8o 



J. BOOTH, E. BOYLAND 



VOL. 12 (1953) 



its comparatively high solubihty in purine solutions enabled measurements to be made 

 over a wide range of concentrations. The effect of different concentrations of caffeine 

 and deoxyribonucleic acid was investigated and an interesting difference observed. The 

 molecular ratio decreased with increasing concentration in the case of caffeine and 

 increased in the case of DNA. 



The solubilities were determined as before using caffeine concentrations ranging 

 from 0.0014 M to 0.07 M and sodium deoxyribonucleate concentrations equivalent to 

 0.00023 M to 0.0042 M nucleotide. The suspensions were shaken at 22° for i h since 

 preliminary experiments had shown that there was no increase in solubility after this 

 time. When measuring the concentration of dibenzacridine in the sodium deoxyribo- 

 nucleate, it was necessary to add o.i ml of 2 A^ NaOH to the filtrate on diluting, since 



3001- 



42 

 O 



e 



1 200 



1 



c 



o 

 "6 



o 



c 



5 100 



0.5 1 1.5 2 2.5 3 



Time (hours) 

 Fig. 5. Effect of amount of 3 : 4 : 5 : 6-dibenzcarbazole added on precipitation of the dibenzcarbazole- 



tetramethyluric acid complex, x X 200 mg/1 dibenzcarbazole in 0.08 M tetramethyluric acid; 



# % 50 mg/1 dibenzcarbazole in 0.08 M tetramethyluric acid. 



ionisation of the dibenzacridine occurred and the ion has a different absorption spectrum 

 from the unionised molecule. The results are shown in Table II (M.R. values for deoxy- 

 ribonucleate are calculated as before). 



In the case of hydrocarbons dissolved in caffeine and tetramethyluric acid solutions 

 studied by Weil-Malherbe^ the M.R. was either constant or decreased with increase 

 in purine concentrations. Neish^, however, had observed that the M.R. for the solubility 

 of 2-naphthylamine, 2-aminofluorene and benzidine in caffeine, increased with increase 

 in caffeine concentration. 



Preparation of molecular compounds. Saturated ethanolic solutions of the dibenz- 

 carbazole or dibenzacridine were added to aqueous caffeine (0.07 M) or tetramethyluric 

 acid (0.08 M) solutions with gentle shaking, until excess of the compound was precipitated. 

 The excess solid was immediately removed by filtration through Whatman No. i paper. 

 In some cases the filtrate was slightly turbid, but on standing (0.5-6 h) small amounts 

 of crystalline precipitates were formed. These were filtered off, washed once with water 



References p- 8y. 



