Towards Amplified Probing of Weak Intermolecular Interactions on the External Surfaces of Molecular Capsules

Highly sensitive equilibria between homo- and heterodimeric capsular complexes reveal unexpected variations in the aryl-aryl interactions of eight benzoyl fragments grouped in four tight pairs on the outer surfaces of the capsules.

Abstract

We report a sensitive method for comparing weak interactions between aryl rings located on the external surfaces of equilibrating homo- and heterodimeric capsules. Two identical self-complementary resorcin[4]arene tetrabenzoate molecules and one tetramethylammonium cation form in CDCl₃ hydrogen-bonded homodimeric capsules whose exteriors are decorated with four tight pairs of weakly interacting aryl rings. The pair wise mixing of six different homodimers establishes their equilibria with the corresponding heterodimeric species in which two types of aryl rings exert on each other some gentle forces. This equilibrium is significantly shifted either towards homo- or heterodimers depending on the nature and location of the substituents in the weakly interacting aryl rings. The thermodynamic favorability or disadvantage of the heterodimerization is determined by stronger or weaker aryl-aryl attractions in the hetero- or homodimeric capsules, respectively. The four-fold amplification of weak aryl-aryl interactions on the external surfaces of the equilibrating capsules is responsible for high sensitiveness of our approach.

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