PURINES 295 



From Nucleic Acid. (Jones.) 



50 gm. of nucleic acid are hydrolysed by heating in a boiHng water-bath 

 under a reflux condenser for 2 hours with 200 c.c. of 10 per cent, sulphuric 

 acid. The hot solution is treated with concentrated ammonia until it is 

 neutral, the ammonia being added slowly as soon as the precipitation of 

 guanine begins. An excess of ammonia is added until 2 per cent, is present. 



The guanine which is precipitated in a granular form is filtered off and 

 washed with ammonia. It is suspended in boiling water and dissolved by 

 adding a minimum of 20 per cent, sulphuric acid. The solution is decolorised 

 by boiling with charcoal (the decolorisation does not occur readily if excess of 

 sulphuric acid has been used) and the guanine precipitated by adding am- 

 monia as above ; it is filtered off, dried at 40 and dissolved in 20-25 

 times its weight of boiling 5 per cent, hydrochloric acid. Pure guanine 

 hydrochloride crystallises out on cooling. It is filtered off, washed with dilute 

 hydrochloric acid and dried in the air. 



Pure guanine is prepared from the hydrochloride by dissolving it in boiling 

 i per cent, hydrochloric acid and adding amrnqnia. 



Adenine is prepared from the ammoniacal filtrate and washings after 

 filtering off guanine which may deposit on standing (see under Adenine). 



From Tissue Extracts. 



It is precipitated by ammoniacal silver nitrate or copper sulphate and 

 sodium bisulphite and separated from other purine bases as described on 

 p. 584- 



Properties. 



Guanine forms a colourless, generally amorphous, powder. It is insol- 

 uble in water, alcohol, ether and soluble with difficulty in ammonia. It is 

 easily soluble in all mineral acids and alkalies. 



The sulphate (C 5 H 5 N 6 O) 2 . H 2 SO 4 . 2H 2 O and other salts are generally 

 decomposed by water. 



The metaphosphate C 6 H 5 N 5 O . HPO 3 . *H 2 O is precipitated on adding 

 metaphosphoric acid to its solution ; it is stable to water and is soluble with 

 difficulty in water and dilute acids. 



Guanine forms a very insoluble picrate, C 5 H 5 N 5 O . C 6 H 3 N 3 O 7 + H 2 O. 

 The picrates of xanthine and hypoxanthine are more soluble. 



Its compound with silver nitrate C 5 H 5 N 5 O . AgNO 3 is almost insoluble in 

 cold nitric acid, but more soluble in hot, from which it crystallises on cool- 

 ing. 



Potassium ferricyanide gives prismatic yellow-brown crystals with dilute 

 solutions of guanine. 



Reactions. 



Guanine on evaporation with dilute nitric acid leaves a brownish-red residue, 

 which becomes bluish- violet on heating. The combinations with picric acid 

 and potassium ferricyanide distinguish it from xanthine and hypoxanthine ; 

 its behaviour towards metaphosphoric acid from hypoxanthine and adenine. 



