Extremely strong tubular stacking of aromatic oligoamide macrocycles

Abstract

As the third-generation rigid macrocycles evolved from progenitor 1, cyclic aromatic oligoamides 3, with a backbone of reduced constraint, exhibit extremely strong stacking with an astoundingly high affinity (estimated lower limit of K_dimer > 10¹³ M⁻¹ in CHCl₃), which leads to dispersed tubular stacks that undergo further assembly in solution. Computational study reveals a very large binding energy (−49.77 kcal mol⁻¹) and indicates highly cooperative local dipole interactions that account for the observed strength and directionality for the stacking of 3. In the solid-state, X-ray diffraction (XRD) confirms that the aggregation of 3 results in well-aligned tubular stacks. The persistent tubular assemblies of 3, with their non-deformable sub-nm pore, are expected to possess many interesting functions. One such function, transmembrane ion transport, is observed for 3.