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 chainstopper. 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.

Scope and Limitations of Supramolecular Autoregulation

“…5,6 Ditopic supramolecular compounds have the ability to form either rings (K intra ) or linear polymers (K inter ), where the stability of the rings can be defined by the effective molarity (EM = K intra / K inter ). 7,8 Since the EM represents a local concentration, the formation of intramolecular contacts, i.e.…”

Model-driven engineering of supramolecular buffering by multivalency

“…To analyze how multivalency affects supramolecular buffering, we expanded our previous model describing supramolecular buffering by divalent UPy monomers ( 29 ). To this end, we developed models that describe ring–chain competition of tri- and tetravalent UPy monomers, followed by the inclusion of NaPy dimerization with UPy chain ends.…”

“…2 C ). Interestingly, at low NaPy concentrations both the mono- and trivalent UPy titration curves have a slope of unity, while the di- and tetravalent UPy curves have lower slopes, the latter indicative of buffering of free NaPy by cyclic species ( 29 ). Furthermore, the slope of the tetravalent UPy titration curve at low NaPy concentrations is lower than that of the divalent.…”

“…Recently, our group reported on a two-component supramolecular buffering system based on a self-associating divalent ureidopyrimidinone (UPy) molecule and a monovalent naphthyridine (NaPy) molecule that undergoes dimerization with UPy chain ends ( 29 , 30 ) ( Fig. 1 A ).…”

Fluorescent Supramolecular Polymeric Materials

“…In this Review, we mainly focus on fluorescent supramolecular polymeric materials prepared from low molecular weight monomers and summarize recent progress for their preparation, fluorescent properties, and applications. Specifically, we classify the fluorescent supramolecular polymeric materials depending on the types of main driving forces for supramolecular polymerization, including multiple hydrogen bonding, electrostatic interactions, π–π stacking interactions, metal‐coordination, van der Waals interactions and host−guest interactions . Roughly, multiple hydrogen bonding is famous for its directionality and excellent reversibility, and it can act as an effective way to regulate chromophore aggregation and further control the photochemical properties of fluorescent supramolecular polymeric materials .…”