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



79 



The effect of pH on the amount of 3:4-5:6-dibenzcarbazole remaining in solution 

 after the precipitation of the molecular complex is almost negligible, but the amount 

 which dissolves before precipitation begins, and therefore, the amount precipitated as a 

 molecular compound increases with an increase in pH (Fig. 3). 



£4001 



S 

 ■8 



p. 300 



-Q 



■6 



200- 



100 



8 



10 



12 PH 



Fig. 3. Effect of pH on the pre- 

 cipitation of the 3 :4-5 :6-dibenz- 

 carbazole-caffeine complex. Fj cone, 

 of dibenzcarbazole in 0.07 M 

 caffeine before precipitation of the 

 complex; F^ cone, of dibenz- 

 carbazole in 0.07 M caffeine after 

 precipitation of the complex; F^- 

 F^, dibenzcarbazole precipitated as 

 complex. 



300- 



f 



■Q 



C>l00i 



0-0- -o.. 



-■o.. 



-o- 



0.5 



1.5 



2.5 3 



Time (hours) 



3.5 



Fig. 4. Effect of purine cone, on precipitation of 3:4-5:6- 

 dibenzocarbazole-caffeine complex. ® (S), cone, of di- 

 benzcarbazole in 0.07 M caffeine; x X, in 0.046 M 



caffeine; O -O, in 0.023 ^^ caffeine. 



Effect of purine concentration on the precipitation of the 3 : 4-5 : 6-dibenzcarbazole- 

 caffeine complex. The concentration of dibenzcarbazole at various intervals of time after 

 mixing was estimated, using 0.07, 0.046 and 0.023 ^^ solutions of caffeine. The results 

 showed that the maximum concentration of dibenzcarbazole, the amount of complex 

 precipitated and the dibenzcarbazole remaining in solution when the equilibrium had 

 been reached increased with increase of caffeine concentration. The time required to 

 reach the maximum concentration of dibenzcarbazole and to reach equilibrium however 

 was not affected (Fig. 4). 



Effect of amount of dibenzcarbazole added on the precipitation of the complex. In these 

 experiments suspensions of 20, 50, 100 and 200 mg/1 of 3 :4-5 :6-dibenzcarbazole in 0.07 

 M caffeine solution were examined. The more concentrated suspensions produced a 

 greater maximum concentration of dibenzcarbazole in solution before precipitation of 

 the complex and a shorter time was required for the equilibrium to be reached. 



Similarly, by reducing the amount of dibenzcarbazole added to a 0.08 M solution 

 of tetramethyluric acid from 200 mg/1, when the maximum dibenzcarbazole concen- 

 tration was reached too quickly for detection, to 50 mg/1, an increase to a maximum 

 occurred followed by a decrease (Fig. 5) . 



Effect on purine concentration on the solubility of 3 : 4-6 : y-dibenzacridine. [No pre- 

 cipitation of com/)/^a;.) 3:4-6 :7-Dibenzacridine was chosen for this investigation because 

 References p- 8y. 

 5 



