Structure of Mixed Phosphatidylethanolamine and Cholesterol Monolayers in a Supported Hybrid Bilayer Membrane Studied by Sum Frequency Generation Vibrational Spectroscopy

Abstract

The structure of hybrid bilayer membranes (HBMs) containing either a pure cholesterol or mixed cholesterol/dipalmitoylphosphatidylethanolamine (DPPE) proximal layer adsorbed onto an octadecanethiol (ODT) self-assembled monolayer (SAM) on a gold substrate have been investigated by sum frequency generation (SFG) spectroscopy. The HBMs were formed by the adsorption of either a pure cholesterol or mixed DPPE/cholesterol monolayer from the air/water interface of a Langmuir-Blodgett trough at surface pressures of 1, 20, or 40 mN·m(-1). SFG spectra were also recorded of HBMs where cholesterol was replaced by cholesterol-d(7), in which the terminal isopropyl group of the alkyl chain of cholesterol was isotopically labeled. In order to isolate the contribution to the SFG spectra from the cholesterol in the mixed cholesterol/phospholipid films, DPPE-d was used, in which the alkyl chains of the phospholipid were deuterated. The infrared spectra of solvent-cast cholesterol and cholesterol-d(7) films were recorded to aid with assignment of the SFG spectra of the HBMs. Features corresponding to methyl, methylene, and methine stretches of cholesterol were identified in the SFG spectra. Information on the polar orientation of SFG-active groups was obtained from the phases of the spectral features. The structure of the HBMs showed little dependence on the surface pressure at which they were formed. SFG spectra of HBMs with a mixed cholesterol/DPPE proximal layer were very similar to the spectra of HBMs with a pure cholesterol proximal layer, although the features in the spectra were more intense than anticipated for a film with half the number of cholesterol molecules, indicating that DPPE did have some effect on the orientation of cholesterol molecules in the film.

Effect of Ca 2+ to Sphingomyelin Investigated by Sum Frequency Generation Vibrational Spectroscopy

“…The peaks centered at $2874, 2926, 2942, 2953, and 2963 cm À1 can be assigned to CH 3 symmetric stretching (CH 3 ss), CH 2 Fermi resonance, CH 3 Fermi resonance, CH 2 ss in the headgroup, and CH 3 asymmetric stretching (CH 3 as), respectively (26)(27)(28)30,32,33,(51)(52)(53)(54)(55)(56). The exact assignments of all of the peaks are beyond the scope of this article.…”

Unified treatment and measurement of the spectral resolution and temporal effects in frequency-resolved sum-frequency generation vibrational spectroscopy (SFG-VS)

“…We first describe the basic formulation of the SFG-VS process in both time-and frequency domains, and then discuss the spectral resolution and temporal effects of the BB-SFG-VS spectra of cholesterol at the air/water interface. Cholesterol is chosen because there have been several SFG studies on its spectra, [46][47][48][49] and, aside from its biological importance, its SFG spectrum in the C-H stretching vibration region is complicated enough to be a good example to illustrate the analysis possible with HR-BB-SFG-VS. We show how the parameters from the sub-wavenumber resolution SFG spectra can be used not only to understand but also to quantitatively reproduce the temporal effects in lower resolution SFG measurements. These developments shall provide not only a unified picture in understanding both the frequency-domain and the time-domain SFG responses of the complex molecular interface, but also novel experimental approaches to directly and conveniently measure them.…”

Protein-Phospholipid Interactions in Nonclassical Protein Secretion: Problem and Methods of Study

“…have studied vesicle fusion and Langmuir-Blodgett deposition onto self-assembled alkanethiol monolayers, probing the phase transition temperature of the fabricated membranes, and investigating the interaction between cholesterol and PL in the HBM [165–168]. Davies and co-workers have explored the effect of deposition surface pressure on the ordering of PL and alkanethiol monolayers, with and without cholesterol present [168,169]. Lis et al .…”