ULTRAVIOLET IRRADIATION OF PYRIMIDINE DERIVATIVES: IV. ANIONIC EFFECTS ON THE PHOTOLYSIS OF CYTOSINE AND O-METHYLCYTOSINE

Abstract

The course of the photochemical reactions involved in the photolysis of O-methylcytosine is strongly affected by the presence of various anions. Similar anionic effects were noted during the photolysis of cytosine but the products of this reaction appeared to be less suitable for further investigation. Ultraviolet irradiation of O-methylcytosine in water leads to destruction of the characteristic absorption bands, while irradiation in phosphate leads to the production of a new compound with marked absorption at 300 mμ, and irradiation in pyrophosphate, glycero-phosphate, citrate, or cacodylate leads to the production of compounds with marked absorption at 274 mμ. The phosphate-dependent photolysis of O-methylcytosine has been studied in some detail and the product has been isolated and purified. Apparently the H2PO4− ion acts as a catalyst in a reaction which involves the loss of 1 mole of ammonia and the addition of 2 moles of water to O-methylcytosine.