Activated Carboxy-Terminated Monolayers Investigated by Sum Frequency Generation Spectroscopy

Abstract

The formation and structure of isotopically asymmetric supported bilayer membranes (SBMs) has been investigated using sum frequency generation (SFG) vibrational spectroscopy supplemented by reflection absorption infrared spectroscopy (RAIRS). The bilayers were composed of a proximal and distal leaflet of the phospholipid dipalmitoyl phosphatidylethanolamine (DPPE) supported on a gold surface. The proximal leaflet was chemically tethered to the gold via an 11-mercapto-undecanoic acid (MUA) self-assembled monolayer (SAM) that had been chemically modified to produce an activated succinimidyl ester headgroup using N-hydroxysuccinimide (NHS) and N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide (EDC). The activation of the MUA and the tethering of the DPPE were monitored and confirmed using SFG and RAIRS. The distal leaflet of the bilayer was added using either vesicle fusion (VF) or Langmuir-Blodgett (LB) deposition. To gain insight into the structure of each layer of the SBM perdeuterated DPPE (d-DPPE) and MUA (d-MUA) were used to create SBMs with a layer that was isotopically distinguishable from the rest. The polar orientation and conformational ordering of the lipids was determined using SFG. It was found that the tethering of the proximal lipid leaflet resulted in an increase in the conformational order of the MUA SAM. Furthermore, by careful analysis and comparison of spectra recorded in both the C-H (2800-3000 cm(-1)) and C-D (2000-2300 cm(-1)) stretching regions it was concluded that a better ordered and more biologically relevant lipid bilayer was formed when the distal leaflet was added using LB deposition. On the other hand the SFG spectra of the SBMs in which the distal leaflet was added by VF showed little evidence of conformational ordering on the time scale of minutes, suggesting the presence of an incomplete monolayer or of multilayer formation.

Multi-Technique Investigation of a Biomimetic Insect Tarsal Adhesive Fluid

“…The relative ratio of CH 3 symmetric to CH 2 symmetric stretch amplitudes has been shown to be indicative of the relative organization of a layer of hydrocarbons, with larger values indicating a more uniform angle in relation to the surface (Casford et al, 2014;Adams et al, 2017). These values, and the trend between substrates, were similar for the same substrates in the natural and biomimetic fluid spectra, with values of 3.46 ± 0.40 and 1.03 ± 0.07 for the dPS and dPEO spectra of the natural fluid and 4.47 ± and 1.70 ± for spectra of the same surfaces with biomimetic fluid.…”

Immobilization approaches can affect protein dynamics: a surface-enhanced infrared spectroscopic study on lipid–protein interactions

“…31,33 Thiol tail groups are suitable to link SAMs on gold films whereas functional head groups of SAMs can be applied for the selective immobilization of biomolecules. [34][35][36][37] In a previous SEIRA study, we have devised SAMs of mixed NHS-PEG-SH (10 kDa) (NHS: N-hydroxysuccinimide) and MT (PEG) 4 (methyl-and sulfhydryl-terminated PEG) for immobilization of poly-L-lysine (PLL) to gold. 27 In this work, we used SAMs of 5 kDa NHS-PEG-SH (Nanocs) and MT(PEG) 4 (Thermo Scientific), thereby we reduced the length of the NHS-PEG-SH linker molecules to ≈30 nm and facilitated protein immobilization closer to the gold surface leading to more enhancement of the absorbance signal.…”

Ultrathin Supported Lipid Monolayer with Unprecedented Mechanical and Dielectric Properties

“…In living cells lipid membrane forms indeed a natural insulator which plays an efficient role as barrier to both ionic and electronic transport associated with an electrical resistance of the order of several giga‐Ohms in magnitude . These unique properties make them very attractive to be used as ultrathin dielectric layer in electronic devices and have recently raised interest, marked by the increasing number of studies reporting the formation of lipid layers on various substrates such as silicate, H‐terminated silicon surface, gold, alkylated surfaces and more recently graphene, graphene‐oxide, or polymeric substrates such as poly(ethylenedioxythiophene):poly(styrene sulfonate) sodium (PEDOT:PSS) . So far in most studies lipid layers have been used as biocompatible interfaces or as ionic barriers in field effect transistors to study ion channels in lipid membranes .…”