Induced asymmetry in lipid bilayers detected by sum frequency vibrational spectroscopy
T h e U n i v e r s i t y o f U t a h G r a d u a t e S c h o o l STATEMENT OF THESIS APPROVAL The thesis of Michael P. Cooper has been approved by the following supervisory committee members: ABSTRACT Phospholipids, a major constituent of cell membranes, contain a hydrophobic tail and a hydrophilic head group. Cell membranes are composed of two leaflets forming a bilayer. The hydrophobic tails form the bilayer core while the hydrophilic headgroups form the exterior of the bilayer. While
... layer. While phospholipids have a similar structure in general, there is variety among headgroup moieties as well as tail moieties. In living cells, phospholipids are distributed asymmetrically between the two leaflets of the bilayer according to head group chemistry. However, it has been shown that phospholipids can undergo rapid flip-flop between the two leaflets, which would favor a symmetric distribution due to mixing. Sum frequency vibrational spectroscopy (SFVS), a surface specific technique, can be used to determine the amount of asymmetry in a lipid bilayer on a planar support. As such, SFVS was used to study one possible mechanism of bilayer asymmetry maintenance, namely electrostatic association. Specifically, asymmetry was induced in bilayers consisting of 1,2-distearoyl-sn-glycero-3-phosphatidylcholine and 1,2-distearoyl-sn-glycero-3-phosphatidylserine by electrostatic interaction with the positively charged polypeptide polylysine. Lipid bilayers were created on planar silica surfaces through the Langmuir-Blodgett/Langmuir-Schaefer deposition method. To confirm the validity of using the Langmuir-Blodgett/Langmuir-Schaefer deposition method for the asymmetry study, mass iv spectrometry was used to verify bilayers of a known composition that were formed on a silica substrate.