Structure and stability studies of mixed monolayers of saturated and unsaturated phospholipids under low-level ozone

Abstract

In the present study, stability and structure of single and binary mixed monolayers of an unsaturated phospholipid, DOPC, and a saturated phospholipid, DPPC-d75, on the water surface, were explored using the π-A isotherm, atomic force microscopy (AFM) and sum frequency generation (SFG) vibrational spectroscopy in various environments. Our results demonstrated that DOPC in the monolayers becomes unstable after the exposure to a low concentration of ozone (20 ± 10 ppb) or even to ambient laboratory air, which has a similar ozone level, but is stable in nitrogen or oxygen. DOPC can be selectively oxidized by a trace amount of ozone in the ambient environment but can be partially inhibited by the presence of DPPC in the monolayer. The present study provides useful information for understanding the physicochemical properties of the cell membranes.

Atmospheric chemistry of bioaerosols: heterogeneous and multiphase reactions with atmospheric oxidants and other trace gases

“…Several studies by Finlayson-Pitts and co-workers have shown that unsaturated phospholipids are readily oxidized by O 3 from the “top down” to generate secondary ozonides and a number of products. 122–124 The group of Ye 125,126 probed the structure and stability of phospholipids in low ozone concentration by a combination of π–A isotherms, vibrational spectroscopy, and force microscopy. Their results demonstrate that the CC moieties in the unsaturated lipids are selectively oxidized by a trace amount of ozone in the ambient environment.…”

Interfacial Structure of Soft Matter Probed by SFG Spectroscopy

“…The present results suggest that the unsaturated phospholipids can be selectively oxidized by a trace amount of ozone in the ambient environment, while the oxidation of DOPC is partially inhibited by the presence of DPPC in the mixed monolayers . We are continuing to study the structure and stability of different unsaturated lipid molecules in a variety of environments.…”

“…Figure shows SFG spectra of a DOPC monolayer prepared in (a) nitrogen and (b) low‐level ozone environments (black squares) . The SFG spectrum after exposure to ozone is significantly different from that in nitrogen.…”

“…Furthermore, we studied the structure and stability of mixed monolayers of DOPC and DPPC‐ d 75 in different ratios (Figure , red circles and blue triangles) . The disorder factor, deduced from the d + / r + ratio, for the DOPC in the mixed monolayer clearly decreases, indicating that conformational ordering of DOPC is largely improved by mixing with saturated lipids.…”

“…In the present Personal Account, our recent SFG studies on the molecular structures at interfaces of functional soft matter such as polymers, self‐assembled monolayers (SAMs) and Langmuir–Blodgett (LB) ultrathin layers and lipid bilayers in various environments will be briefly reviewed. A general model dealing with the optical interference effect in thin layers of soft matter, which can dramatically affect the SFG spectral shape and intensity, will be introduced first.…”