In Situ Monitoring of the Unsaturated Phospholipid Monolayer Oxidation in Ambient Air by HD-SFG Spectroscopy

Ken Ichi Inoue, Chunji Takada, Lin Wang, Akihiro Morita, Shen Ye

Research output: Contribution to journalArticlepeer-review

13 Citations (Scopus)


The pulmonary surfactant monolayer is indispensable for the respiratory system. Recently, it was reported that some unsaturated lipids of the pulmonary surfactants are oxidized by low-level ozone in ambient air. However, the molecular-level understanding of the reaction mechanism is still limited due to technical difficulties. We applied heterodyne-detected sum frequency generation (HD-SFG) spectroscopy to probe the reaction process of an unsaturated phospholipid monolayer (1-palmitoyl-2-oleoyl-glycero-3-phosphocholine, POPC), which is one of the major lipids in the pulmonary surfactant, under low-level ozone (30 ± 5 ppb). The HD-SFG spectroscopy realized the accurate peak assignments of the spectra and the identification of molecular species with high sensitivity, which were impossible with previous measurements. The time-resolved spectra indicated that the C=C moiety in the unsaturated alkyl chain is selectively oxidized by ozone with a time constant of 22 ± 3 min by first-order reaction kinetics. Furthermore, it was revealed for the first time that the reaction product of the POPC monolayer under low-level ozone is not the carboxylic form but the aldehyde form based on the vibrational spectroscopy results. The present study has deepened our molecular-level understanding of the oxidation mechanism of unsaturated lipids that are widely found in many biological systems.

Original languageEnglish
Pages (from-to)5246-5250
Number of pages5
JournalJournal of Physical Chemistry B
Issue number25
Publication statusPublished - 2020 Jun 25


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