Ion‐Pair Recognition by Ditopic Macrocyclic Receptors

Smith, Bradley D.

doi:10.1002/chin.200646243

Cited by 5 publications

(6 citation statements)

References 32 publications

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“…anion cation (2) Cooperativity factors that are greater than 1 indicate additional stabilization is present within the ternary ion-pair complex, i.e., positive cooperativity. We determined the cooperativity factors in solution-phase experimental studies involving NaClO 4 and NaI binding.…”

Section: ■ Introductionmentioning

confidence: 99%

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Electrostatic and Allosteric Cooperativity in Ion-Pair Binding: A Quantitative and Coupled Experiment–Theory Study with Aryl–Triazole–Ether Macrocycles

et al. 2015

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Cooperative binding of ion pairs to receptors is crucial for the manipulation of salts, but a comprehensive understanding of cooperativity has been elusive. To this end, we combine experiment and theory to quantify ion-pair binding and to separate allostery from electrostatics to understand their relative contributions. We designed aryl-triazole-ether macrocycles (MC) to be semiflexible, which allows ion pairs (NaX; X = anion) to make contact, and to be monocyclic to simplify analyses. A multiequilibrium model allows us to quantify, for the first time, the experimental cooperativity, α, for the equilibrium MC·Na(+) + MC·X(-) ⇌ MC·NaX + MC, which is associated with contact ion-pair binding of NaI (α = 1300, ΔGα = -18 kJ mol(-1)) and NaClO4 (α = 400, ΔGα = -15 kJ mol(-1)) in 4:1 dichloromethane-acetonitrile. We used accurate energies from density functional theory to deconvolute how the electrostatic effects and the allosteric changes in receptor geometry individually contribute to cooperativity. Computations, using a continuum solvation model (dichloromethane), show that allostery contributes ∼30% to overall positive cooperativity. The calculated trend of electrostatic cooperativity using pairs of spherical ions (NaCl > NaBr > NaI) correlates to experimental observations (NaI > NaClO4). We show that intrinsic ionic size, which dictates charge separation distance in contact ion pairs, controls electrostatic cooperativity. This finding supports the design principle that semiflexible receptors can facilitate optimal electrostatic cooperativity. While Coulomb's law predicts the size-dependent trend, it overestimates electrostatic cooperativity; we suggest that binding of the individual anion and cation to their respective binding sites dilutes their effective charge. This comprehensive understanding is critical for rational designs of ion-pair receptors for the manipulation of salts.

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Section: ■ Introductionmentioning

confidence: 99%

“…Cooperativity is a powerful strategy for forming high-fidelity species during molecule-mediated recognition of ion pairs and for effecting allosteric control over binding events . Such ion-pair recognition has many applications, including ion extraction, membrane transport, and catalysis .…”

Section: Introductionmentioning

confidence: 99%

Electrostatic and Allosteric Cooperativity in Ion-Pair Binding: A Quantitative and Coupled Experiment–Theory Study with Aryl–Triazole–Ether Macrocycles

et al. 2015

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“…In fact, as a general rule, receptors that serve to bring the targeted anions and cations close enough to one another (and thus favoring electrostatic interactions between the co-bound ions) have proved particularly effective. Independent of the underlying mechanism, the operational goal in creating ion pair receptors has been to achieve a high level of control over the ion recognition and, where relevant, release processes. ,,− …”

Section: Introductionmentioning

confidence: 99%

Macrocycles as Ion Pair Receptors

et al. 2019

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Cation and anion recognition have both played central roles in the development of supramolecular chemistry. Much of the associated research has focused on the development of receptors for individual cations or anions, as well as their applications in different areas. Rarely is complexation of the counterions considered. In contrast, ion pair recognition chemistry, emerging from cation and anion coordination chemistry, is a specific research field where co-complexation of both anions and cations, so-called ion pairs, is the center of focus. Systems used for the purpose, known as ion pair receptors, are typically di-or polytopic hosts that contain recognition sites for both cations and anions and which permit the concurrent binding of multiple ions. The field of ion pair recognition has blossomed during the past decades. Several smaller reviews on the topic were published roughly 5 years ago. They provided a summary of synthetic progress and detailed the various limiting ion recognition modes displayed by both acyclic and macrocyclic ion pair receptors known at the time. The present review is designed to provide a comprehensive and up-to-date overview of the chemistry of macrocycle-based ion pair receptors. We specifically focus on the relationship between structure and ion pair recognition, as well as applications of ion pair receptors in sensor development, cation and anion extraction, ion transport, and logic gate construction. CONTENTS 3.4.

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“…Synthetic receptors that recognize ion pairs are potentially useful for many technical applications including purification, templated synthetic chemistry, catalysis, membrane transport, and drug delivery. − To date, most of the effort has focused on receptors that recognize alkali or alkaline metal salts as either contact or separated ion pairs. The goal of many published studies has been to develop heteroditopic receptors with distinct anion and cation sites and to show that they exhibit positive binding cooperativity .…”

Section: Introductionmentioning

confidence: 99%

Shape-Selective Recognition of Quaternary Ammonium Chloride Ion Pairs

Smith

2019

J. Org. Chem.

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Synthetic receptors that recognize ion pairs are potentially useful for many technical applications, but to date there has been little work on selective recognition of quaternary ammonium (Q+) ion pairs. This study measured the affinity of a tetralactam macrocycle for 11 different Q+·Cl– salts in chloroform solution. In each case, NMR spectroscopy was used to determine the association constant (K a) and the structure of the associated complex. K a was found to depend strongly on the molecular shape of Q+ and was enhanced when Q+ could penetrate the macrocycle cavity and engage in attractive noncovalent interactions with the macrocycle’s NH residues and aromatic sidewalls. The highest measured K a of 7.9 × 103 M–1 was obtained when Q+ was a p-CN-substituted benzylic trimethylammonium. This high-affinity Q+·Cl– ion pair was used as a template to enhance the synthetic yield of macrocyclization reactions that produce the tetralactam receptor or structurally related derivatives. In addition, a permanently interlocked rotaxane was prepared by capping the end of a noncovalent complex composed of the tetralactam macrocycle threaded by a reactive benzylic cation. The synthetic method provides access to a new family of rotaxanated ion pairs that can likely act as anion sensors, molecular shuttles, or transport molecules.

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Ion‐Pair Recognition by Ditopic Macrocyclic Receptors

Abstract: ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Cited by 5 publications

References 32 publications

Electrostatic and Allosteric Cooperativity in Ion-Pair Binding: A Quantitative and Coupled Experiment–Theory Study with Aryl–Triazole–Ether Macrocycles

Electrostatic and Allosteric Cooperativity in Ion-Pair Binding: A Quantitative and Coupled Experiment–Theory Study with Aryl–Triazole–Ether Macrocycles

Macrocycles as Ion Pair Receptors

Shape-Selective Recognition of Quaternary Ammonium Chloride Ion Pairs

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