76 J. BOOTH, E. BOYLAND VOL. 12 (1953) 



EXPERIMENTAL 



All absorption measurements were made with a Unicam SP.500 photoelectric 

 spectrophotometer, readings being taken at intervals of i m^. Whatman No. 42 paper 

 was used for filtration except when stated to the contrary. 



The solubility of polycyclic compounds 



Preparation of suspensions. Polycyclic compounds were ground in a hand homoge- 

 niser with water until the particles became wet and finely divided. The suspensions were 

 filtered and the solids washed several times with water. The solid material was then 

 washed off the filter paper and diluted with water to make a suspension containing 

 approximately 200 mg/ioo ml. After diluting a sample with ethanol to dissolve the solid, 

 the concentration was estimated by comparing the absorption at a wavelength of maxi- 

 mum absorption for the particular compound with a standard absorption curve. 



Solubility in water. A mixture of i 1 water and i ml of the previously prepared 

 suspension of the aromatic compound was shaken gently at 22° for 3 hours. After 

 filtration the filtrate was extracted with three 50 ml portions of benzene. The combined 

 benzene extracts were dried over Na2S04, evaporated to a small volume and made up 

 to 10 ml with benzene. The concentration increased thus 100 times was measured with 

 the photoelectric spectrophotometer. 



Solubility in purine solutions. The 0.2% suspension (i ml) was added to 9 ml of 

 aqueous purine solution, shaken gently at a constant temperature (22°) for the required 

 time and then filtered. The filtrate was diluted with known volumes of ethanol and the 

 concentration of the aromatic compound estimated by measurement of the absorption 

 at the wavelength of one of the maxima of the substance concerned. The standard 

 optical density measurements used for these determinations were made in the same 

 concentrations of ethanol as the unknown solution, because absorption differs in different 

 proportions of ethanol and water. The lowest concentration of ethanol used was 50%. 

 This method is restricted to those substance which absorb at wavelengths greater than 

 330 m/x since the purines themselves absorb below this wavelength. 



The solubilities of the three isomers of dibenzcarbazole and dibenzacridine at room 

 temperature were determined in this way in saturated solutions of caffeine (0.07 M) and 

 of tetramethyluric acid (0.08 M). These aromatic compounds were also soluble in sodium 

 deoxyribonucleate (DNA) (0.1%). More concentrated solutions of DNA were too 

 viscous to filter and could not be used for determinations by this method. 



The Molecular Ratio (M.R.) is calculated as 



Mols. of purine in solution 



Mols. of aromatic compd. in solution 



i.e. the number of mols. of purine required to dissolve i mol. of aromatic compound 

 [of. Weil-Malherbe^). In calculating the M.R. for the deoxyribonucleate solution an 

 arbitrary mol. wt. of 391 (equivalent to that of the sodium salt of adenyhc acid) was 

 used. 



Change in solubility ivith time of shaking. By adding 5 ml of the 0.2 °o suspension of 

 aromatic substance to 45 ml of saturated purine solution, suspensions of excess solid in 

 0.063 ^^ caffeine or 0.072 M tetramethyluric acid were obtained. These were shaken at 



References p. 8y. 



