Thermodynamic stability of hydrogen-bonded nanostructures: a calorimetric study

The self-assembly of hydrogen-bonded aggregates (rosettes) in solvent mixtures of different polarity has been studied by calorimetry. The C(50) parameter, the concentration when 50 % of the components are incorporated in the assembly, is used to compare assemblies with different stoichiometry. C(50) for the single rosette 1(3).(BuCYA)(3) (1=N,N-di(4-tert-butylphenyl)melamine; BuCYA=n-butylcyanuric acid) in 1,2-dichloroethane is 25 microM, whereas for double rosettes 2 a(3).(BuCYA)(6) and 2 b(3).(BuCYA) (2=calix[4]arene-dimelamine) it is 0.7 and 7.1 microM, respectively. DeltaG degrees, DeltaH degrees, and TDeltaS degrees values indicate that the thermodynamics of double rosettes reflect the independent assembly of two individual single rosette structures or two rosettes reinforced by additional stabilizing interactions. In more polar solvents the stability of double rosettes decreases. From the correlation of DeltaG degrees with solvent polarity it is predicted that it should be possible to assemble double rosettes in methanol or water. The assembly of 2 b(3).(BuCYA)(6) in 100 % MeOH was proven by (1)H NMR and CD spectroscopy.