Determination of the thermodynamic functions (parameters) of the intermolecular self-association of N
6-monomethyladenosine (m
6 Ado) and N
6, N
6-dimethyladenosine (m
26 Ado) in water has been made by solution calorimetric dilution measurements at 298.15K. The standard enthalpy change Δ
H° and standard entropy change Δ
S° of self-association were as follows; Δ
H°: -43∼-50 and -38±3kJ mol
-1, Δ
S°: -122∼-147 and -100±11kJ K
-1 mol
-1 for m
6 Ado and m
26 Ado, respectively. From these values, it is clear that the methylation, especially the dimethylation, of N
6-amino group of adenosine leads to a higher stacking equilibrium quotient than that of adenosine in consequence of an increased value of Δ
S°. This supports that intermolecular association of N
6-methylated adenosines is partly due to a contribution of substituted methyl groups to the formation of hydrophobic bond.
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