THE U.V. PHOTOCHEMISTRY OF CYTIDYLIC ACID

Abstract The ultraviolet (u.v.) irradiation of the 3' isomer of cytidylic acid (Cp) produces the hydrate (Cp*) with water added across the 5–6 double bond. The yield of this photo-product has been measured by, (a) separating the photoproduct by electrophoresis and (b) by observing the loss in absorbance. When corrections are made for reversal of the hydrate during the experiment, both methods gave the same result. Cross sections and quantum yields for the production of the hydrate were measured over the wavelength range 220 to 290 nm and over a pH range from 1 to 10. The quantum yield is markedly dependent on pH being higher by a factor of 6 to 10 for the neutral form. We have also demonstrated the existence of a very short lived photoproduct (half life 8–9 min) in both Cp3' and Cp5': The nature of this short lived product is not known.