FREE RADICALS OF BIOLOGICAL INTEREST: I. ELECTRON SPIN RESONANCE SPECTRA OF TOBACCO SMOKE CONDENSATES

Smoke condensates, prepared from tobacco smoke, are shown to contain a variety of paramagnetically active centers. Some of these have lifetimes of a few seconds. Smoke condensates, when dissolved in sulfuric acid, give rise to at least two cation radical species. The more short-lived species may be the anthracene or an anthracene-type cation radical species and the more long-lived one may be a cation radical related to, but not identical with, the 3,4-benzpyrene cation radical.When 3,4-benzpyrene is heated to near its melting point, considerably more intense electron spin resonance (e.s.r.) spectra are obtained. The heated benzpyrene sample, when dissolved in sulfuric acid, also gives a more intense, but otherwise similar, spectrum than an unheated sample. These observations indicate that, on heating benzpyrene, additional free radicals are formed, and this may account for the relatively high carcinogenicity of tobacco smoke condensates.The e.s.r. spectrum of 3,4-benzpyrene in sulfuric acid undergoes an approximately 10-fold increase in signal intensity when similar amounts of 3,4-benzpyrene-6,7-quinone are added to the mixture. The latter compound on its own does not afford a detectable signal under these conditions. This indicates that the ability of known carcinogenic substances, such as 3,4-benzpyrene, to give rise to free-radical species can be appreciably affected by the molecular environment.