Social Self-Sorting in Aqueous Solution

Abstract

Self-sorting-the ability to efficiently distinguish between self and nonself-is common in nature but is still relatively rare in synthetic supramolecular systems. We report a 12-component mixture comprising 1-11 and KCl that undergoes thermodynamically controlled self-sorting in aqueous solution based on metal-ligand, ion-dipole, electrostatic, charge-transfer interactions, as well as the hydrophobic effect. We refer to this molecular ensemble-characterized by high-fidelity host-guest interactions between components-as a social self-sorting system to distinguish it from narcissistic self-sorting systems based on self-association processes. The influence of several key variables-temperature, pH, concentration, and host/guest stoichiometry-was explored by a combination of simulation and experiment. Variable temperature NMR experiments, for example, revealed a kinetically controlled irreversible process upon cycling from 298 to 338 K, which is an emergent property of this molecular ensemble. Variable pH and concentration experiments, in contrast, did not reveal any emergent properties of the molecular ensemble. Simulations of a four-component mixture establish that by proper control of the relative magnitude of the various equilibrium constants, it is possible to prepare socially self-sorted mixtures that are responsive (irresponsive) to host/guest stoichiometry over narrow (broad) ranges. The 12-component mixture is relatively irresponsive to host/guest stoichiometry. Such social self-sorting systems, like their natural counterparts, have potential applications as chemical sensors, as artificial regulatory elements, and in the preparation of biomimetic systems.