Cone Angles Quantify and Predict the Affinity and Reactivity of Anion Complexes between Trifluoroborates and Rigid Macrocycles.

Steric manipulation is a known concept in molecular recognition but there is currently no linear free energy relationship correlating sterics to the stability of receptor-anion complexes nor to the reactivity of the bound anion. By analogy to Tolman cone angles in cation coordination chemistry, we explore how to define and correlate cone angles of organo-trifluoroborates (R-BF ) to the affinities observed for cyanostar-anion binding. We extend the analogy to a rare investigation of the anion's reactivity and how it changes upon binding.

High-fidelity Recognition of Organotrifluoroborate Anions (R-BF ) as Designer Guest Molecules.

The recognition of boron compounds is well developed as boronic acids but untapped as organotrifluoroborate anions (R-BF ). We are exploring the development of these and other designer anions as anion-recognition motifs by considering them as substituted versions of the parent inorganic ion. To this end, we demonstrate strong and reliable binding of organic trifluoroborates, R-BF , by cyanostar macrocycles that are size-complementary to the inorganic BF progenitors.

Revealing the Hidden Costs of Organization in Host-Guest Chemistry Using Chloride-Binding Foldamers and Their Solvent Dependence.

Preorganization is a key concept in supramolecular chemistry. Preorganized receptors enhance binding by minimizing the organization costs associated with adopting the conformation needed to orient the binding sites toward the guest. Conversely, poorly organized receptors show affinities below what is possible based on the potential of their specific binding interactions.

Polarity-Tolerant Chloride Binding in Foldamer Capsules by Programmed Solvent-Exclusion.

Persistent anion binding in a wide range of solution environments is a key challenge that continues to motivate and demand new strategies in synthetic receptor design. Though strong binding in low-polarity solvents has become routine, our ability to maintain high affinities in high-polarity solvents has not yet reached the standard set by nature. Anions are bound and transported regularly in aqueous environments by proteins that use secondary and tertiary structure to isolate anion binding sites from water.

Zero-Overlap Fluorophores for Fluorescent Studies at Any Concentration.

Fluorophores are powerful tools for the study of chemistry, biology, and physics. However, fluorescence is severely impaired when concentrations climb above 5 μM as a result of effects like self-absorption and chromatic shifts in the emitted light. Herein, we report the creation of a charge-transfer (CT) fluorophore and the discovery that its emission color seen at low concentrations is unchanged even at 5 mM, some 3 orders of magnitude beyond typical limits.

Programmed Negative Allostery with Guest-Selected Rotamers Control Anion-Anion Complexes of Stackable Macrocycles.

A new rotamer-based strategy for negative allostery has been used to control host-host interactions and product yield upon anion complexation. Coassembly of anion dimers as guests inside two cyanostar macrocycles drives selection of one rotamer in which all ten steric groups get directed outward to destabilize triply stacked macrocycles. A large entropy penalty (Δ S) is quantified upon anion binding when the multiple dynamic rotamers collapse down to one.

Inchworm movement of two rings switching onto a thread by biased Brownian diffusion represent a three-body problem.

The coordinated motion of many individual components underpins the operation of all machines. However, despite generations of experience in engineering, understanding the motion of three or more coupled components remains a challenge, known since the time of Newton as the "three-body problem." Here, we describe, quantify, and simulate a molecular three-body problem of threading two molecular rings onto a linear molecular thread.