Abstract:

Salicylic acid (SA), the active ingredient of aspirin, is effective in various medical treatments such as cosmetology and anticancer therapy. We investigated the photophysical and photochemical behavior of SA using 266 nm laser flash photolysis. Results demonstrate that SA can be photoionized and photoexcited by 266 nm photons to give SA+· and 3SA*. SA is highly photosensitive and can be photoionized via a monophotonic process with a quantum yield of 0.21. Under the aerobic conditions we find that in cells, hydrated electrons easily combine with oxygen to generate O-·20 , which can kill cancer cells. SA+·can be converted into neutral radicals by deprotonation and its pKa value is 2.95. SA also can be oxidized by SO-·4 and the rate constant is 2.28×109 L·mol-1·s-1, which further confirms the photoionization ability of SA. In addition, SA can be excited to 3SA*, which then generates 1O2*. This research provides introductory theory for the potential of SA to be used as an anticancer drug.

Key words: Salicylic acid, Laser flash photolysis, Photoionization, Quantumyield, Anticancer mechainism