Photo-Oxides of Carcinogenic Hydrocarbons

Abstract

IN a recent note under the above title¹, Prof. J. W. Cook described a number of water-insoluble peroxidic photo-oxides derived from carcinogenic hydrocarbons. Experiments made in Cambridge during the past year indicate that a photochemical oxidation product, which is different in character both from those prepared by Cook and from the alkali-soluble materials prepared by Boy land, can be obtained from 3: 4-benzpyrene under suitable conditions. 10 c.c. of a 0·1 per cent solution of the hydrocarbon in benzene (B.D.H., 'Specially Pure') is irradiated for one hour in an open Petri dish placed three inches below a neon-sensitized mercury lamp of the type described by Melville², nearly all the energy radiated from which is concentrated in the 2536 A. resonance line. The remaining benzene is quickly evaporated off in a current of air, and the dry residue is extracted with 10 c.c. of glass-distilled water or with weak alkali (M./500 NaHCO₃) and filtered. The resulting solution is colourless—unlike the solid residue—and its absorption spectrum, I, contains two very well-defined bands, with maxima of intensity at about 3600 A. and 2760 A. respectively. When the aqueous solution is allowed to stand, the band at 3600 A. disappears, while that at 2760 A. becomes less intense, in the course of 3–4 hours, II. The spectrum is not of the dihydroanthracene type such as is that, for example, of the water-soluble endosuccinate derivative of 1: 2: 5: 6-dibenzanthracene. It indicates, however, that a labile water-soluble photo-oxidation product can be prepared from 3: 4-benzpyrene, even though this compound gives no photo-oxide of the peroxidic type. Schulman and Rideal³ have shown that the labile constituent of the aqueous solution can be adsorbed readily on to protein monolayers. These observations may be correlated and compared with the experiments on the photodynamic activity of the hydrocarbons described by Mottram⁴.