Ion‐Pair Binding: Is Binding Both Binding Better?

Roelens, Stefano; Vacca, Alberto; Francesconi, Oscar; Venturi, Chiara

doi:10.1002/chem.200900342

Cited by 52 publications

(49 citation statements)

References 49 publications

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“…Of the seven species, compound 2 and TBA + ·Cl À are added into solution, and both TBA + and Cl À ions are known from Equation (3) to be present in solution. Therefore, and in an extension to the work by Roelens et al, [28] we present independent evidence of the charged complexes 2·Cl À and 2 2 ·Cl À , and of the neutral 2·Cl À ·TBA + ion-pair complex. After this expanded model is corroborated, only then can it be used with confidence to analyze the titration data as a means to accurately compare the chloride affinities of 1 and 2.…”

Section: Resultsmentioning

confidence: 54%

“…Thus, the next sections outline experiments that are used to identify and confirm the correct binding model. Herein, we started by employing the approach reported by Roelens et al [28] to analyze the NMR spectra for some insights into additional equilibria. At first glance, a simple 1:1 and 2:1 binding model [Eqs.…”

Section: Resultsmentioning

confidence: 99%

“…The ion-pairing problem, so well laid out by Roelens et al, [28] is the absence of an accepted and general way to handle multiple equilibria at the same time, such as complexation [Eqs. (1) and (2)] and ion pairing [Eqs.…”

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confidence: 99%

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Aromatic and Aliphatic CH Hydrogen Bonds Fight for Chloride while Competing Alongside Ion Pairing within Triazolophanes

Hua

Ramabhadran

Uduehi

et al. 2010

Chemistry A European J

109

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Triazolophanes are used as the venue to compete an aliphatic propylene CH hydrogen-bond donor against an aromatic phenylene one. Longer aliphatic C-H...Cl(-) hydrogen bonds were calculated from the location of the chloride within the propylene-based triazolophane. The gas-phase energetics of chloride binding (ΔG(bind) , ΔH(bind) , ΔS(bind) ) and the configurational entropy (ΔS(config) ) were computed by taking all low-energy conformations into account. Comparison between the phenylene- and propylene-based triazolophanes shows the computed gas-phase free energy of binding decreased from ΔG(bind) =-194 to -182 kJ mol(-1) , respectively, with a modest enthalpy-entropy compensation. These differences were investigated experimentally. An (1) H NMR spectroscopy study on the structure of the propylene triazolophane's 1:1 chloride complex is consistent with a weaker propylene CH hydrogen bond. To quantify the affinity differences between the two triazolophanes in dichloromethane, it was critical to obtain an accurate binding model. Four equilibria were identified. In addition to 1:1 complexation and 2:1 sandwich formation, ion pairing of the tetrabutylammonium chloride salt (TBA(+) ⋅Cl(-) ) and cation pairing of TBA(+) with the 1:1 triazolophane-chloride complex were observed and quantified. Each complex was independently verified by ESI-MS or diffusion NMR spectroscopy. With ion pairing deconvoluted from the chloride-receptor binding, equilibrium constants were determined by using (1) H NMR (500 μM) and UV/Vis (50 μM) spectroscopy titrations. The stabilities of the 1:1 complexes for the phenylene and propylene triazolophanes did not differ within experimental error, ΔG=(-38±2) and (-39±1) kJ mol(-1) , respectively, as verified by an NMR spectroscopy competition experiment. Thus, the aliphatic CH donor only revealed its weaker character when competing with aromatic CH donors within the propylene-based triazolophane.

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Section: Resultsmentioning

confidence: 54%

Section: Resultsmentioning

confidence: 99%

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Aromatic and Aliphatic CH Hydrogen Bonds Fight for Chloride while Competing Alongside Ion Pairing within Triazolophanes

Hua

Ramabhadran

Uduehi

et al. 2010

Chemistry A European J

109

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“…54 Although early attempts to stabilise both species of an ion-pair involved using a binary host system 55 -also called a dual-host or dual-receptor, in which two separate hosts are invoked-there was considerable appeal for engineering both recognition sites into a single receptor, such that selective binding of a target ion-paired salt can be achieved. The field of heteroditopic receptors now dominates the literature.…”

Section: Heteroditopic Receptorsmentioning

confidence: 99%

Solution-phase counterion effects in supramolecular and mechanostereochemical systems

2011

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The self-assembly of molecular components into complex superstructures involves the subtle interplay of various noncovalent forces. Charged species are often utilised in self-assembly processes as a result of the favorable π-π, cation-π, electrostatic, and hydrogen bonding interactions that form between these species. Although the counterions associated with these charged species can exert significant effects on the synthesis, stability, and operation of superstructures in solution, rarely are the counterions considered, leading to misinterpretations and misunderstandings of the studied systems. In this tutorial review, we discuss a variety of solution-phase counterion effects, from the fundamental origins to innovative ways in which these effects are exploited for useful functions.

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“…Instead of using turn-on factors, we employed an accurate binding model 4b, 26 that faithfully represents all the important equilibria present in solution. These include anion binding, K anion , cation binding, K cation , and the ternary ion-pair binding, β overall (Figure 1), from which we determine the cooperativity factor, α:…”

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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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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Ion‐Pair Binding: Is Binding Both Binding Better?

Cited by 52 publications

References 49 publications

Aromatic and Aliphatic CH Hydrogen Bonds Fight for Chloride while Competing Alongside Ion Pairing within Triazolophanes

Aromatic and Aliphatic CH Hydrogen Bonds Fight for Chloride while Competing Alongside Ion Pairing within Triazolophanes

Solution-phase counterion effects in supramolecular and mechanostereochemical systems

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

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