Thermodynamic Stability of Hydrogen‐Bonded Nanostructures: A Calorimetric Study

Abstract

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.

Self‐Assembly of a Highly Organized, Hexameric Supramolecular Architecture: Formation, Structure and Properties

“…The values obtained were Δ H =(−540±30) kJ mol −1 and Δ S =(−1.3±0.1) kJ mol −1 K −1 . The value of the enthalpy in the present system is more than twice as large as that found for the assembly of a planar hexameric entity through extensive hydrogen bonding11d (Δ H =−540 versus 210 kJ mol −1 ) 11d. The larger number of hydrogen bonds (30 versus 18) and other types of weak interactions present in our system might explain this difference, but also the solvent used in the literature is 1,2‐dichloroethane, whereas we have used [D 4 ]‐ o ‐DCB.…”

“…This could be explained by the fact that in the present system the monomer is flexible and can adopt a large number of conformations in solution, whereas in its hexameric form this conformational flexibility is greatly reduced. Conversely, in the literature case,11d the monomeric entity is more rigid, therefore the entropic cost on assembly of the system is expected to be lower. In summary, at room temperature the Gibbs free energy of our system in [D 4 ]‐ o ‐DCB lies around −150 kJ mol −1 , compared to the −120 kJ.…”

On the Transfer of Chirality, Thermodynamic Stability, and Folding Characteristics of Stereoisomeric Gated Baskets

“…To probe the thermodynamic stability of folded ( P )‐ 2 (–)/( M )‐ 2 (+) in polar solvents,18b,30 we incrementally added strong hydrogen‐bond acceptor [D 6 ]DMSO ( β s = 8.9)31 to the basket dissolved in CDCl 3 and monitored the process by 1 H NMR spectroscopy (Figure 5, A; see also Figure S13 in the Supporting Information). The chemical shift of the N–H resonance moved upfield as the proportion of [D 6 ]DMSO solvating the amide groups in ( P )‐ 2 (–)/( M )‐ 2 (+) increased (Δ δ = 1.90 ppm, Figure 5, A, B).…”

Estudio termodinámico para la obtención de nanohidroxiapatita por el método de microondas

“…Diversas investigaciones se han enfocado en el estudio de las propiedades termodinámicas del material para establecer la energía necesaria a la cual se lleve a cabo la reacción [21][22][23], Cualquier cambio en las condiciones del sistema de síntesis, conlleva a un cambio en las energías de reacción, por lo consiguiente si se desea implementar la síntesis de HAp a menores temperaturas, se debe evaluar la energía que se requiere para la formación de la HAp a las condiciones óptimas (200°C por 30 min.) y buscar un ajuste en la energía a menores temperaturas, variando factores como el pH y tiempo de reacción, lo cual es posible a través de la energía libre de Gibbs.…”