Direct Determination of the Gas-Solid Interface Reaction Products of Melatonin with Ozone by Laser-Induced Acoustic Desorption - Mass Spectrometry (LIAD-MS)

Melatonin is a potent defensive molecule against oxidative damage. The knowledge of the interaction between melatonin and reactive oxygen species (ROS) is important for understanding antioxidant mechanisms. However, direct observation of reaction products of melatonin with ozone (a reactive oxygen species) in vitro is absent. In this paper, a simple and rapid method using a laser-induced acoustic desorption time-of-flight mass spectrometer (LIAD-TOFMS) is reported to characterize the reaction products of melatonin with ozone at the gas-solid interface. The advantage of this approach is the direct analysis of the products without secondary treatment. A series of oxidation products were observed, including primary hydroxymelatonin (HO-MLT), N-1-acetyl-N-2-formyl-5-methoxykynurenin (AFMK), and secondary (N-1-acetyl-5-methoxykynurenin, AMK). Another significant finding is two pathways for the reaction of melatonin with ozone in vitro. These results demonstrate a novel strategy for the direct determination of reaction products at the gas-solid interface.