Kinetic studies of the rich interaction of cannabinoids with oxygen-centered radicals and excited carbonyl compounds

Laser flash photolysis techniques have been employed to measure absolute rate constants and transient spectra for reactions of alkoxyl radicals and ketone triplets with several cannabinoids, including tetrahydrocannabinol (THC) and cannabidiol (CBD) that show rich free radical chemistry as hydrogen atom donors towards alkoxyl radicals. Consistent with their proposed antioxidant activity, the reactive centers in these molecules are the phenoxyl groups. While these molecules also have allylic hydrogens, these seem to play a minor role in their free radical reactions. With excited carbonyls, hydrogen transfer competes with charge-transfer quenching which plays an important role with both benzophenone and xanthone triplets. In the case of THC, charge transfer interactions with carbonyl triplets, rather than hydrogen transfer, is the dominant reaction path. Tests with commercial cannabinoid oil compositions show kinetic and spectral results entirely consistent with those obtained with pure samples, thus suggesting that the hydrogen donor properties and antioxidant activity of cannabinoids are retained in these commercial formulations.