Nitrocen Dioxide-Initiated Peroxidation of Liposomal Membrane Systems

Abstract

Liposomes were used as a model membrane system to study the peroxidation of lipids by nitrogen dioxide (Nod. Small unilammelar liposomes of l-α-dilinoleoyl phosphatidylcholine or l-α-dilinolenoyl phosphatidylcholine were prepared by sonication. Exposure to NO₂ was a bubbler apparatus at 1–10 ppm for 0–15 min. Initiation of phospholipid peroxidation was measured by diene conjugation at 232 nm for l-α-dilinoleoyl phosphatidylcholine liposomes and at 235 nm for l-α-dilinolenoyl phosphatidylcholine liposomes. The rate of peroxidation was consistent with a second-order rate model. The second-order rate constant for diene conjugation of l-α-dilinoleoyl phosphatidylcholine was 1.5 × 10⁻-³ M⁻¹ s⁻¹ and far l-α-dilinoleoyl phosphatidylcholine was 3.1 × 10⁻-³ M⁻¹ s⁻¹. The peroxidation reaction did not occur as a result of indirect reaction of the phospholipid with nitrite, and the rate constants are consistent with a mechanism of allylic hydrogen abstraction.