Thermochemistry of aqueous solutions of alkylated nucleic acid bases: III. Enthalpies of hydration of uracil, thymine and their derivatives

• Published in: Biophysical chemistry 1980-02, Vol.11 (1), p.17-21
• Main Authors: Teplitsky, A.B., Yanson, I.K., Glukhova, O.T., Zielenkiwicz, A., Zielenkiewicz, W., Wierzchowski, K.L.
• Format: Article
• Language: English
• ISSN: 0301-4622; 1873-4200
• DOI: 10.1016/0301-4622(80)85003-4

Enthalpies of sublimation Δ H 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 Δ H 0 sol in water of aBcylated compounds were obtained calorimetrically. Hence the calculated enthalpies of hydration: Δ H 0 hydrsubal = Δ H 0 sol - Δ H 0 subl, were corrected for energies of cavity formation in pure liquid water to yield enthalpies of interaction Δ H 0 sint of the solutes with their hydration shells. For uracil Δ H 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 CH 2 −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.