title: Thermochemistry of aqueous solutions of alkylated nucleic acid bases. III. Enthalpies of hydration of uracil, thymine and their derivatives.
abstract: Enthalpies of sublimation DeltaH(0)(subl) crystalline uracil, thymine and their methylated derivatives as well as of N,N-diethylthymine were determinated by the quartz-resonator method and mass spectrometry. Enthalpies of solution at infinite dilution DeltaH(0)(sol) in water of aBcylated compounds were obtained calorimetrically. Hence the calculated enthalpies of hydration: DeltaH(0)(hydrsubal) = DeltaH(0)(sol) - DeltaH(0)(subl), were corrected for energies of cavity formation in pure liquid water to yield enthalpies of interaction DeltaH(0)(sint) of the solutes with their hydration shells. For uracil DeltaH(0)(int) = -59.8 kJ mole(-1) was obtained in this way. This value decreased linearly on N-methyl substitution with a mean increment of about 6.5 kJ mole CH2(-1). After C(5) or C(6) ring substitution it increased by about 3 kJ. These results are discussed in connection with heat of dilution data and theoretical schemes of hydration.
authors.affiliation: Physico-Technical Institute of Low Temperatures, Ukr. SSR, Academy of Sciences, 310164 Kharkov, USSR.
authors.forename: A B
authors.initials: AB
authors.lastname: Teplitsky
authors.forename: I K
authors.initials: IK
authors.lastname: Yanson
authors.forename: O T
authors.initials: OT
authors.lastname: Glukhova
authors.forename: A
authors.initials: A
authors.lastname: Zielenkiwicz
authors.forename: W
authors.initials: W
authors.lastname: Zielenkiewicz
authors.forename: K L
authors.initials: KL
authors.lastname: Wierzchowski