VOL. 12 (1953) CARCINOGENIC COMPOUNDS, PURINES AND NUCLEIC ACID 



77 



a constant temperature: samples (2 ml) withdrawn at various intervals of time after 

 mixing were filtered and the concentration of the substance under examination estimated 

 in the filtrates as before. 



In the case of the hydrocarbons studied in this way {e.g. 3 : 4-benzpyrene and pyrene), 

 the concentration of hydrocarbon in the filtrate increased during the first 15 to 30 min 

 to a constant value. 



The solubilities of the three dibenzcarbazoles in caffeine solution, however, increased 

 to a maximum and then decreased to a steady level. When 3 : 4 : 5 : 6-dibenzcarbazole 

 was added to a tetramethyluric acid solution under these conditions, the decrease in 

 concentration started immediately, presumably because the maximum concentration 

 was reached within a few seconds of mixing (but see page 79). 



Of the three dibenzacridines studied in tetramethyluric acid solution at 37", only the 

 1 :2-8:9-isomer showed a slow decrease in concentration after the initial rise (Table I 

 and Figs, i and 2). When the whole of the mixture was filtered, after shaking for the 



TABLE I 



SOLUBILITY OF AROMATIC COMPOUNDS IN PURINE SOLUTIONS 



DBC = Dibenzcarbazole. 



DBA = Dibcnzacridine. 



DNA = Deoxyribonucleic acid (M.R. calculated on Mol.Wt. of sodium salt of adenylic acid). 



(Concns. shown in table are for il/ concn. of aromatic compound.) 



time required to obtain maximum concentration, a small amount of crystalline material 

 separated from the filtrate on standing. This was due to formation of molecular compounds 

 identical with those described below (page 80) . 



Effect of pH on the 3 : 4-5 : 6-dibenzcarbazole-caffeme complex. The solutions were 

 buffered with Mcllvaine's sodium phosphate-citric acid standard buffer solutions for pH 

 2-8, and 0.05 M sodium carbonate-sodium borate mixtures for pH 9-11. Mixtures of 

 8 ml 0.087 M caffeine, i ml buffer solution and i ml 0.2% 3: 4- 5: 6-dibenzcarbazole 

 suspension were added to each of ten 25 ml flasks giving suspensions of solid in 0.07 M 

 caffeine. 



The mixtures were shaken at 22° for 20 min to give maximal concentrations and 

 excess 3: 4- 5: 6-dibenzcarbazole removed by filtration. Immediately after filtration i ml 

 was removed from each filtrate for estimation of dibenzcarbazole concentration (F^). 

 The remainder of the filtrates were shaken for a further 18 hours at 22°, again filtered 

 and the dibenzcarbazole concentration in these filtrates estimated [F,^. Thus the differ- 



References p. 8y. 



