THERMOCHEMISTRY OF AQUEOUS-SOLUTIONS OF ALKYLATED NUCLEIC-ACID BASES .9. ENTHALPIES OF HYDRATION OF 9-METHYL-8-ALKYLADENINES AND 6,9-DIMETHYL-8-ALKYLADENINES

Enthalpies of solution in water, DELTAH-degrees-(sol), and enthalpies of sublimation, DELTAH-degrees-(sub), were determined experimentally f or a number of crystalline derivatives of adenine: 6,8,9-trimethyladen ine; 6,9-dimethyl-8-ethyladenine; 6,9-dimethyl-8-propyladenine; 6,9-di methyl-8-butyladenine; 8,9-dimethyladenine and 9-methyl-8-ethyladenine . Standard enthalpies of hydration, DELTAH-degrees-(hydr), derived fro m these data were calculated. The latter were discussed together with the values for variously alkylated adenines, determined previously. Th e data obtained show that the dependence of enthalpy of hydration on t he number of methylene groups added upon substitution with 8-n-alkyl g roups of 9-methyladenine and 6,9-dimethyladenine is nonlinear.