Supramolecular buffering by ring-chain competition.

Abstract

Recently, we reported an organocatalytic system in which buffering of the molecular catalyst by supramolecular interactions results in a robust system displaying concentration-independent catalytic activity. Here, we demonstrate the design principles of the supramolecular buffering by ring-chain competition using a combined experimental and theoretical approach. Our analysis shows that supramolecular buffering of a molecule is caused by its participation as a chain stopper in supramolecular ring-chain equilibria, and we reveal here the influence of various thermodynamic parameters. Model predictions based on independently measured equilibrium constants corroborate experimental data of several molecular systems in which buffering occurs via competition between cyclization, growth of linear chains, and end-capping by the chain-stopper. Our analysis reveals that the effective molarity is the critical parameter in optimizing the broadness of the concentration regime in which supramolecular ring-chain buffering occurs as well as the maximum concentration of the buffered molecule. To conclude, a side-by-side comparison of supramolecular ring-chain buffering, pH buffering, and molecular titration is presented.