Thermochemistry of aqueous solutions of alkylated nucleic acid bases V. Enthalpies of hydration of N-methylated adenines |
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| Authors: | Anna Zielenkiewicz Wojciech Zielenkiewicz Leonid F Sukhodub Olga T Glukhova Alexander B Teplitsky Kazimierz L Wierzchowski |
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| Affiliation: | (1) Institute of Physical Chemistry, Polish Academy of Sciences, 01-224 Warszawa;(2) Technical Institute of Low Temperatures, Ukr. Academy of Sciences, 310164 Kharkov, USSR;(3) Institute of Biochemistry and Biophysics, Polish Academy of Sciences, 02-532 Warszawa |
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| Abstract: | Enthalpies of solution in water,  H
sol
o
, and of sublimation, H
subl
o
, were determined experimentally for a number of crystalline N-methyl adenines: m6Ade, m
2
6,6
Ade, m9Ade, m
2
6,9
Ade, and m
3
6,6,9
Ade. Derived standard enthalpies of hydration H
hydr
o
, were corrected for the calculated cavity terms H
cav
o
to yield enthalpies of interaction H
int
o
of the solutes with their hydration shells. The increments of H
int
o
per unit area of the water-accessible molecular surface S
B
,  H
int
o
(CH3)/S
B
(CH3), for the particular methyl groups: is considered to be the net effect of the gain in the energy resulting from van der Waals' interactions and of the loss in the energy due to polar interactions upon methyl substitution. It proved to vary somewhat numerically in agreement with the theoretically predicted hydration schemes of adenine. Comparison of H
int
o
/S
B
value for adenine with those previously determined for uracil and thymine indicates that the aminopurine moiety is less hydrated than the diketopyrimidine ring. |
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| Keywords: | Enthalpy of solution enthalpy of sublimation enthalpy of hydration enthalpy of cavity formation enthalpy of interaction with water N-methylated adenines |
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