RATE CONSTANTS FOR THE DEHYDRATION OF SINGLE AND DOUBLE HYDRATES OF CYTIDYLYL (3‘‐5’)–CYTIDINE

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Abstract
Abstract— Cytidylyl (3′‐5′) cytidine (CpC) was irradiated with ultraviolet light (u.v.) to produce the single hydrate (a mixture of C*pC and CpC*) and the double hydrate C*pC* which were separated by electrophoresis. These photoproducts rapidly dehydrate to CpC and deaminate to a mixture of U*pC and CpU*. The rate constants for dehydration and deamination of the hydrates were evaluated for a range of pH values from 3 to 8 at 0°C. It is observed that the rate constants for decay of C*pC* lie between those for C*pC and CpC* for all pH values studied. Both single and double hydrates show minimum stability around pH 4·5 and maximum stability around pH 8. The maximum rate constants for dehydration of C*pC*, C*pC and CpC* are 0·26, 0·145 and 0.35 hr‐1 respectively and the minimum values are 0.024, 0.011 and 0.091 hr‐1 respectively all at 0°C. The rate constants for deamination of C*pC to U*pC for a range of pH values at 0°C were measured. The amount of deamination product varies from about 2 to 10 per cent of the hydrate depending on pH with the maximum amount being produced around pH 8.