Thermochemistry of Aqueous Solutions of Alkylated Nucleic Acid Bases. X. Enthalpies of Hydration of Cytosine and some Methylated, Hydroxy and Methoxy Derivatives of Cytosine

Enthalpies of solution in water, vapor pressures, and enthalpies of sublimation were determined for cytosine and a number of crystalline derivatives of cytosine: 1-methylcytosine, 1-methyl-N ⁴-hydroxycytosine, 1,5-methyl-N ⁴-methoxycytosine, 1,N ⁴,N ⁴-trimethylcytosine, 1,5,N ⁴-trimethylcytosine, 1,5-dimethyl-N ⁴-methoxycytosine, and l,N ⁴-dimethyl-5-ethylcytosine. Enthalpies of hydration were calculated. The latter were analyzed on the basis of the group additivity method. The relation between enthalpy of hydration and polarity of compounds is discussed.